CALIFORNIA STATE UNIVERSITY, NORTHRIDGE
AN ANALYSIS OF RISK FACTORS PREDICTING
INFECTION IN PROSTHETIC VASCULAR GRAFT SURGERY
A thesis submitted in partial satisfaction of the
requirements for the degree of Master of Science in
Health Science, Epidemiology
by
Helen Victoria O'Brien
May 1984
The Thesis of Helen Victoria O'Brien is approved:
Committee Chairperson
California State University, Northridge
i i
To my husband, John
for his supportl encouragement, and
love throughout this endeavor.
;;i
ACKNOWLEDGEMENTS
I would like to express my sincere gratitude to
the members of my Committee for their advice, guidance,
concern and assistance throughout this endeavor.
The
suggestions and support of Mrs. Helen Brajkovich, Dr.
Fredric Silverblatt, and Or. Roberta Madison have significantly contributed to this paper.
A sincere thanks to Connie for being there.
A f i n a 1 and s i ncere thank s go to my h u s b and J o h n
and my son Steve for their encouragement.
iv
Table of Contents
Page
Dedication • • •
................
i i i
Acknowledgements
iv
List of Tables •
vii
Abstract
• • vi i i
Chapter
1.
2.
3.
Introduction
...........
1
Definitions •
6
Statement of the Problem
8
Purpose of the Study
8
Hypothesis
9
Limitations of the Study
9
Review of the Literature
11
History of Prosthetic Vascular
Surgery • • • • • • • . . • •
11
Review of Relevant Risk Factor Research
16
Summary • •
31
Methodology •
33
Introduction
33
Study Design
33
Selection of Patients •
33
Data Collection Form
34
Selection of Risk Factors •
34
Method of Analysis
......
v
35
Chapter
4.
5.
Page
Results
............
38
Introduction •
38
Analysis of Individual Risk Factors
39
Simultaneous Analysis of Risk Factors
60
Summary
61
Discussion •
62
Conclusions
70
Recommendations for Further Research •
70
References
.......
Appendices
73
76
A.
Data Collection Form ••
76
B.
Comparison of Mean Age and
Categories of Procedures Performed
77
Comparison of Mean Duration of
Surgery and Categories of
Pro c e du r e s Pe r f o rm e d • • • •
78
Comparison of Mean Duration
of Preoperative Hospitalization and
Categories of Procedures Performed •
79
Comparison of Mean Length of Time
to the Appearance of Infection and
Categories of Procedures Performed
80
Summary Table of Risk Factors
and Their Significance Level • • •
81
c.
D.
E•
F.
vi
List of Tables
Table
Page
Infection (Present, Absent) Categorized
by Median Age . • • . . • • . • . • •
40
2.
Infection (Present, Absent) Categorized
by Hematoma (Present, Absent) . • . •
41
3.
Infection (Present, Absent) Categorized
by Di abet e s ( Pre sen t, Ab sen t) • . . •
4-2
Infection (Present, Absent) Categorized
by Pre-existing Infection on an
Affected Extremity (Present, Absent)
44
5.
Categories of Study Group by Infection
(Present, Absent) and Graft Material
46
6.
Infection (Present, Absent) Categorized
by Scheduled or Emergency Surgery . •
47
Infection (Present, Absent) Categorized
by Reoperation within 72 Hours
(Yes, No) • . . . . . • • . • • . • •
48
Infection (Present, Absent) Categorized
by Arteriography through an Affected
Extremity (Yes, No) • • . • • . • • .
49
9.
Infection (Present, Absent) Categorized
by Median Duration of Surgery • •
50
1 0.
Distribution of Postoperative Wound
Infections Categorized by Site • . .
1.
4.
7.
8.
11.
12.
13.
14.
..
52
Infection (Present, Absent) Categorized
by the Duration of Preoperative
Hospitalization • • . • • . • . . • •
54
Distribution of Infection (Present, Absent)
Categorized by Procedure Performed • . •
56
Classification of Infection (Deep,
Incisional) Categorized by the Mean
Length of Time to Appearance
59
Step Zero, P-value of Risk Factors
60
vii
ABSTRACT
AN ANALYSIS OF RISK FACTORS PREDICTING
INFECTION IN PROSTHETIC VASCULAR GRAFT SURGERY
by
Helen Victoria O'Brien
Master of Science, Epidemiology
Patients who develop postoperative wound infections,
following prosthetic vascular graft surgery, may suffer
the consequences of loss of limb or life.
done:
This study was
(1) to ascertain if specific risk factors were
associated with the development of infection and (2) to
identify which if any might be useful in -predicting the
occurrence of infection.
The infection rate in the
present study was 15.4 percent.
This rate is higher
than reported in the literature (0.25 to 6.0 percent).
One hundred and sixty-two clinical records of patients
who had prosthetic vascular graft surgery were reviewed
for the presence or absence of the various risk factors.
Thirteen risk factors, previously identified in the
vi i i
literature, were selected for analysis.
Chi-square
analyses of the data in the present study identified 4
risk factors significantly associated with infection.
Only 1 of the 4 risk factors could be classified as
alterable.
These 13 risk factors were examined using
stepwise logistic regression analysis.
Site of incision
was the only factor to significantly predict infection.
This finding was in agreement with other investigators
who found the site of incision to be a factor in the
development of infection.
ix
CHAPTER ONE
Introduction
It is estimated that approximately 5 percent of the
35 million patients admitted to U.S. hospitals each year
acquire nosocomial infections (7).
These infections
play a role in increasing illness and death and also
contribute to the increased costs of hospitalization.
Preceded only by urinary tract infection, surgical
wound infections are the second most frequent nosocomial
infection and are an important cause of increased costs,
morbidity and death for patients (21).
Any surgical
infection involving an implanted foreign body or substantial necrotic (dead) tissue is likely to have serious
after-effects regardless of the causative agent involved
(21).
Furthermore, a wound containing foreign or necrotic
material is highly susceptible to infection even if few
bacteria are present (21).
Patients requiring prosthetic vascular graft surgery
on their arteries are considered to be at high risk for
developing a surgical wound infection.
This is especial-
ly true when the portion of the artery that has been
removed is replaced by a prosthesis made of a synthetic
material such as dacron.
Manipulation of the artery
during the surgical procedure exposes the vessel to
potential microbial contamination.
1
Trauma to the
2
vessel can also occur during manipulation or through
poor surgical technique.
This trauma can prevent
adequate circulation to the tissue thereby increasing the
chance that necrosis (localized death of tissue) will
occur.
According to Talkington and Thompson (24), many
of the problems encountered in prosthetic vascular graft
surge~
have been overcome.
Among the unresolved
problems, infection is the most ominous.
The incidence
of prosthetic vascular graft infection as reported in
the literature (6, 14) ranges between 0.25 and 6 percent.
The rate of infection for the different sites in which
prosthetic vascular grafts are implanted also varies.
Femoropopliteal (thigh to knee) grafts are reported to
have a 3 percent infection rate, aortoiliac (abdomen to
pelvic area) grafts a 0.7 percent rate of infection while
aortofemoral (abdomen to thigh) grafts have a 1.6 percent
rate of infection.
The overall infection rate for these
various sites combined is reported to be 1.1 percent
(23).
Talkington and Thompson considered this 1.1 per-
cent rate of infection a reasonable standard by which
general performance could be measured by surgeons that do
this type of surgery.
These authors also felt that the
prevention of infection in patients requiring prosthetic
vascular graft surgery was of the utmost importance
because the development of infection usually results in
death and/or loss of limb.
They hoped that with further
3
technical developments the 1.1 percent infection rate
would one day be considered unacceptable.
Prevention
of infection, according to these authors included evaluating the preoperative condition of the patient, the
manner in which the surgical procedure is performed and
the postoperative care of the patient.
Over the past 10 years, guidelines have been established to prevent the development of nosocomial
infections but the effectiveness of these guidelines has
not always been definitely determined.
One component of
these guidelines has included surveillance to detect
potentially preventable risk factors.
Because it is
difficult to carry out scientifically valid studies of
these guidelines, there is little published data that
helps one decide which guidelines or combination of
guidelines are the most effective in reducing the risk of
infection for the least cost.
In recent years, some investigators have estimated
that as many as half of all nosocomial infections are
potentially preventable (7).
The predisposing causes
common to most preventable nosocomial infections are the
diagnostic and therapeutic procedures which patients
undergo while they are hospitalized.
Nosocomial infec-
tions are most likely to be controlled only if hospital
personnel make an effort to identify risk factors that
contribute to the development of infection and change
them when possible.
These efforts may be aimed at
4
changing the risks directly, by changing the environment,
or indirectly, by changing the behavior of personnel who
provide patient care.
Several investigators, as will be noted in the
review of literature, have identified and enumerated individual risk factors which they felt played a part in
the development of infection in patients who have undergone prosthetic vascular graft surgery.
The development
of infection, however, has a multifaceted etiology, and
is the result of many different risk factors.
Further-
more, these risk factors may vary from patient to patient
as well as from one site to another.
Therefore, it is
desirable to evaluate the contribution of multiple risk
factors to the development of infection simultaneously.
Until recently, few attempts have been made to study
the relative importance of multiple factors and their
significance in the development of infection.
One of the
earliest studies evaluating surgical infection in general, was done by Howard, Barker and Culbertson (12) in
1966.
These investigators evaluated the effect of ultra-
violet irradiation of the operating room on several
factors and its contribution to the prevention of infection.
The factors studied were:
(1) type of operation,
(2) level of wound contamination, (3) age, (4) nutritional and metabolic factors, (5) existence of other infections, (6) duration of operation, (7) duration of preoperative hospitalization, (8) race, (9) sex, and (10)
5
urgency of operation.
In 1981, a study conducted by Simchen, Shapiro,
Michel and Sacks (20) analyzed 10 risk factors at one
time and their association with postoperative wound
infections in patients who had colon surgery.
Only 4 of
the 10 factors in this study were independently associated with the development of wound infection.
Platt, Polk, Murdock and Rosner (17), conducted a
prospective study between June 1979 and April 1981 which
showeo that 7 of 21 risk factors, when evaluated simultaneously, were associated with mortality among patients
with urinary catheters (tubes that drain the bladder).
These investigators noted that the acquisition of infection was not associated with severity of underlying
disease.
Twelve potential factors were evaluated by Shapiro,
Munoz, Tager, Schoenbaum and Polk (19), to determine
their association to infection of the operative site in
patients having abdominal or vaginal hysterectomy.
Six
of the risk factors, namely operative approach, type of
service (clinic or private), prophylactic antibiotics,
duration of operation, age and blood loss, were significantly associated with infection.
If significant risk factors for the development of
infection in patients undergoing prosthetic vascular
graft surgery can be identified, they could then be
classified into those that may be preventable such as:
6
(1) the length of time a patient is hospitalized prior to
surgery and (2) performing arteriography vi a the affected
artery.
Some which may not be preventable are diabetes
or whether the operation is elective or an emergency.
Once risk factors are clearly defined, appropriate intervention can be planned.
Concern for optimum quality of patient care in light
of budgetary constraint, and the need for effective utilization of hospital services, has dictated the need for
cost effective management in health care facilities
whether they be community or governmental.
In order to
provide the most care for dollars spent, it is essential
to get a better understanding of risk factors that contribute to infection in prosthetic vascular graft
surgery.
Definitions
For the purpose of this study nosocomial infection,
prosthetic vascular graft, risk factor and surgical wound
infection are defined as follows.
Nosocomial infection.
An infection that develops
during hospitalization and is not present or incubating
at the time of the patient's admission {7).
Prosthetic vascular graft.
A device, implanted
surgically, to replace a missing portion of an artery
·.that has been excised.
7
Risk factor.
An agent or element whose presence is
associated with an increased likelihood that disease
will develop at a later time (15).
Surgical wound infection.
Signs of wound infection
include purulent or nonpurulent drainage from the wound,
erythema of wound edges, separation of wound edges,
stitch abscess, delayed wound healing, and purulence
encountered at reoperation.
They will further be
categorized into incisional (superficial) and deep wound
infection.
The following criteria will be used for iden-
tifying the presence of a wound infection.
A.
Incisional wound infection - any 1 of the
following:
1.
Physician's diagnosis of incisional wound
infection and no previous diagnosis of
incisional wound infection at the same
anatomic site.
2.
Purulent drainage from the operative site.
3.
Nonpurulent drainage from the operative site
with erythema or separation of the wound edges.
Additionally, the incision is not healed within
3 days after the sutures are removed.
B.
Deep wound infection - any 1 of the following:
1.
Physician's definite diagnosis of any of the
following conditions with no previous diagnosis
of deep wound infection at the same site:
8
a.
Abdominal abscess following abdominal
surgery.
b.
Pelvic abscess following abdominal or
pel vic surgery.
c.
Abscess at the operative site with involvement of the prosthetic vascular graft.
2.
Purulent drainage from a drain or fistula and
no previous diagnosis of deep surgical wound
infection at the same site.
3.
Purulence encountered at reoperation at or
near the surgical field of a previous operation and no previous diagnosis of a deep
surgical wound infection at the same site (8}.
Statement of the Problem
This study is being conducted to identify risk
factors that may be significant in predicting the
development of infection in patients having prosthetic
vascular graft surgery.
Purpose of the Study
The purpose of this study is to ascertain if specific risk factors are significant for predicting the
development of infection in patients having prosthetic
vascular graft surgery.
The risk factors chosen from the
literature and selected for analysis are:
(1} age, (2}
hematoma formation, (3} diabetes, (4} pre-existing infection on an affected extremity, (5} pre-existing infection
9
at another site, (6) the material from which the graft is
made, (7) whether the surgery was an elective procedure
or an emergency, (8) reoperation within 72 hours of the
original procedure, (9) whether angiography was performed
through the affected limb prior to surgery, (10) duration
of the surgical procedure, (11) the site of incision,
(12) the duration of preoperative hospitalization and
{13) the procedure that was performed.
These risk fac-
tors are not necessarily listed according to their
importance.
Hypothesis
The null hypqthesis of this study is:
None of the
risk factors selected for analysis will be significant in
predicting the development of infection in patients
having prosthetic vascular graft surgery.
Limitations of the Study:
In this study, the selected risk factors will be
analyzed to determine their significance in predicting
the development of infection only in the initial vascular
procedure.
The purpose for this was to avoid speculation
on when contamination was introduced into the wound,
especially in patients requiring multiple procedures
for additional prosthetic vascular grafts and/or the
removal of clots from prosthetic vascular grafts.
Caution will be needed in trying to generalize
results from this study to all persons undergoing
10
prosthetic vascular graft surgery.
The population to
be used is from 1 Veterans Administration Medical
Center located in Southern California.
The overall
health status of these veterans may vary significantly
from the general population in this geographic area.
It
is recognized that the results of this study may not be
applicable to persons having prosthetic vascular graft
surgery at other Veterans Administration Medical Centers
or other community hospitals.
CHAPTER TWO
Review of the Literature
History of Prosthetic Vascular Surgery
The first crude repair of an artery is credited to
Hallowell, a British surgeon.
It was performed June 15,
1759 and involved an artery of the arm (18).
As long as
223 years ago it was noted that the amputation of an
extremity might be avoided if a major artery could be
repaired rather than tied off.
More than 100 years passed before additional contributions were made in this field.
In 1830, G. J. Gutherie
reported closing a lacerated internal jugular vein.
This
was followed by the joining of 2 vessels in a portocaval
anastomosis (the joining of the portal vein and the vena
cava) by Eck in 1879 (18).
The year 1882 is considered the birth of modern vascular surgery.
In this year, a German surgeon by the
name of Schede, successfully repaired the femoral vein
(the major vessel commencing in the groin and extending
down the thigh) in a man.
During the 20 year period before 1900, experimental
work was done by many individuals.
Much of this was of a
technical nature although reports continued to be published of the successful repair of vessels by various surgeons.
11
12
Experimental and clinical contributions continued
to be made during the first 10 years of this century.
Carrel and Gutherie gave impetus to vascular implants
using autografts (a portion of vessel that is transplanted from 1 part to another part of the same body) and
homographs (a graft of a vessel taken from a donor of
the same species as the recipient).
The first clinical
application of this concept occurred in Madrid by
Goyanes in 1906.
The following year, the first saphenous
vein (referring to either of the 2 main superficial veins
of the leg) graft of an artery was performed by Lexer in
Germany (18).
In spite of over 100 reports of arterial
repair by suturing lacerations, joining of vessels or
vein graft substitutions in man, few surgeons considered
arterial repair or implant worthwhile because of the high
failure rate, usually from the formation of a clot in the
repaired vessel.
During the early years of World War I, German surgeons tried to repair wounded arteries.
However, with
the increased use of high explosives and high velocity
bullets which caused massive wounds, coupled with increased casualties and slow evacuation methods, arterial
repair was considered impractical.
Because there was a
lack of antibiotics and blood transfusions, along with
frequent hemorrhage that one sees in infected vascular
repairs, surgeons continued to favor the procedure of
13
ligation (tying off with a suture) as the preferred method
of managing vascular injuries.
From the years 1920 to 1950 the interest in vascular
surgery was centered primarily on arteriovenous fistulas
(an abnormal joining between an artery and a vein) and
false aneurysms (an aneurysm is a sac formed by the
stretching of the wall of an artery; in a false aneurysm
the wall of the artery is injured and the blood collects
in the surrounding tissues with formation of a sac joining with the artery).
It was during World War II, that
the first vascular center at the Greenbriar General
Hospital at White Sulphur Springs was established by
Seeley.
At about this time, other vascular centers were
also established.
Almost simultaneously, Blakemore,
Lord and Stefko were encouraging the use of a synthetic
tube combined with a vein to bridge the gap between 2
arterial ends.
This method was used during World War II
but complications eventually eliminated its acceptance
and once again, ligation continued to be the preferred
treatment for
v~scular
injuries.
During World War II numerous surgeons attempted
acute arterial repairs; the results were little better
than those following ligation.
A classic review of the
results of arterial repairs that were' performed during
World War II was done by DeBakey and Simeone.
In this
review, 2,471 acute arterial injuries that had been
repaired were evaluated.
The overall amputation rate
14
was approximately 49 percent following arterial ligation.
There were only 81 repairs and only 3 of these involved
end to end anastomosis (joining}.
Nonetheless, the ampu-
tation rate following repair was lowered to 36 percent
(18}.
Because of these results, there was a great inter-
est created in vascular injuries and vascular surgery in
general.
Many individuals including Blakemore, OeBakey,
Shumaker, Simeone and Swan as well as others showed
continued interest and continued to perform research;
this helped to set the stage for the progress in vascular
surgery that has occurred over the past 30 years.
Contri-
butions by these individuals included the development
of new drugs and instruments that are currently being
used in performing prosthetic vascular graft surgery.
The Korean conflict, with its large numbers of
casualties, provided the chance to evaluate the practicability of repairing acute arterial injuries.
For a
second time, under the guidance of Dr. Seeley, a major
vascular center was established in 1950 at Walter Reed
General Hospital.
With methods for the rapid evacuation
of casualties, new vascular instruments, antibiotics,
blood replacement and stabilization of fighting, acute
vascular repairs were begun in the Mobile Army Surgical
Hospitals.
Most of the repairs were by direct anastomo-
sis but there was also an increase in the use of
autologous vein grafts.
A study of vascular injuries re-
sulting from the Korean conflict, and reported by Hughes
15
in 1958, showed 304 major arterial repairs with an amputation rate of 13 percent (18).
Following the Korean conflict, civilian and military
interest in the field of vascular surgery expanded.
An
increased number of civilian hospitals began to report a
sizable number of vascular repairs.
Some of the more
notable were Morris and his group from Houston, reporting
on 220 cases.
Ferguson and the group from Atlanta report-
ed on 200 cases while Patman's group in Dallas reported
on 271 cases.
The largest report was by Perry and his
group, also from Dallas, and consisted of 508 cases.
For
these large groups the amputation rates ranged from 3 to
16 percent (18).
There were other groups also, however,
their number of cases was not as large as those mentioned.
During this time, as the various synthetic prostheses for blood vessel replacement were being developed,
they were used primarily in the repair of acute vascular
injuries.
However, there was a higher percentage of
complications from infection following the placement of a
foreign body in a contaminated wound.
By the time the fighting in Vietnam started, the
army had developed guidelines for the repair of acute
vascular injuries in the combat zone.
For the first time
in any war, a surgeon capable of performing vascular
repair was assigned to every military hospital in
Vietnam.
16
The Vietnam Vascular Registry was started at Walter
Reed General Hospital in 1966 to document and follow all
who suffered vascular trauma in Vietnam.
As of 1972,
there have been approximately 7,500 individuals names and
copies of records included in the registry.
In addition
to the preliminary and interim reports to evaluate the
success of the various methods of vascular repair, other
areas of study have been pursued by the registry especially in areas of controversy.
These included the
extent of arterial resection during debridement (surgical
removal of lacerated, necrotic or contaminated tissue);
the repair of venous injuries; the use of vascular
prosthesis in contaminated wounds; the use of fasciotomy (a surgical incision that transects a band of
fibrous tissue that forms a covering for muscles and
organs of the body); and the management of wounds of
the heart and great vessels just to mention a few (18).
It is unfortunate that trauma, war and conflict have
served as the impetus for the developments in prosthetic
graft surgery.
Review of Relevant Risk Factor Research
Many studies have been conducted which identify risk
factors that have contributed to the development of infection in patients who had prosthetic vascular graft
surgery.
These factors, however, have been analyzed and
presented separately.
17
The previously performed studies include risk factors
analyzed in this study.
In reviewing the literature, it
was noted that risk factors considered significant by
some investigators were reported as not significant by
others.
Additional evaluation of the various risk
factors is necessary to clarify and more clearly define
the role that these risk factors play in the development
of infection.
Age.
Increasing susceptibility to infection in older
persons and the very young has been recognized for many
years.
The susceptibility to infection in older persons
is attributed to the gradual decline of host defense
mechanisms which begin to occur at about 25 years of age.
There is also evidence that the host's defense mechanisms
are less effective in the very young than at maturity.
In 1972, in the study by Howard, et al, (12) the
contribution of age on the development of surgical
infection in general was analyzed.
They concluded that
the age of the patient probably plays a significant and
direct role in determining the risk of surgical wound
infection.
The very young and very old were found to be
more at risk of developing infection.
They found the
lowest rate of infection in the 15 to 24 year group.
There was a gradual increase in the infection rate as
age increased, with the 65 to 74 year group having the
highest rate of infection.
18
Hooten, et al, (11) conducted a study on multiple
risk factors and the development of general surgical
wound infections.
They found that certain risk factors,
such as age, which is highly associated with the occurrence of infection when analyzed separately, appears to
be less important (although not trivial) when analyzed
with other factors.
Hammersten, Holm and Schersten (9) evaluated the
effect of age and the development of infection on
patients having prosthetic vascular graft surgery.
The
mean age of this population was 67 years, with a range of
35 to 90 years.
In that study, the mean age of the
infected patients did not differ from the mean age of
this whole population.
A retrospective analysis of 1,173 patients having
prosthetic vascular graft surgery conducted by Landreneau
and Raju (13) found no significant association between
age and the development of infection.
DeBakey and McCollum (3) have long felt that age itself is not a contraindication to surgical treatment in
atherosclerotic occlusive disease (blockage of arteries
by the formation of lipid plaques within the vessels) in
selected cases.
Prosthetic vascular grafts have been
used for a number of years in the treatment of patients
with arterial disease.
According to DeBakey and McCollum
the elderly patient should not be denied the opportunity
for surgical treatment solely because of his age.
With
19
proper preoperative evaluation, intraoperative technique
and careful postoperative care, these patients can be
expected to do well.
As can be seen the effect of age on
the development of infection is not completely resolved.
Hematoma.
The formation of a hematoma (a localized
collection of clotted blood) was found to contribute to
the development of infection in the analysis of data
presented by Hoffert, et al, (10), Hammersten, et al,
(9), and Bouhoutsos, et al, (2).
Hoffert (10) and his group were impressed by how
frequently postoperative bleeding in the surgical site
played a major role in the development of subsequent
infection.
(~0
This was found in 6 of the 12 infected cases
percent) identified in their study.
The question
arises on how important is this 50 percent rate.
A 50
percent occurrence of infection could be attributed to
chance and chance alone, and indeed may not really be
considered a risk factor.
Hammersten, et al, (9) noted the importance of
careful hemostasis (the arrest of bleeding) by the
fact that postoperative hematoma doubled the infection
frequency in the population that they evaluated.
In
non-infected patients they noted an 11 percent incidence
of hematoma formation, whereas there was a 20 percent
incidence of hematoma formation in cases that became
infected.
20
Bouhoutsos, et al, (2) noted that in 5 of the 12
cases (41.7 percent) of groin infection in their series,
a hematoma was present soon after surgery.
They conclu-
ded that careful suturing of the anastomosis is important,
for a hematoma can predispose to infection.
It is not unreasonable to assume that hematoma formation would contribute to the development of infection.
Especially when one realizes that blood is added to
laboratory culture media as a nutrient to enhance the
growth of bacteria.
However, one must keep in mind that
factors that contrihute to hematoma formation, for instance poor surgical technique, may also increase the
possibility of an infection developing.
Diabetes.
The role of diabetes and its contribution
to the development of infection has been contradictory in
a review of the literature.
Unfortunately most investiga-
tors did not elaborate on their findings.
The assumption
that diabetics are more susceptible to infection than
nondiabetics has been generally accepted by physicians
and surgeons.
When diabetes is uncontrolled, wound
healing is impaired and local response to inflammation
is delayed.
Infections of the extremities occur more
frequently among diabetics because of the increased prevalence of peripheral vascular disease in that population.
Papa, Halperin, and Adar (16) conducted a retrospective study in which they examined the frequency,
21
predisposing factors, management and outcome of infections following vascular operations during the period of
1973 through 1979.
They stated that diabetes did not
increase the rate of infection.
This conclusion was
based on a previous study in which one of the authors
(Adar) had participated.
Papa, et al, however, did not
elaborate on this study.
Landreneau and Raju (13) included diabetes as a risk
factor and analyzed its contribution to the development
of infection in prosthetic vascular graft surgery.
There
was no significant association between diabetes and the
incidence of postoperative wound infection.
The method
of analysis was not discussed in the presentation.
Hoffert, et al, (10) noted in their analysis of 12
prosthetic vascular graft cases that developed infection
that 8 were non-diabetics, and 4 were diabetics (33
percent).
Hammersten, et al, (9) found a higher frequency of
infections among diabetic patients (25 percent) requiring
prosthetic vascular graft surgery as compared to nondiabetic patients (10 percent). Seventeen percent of
their total population (n = 304) were diabetics.
I n the stu dy reported by Sz i 1 a gy i , e t a 1 , ( 2 3 ) wh i c h
examined 1 ocal factors ( 1 ocal factors were defined as
diabetes and gangrene, diabetes alone, gangrene alone,
and obesity) predisposing to infection no significant
trend could be detected.
They found diabetes with or
"
'
22
without ischemic (deficiency of blood to a part due to
blockage of a vessel) tissue changes had a predictable
but relatively slight role in the initiation of wound
infection in prosthetic vascular graft surgery.
Stipa and Wheelock (22) conducted a study comparing
diabetics to non-diabetics in one type (femoropopliteal)
of prosthetic vascular graft surgery.
dence of infection was 6 percent.
The overall inci-
There were 6 cases of
infection among 73 patients in the diabetic group and 4
infected cases among 67 patients in the non-diabetic
group.
Based on that data, they concluded that diabetes
did not increase the risk of infection in prosthetic
vascular graft surgery, but did not elaborate further.
Pre-existing Infection on an Affected Extremity.
The role that pre-existinq infection contributes to the
development of infection in prosthetic vascular graft
surgery, whether on an affected extremity or elsewhere in
the body, has been noted by several investigators.
An extensive review of the literature through 1974
was the basis of a report
Greenfield (14).
by
Liekweg, Levinson and
This report also included the results
of orosthetic vascular graft operations performed at the
Medical College of Virginia Hospitals.
These authors
noted that the person with an open lesion on the foot was
at high risk of prosthetic vascular graft infection when
one of the anastomoses lies in the groin.
In this report,
23
it was noted that a large number of the patients had endstage disease (disease so severe, that there is virtually
no hope of saving the extremity) and open lesions on the
extremities.
This was thought to be a major factor in the
high incidence of groin infections seen at that hospital.
Hoffert, et al (10) found that in 9 of the 12 infected prosthetic vascular grafts studied, there was an
open, infected lesion present on the extremity at the
time surgery was performed.
The majority of the lesions
were confined to the toes.
In the Goldstone and Moore (6) series on infected
prosthetic vascular grafts (14 of 566) it was noted that
2 patients had infected lesions of the lower limb as the
primary indication for surgery.
There was a higher frequency of infection in patients
undergoing prosthetic vascular graft surgery who had obvious gangrene (17 percent) according to Hammersten, et al,
(9) also.
Finally, Papa, et al, (16) noted that the presence
of an infected ischemic foot ulcer before surgery had
been shown to be a predisposing factor in the development
of infection.
Once again, this conclusion was based on
the previous study in which Adar had participated and
there was no further explanation.
Pre-existing Infection at Another Site.
In this re-
view of the literature, the role of pre-existing infection
24
at a site other than the affected extremity was mentioned
by 2 investigators.
Goldstone and Moore (6) reviewed their results with
infected prosthetic vascular grafts in 1974.
An attempt
was made to identify a source of potential contamination
that could have been a precipitating cause of infection.
Two of the patients had incidental appendectomy at the
same time as their vascular surgery.
One patient had
post-operative obstruction of the small bowel with peritonitis (inflammation of the serous membrane lining the
abdominal and pelvic walls).
One patient had a previous
urinary tract infection with the same organism just prior
to the appearance of graft infection.
Liekweg, et al, (14) stated that concomitant infection elsewhere in the body played a large part in the
onset of infection.
An infection in the opposite groin
was noted in 21 percent of the graft infections in which
similar bacteria were grown from infected wounds of the
opposite lower extremity.
It is well known that if an infection exists in a
certain part of the body, the bacteria causing this infection can be implanted elsewhere in the body by means
of the circulating blood.
Bacteria from pre-existing
infection can attach themselves to prosthetic vascular
grafts, thus contributing to the development of infection.
Graft Material.
It is common knowledge that a
25
foreign body will enhance and perpetuate infection and it
seems unrealistic to believe that a vascular prosthesis
will act differently.
It is true that some plastic pros-
theses are relatively non-reactive but they are certainly
not inert (5).
Papa, et al, (16) examined the rate of infection in
which a prosthetic vascular graft made of synthetic
material was implanted as compared to vein grafts.
The
rate of infection in the 387 synthetic implantations was
5.7 percent.
In the 124 vein grafts the rate was less
than 1 percent.
They concluded that the insertion of a
prosthetic vascular graft, especially a synthetic one,
was a predisposing factor to infection.
Liekweg, et al, (14) also found that the type of
graft employed was a factor of critical importance.
Of
the 164 infected cases reviewed, 132 involved synthetic
grafts.
A 6 percent incidence of infection (12 of 201) in
arterial graft surgery was reported by Hoffert, et al,
(10).
They found that dacron grafts had been used in 5
of the infected cases and nylon grafts in 5 cases.
Homo-
grafts had been used in 2 cases and an autologous vein
graft in 1 case.
One patient had 2 grafts implanted.
The utilization of a vascular graft made from synthetic material appears to be a factor in the development of infection in patients requiring prosthetic
vascular graft surgery.
26
Elective Versus Emergency Operation.
In the review
of literature. 1 study was found that examined the rate
of prosthetic vascular graft infection comparing elective
procedures to emergency procedures.
One could speculate
that a patient requiring an emergency operation would be
at a higher risk of developing an infection.
possible reasons for this might be:
Several
(1) occlusion of a
vessel preventing adequate circulation to the area,
enhancing the development of necrotic tissue, (2) any
underlying chronic illness (diabetes, hypertension) may
not be under control and therefore the successful outcome
of the operation would be lessened, and (3) if the patient
had any pre-existing infections either on an affected limb
or elsewhere, there would be little chance to have it
completely under control.
In 1977, a report by Hammersten, et al, (9} was
published.
The purpose of this report was "to give
frequency figures of wound infections and the infectious
complications during 5 years of prosthetic vascular graft
surgery and to evaluate factors influencing this frequency." They studied 304 patients who were operated on
between 1969 and 1974 and found that 75 percent of the
operations were classified as elective.
Elective surgi-
cal cases had a 15 percent rate of infection, whereas
emergency cases had a 5 percent rate of infection.
They
attributed the difference in infection between emergency
and elective operation to the fact that emergency
I
27
operations were performed after a shorter preoperative
hospital stay.
The shorter preoperative hospital stay,
according to these authors, decreased the chances of the
patient becoming colonized with disease causing bacteria
that may be found in the hospital environment.
Early Reoperation.
Early reoperation. as a poten-
tial risk factor in the development of infection in
prosthetic vascular graft surgery, was mentioned briefly
by 2 investigators.
Papa, et al, (16) noted that the need for early reoperation had previously been shown to be a predisposing
factor.
Again this was based on the study in which Adar
had previously participated.
They did not elaborate
further on this statement.
Becker and Blundell (1) reviewed infected grafts in
14 patients.
In 11 of these patients factors predis-
posing to infection were identified.
In 6 of the 11
infected patients (54.5 percent) reoperation was noted to
be a risk factor.
This may also be attributed to chance
rather than reoperation.
If manipulation of the vessel at the time of the original operation exposes the artery to potential microbial
contamination then so would reoperation.
Reoperation
could further expose the artery to additional trauma and
interruption of circulation. adding to the possibility of
further necrosis through poor surgical technique.
'
28
Therefore, it would be reasonable to assume that early reoperation may contribute to the development of infection.
Arteriography.
An extensive review of the literature
relevant to prosthetic vascular graft infections was
published in 1977.
In this review it was noted that al-
though there was no evidence available in the literature,
percutaneoijs, transfemoral, arteriography, with subsequent
prosthetic vascular grafting in the groin region represented another distinct risk in the development of infection
( 14) •
To examine the relationship between preoperative and
postoperative wound complications and infections,
Landreneau and Raju (13) did a retrospective analysis of
1,173 patients who had undergone surgery for lower limb
ischemia.
Among the 1,173 patients, arteriography was
performed by the transaxillary route in 158 (13.5 percent).
In all others, arteriography was performed
through the inguinal (groin) approach. mostly through
the right side.
These investigators state, "there was a
significant increase in the incidence of postoperative
groin wound complications when arteriography was performed through the transfemoral rather than the transaxillary approach (3.7 percent compared to 0.6 percent)."
This was the only study available that addressed the
role of arteriography in the development of infection in
prosthetic vascular graft surgery.
,, '
29
Duration of the Surgical Procedure.
Duration
(length of time) of surgery was mentioned by 3 investigators.
As a risk factor, contributing to the development
of infection, the findings as presented are contradictory.
Liekweg, et al, (14) found that the duration of an
intraabdominal procedure was a definite factor in the incidence of wound infection following prosthetic vascular
surgery.
Landreneau and Raju (13) found no significant association between the length of time it took to perform
surgery and wound infection following prosthetic vascular
graft surgery.
No information was presented on the
method of analysis nor was raw data provided in either of
these published articles.
Hammers ten, et al, (9) hO\'/ever, noted a 15 percent
rate of infection in prosthetic vascular graft operations
lasting longer than 2 hours.
These investigators con-
cluded that the increased infection frequency in long
operative procedures were thought to be due to either an
increased risk of contamination of the wound or that an
extended operation means a more extensive surgical procedure with more traumatized tissue.
Site of Incision.
Papa, Halperin and Adar (16)
reviewed 931 prosthetic vascular graft operations that
had been performed at the Chaim Sheba Medical Center in
Israel.
Twenty-six wound infections (2.8 percent) were
30
found.
Of these 931 cases, there were 785 groin inci-
sions identified, of the 26 previously identified
infections 21 (80 percent) occurred in the groin
incisions.
The overall rate of infection in the groin
incisions was 2.7 percent.
From these results it was
concluded that a groin incision was a predisposing factor
to infection following prosthetic vascular graft surgery.
In Goldstone and Moore•s (6) review of infected
arterial grafts, the highest incidence of overall
infection occurred in aortofemoral and axillofemoral
procedures.
Twelve patients in this series had one or
more late revisions of the original arterial graft and
had subsequent development of infection in the same anatomic region.
In 8 of these 12 patients the area of
infection was located in the groin.
Hoffert, et al, (10) noted in their series of infected prosthetic vascular grafts that the most common
presenting site of infection was the inguinal (groin)
area.
Finally, in a retrospective review of 3,347 cases by
Szilagyi, et al, (23) it was noted that after analyzing
the various sources of infection the most common factor
"resided in the dermis and in particular the dermis of
the inguinal region."
The inguinal skin appeared to be
the source of infection in 23 of 40 infections according
to these authors.
31
After reviewing the literature, it would seem that a
groin incision carries with it a high risk of becoming
infected when prosthetic vascular graft surgery is
performed.
Duration of Preoperative Hospitalization.
In an
analysis of risk factors for surgical patients in
general, Hooten, et al, (11) noted the following.
Those
patients with a low risk of developing a surgical wound
infection had minor underlying illness and generally had
operations of short duration or, (2) a short preoperative
hospitalization and no previous infection.
Hammersten, et al, (9) were the only investigators
who examined the effect of prolonged preoperative hospitalization on the development of prosthetic vascular
graft infection.
In this study, prolonged preoperative
hospitalization was defined as longer than 2 days.
They
found a 20 percent infection rate in patients hospitalized
2 days or longer whereas there was an 8 percent infection
rate for patients hospitalized less than 2 days.
They
felt that patients with a long preoperative stay had an
increased opportunity to become colonized with pathogenic
(disease causing) organisms.
Summary
In this review of the literature, frequency distributions and percentages were the usual statistical
techniques employed to analyze the various factors.
If
32
other statistical techniques were used to determine
which of the factors were significant they were not
mentioned by the various authors.
The analysis of the various risk factors in this
review of the literature was on individual risk factors.
None of the studies identified, examined the contribution
of multiple risk factors analyzed simultaneously.
Many equivical results, requiring further study and
analysis, were noted and documented in this review of the
literature.
Contradictory results were also noted (for
instance, diabetes) and require further investigation
before any definite conclusions can be made on the
role these risk factors play in the development of infection.
CHAPTER THREE
Methodology
Introduction
This study involved the collection of data to test
risk factors which may be used to predict the development
of postoperative wound infection following prosthetic
graft surgery.
Employing multivariate analysis, 13 pre-
viously identified risk factors were tested.
Study Design
This was a retrospective study.
Data were obtained
by reviewing the records of 164 patients who had prosthetic vascular graft surgery between the years 1976 and
1981.
Patient records were followed to December 1983 to
determine those patients who developed infection.
Hope-
fully, by following these cases through 1983, patients
having surgery in the later years (1979, 1980, 1981) that
may have developed late infections would not be missed.
Selection of Patients
All patients who had prosthetic vascular graft
surgery from the year 1976 through 1981 were eligible
for analysis.
The prosthetic vascular grafts that were
selected for analysis in this study were those that had
been placed in the axillary area, the abdominal cavity,
33
34
and·lower extremities.
Both male and female patients
were accepted into the study.
Data Collection Form
A data collection instrument was devised and used to
assure uniform collection of information for all cases.
To maintain patient confidentiality the data collection
sheets were numbered consecutively.
A copy of the data
collection form has been included in the Appendix.
Selection of Risk Factors
The presence or absence of risk factors that were
previously identified in the literature were selected for
analysis.
These consisted of the following:
(1) age,
(2) hematoma formation, {3) diabetes, (4) pre-existing
infection on an affected extremity, (5) pre-existing
infection at another site, (6) the material from which
the graft is made, (7) whether the surgery was an elective procedure or an emergency, (8) reoperation within
72 hours of the original procedure, (9) whether angiography was performed through the affected limb prior to
surgery, (10) the duration of the surgical procedure,
(11) the site of incision, (12) the duration of preoperative hospitalization and (13) the procedure that was
performed.
Two additional factors were selected to provide
information about the infections that occurred.
The
first was the classification of the wound infection into
p '
35
incisional, which included the skin, subcutaneous and
subdermal tissues but not the graft, and deep which involved the graft itself or adjacent structures.
It is
well know that if skin and incisional wound infections
are ignored and not managed properly, the consequence of
graft involvement is more likely.
The second factor was the length of time it took for
the infection to appear.
Several investigators noted the
length of time it took for some infected grafts to become
apparent.
One study (6) noted that the interval between
the placement of the graft and the appearance of infection
ranged from 1 week to 87 months.
The mean interval be-
tween grafting and infection was 15 months and the median
interval was 3 1/2 months.
In another study (14) the
mean interval between surgery and the recognition of
infection in 128 cases in which time sequence was documented was 27 weeks.
Finally, in a study in which 37
patients became infected (9) the majority of infections
appeared 8 to 12 days postoperatively.
Because of the
wide variation of time from date of surgery to appearance
of infection, time to infection was analyzed in this
study.
Method of Analysis
All statistical analyses were computed using the
Biomedical Program (BMOP) at the CSUN computer center.
Descriptive statistics, using BMDP2D, (frequency
9
'
36
distributions) were computed to determine the distribution of study factors among the patients.
BMDP program 3D was also used, this program allowed
for the comparison of the means of 2 groups by computing 2 sample t-tests.
In categorical factors having
more than 2 groups, all possible pairings of the groups
were compared.
(1)
The various categorical risk factors:
infection (present, absent), (2) hematoma (yes, no),
(3) diabetes (yes, no), (4) pre-existing infection on an
affected extremity (yes, no), ( 5) pre-existing infection
at another site (none, urinary tract infection, respirat o ry i nf e c t i o n , o the r s i t e ), ( 6 ) graft ma t e r i a 1 ( da c ron ,
autologous, combined), (7) scheduled or emergency, (8)
reoperation within 72 hours (yes, no), (9) angiography
through the affected extremity (yes, no), (10) incisional
site that became infected (abdomen, chest, groin,
popliteal, tibial), and (11) for all procedures that
were performed.
Classification of wound infection and
the length of time it took for infection to become
apparent were also analyzed in this manner.
Chi-square tests (BMDP-4F) (two way and multiway
tables) were utilized to analyze the association between
the outcome factor (infection or no infection) and the
risk factors previously identified.
Chi-square tests
were also used to test the association between the
type of wound infection (incisional or deep) and length
of time to the appearance of infection.
37
Multiple logistic regression analysis was performed
(using BMDPLR) to attempt to predict which individuals
would develop an infection based on the selected set of
risk factors (predictors).
This program selects patient
predictive factors in a stepwise manner.
These predic-
tive factors can be categorical or continuous and the
program estimates the coefficients for a predictive
equation.
The predictive factors enter the equation, 1
at a time, the most significant predictor being selected
first.
With the first predictor in the equation, the
second most significant predictor is entered into the
equation.
The stepwise selection of predictors continues
in this manner, the most significant being selected when
the previous most important predictor(s) has been entered into the analysis.
The stepwise selection ceases when
additional predictors will no longer significantly distinguish into which of the 2 groups (infection or no
infection) the individual will be classified.
CHAPTER FOUR
Results
Introduction
This section provides a description of the patients
that had prosthetic vascular graft surgery during the
period of time specified earlier, namely the years 1976
through 1981.
The statistical analysis of the hypothesis
and a comparison of characteristics of those patients
that developed an infection will also be found in this
section.
All statistical tests were considered signifi-
cant at the alpha= 0.05 level.
The number of charts with complete information for
each risk factor varied throughout the record review,
therefore, all data and tables in this section provide
totals which reflect the documentation of the presence or
absence of the various risk factors.
Two hundred patients were identified as having prosthetic vascular graft surgery during the selected time
period.
Of this number, 6 were considered ineligible for
analysis because of the following reasons:
(1) 2
patients had their original prosthetic vascular graft implanted at other hospitals, (2) 3 patients had their
original surgery prior to 1976 with subsequent multiple
procedures, and (3) 1 patient had multiple procedures
performed prior to the appearance of infection.
38
It should
39
be noted that 4 of these 6 patients developed infections.
Thirty of the remaining 194 patients that were identified transferred to other Veterans Administration
Medical Centers for follow-up therefore their clinical
records were not available for analysis.
One hundred and
sixty-four records were available for analysis and the
results of this study were based on these cases.
At this
point 2 additional cases were rejected for the following
reasons: (1) 1 patient did not return for follow-up
after discharge, and (2) 1 patient had a large portion
of his clinical record missing and infection status could
not be determined.
The study included only 2 females
therefore they were included in the overall analysis of
the data.
In this study 25 infections developed in the 162
cases that were examined for an infection rate of 15.4
percent.
Analysis of Individual Risk Factors
Age of the Study Group.
The youngest patient in-
cluded in this study was 45 years of age and the oldest
was 86 years old, for a range of 41 years.
The mean age
of the study group was 62.7 years of age and the median
was 61 years of age.
Seventy-two patients (44.4 percent)
were younger than the median age and 90 (55.6 percent)
were 61 years of
~ge
or older.
40
The mean age of the patients that developed an infection (n
= 25) was 62.3 years of age as compared to
62.7 for those that did not develop infection (n = 135).
There was no difference in the mean age between these 2
groups.
Age, as a risk factor, was examined using the median
age (61 years) to form 2 groups.
There was no signifi-
cant association between infection/no infection and age.
(See table 1).
Table 1
Infection (Present, Absent) Categorized
by Median Age
Infection
Age:
No Infection
n
#
Less than 61
72
14
8.8
58
36.3
61 or older
88
11
6.9
77
48. 1
Total:
160
25
15.6
135
84.4
(x2
= 1 • 4 5; df =
1; p
%
%
#
= 0.2288)
From the analysis of the data it would appear that age,
was not a significant risk factor (p=0.23) for the
development of infection.
Infection occurred in 19.4
percent of the patients less than 61 years of age while
12.5 percent of the patients 61 years or older developed
infection.
{.\
41
Hematoma.
The next risk factor that was analyzed
was postoperative hematoma.
Seven patients developed
hematoma following surgery.
The mean age of these 7
patients was 63.7 years of age.
The youngest was 55
years of age and the oldest was 86 years of age.
The
mean age of the 149 patients not developing a hematoma
was 62.7 years of age and ranged from 45 to 85 years.
Although the group that developed hematoma was slightly
older than those not developing hematoma the difference
was not significant (p
= 0.736).
Chi square analysis was utilized to determine if the
risk factor hematoma was associated with the development
of infection in this group of patients.
(See table 2).
Table 2
Infection (Present, Absent) Categorized
by Hematoma (Present, Absent)
Infection
No Infection
Hematoma:
n
#
%
#
%
Present
7
2
1.3
5
3.2
150
22
14.4
128
81.5
157
24
15.3
133
84.7
Absent
Total:
(X2
= 0.999; df = 1 ; Fisher's exact
p
= 0.2906)
Postoperative hematoma was not significantly associated
with the development of infection in this group of
'
42
patients (p
= 0.2906).
Only 2 patients with a hematoma
developed infection.
Diabetes.
The third factor that was analyzed in
this study was the potential role of diabetes in the
development of infection.
Twenty-four patients having
prosthetic vascular graft surgery were identified as
diabetics, 135 were not diabetics and 5 patients had this
information missing from their record.
Chi-square analysis was performed to see if there was
an association between diabetes and the development of
infection.
(See table 3).
Table 3
Infection (Present, Absent) Categorized
by Diabetes (Present, Absent)
Infection
Diabetes:
n
Present
Absent
Total:
(X2
No Infection
%
%
24
1
0.6
23
1 4. 5
135
23
14.5
112
70.4
159
24
1 5. 1
135
84.9
= 2.634; df = 1; Fisher•s exact p = 0.0856)
As seen in table 3, of the 24 patients identified as
being infected only 1 was diabetic.
There was no
significant association between developing infection and
43
the presence of diabetes in this group of patients
(p
= 0.0856).
Pre-existing Infection on an Affected Extremity.
Sixteen patients who had prosthetic vascular graft
surgery were reported to have an infected lesion on an
affected extremity.
There was no significant difference
in the mean age of patients having infected lesions when
compared to the group that did not (p = 0.4432).
When the mean length of time it took to perform
surgery was analyzed for these 16 patients, it was found
that in those with a pre-existing infection on an affected extremity the mean duration of surgery was 7 hours
and 9 minutes while in the group without an infected
lesion it was 5 hours and 12 minutes.
T-test analysis
showed that this difference was statistically significant
(p
= 0.0265).
There was a significant association found between
this risk factor and the development of infection (see
table 4) when evaluated by chi-square analysis.
44
Table 4
Infection (Present, Absent) Categorized by
Pre-existing Infection on an
Affected Extremity
(Present, Absent)
Infection
Infected
Extremity
n
Present
Absent
Total:
(X2
=
%
No Infection
#
%
6.4
16
6
3.8
10
141
18
11.5
123
78.3
157
24
1 5. 3
133
84.7
6.788; df
= 1; p =
Six of the 16 patients
0.0092)
who had infected lesions prior to
surgery developed postoperative wound infections.
As a
single risk factor, a pre-existing infection on an affected limb, appears to have a significant association to
the development of infection in this group of patients
(p
= 0.0092).
Pre-existing Infection at Another Site.
Eight
patients were found to have a pre-existing infection in
another site at the time prosthetic vascular graft surgery
was performed.
Three patients had genitourinary tract
infections, 1 patient had a respiratory tract infection,
1 patient had an epididymitis and 3 patients were
found to have various types of wound infections from
45
previous surgical procedures.
There was no statistical
differences in the mean ages of these groups of patients.
There was a significant difference noted in the mean
duration of surgery in the group that had pre-existing
infections when compared to patients without pre-existing
infection (p
= 0.0317).
A possible explanation for this
difference could be the discovery of an infection that
was found at the time of surgery.
There was no significant association found when chisquare analysis was performed on this risk factor to
determine its association in the development of infection
(p = 0.6746).
None of the patients who had a pre-
existing infection at the time of surgery developed a
postoperative wound infection.
Graft Material.
In the present study, the pros-
thetic vascular grafts utilized were made of dacron,
autologous vein or a combination of the 2 previously
mentioned materials.
No significant difference was found
when the mean age of these 3 groups of patients were compared to each other.
One hundred and forty-five patients (89.5 percent)
had dacron vascular grafts implanted; 18 (12.4 percent)
became infected.
Fourteen patients (8.6 percent) had
autologous vein grafts implanted; 6 of these grafts (42.9
percent) became infected.
Only 3 patients (1 .9 percent)
had grafts composed of a combination of material; 1
(33.3 percent) became infected.
(See table 5)
46
Table 5
Categories of Study Group by Infection
(Present, Absent) and Graft Material
Infection
No Infection
Graft Material: n
#
%
#
145
18
1 1.1
127
78.8
14
6
3.7
8
4.9
3
1
0.6
2
1.2
162
25
15. 4
137
84.6
Dacron
Autologous
Combined
Total:
%
(X2 = 9.817; df = 2 . p = 0.007)
'
A significant association was found between graft material and the development of infection when chi-square
analysis was performed on this risk factor.
Graft
material, when analyzed as a single risk factor appears
to be significantly associated with the development of
infection in this group of patients (p = 0.007).
Scheduled versus Emergency Surgery.
Of the 162
cases available for analysis, it was found that 145 were
scheduled operations and 17 operations were performed as
emergency procedures.
The mean age of patients requiring
emergency surgery was greater than those having scheduled
procedures, however, this difference was not statistically significant (p
= 0.87).
47
Twenty-four cases that were scheduled became infected; 1 case performed as an emergency procedure became
infected.
There was no significant association between
infection and whether the procedure was performed as a
scheduled procedure or an emergency procedure.
(See table
6) •
Table 6
Infection (Present, Absent) Categorized
by Scheduled or Emergency Surgery
Infection
Category:
n
#
Scheduled
145
24
Emergency
17
162
Total:
(X2
= 1 .327; df =
Reoperation.
No Infection
#
%
14.8
1 21
7 4. 7
1
0.6
16
9.9
25
15.4
137
84.6
%
1 . Fisher•s exact p
'
= 0.2213)
Of the 25 patients that developed
postoperative prosthetic vascular graft infections, 4
required reoperation within 72 hours.
The mean age of
patients requiring reoperation (65.9 years of age) was
slightly older than patients not requiring reoperation
(62.3 years of age).
The difference in age between these
2 groups was not statistically significant (p
= 0.88).
Reoperation was also examined as an individual risk
factor utilizing chi-square analysis.
No significant
48
association was found between infection and reoperation
in this study.
(See table 7).
Table 7
Infection (Present, Absent) Categorized by
Reoperation within 72 Hours (Yes, No)
Infection
Reoperation:
No Infection
n
#
%
#
%
Yes
13
4
2.5
9
5.6
No
14 7
21
1 3. 1
126
78.8
160
25
1 5. 6
135
84.4
Total:
(X2 = 2.46; df = 1; Fisher's exact p = 0.1167)
Four patients (30.8 percent) requiring reoperation developed infection in this study.
Arteriography.
In this study, 63 ( 46.7 percent) of
the patients had arteriography performed through an
affected extremity and 72 (53.3 percent) did not.
The
mean age of patients having arteriography through the
affected extremity (62.4 years of age) was not significantly different (p = 0.2374) from those having
arteriography through a non-affected limb (62.7 years of
age).
The risk factor, arteriography through an affected
extremity, was examined using chi-square analysis to
49
ascertain if there was a significant association between
it and the development of infection.
The result of this
analysis is documented in Table 8.
Table 8
Infection (Present, Absent) Categorized
by Arteriography Through an Affected
Extremity (Yes, No)
Arteriography
Through an
Affected
Extremity
Infection
n
#
No Infection
#
%
%
Yes
63
9
6.7
54
40.0
No
72
11
8.1
61
45.2
14.8
115
85.2
Total:
(X2
20
135
= 0.026;
df
= 1;
p
= 0.8714)
There was no significant association between
arteriography through the affected extremity and the
development of infection in this study (p = 0.8714).
Duration of Surgery.
When this risk factor was
analyzed it was noted that the minimum length of time it
took to perform surgery in which a prosthetic vascular
graft was implanted was 1 hour and 30 minutes and the
maximum length of time recorded was 15 hours.
The mean
length of time was 5 hours 35 minutes, the median was 5
hours and the mode was 4 hours.
The mean length of time
50
it took to perform surgery in the group of patients that
became infected was 5 hours 26 minutes.
The mean length
of time it took to perform surgery in the non-infected
group of patients was 5 hours 17 minutes.
The difference
in the mean length of time it took to perform surgery in
these 2 groups was not significant
= 0.054).
(p
Evaluation of this risk factor, duration of surgery,
by chi-square analysis was performed utilizing the median
as the measure to form 2 groups.
The results of this
analysis are presented in Table 9.
Table 9
Infection (Present, Absent) Categorized
by Median Duration of Surgery
Duration of
Surgery:
Infection
No Infection
n
#
Less than 5 hours
75
13
8. 1
62
38.5
5 hours or 1 onger
86
12
7.5
74
46.0
1 61
25
1 5. 5
136
84.5
Total:
(x2
%
#
%
= 0.349; df = 1; p = 0.5547)
Th e du r a t i o n of s ur ge ry f o r 8 6 p a t i e nt s ( 5 3 • 4 p e r c e nt ) wa s
5 hours or longer.
There was no significant association
between infection and duration of surgery in this study
(p
= 0.556).
51
Site of Incision.
In this study, all possible
comparisons of mean age were performed for the various
categories of incisional sites that became infected.
There was a significant difference in mean age only when
the group that developed abdominal wound infections was
compared to the group that developed infection at more
than one site (p = 0.0504).
The patients developing
abdominal wound infections were slightly older.
When the mean duration of surgery was evaluated,
patients who developed infected groin incisions had
longer operations than patients who developed infected
abdominal incisions.
The difference between the mean
duration of surgery for these 2 groups was significant
(p = 0.0382).
The distribution of the various incisional sites
that became infected are found in table 10.
52
Table 10
Distribution of Postoperative Wound Infections
Categorized by Site
Percent of
Infection by Site
Site:
n
Abdominal Infections
3
12
15
60
Popliteal Infections
1
4
Chest Infections
3
12
Multiple Sites
3
12
Groin Infections
Tot a 1:
25
100.0
One hundred and thirty-eight (84.65 percent) of the
patients did not develop an infection.
Site of incision
does appear to be a risk factor (p = <0.0005) in patients
requiring prosthetic vascular graft surgery.
Of the 25
wound infections that occurred in this group 15 (60
percent) developed infection in groin incisions.
Duration of Preoperative Hospitalization.
The
minimum length of time a patient was hospitalized prior
to surgery was one day (day of admission was counted as
day 1).
The maximum number of days was 76.
of central tendency were:
days, and mode 7 days.
The measures
mean 13.8 days, median 11
In the group of patients that
developed infections the mean number of days
53
hospitalized prior to surgery was 13.6 days (range 2 to
38 days).
In the non-infected group of patients the mean
number of days hospitalized prior to surgery was 13.9
days (range 1 to 76 days).
This different was not sta-
tistically significant.
The mean number of days hospitalized prior to surgery was significantly different for patients having
autologous vein grafts when compared to patients having
dacron grafts (p = 0.0038).
Patients having autologous
vein grafts were hospitalized for a longer time prior to
surgery than those having dacron grafts.
To analyze the association of this risk factor,
duration of hospitalization prior to surgery, the median
(11 days) was utilized to form 2 groups.
Chi-square
analysis was utilized for this evaluation which is presented in table 11.
54
Table 11
Infection (Present, Absent) Categorized by the
Duration of Preoperative
Hospitalization
Infection
Days:
No Infection
n
#
Less than 11
77
11
6.8
66
40.7
1 1 or more
85
14
8.6
71
43.8
162
25
15.4
137
84.6
Total:
x2
%
#
%
= 0.148; df = 1 '. p = 0.7007)
There was no significant association found between infection and duration of preoperative hospitalization
(p
= 0.7007).
Duration of preoperative hospitalization
was not a significant risk factor for this group.
Procedure Performed
In this study, 16 types of prosthetic vascular graft
implants were performed on the study group.
When the
mean aqe of patients was compared according to the procedure performed, a significant difference was found between
some categories.
A table with these data has been in-
cluded in the Appendix.
(See Appendix B).
When the mean duration of surgery was compared according to the procedure performed a significant difference
was found between some of the categories also.
A table
,,
55
with these data has been included in the Appendix.
(See
Appendix C).
A significant difference in the mean duration of
preoperative hospitalization was found when 4 procedures
were compared.
A table with these data has also been
included in the Appendix.
(See Appendix D).
The risk factor, procedure performed, was analyzed
to determine if there was any association between the
procedure and the development of infection.
The distri-
bution of the procedures performed and whether infection
developed are presented in table 12.
'
56
Table 12
Distribution of Infection (Present, Absent)
Categorized by Procedure Performed
Infection
Procedure:
Aortobifemoral
Aortobiiliac
Femorofemoral
Ao rto iliac/
Aortofemoral
Femoropopl i teal
.a.xi 11 ofemoral
Femorotibial
Aortic Straight
Tube
Axilloaxillary
Axillopopliteal
Bilateral
Axillotibial
Femoroooplitealtibial
Femorofemoralpopliteal
Axi 11 obi femoral
Aortobifemoralpopliteal
Straight Popliteal
Total:
No Infection
n
#
%
59
31
7
10
6
2
1
0
3.7
1.2
0.6
0.0
53
29
6
10
32.7
1 7. 9
3.7
6.2
17
2
2
11
0
2
0
8
4.9
0.0
1.2
0.0
9
0
5.6
1.2
0.0
11
6.8
1
0
0.6
0.0
2
1
1
1
0.6
0.6
2
3
0
1
o.o
1
2
#
%
2
0.6
2
1.2
1.2
0
0.0
1
0.6
3
7
1
1
0.6
0.6
2
6
1.2
3.7
4
1
0.6
3
1.9
162
25
15.4
137
84.6
When an analysis of the procedure that was performed is
evaluated as a single risk factor its association in the
development of infection in this group of patients is
significant (p = 0.0003).
Classification of Wound Infection.
In this study,
the classification of the infection into incisional wound
57
infection or deep wound infection was also examined.
Of
the 25 prosthetic vascular grafts that became infected 80
percent (n = 20) were classified as incisional wound infections and 20 perecent (n
= 5)
were deep wound infections.
When these 2 groups were analyzed for the length of time
it took for the infection to become apparent the following
was noted.
In the group that developed incisional infec-
tions the mean length of time it took for the infection
to become apparent was 54.04 days whereas the mean length
of time in the group developing deep infections was 711.6
days.
This difference was significant (p =<0.0001).
A significant difference was noted when mean dura-
tion of surgery in the patients who developed incisional
infections (mean 6 hours 41 minutes) was compared to noninfected patients (mean 6 hours 28 minutes) (p
There was no sigificant difference in:
= 0.0377).
(1) the mean
duration of surgery and classification of wound infection
(p = 0.3947), (2) the mean duration of surgery when the
group that developed deep infection was compared to those
who did not develop infection (p = 0.8069), (3) age, or
(4) duration of preoperative hospitalization when
patients developing incisional infection were compared to
those developing rleep infection.
Length of Time to the Appearance of an Infection.
The length of time that elapsed from the time of surgery
to the appearance of infection varied widely in this
58
study.
The minimum time to the appearance of infection
was 6 days while the maximum time was 2,130 days.
The
mean number of days before the appearance of infection
was 28.46 days.
(n
(n
= 15)
= 10)
Infection became apparent in 60 percent
in less than 28.5 days whereas in 40 percent
of the patients the appearance of infection took
28.5 days or more.
As mentioned earlier, the difference in the mean
length of time for infection to become apparent and
classification of wound infection was significant.
Mean length of time to the appearance of infection
was measured in the 3 categories of graft material.
The
difference in this mean length of time was significant
(p = 0.0240) only when the group having autologous grafts
(n
= 14)
was compared to the group having grafts made of
combined material (n
= 3).
It took longer for infection to become apparent if
the patient had arteriography through the affected extremity prior to surgery.
(p
This difference was significant
= 0.0213).
When mean length of time to the appearance of in-
fection and the various incisional sites that became
infected were compared, the following were found to be
significant.
The mean length of time for abdominal wound
infections (n
= 3) was 209.3 days compared to a mean of
53 days for chest wound infections (n = 3) (p = 0.0399).
In the group of patients developing multiple site
59
infections {n = 3) the mean length of time for infection to
become apparent was 447.7 days compared to 53 days in the
chest wound infections {p
= 0.0210).
The mean length of time to the appearance of infection was significant when certain operative procedures
were compared to each other.
A table with this data has
been included in the Appendix.
(See Appendix E).
Chi-square analysis was performed on these 2 factors
to see if there was any association between classification
of wound infection and length of time to the appearance of
infection.
The results are presented in table 13.
Table 13
Classification of Infection (Deep, Incisional)
Categorized by the Mean Length
of Time to Appearance
Classification:
Incisiona1
Deep
Total:
(X2
28.5 days
and more
Less than
28.5 Days
n
#
%
#
%
20
13
52.5
7
28.0
5
2
8.0
3
12.0
25
15
60.5
10
40.0
= 1 .042; df = 1; Fisher's exact p = 0.3012}
There was no significant association between classification
of wound infection and length of time to the appearance of
infection in this group (p = 0.3012).
60
Simultaneous Analysis of Data Utilizing
Stepwise Logistic Regression
A stepwise logistic regression analysis was computed
for the 13 risk factors previously analyzed.
The limit set for a risk factor to enter the equation was a p-value of 0.5; the limit set for a factor to
be removed was a p-value of 0.6.
At step zero, with no risk factor in the equation
the p-values of the risk factors were as presented in
table 14.
Table 14
Step 0
P-value of Risk Factors
Risk Factor
p-value
Age
Hematoma
Diabetes
Infection affected extremity
Infection another site
Graft material
Reoperation
Scheduled/Emergency
Arteriography
Duration of surgery
Site of incision
Preoperative hospitalization
Procedure performed
0.2399
0.3555
0.1446
0.0033
0.6390
0.0064
0.3557
0.2818
0.9377
0.4549
0.0000
0.9454
0.0005
At step 1 of the analysis, the risk factor site of incision (p
= 0.0000)
entered the equation.
With this risk
factor in the equation the p-values of the risk factors
were re-evaluated.
At this point, no risk factor had a
61
p-value of 0.5 or less, the previously established
p-value to enter the analysis.
Therefore, no additional
risk factor could enter the equation.
The conclusion of
this analysis is that incisional site is the best predictor of whether or not an infection would occur in this
group and that the other risk factors that were analyzed
would not enhance the prediction of infection.
Summary
In this analysis of data there was a significant
association between 4 individual risk factors, specifically infection in an affected extremity, graft
material, site of incision and procedure performed,
and the development of infection when chi-square
analysis was done.
(See Appendix F).
When all of the risk factors were evaluated simultaneously, using stepwise logistic regression 1 risk
factor, site of incision, was identified as being
significant in the prediction of infection for this
group of patients.
CHAPTER FIVE
Discussion
Thirteen risk factors that had been previously identified in the literature were evaluated for their association
in the development of infection.
In this study, the
evaluation of these 13 risk factors differed in that the
risk factors were evaluated using chi-square analysis to
determine if they were significantly associated with the
development of infection.
In the present study 4 of the
13 risk factors were found to be significantly associated
with the development of infection when evaluated in this
manner.
The 13 risk factors were then analyzed simul-
taneously using stepwise logistic regression to attempt
to identify those that might best predict whether or not
a patient might develop an infection.
There were 25 postoperative wound infections identified in the 162 cases analyzed for a 15.4 percent
infection rate.
This rate is higher than the 1.1 percent
overall rate of infection considered acceptable by
Talkington and Thompson (24) and it is also higher than
the 0.25 to 6 percent range reported by other investigators (6, 14).
In the present study, 80 percent (n = 20) of the
wound infections were incisional and 20 percent (n = 5)
were deep wound infections.
The mean length of time
62
63
for deep wound infections to become apparent was significantly longer (p = <0.0001) than incisional wound
infections.
Previous investigators (6, 9, 14) noted a wide variation of time from date of surgery to appearance of
infection.
The minimum length of time to the appearance
of infection in this study was 6 days with a maximum of
2,130 days.
The mean number of days before infection
became apparent was 28.5 days.
Infection became apparent
in 60 percent (n = 15) of the cases in less than 28.5
days.
In 40 percent of the cases (n = 10) the appearance
of infection took 28.5 days or more.
association (p
= 0.3012)
No significant
was found between classification
of wound infection and length of time to the appearance
of infection by chi-square analysis.
It is possible
that this lack of significance was influenced by the
measure (mean) selected to form the two groups as, when
evaluated using the t-test, there was a significant
difference when classification of wound infection and
length of time to infection were compared.
It should
be noted that deep infection in 2 patients became
apparent at 1,321 days and 2,130 days after surgery.
This may account for the difference being significant
by t-test.
Using stepwise logistic regression, the 13 risk
factors were evaluated for their ability to predict
the development of infection.
Only the factor site of
64
incision (p =0.0000) entered the predictive equation.
With this factor in the equation no other factor entered
the analysis.
In the present study the sites of inci-
sions that became infected were the groin (n
= 15),
abdomen (n = 3), chest (n = 3), multiple sites (n = 3)
and popliteal incision (n = 1).
Over half of the infec-
tions that occurred in this group of patients developed
in groin incisions.
Several investigators (16, 6, 10,
23) had noted previously that groin incisions had a
greater propensity for the development of infection than
other incisional sites.
The findings in this study
are in agreement with other investigators.
Individual evaluation of the various risk factors by
chi-square analysis identified 4 as being significantly
associated with the development of infection.
These
were incisional site (p = <0.0005), procedure performed
(p = 0.0003), graft-material (p = 0.007) and pre-existing
infection in an affected extremity (p = 0.009).
When incisional site was analyzed as an individual
risk factor a significant association (p = <0.0005) between it and the development of infection was found.
The
sites and number where the infections occurred are as
shown above.
There was a significant difference in the
mean duration of surgery in patients developing groin
infections when compared to patients developing an infection in more than 1 site (p = 0.0382).
Duration of
surgery was longer in the group that developed groin
65
infection.
It is possible that this longer duration of
surgery rather than site of incision alone contributed to
the increased number of groin infections.
However, when
the results of the stepwise logistic regression are
examined, this factor (duration of surgery) was not
significant.
Patients who developed abdominal infections
were found to be older than patients developing an infection in multiple sites.
The difference in the mean age
of these 2 groups was significant (p
= 0.0504).
This
age difference cannot be explained.
The significant association (p
= 0.0003)
between the
procedure performed and the development of infection substantiates the importance of incisional site as a risk
factor.
Ten {62.5 percent) of the 16 procedures that
were identified in this study necessitated the use of
groin incisions.
The risk of infection may vary from
patient to patient and from site to site.
As noted by
other investigators (6, 14, 23) the risk of infection
can also vary from one procedure to another.
Procedures
which require groin incisions carry a high risk for
infection.
In this study, 89.5 percent {n = 145) of the
patients had prosthetic vascular grafts composed of
dacron implanted.
in 8.6 {n
= 14)
Autologous vein grafts were utilized
of the patients and 1.9 percent (n
= 3)
of the patients had implants composed of a combination
of autologous and dacron material.
A significant
66
association (p
= 0.007)
was found between graft material
and the development of infection.
The role that implan-
ted foreign bodies play in the development of infection
should not be underestimated.
The importance of graft
material and its contribution to infection was identified
by several investigators (16, 14, 10).
The findings in
this study are in agreement with these investigators.
Pre-existing infection on an affected extremity was
found in 16 (10.2 percent) patients.
In this evaluation
of risk factors, a significant association (p
= 0.0092)
was found between this factor and infection.
This result
agrees with those of Liekweg, et al, (14), Hoffert, et
al, (10), and others (6, 9, 16).
When mean duration of
surgery in patients developing infection was compared to
those not developing an infection, there was a significant difference (p = 0.0265) between the 2 groups.
There was no significant association found between
the remaining 9 risk factors and the development of
infection when analyzed as single risk factors.
These
remaining factors will be briefly discussed as the findings in this study relate to previous research.
In contrast to the findings of Howard, et al, (12)
and Hooten, et al, (11) age was not significantly associated with the development of infection (p
this group of patients.
= 0.23) in
In the present study, age was
not a risk factor and this was in agreement with other
investigators (9, 13).
It does lend support to DeBakey
67
and McCollum•s (3) belief that age itself is not a contraindication to prosthetic vascular graft surgery.
According to several investigators (2, 9, 10) hematoma in the surgical site was felt to contribute to the
development of infection following prosthetic vascular
graft surgery.
The analysis of data in this evaluation
does not support those findings.
There was no signifi-
cant association between infection and hematoma in this
study (p = 0.2906).
Diabetes as a risk factor, contributing to the
development of infection, was noted only by Hammersten,
et al, (10).
Other investigators (16, 13, 10, 23, 22)
did not share this view.
In the present study no signi-
ficant association was found between diabetes and
infection (p
= 0.0856).
A significant difference in mean
age was found between diabetic (n
= 24)
and non-diabetic
(n = 135) patients requiring prosthetic graft surgery
(p
= 0.0138).
This age difference could be attributed to
the increased occurrence of peripheral vascular disease
in diabetics.
The process could begin at a younger age,
therefore, surgery would be necessary at a younger age.
Goldstone and Moore (6) and Liekweg, et al, (14)
found pre-existing infection at another site to be a
contributing factor in the development of infection in
patients undergoing prosthetic vascular graft surgery.
Eight patients in this evaluation were identified as
having a pre-existing infection in another site.
No
68
significant association (p
= 0.6746)
this risk factor and infection.
was found between
It should be noted that
none of the patients with a pre-existing infection at
another site developed a wound infection.
In this study, 13 patients had reoperation within 72
hours.
Of the 25 patients that developed postoperative
wound infections 4 required reoperation within 72 hours.
Unlike previous investigators (16, 1), there was no significant association between reoperation and infection
(p
= 0.1167)
in this evaluation.
There was no significant association (p
= 0.2213)
found between scheduled versus emergency surgery and
infection in this research.
Of the 17 cases that were
performed as emergency procedures only 1 became infected.
This finding agrees with Hammersten, et al, (9) who found
a lower rate of infection in patients requiring prosthetic vascular graft implants which were performed as
emergency procedures.
The role of arteriography in the development of
infection following prosthetic vascular graft surgery was
evaluated by Landreneau and Raju (13).
These investiga-
tors found an increase of "complications" when arteriography was performed through an affected extremity.
In
the present study, there was no significant association
(p
= 0.8714)
between arteriography through an affected
extremity and infection.
69
Duration of surgery was examined as a risk factor
after noting that previous investigators reported different results.
Liekweg, et al, (14) found duration of
surgery a definite factor, while Landreneau and Raju (13)
found no significant association.
Hammersten, et al, (9)
noted an increase of infection if the procedure was
longer than 2 hours.
In this study, there was no signi-
ficant association (p
= 0.5547)
noted between duration
of procedure and infection.
The final non-significant risk factor to be discussed is duration of preoperative hospitalization.
Current literature in the field of infection control
(11) has noted that colonization of the patient by pathogenic bacteria can occur if patients are admitted to the
hospital for a longer time than necessary.
Hammersten,
et al, (9) found a higher rate of infection in patients
that were hospitalized longer than 48 hours.
In this
study, only 17 patients were in the hospital 48 hours or
less.
These were the 17 patients classified as having
emergency surgery.
When duration of preoperative hos-
pitalization was analyzed using the median (11 days), no
significant association (p
nificant difference (p
= 0.7007)
= 0.0038)
was found.
A sig-
was found when the mean
duration of preoperative hospitalization was compared to
type of graft material used at surgery.
Patients who
had autologous vein grafts implanted were hospitalized
longer than patients having dacron grafts implanted.
70
Conclusions
If incisional site is the best predictor, in the
present study, for the development of infection, it would
not be considered an alterable risk factor.
However,
there may be some alternative procedures for reducing the
risk of infection in relation to the incisional site.
For instance, several studies have shown that groin
incisions are frequently associated with infection.
Evaluation of preoperative preparation of the incisional
site might indicate areas that could be improved upon.
Some of these improvements might include type of soap
used, type of antiseptic solution used and whether the
site is shaved or not, as well as postoperative site
care.
When individual risk factors are examined, incisional
site, procedure performed and graft material used would be
considered unalterable.
The only factor that one might
alter is pre-existing infection on an affected extremity.
The importance of eliminating this potential source of
infection becomes quite apparent.
Unless the patient•s
life or extremity is threatened, surgery should be
deferred until the infection is eliminated.
Some areas for further research based on the findings
of this study include:
1.
Comparative studies evaluating the preoperative preparation of the incisional site.
Protocols evaluating scrub and/or antiseptic
71
solutions can be devised.
This type of study
could also include whether or not to shave the
incisional site.
2.
Replication of this study in one or more
medical facilities to definitely determine if the risk factors found to be
significant in this study are significant
in other groups.
3.
Examination of other risk factors or procedures that would assist in predicting
whether an infection would or would not
occur in patients requiring prosthetic
vascular graft surgery.
4.
Limit the scope of future study by
evaluating only one specific surgical
procedure.
For instance, only aortobi-
femoral or femorofemoral or femoropopl i teal
implants.
5.
Consideration of cooperative studies among
various medical facilities to evaluate
procedures that are infrequently performed.
From this study, it is apparent that infection in a
prosthetic vascular graft may not become apparent for a
long period of time, in fact years.
If a patient who has
had this type of surgery should complain of non-specific
symptoms of infection, for instance occasional fever and
72
chills, loss of appetite, tiredness with or without pain
or discomfort in the operative site, infection should be
suspected.
This is true even if the incisional site is
well healed and without signs of infection.
References
1.
Becker RM, Sundell PE.
cation grafts:
Infected aortic bifur-
experience with fourteen patients.
Surg 1976; 80: 544-49.
2.
Bouhoutas J, Chavatzas 0, Martin P, et al.
Infected synthetic arterial grafts.
Br J Surg
1974; 61: 108-11.
3.
4.
OeBakey ME, McCollum CH.
elderly.
Med Instrum 1982; 16: 89-90.
Dixon WJ.
BMOP statistical software.
CA:
5.
Vascular grafts in the
Berkeley,
University of California Press, 1981.
Fry WJ, Lindenauer SM.
Infections complicating
the use of plastic arterial implants.
Arch Surg
1976; 94: 600-09.
6.
7.
Goldstone J, Moore WS.
Infections in vascular
prosthesis:
clinical manifestations and surgical
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Am J Surg 1974; 128: 225-33.
Haley RW, Quade 0, Freeman HE, et al.
Study
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J Epidemiol 1980; 111: 472-85.
8.
Haley RW, Quade 0, Freeman HE, et al.
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111: 635-44.
73
Algorithms
Am J Epidemio1 1980;
Am
74
9.
Hammersten J, Holm J, Schersten T.
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Infections in
J Cardiovasc Surg 1977; 18:
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10.
Hoffert PW, Gensler S, Haimovici H.
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Infections
Arch Surg 1965; 90:
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11.
Hooten TM, Haley RW, Culver DH, et al.
The joint
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occurrence of nosocomial infection.
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r~ed
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12.
Howard JM, Barker WF, Culbertson WR, et al.
Factors influencing the incidence of wound infect i o n•
13.
An n Sur g 1 9 6 4 ; ( Su pp1 em e nt) 1 6 0 : 3 2- 81 •
Landreneau MD, Raju S.
Infections after elective
bypass surgery for lower leg ischemia:
the influ-
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14.
Liekweg WG, Levison SA, Greenfield LJ.
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Infections
incidence, anatomic location,
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In:
Infections of prosthetic heart valves
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15.
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Mausner JS, Bahn AK.
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Papa MZ, Halperin Z, Adar R.
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Israel J Med Sci 1981, 17: 257-59.
p '
75
17.
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Mortality
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Rich NM, Hughes CW.
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Shapiro M, Munoz A, Tager IB, et al.
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21.
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23.
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Appendix A
Data Collection Form
Identification number
Day of Adm
Age
-----------Sex------------
Day of Surgery
Day of Discharge________
Procedure Performed
-----------------------------------------
Length of Surgery
--------------Material
of Graft
--------------
Arteriography via affected limb prior to surgery
Emergency
Y
N
M
Scheduled
Reoperation within 72 hours
Infection on affected limb
Infection in other site
Hematoma formation Y
Y
N
Y
N
Y
M
N
Y
N
M
Y
N
M
Diabetes
M
M
specify
-----------------------------
N M Postoperative infection
y
N
M
Site {s) of infection
----------------------------------------
Classification
deep
superficial
none
Length of time to infection___________________________________
76
Appendix B
Comparison of Mean Age and Categories
of Procedure Performed
Group One
Group Two
N
N
p-Va1ue
Procedure
Aortobifemora11
Aortobi i1 i ac
59
30*
0.006
Ao rto bi femora 1 I
Aortoi1iac
Aortofemoral
59
10*
0.0017
Aortobi femoral I
Axillofemoral
59
2*
0.0130
Aortobi femoral I
Axi1loaxi1lary
59
2*
0.0195
Aortobi il i acl
Femorofemoral
30*
8
0.0171
Aortobi il i acl
Femorotibial
30*
2
0.0491
Femo rof emo ral I
Aortoiliac
Aortofemora1
8
10*
0.0302
Femorofemora11Aortic
Straight Tube
8
11*
0.0435
Femorofemoral I
Axil1oaxillary
8
2*
0. 0 01 3
Femo rof emo ra 1 I
Axil1ofemoral
8
2*
0.0009
* indicates the greater mean age
77
Appendix C
Comparison of Mean Duration of Surgery and
Categories of Procedure Performed
Group One
Group Two
N
N
p-Value
Procedure
Aortobifemorall
Aortobiiliac
59*
30
0.0191
Aortobi femoral I
Femoropopliteal
59
17*
0.0298
Aortobi femoral I
Axillobifemoral
59
3*
0.0466
Aortobi il i acl
Femoropopliteal
30
17*
0.0001
Aortobi i1 i acl
Ax ill obi femoral
30
3*
0.0001
Aortobi il i acl
Axillobifemoropoliteal
30
7*
0.0000
Femorofemoral
Femoropopliteal
8
17*
0.0209
Femorofemoral I
Axillobifemoral
8
3*
0.0063
FemorofemoraliAortobi- 8
femoropopliteal
7*
0.0034
Femo rof emo ral I
Straight Popliteal
4*
0.0053
8
* indicates the greater mean duration of surgery
78
Appendix D
Comparison of Mean Duration of Preoperative Hospitalization and Categories of Procedures Performed
Group One
Group Two
N
N
Procedure
Aortobil i ac/
Femorofemoral
Femorofemoral/
Femorotibial
p-Value
31
8*
0.0242
8
2*
0.0028
* indicates the greater duration of preoperative
hospitalization
79
Appendix E
Comparison of Mean Length of Time to the
Appearance of Infection and Categories
of Procedures Performed
Group One
Group Two
Procedure
N
N
p-Value
AortobifemoraliStraight
Tube Popliteal
59
4*
0.0000
Ao rtobi il i acl
Femoropopliteal
31
17*
0.0121
Ao rtobi il i acl
Ax i 11 o ax i 11 a ry
31
2*
0.0000
.t\o rtobi il i acl
Femoropoplitealtibial
31
3*
0.0000
Ao rtobi il i acl
Straight
Popliteal Tube
31
4*
0.0000
Femo rof emo ral I
Femoropopliteal
8
17*
0.0356
Femorofemoral I
Femorotibial
8
2*
0.0023
Femo rof emo ral
Axilloaxillary
8
2*
0.0000
Femorofemora1 I
Femoropop1itealtibi a1
8
3*
0.0000
Femorofemora11Axillobifemoral
8
3*
0.0002
Femorofemora11Straight
Tube Popliteal
8
4*
0.0012
* greater mean length of time to the appearance of
infection
80
Appendix F
Summary Table of Risk Factors and
their Significance Level
Risk Factor
Chi-square
Value
Significance
Level
p-Value
df
Age
1.45
1
ns*
0.2288
Hematoma
0.999
1
ns
0.2906
Diabetes
2.634
1
ns
0.0856
Infection on
affected limb
6.788
1
<.01
0.0092
Infection at
another site
1 • 53 3
3
ns
0.6746
Graft material
9.817
2
<. 01
0.0074
Reoperat1on
2.462
1
ns
0.1167
Scheduled/
Emergency
1 • 3 27
1
ns
0.2213
Arteriography
via affected
1 imb
0.026
1
ns
0.$3714
Duration of
operation
0.349
1
ns
0.5547
5
<.005
0.0000
0.148
1
ns
0.7007
40.981
15
<.005
0.0003
Incisional site
Preoperative
hospitalization
Procedure
performed
162.0
* not statistically significant
81