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The Radiographer – vol. 51: 71-76
Computed Tomography Colonography:
Patient Tolerance to CO2 Insufflation
Monique D. Gaspar
Abstract
Computed Tomography (CT) colonography, also known as “virtual colonoscopy” is a relatively new technique for colorectal evaluation. It allows imaging of the colonic mucosa and wall similar to those obtained during conventional colonoscopy. The aim of
the present study was to investigate patient tolerance to carbon dioxide (CO2) insufflation during CT colonography and whether
the CO2 insufflation was adequate to distend the bowel sufficiently for radiological diagnosis. This study also aimed to demonstrate a relationship between patient age and patient tolerance to CO2 insufflation. This research investigated 22 patients (50 per
cent male, mean age 64 years) with a variety of clinical indications. CO2 was insufflated through a rectal catheter to the maximum
extent of patient tolerance. Volumetric data of the abdomen and pelvis was acquired in a single breathold using a GE Lightspeed
Plus multislice CT scanner with the patient in the supine and prone positions. The CO2 insufflation time for the supine and prone
series was recorded and the patients rated their tolerance to the CO2 insufflation based on a modified Likert scale. The results
were analysed using scatter graphs and Pearson’s Correlation Coefficient, mapping the CO2 insufflation time for the prone and
supine series and comparing it to patient age. The findings indicate that there was a statistical significance between patient age
and patient tolerance (r=-0.47), however, no statistical significance was found between the other variables. This may be due to several reasons including variable bowel length and a small sample. Additional studies are required with a larger sample in order to
further investigate this topic.
INTRODUCTION
Colorectal cancer is one of the most common non skin malignant
diseases affecting both men and women in Australia.1 The risk of
developing colorectal cancer increases with age and in those
with genetic risk factors. It is believed that most cancers arise
from pre-existing adenomatous polyps.2 Detection and removal
of these polyps can prevent the disease from occurring and has
been associated with a reduction in the prevalence of colorectal
cancer and colorectal mortality.2 It can take from 10 to 15 years
for an adenomatous polyp to become an invasive cancer.3 Thus,
there is a considerable time for detection and clinical intervention if the proper screening methods are used. Colonoscopy can,
in most cases, visualise the entire colon and is the “gold standard” of examination methods.4 However, the procedure does not
permit passage through obstructions or twisted portions of
bowel. Furthermore, colonoscopy is associated with the risk of
bowel perforation, mortality and is invasive.4 These disadvantages can result in decreased patient compliance.
Computed Tomography (CT) colonography (“virtual
colonoscopy”) is a relatively new technique that attempts to
solve some of the problems associated with conventional
colonoscopy. It allows the study of inside wall and outside of the
colon, designed to make delineation of colonic lesions such as
polyps easier.1,2 Patients require full colonic evacuation, insufflation and data acquisition with the patient in the supine and prone
positions. Previous research has focused on the areas of determining appropriate bowel cleansing methods prior to the examination,5,6 the appropriate technique of CT colonography (comparison of multislice and single slice)1,3,7,8,9 and in determining the
sensitivity and specificity of detecting colorectal polyps using
CT colonography as compared to conventional colonoscopy and
Correspondence to:
X-ray Department, John Fawkner Hospital
275 Moreland Road, Coburg VIC Australia 3058
Tel: +61 3 9383 1633 (w)
e-mail: [email protected]
other techniques.10,11
However, patient acceptance is one of the most important
factors in the analysis and determination of the success of the CT
colonography examination.19 To date there is limited research
published concerning patient acceptance and tolerance of CO2
insufflation for adequate distension during CT colonography.
The major cause of poor patient acceptance is due to the bowel
preparation, perception of embarrassment and abdominal discomfort from the CO2 insufflation.12 Conversely, patient acceptance of CT colonography was found to be more comfortable
when compared with other full colonic examinations such as barium enema or colonoscopy.4,13 In a study by Dr Maria Svensson
from the Sahlgrenska University Hospital in Sweden,14 patient
satisfaction, discomfort and embarrassment was assessed by
questionaries to patients who underwent CT colonography
immediately followed by conventional colonoscopy. Overall, 69
per cent of patients considered colonoscopy to be more difficult.
CT colonography was not considered to be painful by 57 per cent
of patients compared with 26 per cent for colonoscopy.14 More
patients rated their pain higher during colonoscopy than CT
colonography. The major complaint from patients was the discomfort from insufflation of the colon during CT colonography.14
An optimal CT colonography study requires a clean well distended colon to prevent mucosal surfaces from collapsing.5,6
Because accurate diagnosis relies on adequate insufflation, poor
colonic distension can lower the examinations sensitivity to
unacceptable levels.15 Insufflation is important because polyps
cannot generally be detected in collapsed colon segments.
Therefore, as distension worsens, so does the accuracy of the
examination. The degree of distension is dictated by patient tolerance which is increased by the use of spasmolytic agents such
as Hyoscine Butylbromide.16 However, the benefit of the spasmolytic agents is controversial. Hung et al.17 investigated the
quantification of distension in CT colonography using three
computer algorithms and another study by Svensson15 examined
bowel wall visualisation during CT Colonography. It was reported that incomplete air filling was most common in the sigmoid
colon but scanning and review in the supine and prone positions
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COMPUTED TOMOGRAPHY COLONOGRAPHY: PATIENT TOLERANCE TO CO2 INSUFFLATION
Figure 1a
compensated for the incomplete distension and provided complete or almost complete visualisation of the bowel wall. This
investigation was similarly studied by Yee et al.16 who concluded that colonic distension was significantly improved by using
supine and prone scanning. Several other studies have been
done evaluating patient acceptance of CT colonography, the
results indicating an acceptable examination for patients with
low levels of pain and discomfort and a high likelihood of having the examination repeated in the future.18,19
Given the key influence of patient tolerance and distension
on CT colonography,14,15,16,17,18,19 it was hypothesised that it would
be beneficial to develop an experiment assessing the amount of
CO2 insufflation related to bowel distension. Therefore, the aim
of this study was to investigate patient tolerance to CO2 insufflation during CT colonography and whether the CO2 insufflation was adequate to distend the bowel sufficiently for radiological diagnosis. Furthermore, this study also aimed to demon-
strate a relationship between patient age and patient tolerance to
CO2 insufflation.
METHODS AND MATERIALS
Subject Description
This study was conduced over a seven week period in a medium size private hospital and was approved by the radiology
department and the University of Sydney. Twenty-two patients
were included in the study which consisted of 11 men (50 per
cent) and 11 women (50 per cent), mean age was 64 years, range
34-87 years. The main clinical indications were diverticular disease, abdominal pain, previous polyps removed, unsuitable for
colonoscopy, rectal bleeding, constipation and screening. There
were no specific criteria for subject selection because a variety
of age groups and socio-economic backgrounds were required.
Nine patients referred immediately following failed colonoscopies did not require as much CO2 insufflation due a partially
distended bowel from the conventional colonoscopy and consequently were excluded from the study. A typical examination
time was approximately 15 minutes in total.
Patient Preparation
In preparation for CT colonography, the colon needs to be prepared with various regimes to remove faeces that interfere with
interpretation. Two days prior to the examination, patients commenced a low fibre diet and one day prior, patients were allowed
only a clear liquid diet. In addition, patients were required to
dissolve two sachets of Colonlytely (sodium sulphate solution)
in a total of four litres of water, drinking at a rate of 1 litre/hour
beginning in the afternoon prior to the examination. Patients
were required to fast six hours prior to the procedure.
On the day of the examination, patients were asked to evacuate their rectum immediately prior to the examination. To
reduce bowel peristalsis and optimise bowel distension an intravenous injection of 20mg of Buscopan (Hyoscine
Butylbromide) was given. A small rubber catheter (16 Fr - 6mm
Foley’s catheter) was inserted into the rectum of the patient and
gentle CO2 insufflation was administered (rate of 1ml/second).
CO2 has a steep diffusion gradient across the colonic wall and is
Figure 2
72
Figure 1b
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M.D. GASPAR
resorbed rapidly and it is thought to decrease patient
discomfort and post examination flatulence.
Patients were encouraged to hold on to the CO2 but
asked to let the technologist know when they were
beginning to feel uncomfortable. Generally this signalled that the colon was well distended, however, a
set time for insufflation was not used since the
length of a person’s colon is variable. Additionally,
an incompetent ileocecal valve will require more
insufflation as CO2 escapes into the small bowel.15
Appendix
Table 2: Data Results
Patient
Age
Gender
CO2 time
Supine (min)
CO2 time
Prone (min)
Patient
Tolerance Rating
CO2
rate
70
78
34
53
76
87
45
48
56
40
45
78
78
74
45
65
74
65
65
72
71
80
Female
Male
Male
Female
Male
Female
Female
Female
Male
Male
Female
Female
Female
Male
Male
Female
Male
Male
Female
Male
Male
Female
1.26
2.00
1.20
1.55
1.23
1.40
1.30
2.20
2.05
2.05
2.10
2.15
2.15
1.30
1.50
2.52
1.70
1.40
2.30
1.10
2.43
2.02
0.32
0.32
0.45
0.55
1.10
1.10
0.30
0.35
1.00
0.40
0.50
0.50
0.50
0.35
0.40
0.37
0.35
0.50
0.40
0.25
0.35
0.30
3.0
3.0
4.0
3.5
1.0
1.0
4.0
3.5
3.5
3.0
3.5
4.0
2.5
3.0
3.0
2.0
2.5
1.0
3.0
2.0
5.0
2.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
Image Acquisition
After insufflation, the catheter was clamped off and
a single supine scout image was obtained to verify
adequate bowel distension (Figure 1). If adequate
bowel distension was present, the CT examination
was performed but if insufficient distension was
achieved (Figure 2), additional CO2 was administered. Patients were scanned first in the supine position in a cephalo-caudad direction encompassing
the entire colon and rectum and then placed in the
prone position. Additional CO2 was given in the
prone position. Following a second scout localising
image, the process was repeated over the same zaxis range. Supine and prone imaging doubles the
radiation dose but was essential to allow optimal
bowel distension, redistribution of residual fluid and
differentiation of faecal material from polyps since
visualisation of mobility of a filling defect implies
residual faecal material.16
A multislice CT scanner (GE Lightspeed Plus)
was used with a 4 X 2.5 mm slice detector configuration, 120kV, 0.5 sec gantry rotation and 200 mA.
A pitch of 1.5 was used so that the entire abdomen
and pelvis was covered within a 15-20 second breathold. CT
slice thickness was 2.5mm with a 1.25mm reconstruction interval on a standard algorithm and a 512 x 512 reconstruction
matrix. Acquired images were sent through an ethernet network
to a dedicated workstation equipped with software that allowed
generation of coronal, sagittal and 3D endoluminal images with
volume rendering. The images were evaluated by a radiologist.
Data Collection
During the examination different variables were recorded on the
data results sheet (Appendix 1) including the patient age, CO2
insufflation rate and time for supine and prone series, clinical
indications, whether insufflation was adequate and any additional comments. The time was determined using a stop watch and
the rate recorded from the CO2 cylinder. After the examination
the patient’s tolerance to the CO2 insufflation was assessed.
Patients were required to answer a question designed to assess
the degree of discomfort they experienced with the whole procedure and specifically with the administration of CO2. However,
because tolerance is a subjective response which is classified as
“intangible personal experiences”20 an arbitrary grade of increasing intensity was identified and each grade was assigned a
numerical score. Assessing patient tolerance to CO2 insufflation
was based on a five level threshold modified Likert scale20 using
the response alternatives defined in Table 1.
Statistical analysis
The results of the examination were tabulated (Appendix 1 –
Table 2) and analysed using scatter graphs and Pearson’s correlation coefficient, mapping the CO2 insufflation time for the
prone and supine series and comparing it to patient age. In addition, patient tolerance was compared to patient age. The mean
values were calculated for the quantitative variables when appropriate.
RESULTS
Twenty-two patients had a CT colonography examination.
Nineteen examinations based on the radiologists report were
rated as excellent distension enabling visualisation of the mucosal wall and three examinations were reported as
Table 1: Tolerance Ranking Scale
only adequate due to inadequate distension in the
sigmoid colon on the supine series. Seven supine
5 = tolerance (tolerable and doesn’t interfere with functioning of examination)
series had to be repeated due to inadequate insuf4 = mild discomfort (starting to become troublesome, perceived consciously)
flation on the scout views consequently resulting
3 = moderate discomfort (become restless and irritable, causing mild stress)
in the addition of extra CO2. 31 per cent of
patients considered the CO2 insufflation to be
2 = painful discomfort (patient complaining)
painful or unbearable. The majority (69 per cent)
1 = unbearable discomfort or intolerable (patient moaning, writhing, not able to continue)
of patients found the CO2 insufflation to be mod-
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COMPUTED TOMOGRAPHY COLONOGRAPHY: PATIENT TOLERANCE TO CO2 INSUFFLATION
CO2 Insufflation Time Supine Series Vs Patient Age
Figure 3
3.00
CO2 Insufflation Time (minutes)
2.50
2.00
1.50
1.00
0.50
0.00
0
5
10
15
20
25
30
35
40 45 50 55 60
Patient Age (years)
65
70
75
80
85
90
95
75
80
85
90
95
CO2 Insufflation Time Prone Series Vs Patient Age
Figure 4
1.20
CO2 Insufflation Time (minutes)
1.00
0.80
0.60
0.40
0.20
0.00
0
5
10
15
20
25
30
35
erately or mildly uncomfortable. The major variables compared
were CO2 insufflation time and adequate bowel distension for
radiological diagnosis, CO2 insufflation time supine series and
patient age (Figure 3, 4), CO2 insufflation time and patient tolerance (Figure 5) and lastly patient tolerance and patient age
(Figure 6). The mean overall tolerance rating was 2.8 and the
mean insufflation time for the supine series was 1.77 minutes
and prone was 0.48 minutes. A Pearson’s correlation coefficient
(r) was determined for several variables. There was no association found with patient age and CO2 insufflation time (r=0.04)
and CO2 insufflation time and patient tolerance (r=0.03).
However, there was a positive correlation of patient age and
patient tolerance (r=-0.47), as the patient age increases, patient
tolerance decreases.
DISCUSSION
CT colonography is a minimally invasive diagnostic method
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The Radiographer – vol. 51, no. 2, August 2004
40 45 50 55 60
Patient Age (years)
65
70
with huge potential for screening of colorectal cancer, post
polypectomy and for abdominal disorders. In this study, patient
tolerance of CO2 insufflation during CT colonography was
examined and whether the insufflation was adequate for radiological diagnosis. Previously published studies evaluated patient
acceptance to CT colonography compared with conventional
colonoscopy.18,19 Of the 22 patients involved in this study, 19
examinations based on the radiologists report were rated as having excellent distension enabling visualisation of the mucosal
wall and three examinations were reported as only adequate.
The three examinations that resulted in reduced distension
resulted from ileocaecal valve incompetence and therefore CO2
escaped into the small bowel. This caused suboptimal distension
within the sigmoid colon. In addition, several patients were
diagnosed with diverticular disease which can also affect the
degree of distension within the bowel. However, scanning in
both the supine and prone positions allowed visualisation of the
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M.D. GASPAR
Patient Tolerance Vs Patient Age
Figure 5
6.0
Patient Tolerance
5.0
4.0
3.0
2.0
1.0
0
0
Figure 6
5
10
15
20
25
30
35
40 45 50 55 60
Patient Age (years)
65
70
75
80
85
90
CO2 Insufflation Time Supine Series Vs Patient Tolerance
6.0
Patient Tolerance
5.0
4.0
3.0
2.0
1.0
0
0.00
0.05
1.00
bowel wall within the sigmoid colon. This is consistent with
Svensson’s (2002) findings15 that prone and supine review can
compensate for incomplete distension as collapsed colonic segments can mimic a tumour. In addition to positional change,
multiplanar reformats helped confirm normal collapsed haustral
folds whilst the endoluminal view demonstrated a smooth
mucosal surface in the collapsed segment where some residual
gas was present.9
Within this study, 31 per cent of patients considered the CO2
insufflation painful or unbearable and 69 per cent of patients
found the CO2 insufflation to be moderately or mildly uncomfortable. This is similar to the study by Langhi et al.13 which
found that discomfort was graded as low by 68 per cent of
patients, moderate by 30 per cent and high by two per cent.
Patients that tolerated a time less than 1.25 minutes on the
supine run were found to have inadequate distension and
required additional CO2. Similarly patients with a CO2 insuffla-
1.50
Time (minutes)
2.00
2.50
3.00
tion time on the prone series less than 0.25 seconds also produced suboptimal distension and required additional CO2.
Therefore, these times could be used as an indicator to determine an appropriate amount of CO2 insufflation in order to
achieve optimal bowel distension for radiological diagnosis.
However, because the length of a person's colon is variable and
patients have different thresholds of pain tolerance determining
a specific time for CO2 insufflation is inappropriate. Rather it
can be used as a guide to indicate when a suitable amount of
CO2 has been insufflated for adequate distension of the bowel.
The results of this study indicated that there was a positive
correlation of patient age and patient tolerance (r=-0.47). As the
patient age increases, patient tolerance decreases. This may be
due to the presence of anal sphincter incontinence in older individuals which causes the CO2 to escape. This requires the addition of more CO2 resulting in longer examination times and
greater discomfort for the patient. Therefore, this can result in
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COMPUTED TOMOGRAPHY COLONOGRAPHY: PATIENT TOLERANCE TO CO2 INSUFFLATION
older patients having a decreased tolerance to the procedure.
Additionally, because the local community is of Italian origin, a
majority of the older patients included in the study were Italian
speaking. Consequently, because of the language barrier they
may have misunderstood the explanation of the procedure.
Thus, they found the CO2 insufflation painful and rated their tolerance lower.
Conversely, when comparing patient age and CO2 insufflation there was no statistical significance found (r=0.04). As
mentioned previously, this can be attributed to the variable
length of a person’s colon and accordingly, patient age cannot
be related to the time of CO2 insufflation. This may also explain
why there was no statistical significance found when CO2 insufflation time and patient tolerance were compared (r=0.03).
Because tolerance is a subjective factor and patients vary in
their pain threshold, a time that is adequate for optimal distension in one patient, may not be tolerated by another.
In addition, the Pearson’s value r may not be statistically
significant because of several limitations inherent within the
study. These include the limited sample size and the short collection time. The sample size was dependent on the number of
CT colonography patients referred by doctors to the department
within the time frame. Consequently, the small sample size
employed made it difficult to translate these observations to the
population level and therefore the results were not generalised.
As a result, this study could be described as a pilot study which
can lead to further investigation using a larger sample over a
longer period of time. The number of subjects may be unrepresentative of the various subject ages and socio-economic background, again due to the short period of time for the experimental work, the age group of patients that are examined within the
department and the surrounding local community.
CONCLUSION
CT colonography is an interesting area of investigation which is
still in the process of evolution as an imaging and screening tool.
It is quick, minimally invasive, is well tolerated and has the
potential to become an effective radiological tool in diagnosing
colonic lesions. Patient acceptance and tolerance of CO2 insufflation is a topic with limited previous research. Increased patient
age was found to have a positive correlation with decreasing
patient tolerance. However, there was no statistical significance
between CO2 insufflation time and patient age and CO2 insufflation time and patient tolerance. Additional studies are required
with a larger sample in order to further investigate this topic.
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Peer Reviewed
Submitted: February 2004
Accepted: June 2004