The Journal of Emergency Medicine, Vol. -, No. -, pp. 1–9, 2013
Published by Elsevier Inc.
Printed in the USA
0736-4679/$ - see front matter
http://dx.doi.org/10.1016/j.jemermed.2013.05.011
Selected Topics:
Prehospital Care
VENTED CHEST SEALS FOR PREVENTION OF TENSION PNEUMOTHORAX IN
A COMMUNICATING PNEUMOTHORAX
Joseph G. Kotora Jr., LCDR, MC, USN, DO, Jose Henao, CDR, MC, USN, MD, Lanny F. Littlejohn, CDR, MC, USN, MD, and
Sara Kircher, BS
Department of Emergency Medicine, Naval Medical Center Portsmouth, Portsmouth, Virginia
Reprint Address: Joseph G. Kotora Jr., CDR, MC, USN, DO, One Harmony Lane, Hackettstown, NJ 07840
chest seals (HyFin!, n = 8; Sentinel!, n = 8, SAM!, n = 8)
was applied. Air was injected to a maximum of 50 mL/kg
twice, followed by a 10% autologous blood infusion, and finally, a third 50 mL/kg air bolus. Survivors completed all
three interventions, and a 15-min recovery period. Results:
The introduction of 29.0 (±11.5) mL/kg of air resulted in tension physiology. All three seals effectively evacuated air and
blood. Hemodynamic compromise failed to develop with
a chest seal in place. Conclusions: HyFin!, SAM!, and
Sentinel! vented chest seals are equally effective in evacuating blood and air in a communicating pneumothorax model.
All three prevented tension pneumothorax formation after
penetrating thoracic trauma. Published by Elsevier Inc.
, Abstract—Background: Tension pneumothorax accounts for 3%–4% of combat casualties and 10% of civilian
chest trauma. Air entering a wound via a communicating
pneumothorax rather than by the trachea can result in
respiratory arrest and death. In such cases, the Committee
on Tactical Combat Casualty Care advocates the use of
unvented chest seals to prevent respiratory compromise.
Objective: A comparison of three commercially available
vented chest seals was undertaken to evaluate the efficacy
of tension pneumothorax prevention after seal application.
Methods: A surgical thoracostomy was created and sealed
by placing a shortened 10-mL syringe barrel (with plunger
in place) into the wound. Tension pneumothorax was
achieved via air introduction through a Cordis to a maximum volume of 50 mL/kg. A 20% drop in mean arterial
pressure or a 20% increase in heart rate confirmed hemodynamic compromise. After evacuation, one of three vented
, Keywords—chest seals;
trauma; combat; tactical
pneumothorax;
thoracic
INTRODUCTION
Grant obtained through the Bureau of Medicine and Surgery,
United States Navy.
The views expressed in this article are those of the author(s)
and do not necessarily reflect the official policy or position of
the Department of the Navy, Department of Defense, or the
United States Government.
Three authors are military service members. This work was
prepared as part of their official duties. Title 17 U.S.C. 105 provides that ‘‘Copyright protection under this title is not available
for any work of the United States Government.’’ Title 17 U.S.C.
101 defines a United States Government work as a work prepared by a military service member or employee of the United
States Government as part of that person’s official duties.
Despite the advances in personal protective equipment,
penetrating chest trauma remains a formidable cause of
injury in tactical medicine. The Joint Theater Trauma Registry, a collective database of all coalition-force casualties
from the conflicts in Iraq and Afghanistan, implicates thoracic trauma as the cause of lethal injury in 5%–7% of all
patients (1,2). The leading mechanisms of lethal injury
among deployed service personnel are improvised
explosive devises (IEDs) and gunshot wounds from
small arms fire (2). Although the blast waves from IEDs
can cause significant lung injury, high-velocity fragments
RECEIVED: 26 June 2012; FINAL SUBMISSION RECEIVED: 29 December 2012;
ACCEPTED: 1 May 2013
1
2
can also cause devastating injury through secondary and
tertiary blast injuries. This is the predominant wounding
mechanism when IEDs cause chest trauma (1). Civilian
tactical operators are at risk for similar kinetic mechanisms of injury.
Open pneumothorax and tension pneumothorax are two
of the most frequently fatal wounds seen among combat
casualties. In addition, these wounds are readily treatable
in the prehospital phase and are therefore two of the leading causes of preventable combat death. In one study examining the prevalence of tension pneumothorax in
injured military personnel, radiographic evidence of tension pneumothorax was discovered in 198 of 978 casualties (3). Although tension pneumothorax is a clinical
diagnosis that should be treated before obtaining any
radiographic study, the study by McPherson et al. underscores the relatively high incidence of missed tension
pneumothorax in combat casualties (3). If the size of the
chest wall defect is equal to or greater than two thirds the
diameter of the trachea, air will preferentially enter the
chest wall during inspiration, rather than the trachea, resulting in respiratory failure and eventual cardiopulmonary
arrest (4). Classical teaching regarding the management of
an open pneumothorax involves placement of an occlusive
dressing over the wound. This procedure has been endorsed by both civilian and military medical organizations
(5). The current recommendation by the Committee on
Tactical Combat Casualty Care (CoTCCC) endorses this
mechanism in their most recent guidelines (6).
Although there are no published data comparing the
vented chest seals to three-sided occlusive dressings,
some have argued against the use of three-sided occlusive
dressings. The Royal College of Surgeons endorses the
use of chest seals in open pneumothoraces, and agree
that a three-sided occlusive dressing is ‘‘often ineffective’’ (7). Equally important, this intervention often
requires frequent ‘‘burping’’ by prehospital medical personnel to relieve air accumulated and avoid development
of a tension pneumothorax (5). When prehospital care
providers in austere and technically difficult environments under low-light conditions are faced with multiple
casualties with penetrating chest trauma, this can become
an arduous task with a high likelihood of increased morbidity and mortality.
In light of these concerns, vented chest seals were developed. These seals are designed to prevent inward airflow through the chest wound, while simultaneously
allowing the evacuation of air from the chest through
the valve during normal spontaneous respiration.
Commercially available chest seals used to treat open
pneumothoraces can fail due to poor adhesion to human
skin (8). Adhesion can be further compromised by blood,
sweat, dirt, and debris. Arnaud et al. studied this phenomenon in 2008 by comparing the Asherman and Bolin chest
J. G. Kotora Jr. et al.
seals for development of tension physiology after application in an open pneumothorax model. The results of
their study did not reveal any evidence of tension pneumothorax after application of a vented chest seal (8).
However, since this study, several chest seals have been
developed and marketed to the United States (US) military and civilian tactical law enforcement agencies. To
date, there has been no published data comparing the efficacy of commercially available vented chest seals
against one another.
The purpose of this study was to test three commercially available vented chest seals (HyFin!, SAM!, and
Sentinel!) currently used by US military units for the
treatment of open pneumothorax in the tactical environment. Each vented seal was assessed for its ability to prevent accumulation of air with resultant development of
tension physiology after application. In addition, each
seal was evaluated for its ability to adequately vent blood
in the face of a hemopneumothorax. In addition to having
a venting mechanism, each chest seal had to meet the
criteria established by the CoTCCC. These criteria are
presented in Table 1.
The study end point was development of tension pneumothorax after application of the chest seal, defined by
any of the following possible entities: a drop in the
mean arterial pressure (MAP), a rise in heart rate, both
a decrease in MAP and a rise in the heart rate, or death.
Bedside ultrasound was utilized to assess the presence
or absence of a pneumothorax, both before and after
Table 1. Committee on Tactical Combat Casualty Care
Required Criteria for Chest Seals (6)
Required Criteria
Approved by the US Food and Drug Administration
Sterile
Long shelf life
Adherence required in the presence of blood, sweat, sand, and
hair
Must conform to Military Standard 8.10 G regarding storage
Low allergic potential
Self adherent
6–8 inches in dimension
Oval shaped
Creation of an occlusive seal
Ventable through lifting of an occlusive flap on the seal with
adequate resealing after lifting
Puncture-resistant packaging
Minimum weight and cube
Maintenance of integrity when folded
Lightweight and rugged
Inexpensive
Favorable clinical data when tested under battlefield conditions
Easy application under battlefield conditions
Built in tabs to facilitate removal
High rate of user acceptance
Configuration for use in low-light conditions
US = United States.
Chest Seals in Penetrating Trauma
3
Table 2. Volume of Air Required to Induce Tension
Pneumothorax before Chest Seal Placement
Volume of Air (mL/kg) to Induce Tension Pneumothorax
Subject
HyFin!
Sentinel!
SAM!
1
2
3
4
5
6
7
8
31.9
18.5
32.4
44.9
30.8
29.1
50.0
50.0
31.0
50.0
15.4
17.6
28.2
23.2
21.1
17.6
18.1
46.8
22.0
17.6
30.0
16.8
24.0
29.1
application of the seal, as well as after each injection of
either air or blood.
Our study group hypothesized that no statistically significant difference exists among the seals, with regard to
prevention of tension pneumothorax or evacuation of
blood after application. Skin adherence was not specifically tested in this study.
METHODS
This randomized, prospective, unblinded laboratory animal trial was approved by the Institutional Animal Care
and Use Committee. All research was conducted in compliance with the Animal Welfare Act, and adhered to the
principles stated in the Guide for the Care and Use of
Laboratory Animals: Eighth Edition (9). Animals were
maintained in a facility accredited by the Association
for Assessment and Accreditation of Laboratory Animal
Care International. Twenty-four Yorkshire Swine (Sus
scrofa) were fed a standard diet and observed for 5 days
to ensure good health. Subjects were fasted the night before the procedure, with water provided ad libitum. Mean
subject weights were 23.2 kg (standard deviation [SD]
3.10; range 18.6–28.2 kg) for the HyFin! chest seal
group, 27.4 kg (SD 4.16; range 22.7–36.4 kg) for the
SAM! chest seal group, and 28.1 kg (SD 4.06; range
22.7–36.8 kg) for the Sentinel! chest seal group.
After premedication with butorphanol (0.1–0.3 mg/kg)
and intramuscular injection of ketamine (20 mg/kg), general anesthesia was induced via facemask with isoflurane
(5%) and oxygen from an MDS Matrx VMC! small animal anesthesia machine (Matrx Medical, Orchard Park,
NY). Animals were then intubated with 6–7-mm endotracheal tubes and maintained on Isoflurane set at 2%, or as
needed for adequate anesthesia. All subjects were
allowed to breathe spontaneously for the duration of the
procedure. The animals were placed in a supine position
on the operating table after intubation. A Philips MP50
IntelliVue monitoring system (Philips Medical Systems,
Böblingen, Germany) was used for continuous monitoring of vital parameters, including heart rate, MAP, oxygen
saturation, temperature, and respiratory rate. After exposure via standard cut-down technique, the right carotid
artery was cannulated with a 20-gauge catheter for continuous arterial blood pressure monitoring. The external
jugular vein was cannulated with a 9Fr central venous
catheter for collection of blood.
As described in a previously validated model, the right
front leg was gently pulled forward and secured in order
to allow access to the chest. An incision through the skin
was made over the fifth intercostal space just inferior to
the axilla. Blunt dissection was then used to create
a hole into the pleural cavity. A 10-mL syringe was cut
to a barrel length of 3 cm and inserted through the hole
into the pleural cavity, such that the flange rested on the
skin surface. A 9Fr angiocatheter was then placed
through the chest wall 10 cm from the created hole via
modified Seldinger technique in order to allow air and
blood injection into the chest cavity. To determine the
amount of air required to induce a tension pneumothorax,
air was injected via the 9Fr catheter in 60-mL aliquots
into the thoracic cavity to a maximum volume of
50 mL/kg. This was discontinued by removing the
plunger when the MAP decreased by 20% from baseline,
or heart rate increased by 20% from baseline. The animal
was observed for a 15-min recovery period, and the MAP
was permitted to return to baseline. Table 2 depicts the
volumes of air required to induce tension pneumothorax
in each subject.
The animals were randomized into three groups of
eight, one group for each of the three chest seals. The
seals included the HyFin! Chest Seal (North American
Rescue, Greer, SC), the SAM! Chest Seal (SAM! Medical Products, Wilsonville, OR), and the Sentinel Battle
Seal (Combat Medical Systems, Fayetteville, NC). Design specifications of each individual chest seal are presented in Table 3. The selected chest seal was placed
Table 3. Chest Seal Specifications, Dimensions, and Characteristics
Specification
SAM! Chest Seal
HyFin! Vent Chest Seal
Sentinel! Battle Seal
Dimensions (inches)
Chest wall preparation device
Seal design (evacuation of blood and air)
Night-vision goggle–compatible
9.2 ! 7.6
Disposable gauze pad
Conventional flutter valve
Yes
6!6
Disposable gauze pad
Laminar vent channel
No
6.5 ! 6.5
Disposable gauze pad
Laminar vent channel
No
4
J. G. Kotora Jr. et al.
over the created wound according to the manufacturer’s
directions in order to test for air evacuation efficacy. As
described previously, air was injected in increments of
60 mL to a maximum of 50 mL/kg. Hemodynamic parameters were monitored and recorded with an a priori
stopping point of either a 20% MAP decrease, an increase
in heart rate by 20% from baseline, or both. The changes
in hemodynamic parameters reflect the presence of tension pneumothorax. If the hemodynamic stopping point
was not reached in the presence of the chest seal, the stopping point was the 50 mL/kg of injected air maximum.
After a 15-min stabilization period, the chest seal was
then evaluated for efficacy in evacuating air in the presence of blood in the chest cavity. Ten percent of the total
blood volume of the animal was collected from the arterial line and injected via the 9Fr catheter into the chest
cavity. The animal was allowed a 5-min stabilization period, followed by an injection of air into the chest in increments of 60 mL, to a maximum of 50 mL/kg. Heart rate
and MAP were again recorded until the heart rate increased by 20% from baseline or MAP decreased by
20% of baseline. Once the required change in parameters
was reached or the maximum amount of air was injected
(50 mL/kg), the animal was monitored for 15 min. During
the stabilization periods, all of the subjects’ vital signs returned to near baseline parameters. The periods of stabilization were built into the design of the study to allow the
subject’s physiology to adjust to the changes induced by
each intervention. Survivors were euthanized via i.v. injection of euthanasia solution (Euthasol, Virbac Animal
Health, Inc., Fort Worth, TX) in accordance with American Veterinary Medical Association guidelines for euthanasia. All three phases are presented for comparison in
Table 4.
Sonographic images were recorded before and after
each intervention using a SonoSite 180 Plus (SonoSite,
Bothell, WA). A standard C60/5 2-MHz transducer probe
was placed in three standard locations over the animal’s
thorax, and images were recorded at a depth of 9.9 cm.
Table 4. Volume of Air Injected during Each Intervention
(mL/kg)
Intervention
Phase 1 Air required to induce
tension pneumothorax
Phase 2 Air injected after chest
seal placement
Phase 3 Air injected after infusion
of blood into thoracic cavity
SD = standard deviation.
Treatment
Group
Mean 6 SD
All groups
29.0 6 11.5
HyFin!
SAM!
Sentinel!
HyFin!
SAM!
Sentinel!
49.7 6 0.9
50.0 6 0.0
50.0 6 0.0
43.7 6 11.8
49.7 6 0.9
50.0 6 0.0
The placement points were forward of the created chest
wound, as described by Arnaud et al. (8). Videography
was unavailable at the time of the study. However, two
board-certified emergency physicians credentialed in
ultrasound viewed all images in real time. These physicians were study investigators, and were therefore unblinded. Air in the chest cavity can be seen as the
absence of lung sliding, and a determination of lung sliding can be different at each of the three points on the
chest. The ultrasound was used to detect the presence
of pneumothorax and hemothorax.
Sample size was determined based on Arnaud et al.’s
2008 model. Statistics were calculated with SPSS Statistics 17.0 (IBM Corporation, Armonk, NY). Results are
presented as mean 6 standard deviation. A one-way
analysis of variance (ANOVA) was used to analyze statistical differences among treatment groups with respect to
weight, total amount of air injected for each pneumothorax phase (in mL/kg), and differences in MAPs and heart
rates at each time point throughout the experiment. The
Least Significant Difference post-hoc test was used for
paired comparisons of group means if the ANOVA
revealed a significant effect. A p value of <0.05 was considered significant.
RESULTS
Mean weight was significantly lower in the HyFin! treatment group compared with the SAM! (p = 0.038) and
Sentinel! groups (p = 0.017). Animal size varied and
was subject to the available inventory at the time of the
study’s execution. However, animal size had little to do
with induction of a tension pneumothorax, as all volumes
were based on 50 mL/kg body weight. Baseline MAP and
heart rate did not differ among groups.
The volume of air required to induce a tension
pneumothorax before chest seal placement was 29.0
( 6 11.5) mL/kg, and was similar among the groups.
Likewise, the air volume injected after chest seal placement did not differ between treatments, and reached the
maximum volume of 50 mL/kg in all subjects in both
the SAM! and Sentinel! groups. In the HyFin! group,
1 subject achieved a 20% decline in MAP with a volume
of 47.7 mL/kg of air injected. However, this subject’s
MAP recovered immediately upon cessation of air injection. After injection of blood into the chest cavity, most
subjects again withstood the maximum volume of air injected of 50 mL/kg, with the exception of 2 subjects in the
HyFin! treatment arm and 1 subject in the SAM! arm.
These subjects received injections of 22.4, 26.9, and
47.4 mL/kg of air before a 20% decrease in MAP, respectively. Again, all MAPs returned to normal rapidly after
cessation of air injection. Consistent with previous
Chest Seals in Penetrating Trauma
phases, there were no significant differences between
treatment arms after this final injection of air. Chest seals
in all groups vented blood after development of a
hemothorax. A moderate decline in MAP attained by
the HyFin! subjects after air injection during both the
second and third injection phase can be visualized in
Table 1. MAP in each group recovered similarly after procedures, and all subjects survived the experiment.
Figure 1 displays the mean change in MAP for each
subject arm over time. The only significant difference
in MAP at any time point was after induction of the first
pneumothorax. The Sentinel! treatment group recovered
more quickly to a higher MAP than the SAM! treatment
group (p = 0.003) at T + 10. However, this MAP difference was experienced before placement of the chest seals.
Once seals were placed, all subjects returned to a similar
MAP, and treatment groups remained similar throughout
the duration of the experiment. As expected, MAP
declined after creation of hemothorax consistently in all
subjects.
After induction of the first pneumothorax and before
chest seal placement, the Sentinel! subjects demonstrated a higher mean heart rate than either the HyFin!
or the SAM! groups at T + 10 (p = 0.026 and
p = 0.023, respectively) and T + 15 (p = 0.025 and
p = 0.040, respectively). Subsequent to chest seal placement, heart rate did not differ for the remainder of the
study.
A Sonosite portable bedside ultrasound was utilized to
investigate the presence of pneumothorax after each intervention. There was excellent inter-rater agreement regarding the presence of a pneumothorax on ultrasound
images. Because both physicians observed the ultrasound
scan in real time, no kappa was necessary.
Figure 1. Changes in mean arterial pressure (MAP) after
each intervention over time. HTX = hemothorax; PTX =
pneumothorax.
5
DISCUSSION
Open pneumothorax, tension pneumothorax, and complex thoracic trauma remain a frequent mechanism of injury and preventable cause of death. Although the use of
an unvented chest seal is effective at sealing an open
pneumothorax, it is completely useless for prevention of
a tension pneumothorax and, in the setting of positive
pressure ventilation, can actually predispose to it. Improved body armor has resulted in a decreased incidence
of thoracic trauma among US military members injured in
Operation Iraqi Freedom and Operation Enduring Freedom. Nonetheless, the incidence of fatal tension pneumothorax has remained constant at 3%–4% of all combat
casualties. This is not appreciably changed from the
classic 5% reported from the Wound Data and Munitions
Effectiveness Team database from Vietnam, despite
numerous technological advances and a more organized
trauma care system in the operational theater (10).
Unvented seals require considerable monitoring and attention to both the device and the patient. The standard
method of tension pneumothorax decompression is the insertion of a 14-gauge, 50-mm catheter into either the second intercostal space in the midclavicular line or the fourth
or fifth intercostal spaces in the mid axillary line. Recent
studies have questioned the effectiveness of needle decompression and whether one site is superior to another. In
addition, these studies have examined whether a longer
catheter is warranted to decrease the failure rate of needle
decompression. Givens et al. reported failure of needle decompression in approximately 25% of potential attempts,
based on measurements obtained via computed tomography in military personnel (11). Sanchez et al. performed
a similar study in an urban trauma center, reporting failure
of a 50-mm catheter in 35%–75% of patients, depending
on the placement location (12). Stevens et al. and Zengerink et al. also question the reliability and efficacy of needle
decompression with 50-mm catheters (13,14). The
development of a tension pneumothorax is not always an
easily treatable condition. Many tension pneumothoraces
occur as preterminal events, unfortunately ending in
cardiopulmonary collapse and arrest. These factors in the
setting of multiple polytrauma patients, poor visibility,
and austere conditions increase the likelihood of adverse
outcomes for patients with open pneumothoraces whose
chests are sealed with an unvented seal. Given the high
failure rate of standard decompresion catheters, the
CoTCCC now recommends the use of an 80 mm
decompression needle inserted in either the 2nd
intercostal space in the midclavicular line, or in the 5th
intercostal space in the anterior axillary line (http://www.
health.mil/dhb/downloads/62812/03_TCCC%20Needle%
20Decompression.pdf).
6
In our experience with the same model described in
this study, lethal tension pneumothorax quickly developed when the same volume of air was infused into a pilot animal with an unvented chest seal applied to the
wound. At present, the CoTCCC recommends the use
of an unvented chest seal. However, our experience
strongly argues against the use of unvented chest seals
due to the increased risk of tension pneumothorax development, as well as the increased clinical attention required by the prehospital tactical medical provider. It
is also important to consider the environment in which
these seals are applied. Currently, the CoTCCC recommends the application of a chest seal during the Tactical
Field Care and Tactical Evacuation phases (6). Although
these phases of care are not conducted under effective
hostile enemy fire, military and tactical civilian medical
providers frequently encounter a fluid environment
where small arms fire, IEDs, or strong enemy resistance
might present again, causing a return to the Care Under
Fire phase. Vented chest seals require less attention by
prehospital tactical medical personnel than unvented
chest seals, especially under these extremely adverse
conditions.
None of the chest seals were trimmed to fit, as described in prior studies. We believed this detracted from
the external validity of the study, as this is not common
practice under tactical battlefield conditions. In addition,
none of the seals were reinforced with adhesive tape, because the CoTCCC requires that chest seals be self adherent in the face of blood, sweat, and debris.
Although there are no documented reports of valve
failure with resultant development of tension pneumothorax in vented chest seals, there are case reports of similar
valves connected to indwelling chest tubes that clotted
and contributed to the development of tension physiology
(15). Although the valves of vented chest seals and the
Heimlich valves of indwelling chest catheters share
some similarities, there are stark differences. Vented seals
are temporary, externally applied devices that are not intended to have direct communication with the lung
pleura. This is in contrast to indwelling chest tubes. In
addition, bending or fracture of the chest tube itself can
contribute to tension pneumothorax development. For
reasons stated here, this would clearly not be an issue
for vented chest seals.
Civilian emergency medical service professionals
have also questioned whether vented chest seals offer
a distinctive advantage over the standard three-sided
seal commonly employed for open chest wounds. A recent publication in the emergency medicine literature
highlights the paucity of data available. Although the
data are limited, the authors suggest vented chest seals
can offer some advantage over the three-sided seal with
regard to practicality and ease of use (16).
J. G. Kotora Jr. et al.
One must note the injury model used in this study evaluated subjects with an isolated thoracic injury, and does
not represent the polytrauma patient. This is often not
the case in combat, and the vast majority of casualties
evacuated from the battlefield sustain multiple injuries
to the head and neck, upper and lower extremities, and
external soft tissues. The mean Injury Severity Score
for casualties transported to a level III facility in Afghanistan is 21.19 (17). Likewise, as mentioned previously,
the most common mechanism of injury in Operation
Enduring Freedom is blast injury from IEDs or some
other explosive mechanism (1,2).
Chest seal adhesion has been considered a problem
when a casualty is covered with blood, sweat, dirt, grease,
or sand. This has led to many tactical medical providers
losing confidence in their abilities, given the high failure
rates and constant need for reinforcement of the device.
All three seals adhered very well on both dry and soiled
skin. All three utilize a strong polyurethane disk mounted
on a hydrogel base, and their adhesion is excellent even in
the face of blood or debris. Unfortunately, we were unable
to accurately evaluate any differences in the adhesive
properties of the individual seals, as there was no objective method of quantifying adhesion to the skin in our laboratory. A device for measuring the tensile strength of the
seal on skin was available at the time of the study; however, the cost of this device was prohibitive. This would
be an area of future research, and would allow investigators to objectively account for differences in adhesion of
various chest seals.
Limitations
In order to induce a hemopneumothorax, 10% of the animal’s blood volume was collected and inserted into the
pleural space via the 9Fr intrathoracic catheter. Although
it might be possible that the removal of blood can contribute to development of hypotension and tachycardia, the
current classes of shock do not support this hypothesis.
The current accepted classes of shock range from Class I
through Class IV, with Class I representing <15% of the
total blood volume, and Class IV representing >40%.
The investigators carefully calculated the volume of blood
that represented 10% of the animal’s total blood volume,
and removed only the volume necessary. Based on the current classes of shock, removal of 10% would fall under
Class I, and should have no effect on vital signs (18).
It is important to note that the vital signs did return to
near baseline shortly after the blood was removed. This
can be seen in Table 1. We considered inserting a 5-min stabilization period between blood removal and insertion
through the catheter, but were concerned that the blood
volume removed would clot, rendering it useless. Future
studies might seek to eliminate this limitation by adding
Chest Seals in Penetrating Trauma
a stabilization period between removal and insertion, removing the volume over a longer period of time, or possibly
adding an anticoagulant to the volume of blood removed.
Overall, ultrasound did not yield any significant data
for the purposes of this study. At present time, ultrasound
can only confirm or deny the presence of a pneumothorax,
but cannot offer quantitative data regarding the volume of
air or size of a pneumothorax. All three seals demonstrated persistent pneumothorax on ultrasound before euthanasia. However, the time period between the final
intervention and the induction with Euthanyl was only
15 min. At present, it is unknown if a vented chest seal
adequately assists in the resolution of a pneumothorax,
or how much time might be required to initiate resolution.
It is also important to mention that this study was completed on intubated, spontaneously breathing models
without the use of positive pressure ventilation. The current system of trauma care in the deployed theater centers
around three levels of care. Level II and III facilities are
able to provide immediate definitive airway control.
The US Marine Corps is currently utilizing emergency
physicians capable of providing rapid sequence intubation and definitive airway management in some of their
Level I facilities. However, at the present time this is
the exception rather than the rule. The majority of Level
I facilities are staffed by generalist physicians who, due to
the lack of resources and equipment, are incapable of providing advanced airway techniques or positive pressure
ventilation. These interventions are frequently delayed
until a patient reaches the comprehensive Level III facilities, which are analogous to fully equipped trauma centers. Although critically wounded patients are ideally
transported from the point of injury to Level III facilities
immediately, it is not uncommon for patients in very remote or austere environments to first stop at Level I or
Level II facilities for immediate care. In addition, with regard to special operations and covert missions, advanced
definitive care might be unavailable for several hours or
days. That being said, patients with open pneumothoraces
can be intubated and placed on positive pressure ventilation, if these interventions are available before arrival at
a comprehensive trauma facility. Vented chest seals are
not currently indicated for ventilated trauma patients, as
these patients all require tube thoracostomy while on
the ventilator with a pneumothorax. The function of the
valve has never been tested on intubated patients connected to a ventilator circuit.
This study was performed on intubated subjects without
ventilator support for two primary reasons. One, most
patients with a communicating pneumothorax will initially
be treated by prehospital providers with basic life-support
skills. That said, it is important to determine what utility
a vented chest seal has in a spontaneously breathing patient
without respiratory assistance. The second reason subjects
7
were not placed on ventilators is physiological. We were
concerned that production of a tension pneumothorax on
a ventilated subject with a fixed tidal volume and respiratory rate would contribute to metabolic acidosis, resulting
in exaggerated hemodynamic compromise. We saw this
as a potential source of bias. We elected to allow the subjects to breathe spontaneously, enabling each subject to
regulate its own acid–base balance. Future studies are
required to determine if vented chest seals would prevent
tension pneumothorax in ventilated trauma patients with
communicating pneumothoraces, and what effects artificial ventilation might have on acid–base balance.
Notably, this model did not test the integrity of the seal
or the vent in a patient with a bronchopulmonary laceration, as is often seen in victims of blast injury. Although
the development of a tension pneumothorax due to a bronchopulmonary laceration is often seen in victims of blast
injuries, they are usually closed pneumothoraces. Application of a vented chest seal would not likely prevent
additional cardiopulmonary insult. Additional study is
required to evaluate the incidence of delayed tension
pneumothorax after application of a vented chest seal in
patients with a bronchopulmonary laceration.
CONCLUSIONS
Our study is the largest randomized, unblinded laboratory
animal study evaluating the use of vented chest seals in
the setting of open pneumothorax and penetrating thoracic trauma. Blinding was not possible with this study,
given the experimental design of the study. At the present
time, our study is the only trial that compares the most
popular vented chest seals currently used by US military
medical providers.
This study failed to demonstrate any significant difference in valve function with regard to evacuation of air or
accumulation of a tension pneumothorax. Although the
seal designs varied significantly, all three devices adequately vented both blood and air from the wound. There
was no clinically or statistically significant difference
among individual seals. None of the animals succumbed
to premature death from tension pneumothorax after seal
placement. All three devices also provided confirmation
of air removal through both visual and auditory cues.
This is of tremendous value because medical personnel
can be given immediate feedback regarding the efficacy
of the device, and can reinforce confidence in the user
that the individual device is functioning properly.
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Chest Seals in Penetrating Trauma
ARTICLE SUMMARY
1. Why is this topic important?
Tension pneumothorax is a significant cause of morbidity and mortality in both military and civilian trauma care.
Many options exist for sealing sucking chest wounds;
however, none perform well in all cases. This leads to inadequate management of communicating pneumothoraces, and potentially unfavorable patient outcomes.
2. What does this study attempt to show?
This study attempts to present an unbiased evaluation
of three of the most popular vented chest seals currently
in use by operational units of the US military. Equally important, this study utilizes a reproducible model that
mimics a common injury pattern seen in both military
and civilian emergency medicine practice.
3. What are the key findings?
All three of the vented seals effectively evacuated blood
and air. None of the subjects developed a tension pneumothorax or suffered hemodynamic compromise once the
seal was in place.
4. How is patient care impacted?
Vented chest seals offer emergency medicine professionals a viable option for management of open pneumothoraces and prevention of respiratory failure or death.
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