• ‘LE COPY
EVALUATION OF SIX CHEST DRAINAGE UNITS FOR
USE IN AEROMEDICAL EVACUATION
Susan K. Nagel, Captain, USAF, BSC
Final Report lor Period September 1988- April 1990
OCT 0 5 sac
Approved for public release; distribution is unlimited.
USAF SCHOOL OF AEROSPACE MEDICINE
Human Systems Division (AFSC)
Brooks Air Force Base, TX 78235-5301
This final report was submitted by personnel of the Chemical Defense Branch, Crew
Technology Division, USAF School of Aerospace Medicine, Human Systems Division, AFSC,
Brooks Air Force Base, Texas, under job order 7930-16-12.
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Evaluation of Six Chest Drainage Units For Use in Aeromedical Evacuation
12. PERSONAL AUTHOR(S)
Nage1, Susan K.
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Final _ from 88709 tq 9Q/Q4 1990. July 19
16 SUPPLEMENTARY NOTATION
18. SUBJECT T1RMS (Continue on reverye if ntcttssry tnd idtntify by block numb*')
Test and Evaluation; Chest Drainage Unit;
19. ABSTRACT (Continue on revene If ntcttstry tnd idtntify by block numb*r)
.The Aeromedical Research Function of the US^M-' School of Aerospace Medicine has completed
Observational performance testin^dn l s¥#aifferent brands of chest drainage units. The
testing program was designed to observe and measure each unit's characteristics in a
simulated operational Aeromedical Evacuation environment. Tne information presented describes
the operational response of the Chest Drainage Units to the stresses of flight and the
special operating instructions vhich apply to some of the units. /.7 Ll \
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UNCLASS IH ED
EVALUATION OF SIX CHEST DRAINAGE UNITS
FOR USE IN AEROMEDICAL EVACUATION
The Aeromedical Research Function of the USAF School of Aerospace
Medicine (USAFSAM) has completed observational performance testing on six
different brands of Chest Drainage Units (CDU). The testing program was designed
to observe and measure each unit's characteristics in a simulated operational
aeromedical evacuation environment. The information presented describes the
operational response of the Chest Drainage Units to the stresses of flight and the
special operating instructions which apply to some of the units.
The Chest Drainage Units tested include:
Argyle Sentinel Seal Dual Chest Drainage Unit
Migada Underwater Chest Drainage Unit
Pleur-Evac Adult-Pediatric, Model A-4000
Pleura Gard Chest Drainage System
Thora Drain III Underwater Drainage System
Thora-Klex Chest Drainage Unit
The Pleur-Evac was previously evaluated and recommended for use in
aeromedical evacuation by this office based on data gathered during hypobaric
chamber experiments using an animal model. It was included in this test to obtain a
complete database of the operational characteristics of chest drainage units used in
The Pleura Gard, Thora Drain, and Thora-Klex were evaluated at the request
of Military Airlift Cemmand/SGNL. The Argyle and Migada were evaluated at the
request of the manufacturers. They were received after the start of the evaluation.
Because the in-flight feasibility test was performed first, these units did not complete
In-flight feasibility is typically performed last after all possible safety concerns
have been addressed. The units have no electrical parts; therefore, electromagnetic
interference (EMI) was not a problem. The units have no trapped gases; therefore,
there were no hazards associated with changing barometric pressure or rapid
decompressions. By performing the in-flight feasibility test first, we were able to
observe which operational characteristics would present the greatest challenge to the
aeromedical crewmembers. The laboratory tests were then designed to measure how
the individual stresses of flight and the use of a Heimlich valve and/or applied
suction affected the operation of the chest drainage unit.
A CDU is used to remove air and liquid from a patient’s pleural cavity. Most
units are divided into three separate chambers. These units operate like the 3*bottle
underwater seal chest drainage system (Fig 1).
AIR & LIQUID
FROM PATIENTS CHEST TUBE
AIR MIX FROM
PATIENTS CHEST &
TO SUCTION PUMP
WATER SEAL SUCTION CONTROL
Figure 1. Normal operation of the 3-bottle
underwater seal chest drainage system.
A chest tube allows air and liquid to drain from the patient's pleural cavity into
the collection chamber. Liquid accumulates and is measured in the collection
chamber; air flows out of this chamber and into the water seal chamber by bubbling
out of the tube below the water seal. The air now travels out of the water seal
chamber and into the suction control chamber.
CDUs which will only operate in the gravity drain configuration do not need a
suction control chamber. The air leaving the water seal chamber can vent directly to
the atmosphere. If the suction control chamber is permanently attached to the
drainage unit, the air will still vent to the atmosphere if the suction control chamber is
not filled with water.
CDUs which operate with applied suction, usually regulate the amount of
suction applied to the pleural cavity by varying the water level in the suction control
chamber. As the chamber's water level is increased, more air is pulled into the pump
through the collection chamber. As the water level is decreased, more air is drawn
from the atmospheric vent through the suction control chamber and into the pump.
Appendixes A, B, and C describe the air and water flow patterns of the 3-
bottle chest drainage system during normal operation, operation during cabin ascent,
and operation during cabin descent.
We developed test procedures to evaluate the safety and human factors issues
associated with the operation of the CDUs tested. The overriding question was
"how do the CDUs operate in flight compared to their operating characteristics on
the ground?" An initial inspection was performed to determine each CDU's
operational characteristics on the ground in four different configurations. These
baseline observations were compared with the observations made during subsequent
tests. The operational characteristic of primary interest was the negative pressure
measured at the patient end of the chest drainage system as a function of the CDU's
configuration and the individual stresses of flight. The individual stresses
considered were vibration, hot and cold storage, altitude, and rapid decompression.
Each chest drainage
unit is capable of operating in four different
1. With Heimlich Valve and With Applied Suction
2. With Heimlich Valve and With Gravity Drain
3. Without Heimlich Valve and With Applied Suction
4. Without Heimlich Valve and With Gravity Drain
The units were tested in each configuration during the altitude and rapid 1 -
decompression experiments. During the vibration and environmental experiments, 1 Cod **
the units were only tested with the Heimlich valve and applied suction (configuration
#1). Only one configuration was tested because these units are only expected to
operate for one 24-h period and the vibration and environmental tests are both very
long compared to the unit's life expectancy. The Heimlich valve and applied suction
configuration was used during these tests because a CDU is only used in
aeromedical evacuation witn a Heimlich valve and measured pressure variations are
more apparent with applied suction that in the gravity drain configuration.
During the applied suction configuration, the Impact 308M Portable Aspirator
was used as the continuous suction source. The suction, negative pressure,
delivered to the CDU fluctuated only slightly during operation, averaging 60 cm
H 2 O. It was not possible to obtain lower negative pressures than this from the
Impact suction unit.
In the first two configurations tested, the tube, which ran from the unit’s
collection chamber, was attached to the exhaust end of the Heimlich valve. The
patient's side of the valve was connected to a pressure transducer which measured
the oressure applied to the transducer relative to the barometric pressure surrounding
the transducer. In the second two configurations, the tube from the collection
chamber was attached directly to the pressure transducer. The pressure transducer
continuously measured the pressure at the patient’s side of the chest drainage
system. The pressures were recorded, once every 15 s, on a Grant 1200 series
Squirrel Meter/Logger data recorder. The recorded pressures were used to compare
different chest drainage units operating under similar configurations to each other
and to compare the different configurations of the same unit.
The measured pressures cannot be used to determine the pressure of a chest
drainage configuration on an actual patient. The pressure transducer does not
directly model all of the variations in the pleural cavity (such as bleeding and air
leaks); a patient will introduce air and liquid into the chest drainage unit - a pressure
transducer will not. The actual pressure inside a patient’s pleural cavity depends in
part on the amount of air and fluid expelled into the pleural cavity and varies with
each breath cycle. The measured pressures though are a good method of
determining how the pressure in the chest will be affected by a CDU during
changing environmental conditions.
During the initial inspection, each CDU was tested in each of the four
configurations for visible cracks or defects, water and/or air leaks, and the ability to
deliver the desired pressure to the pressure transducer ("measured pressure"). In the
applied suction configuration, the desired pressure was 20 cm H 2 0 negative
pressure; in the gravity drain configuration, the desired pressure was zero.
This test was not performed because CDUs do not have any electrical
In-flight feasibility testing was performed to observe the operational
characteristics of the units under aeromedical evacuation conditions. Results of this
test determined which laboratory tests were necessary to evaluate the CDU’s
operational response and identify special operating instructions.
While operating, each unit was vibrated in its X, Y, and Z axes separately.
During the sinusoidal test, the vibration frequency was cycled smoothly from 5 Hz
to 500 Hz and back to 5 Hz five times. This test took 1 h and 15 min for each of the
3 axes. During the random test, the vibration frequency was varied between 5 Hz
and 500 Hz randomly for 30 min for each of the 3 axes.
During the test, each unit was hung from a litter test stand and set up in the
operational mode according to current operational practices. The litter test stand was
attached to the vibration table. The pressure transducers, Heimlich valves, and
suction pumps were set up on nonvibrating surfaces so that the measured pressures
would only be affected by changes from the vibrating chest drainage units.
Hot and cold storage tests were performed. The hot storage temperature was
140 °F (60 °C); the cold storage was -40 °F (-40 °C). Prior to each test, the units
were cleaned and dried. After 6 h at the storage temperature, the environmental
chamber was returned to approximately 78 °F (26 °C), and the units were allowed
to equilibrate. As each unit was removed from the chamber, it was visually
inspected for defects, filled, and operated with the Heimlich valve and applied
suction. Following 20 min of operation, the units were inspected for air and water
leaks, and the measured pressure was recorded.
Altitude tests were performed in the USAFSAM hypobaric chambers.
Altitudes above ground level are simulated by decreasing the barometric pressure
within the chamber to that corresponding to the desired altitude. Therefore, without
ever "leaving the ground," the effects of changing altitude can be observed and
measured in the chamber. During these tests, the equipment was directly monitored
and operated by the investigator.
Each unit was tested at least once in each of the four configurations. Each test
started with approximately 2 min of ground operation to record the initial set-point
(desired) pressure. The chamber then ascended to an equivalent pressure altitude of
10,000 ft at a rate of 500 ft/min by decreasing the barometric pressure from 760
mm Hg to 523 mm Hg. After 20 min at 10,000 ft, the chamber descended back to
ground level at 500 ft/min. The test was concluded after approximately 5
min of ground operation.
Rapid decompression tests were performed in the USAFSAM hypobaric
chambers using the same principle of reducing the barometric pressure within the
chamber to that corresponding to the desired altitude. During this test, only the
CDUs, suction pumps, and pressure sensors were in the chamber. The data
recorder and investigator remained outside of the chamber. The test was observed
through the chamber windows.
Most of the units were tested at least once in each of the four configurations.
Each test started with approximately 2 min of ground operation. The chamber then
ascended to an equivalent pressure altitude of 8,000 ft at a rate of 500 ft/min. After
the units stabilized (3 to 5 min) at 8,000 ft, the chamber was rapidly decompressed
to an equivalent altitude of 40,000 ft in 1 s. Chamber pressure remained at a
40,000-ft altitude equivalent until the units stabilized (3 to 5 min) and was increased
to a ground level equivalent at a rate of 5,000 ft/min. The second and third rapid
decompressions (RD) were performed over 7 to 60 s. (The actual RDs occurred in
a random order.)
All of the CDUs except the Migada were able to deliver the desired pressure in
all four configurations. The Migada does not have a suction control mechanism;
therefore, the measured pressure during the applied suction tests (with or without the
Heimlich valve) was equal to that supplied by the suction source. The Migada
averaged 60 cm H 2 O negative pressure while the desired pressure was 20
cm H 2 O negative pressure.
The Impact suction pumps were adjusted to deliver the lowest suction
pressure possible. The Impact's suction pressure could not be adjusted low enough
to allow the "gentle bubbling" in the suction control chamber which is described in
the operating instructions of most units. The "vigorous bubbling" observed in these
units did not seem to adversely affect the measured pressure.
The in-flight feasibility tests were performed on the C-9A aeromedical
evacuation aircraft. During the tests, the measured pressure was recorded while the
units were operated in the applied suction with Heimlich valve configuration #1.
The Thora-Klex, Thora Drain, and Pleura Gard Units were tested. Results indicate
that both vibration and barometric pressure changes influence the unit’s measured
pressure. As a general observation, the measured pressure increased (became less
negative) during ascent and decreased (became more negative) during descent. The
measured pressures also appeared to be affected by the aircraft's vibration; the
measured pressure would fluctuate slightly about an average value during flight and
then stabilize after landing when the aircraft engines were turned off.
Additionally the changing barometric pressure affected the water levels within
the suction control and water sea) chambers during ascent and descent. During
ascent, air from the collection chamber would bubble out of this chamber through the
water seal into the water seal chamber, then the air would bubble out of the water
seal chamber into the suction control chamber, and finally exhaust into the aircraft's
environment. During descent, water from the suction control and water seal
chamber appeared to be pushed into the collection chamber.
During the flight, it was necessary to closely monitor the water levels in the
water seal and suction control chambers. As cabin air was drawn through the
suction control chamber by the Impact suction pump, the water in this chamber
would quickly evaporate. This water loss, combined with the redistribution of the
water within these chambers during aircraft descents, made it necessary to frequently
add water to the suction control chamber. It was also necessary to add water to the
water seal chamber after aircraft descents.
During the cruise phase of flight, the thumb screw on the Thora-Klex was
observed "walking" in and out of its housing, thereby changing the measured
pressure; this was attributed to aircraft vibration.
All the units successfully passed the environmental tests.
Structurally, all the units passed the vibration tests. They remained attached to
the test litter and did not develop air or water leaks.
The Thora-Klex uses a "thumb screw" adjustment for suction control. As
observed in flight, at certain frequencies of vibration, the thumb screw would "walk"
in and out of its housing. This would cause variations in the measured pressure of
8.8 to 41.4 cm H 2 O negative pressure.
The Argyle’s suction control regulator unthreaded itself once during the Z-axis
test (vertical vibration); it was immediately replaced without interrupting the rest of
Several altitude tests were necessary to determine what was happening inside
each of the chest drainage units. Figure 2 shows the general response of all of the
CDUs in each configuration to the changing barometric pressure occurring during
normal aeromedical evacuation flights. Basically, from the set-point pressure, the
measured pressure would increase slightly during ascent from ground level to the
10,000-ft equivalent pressure altitude. If the set-point pressure was zero (gravity
drain configurations), the measured pressure at ground level was zero; during ascent
the measured pressure would increase to approximately 2 to 3 cm H 2 O positive
pressure. During the applied suction configurations, the set-point pressure was
approximately 20 cm H 2 O negative pressure; during ascent, the measured
pressure increased to approximately 17 cm H 2 O negative pressure. For all
configurations, the measured pressure would return to the set-point pressure when
the chamber's altitude stabilized at 10,000 ft.
During descent, the measured pressure for all units in any configuration
would decrease - become more negative. For most units, the measured pressure
would vary between 24.5 and 65.0 cm H 2 O negative pressure regardless of
operating configuration. In the applied suction configurations, the Migada’s
measured pressure varied from 73.8 to 102.2 cm H 2 O negative pressure. The
Argyle varied from 160.4 to 216.6 cm H 2 O negative pressure.
The large negative pressure delivered by the Migada stems from its lack of a
suction control mechanism. Although the desired negative pressure was 20
cm H 2 O, the set point pressure (starting pressure at ground level) was approximately
60 cm H 2 O negative pressure. The Migada's measured pressure decrease from 60 to
10 . 000 '
Figure 2. Flight profile and typical CDU reaction
during the altitude test.
- Altitude Profile
102 cm H 2 O negative pressure is comparable to another unit's measured pressure
decrease of 20 to 70 cm H 2 O negative pressure.
The Argyle has a "stopper" incorporated in the water seal chamber and the
patient assessment (suction control' chamber. Th’se stoppers prevent cabin air from
entering the unit through the atmospheric vent. Tie introduction of cabin air into the
CDU equalizes the pressure between the unit and the cabin atmosphere and reduces
the measured negative pressure. The tradeoff is that while the Argyle effectively
prevents cabin air from entering the CDU's collection chamber, doing so generates a
large negative measured pressure. The negative pressure may be reduced by
opening the ru.?» jd vent. This action allows cabin air to enter the unit and equalize
the pressures within the different chambers.
Whenever cabin air is introduced into any unit, it bubbles through the suction
control chamber into the water seal chamber and finally into the collection chamber.
During this process, the air often carries water from the suction control chamber into
the water seal chamber and then into the collection chamber. At the end of this
process, the water levels in the suction control and water seal chambers have been
reduced and the fluid volume in the collection chamber has been increased.
For all of the units tested, the addition of the Heimlich valve did not have a
significant effect on the measured pressure.
During the rapid decompression experiments, the measured pressure of all of
the units, regardless of configuration, was positive. The measured pressure increase
occurred as the chamber's barometric pressure was reduced from an equivalent
pressure altitude of 8,000 ft to 40,000 ft. It was caused as the air inside the CDU
expanded and forced its way out of the unit. Frequently during the Is and 7 s RDs,
the air would move through the water seal chamber so fast that it would drag the
v/ater along with it. This action would leave the CDU with low water levels in the
water seal and suction control chambers after the RD. The measured pressures
returned to their approximate set point after approximately 5 min at 40,000 ft.
During descent, the measured pressures ranged from 0.8 to 262.6 cm H 2 O
negative pressure. Results indicate that the measured pressure does not depend on
the type of CDU tested, ihe CDU's configuration, or the length of the RD; in fact,
no particular pattern was evident.
The Migada was only tested with the Heimlich valve because during descent
water from the collection chamber (which doubles as the water seal) was first forced
up into the collection tube; then bubbles of air and water were forced into the tube-
sometimes as far as the Heimlich valve. The Migada was not tested without the
Heimlich valve to protect the pressure sensor from possible water damage.
Experimental results were reviewed by Dr Leach, Chief of Thoracic Surgery,
Wilford Hall USAF Medical Center, Lackland AFB, TX. Basically, although there
is a wide range of measured pressures, there is no clinical evidence suggesting that
any of the units used in aeromedical evacuation would be harmful to a patient.
Therefore, all of the units are recommended for approval for aeromedical evacuation
use; but there are important points that should be considered during their use.
For patient safety, a Heimlich valve should be used with every type of chest
drainage unit. The addition of a Heimlich valve does not adversely affect the
operation of the CDU or the measured pressure, and it should be placed as close as
possible to the patient's chest tube.
Monitor the water levels in the water seal and suction control chambers
closely; add water as necessary prior to takeoff and after stabilization at the cruising
cabin altitude. Dry cabin air will cause the water to evaporate quickly, especially the
water in the suction control chamber. Generally, it is not necessary to adjust the
water levels during ascent or descent.
On the ground, after every descent, slowly vent or open the unit to equalize
the pressure between the collection chamber and the atmosphere. The Heimlich
valve will prevent air from entering the patient's pleural cavity. After the pressure
has equalized, readjust the water levels in the water seal and suction control
chambers as necessary. This is a very important step for any unit which is separated
into 3 chambers; during descent the water seal may have been forced into the
collection chamber and the patient is protected only by the Heimlich valve. To
restore the CDU to working order, the water levels in the water seal and suction
control chamber must be reestablished!
Multiple descents may increase the liquid level in the collection chamber to the
point that it would be necessary to change or drain the collection chamber more
frequently than during ground operation.
At the end of a day's flight or at least once every 24 h, remove and replace the
Heimlich valve and chest drainage unit under sterile conditions.
All units experienced a slight increase in the measured pressure during ascent.
This increase averaged 2 to 3 cm H 2 O positive pressure above the initial set-point
pressure. While this is barely noticeable in the applied suction configuration, it can
cause a slight positive pressure to develop in the patient's collection tube when the
gravity drain configuration is used. Patients who require a definite negative pressure
should be connected to a CDU in the applied suction configuration.
The Argyle most effectively prevents air from entering the collection chamber
during descent; but this unit had the greatest negative measured pressure. It is
possible to manually vent this unit to reduce the negative pressure in the system to
the desired level.
The Migada and Thora-Klex units do not have the ability to provide accurate,
controllable suction to the patient. If controllable suction is required, one of the
other units should be used.
In the event of a rapid decompression, nothing can be done to prevent the
positive pressure that occurs as the air inside the unit moves into the cabin's
atmosphere. It is possible that the water seals will be blown out of the unit with the
air, but the Heimlich valve will continue to separate the patient from the cabin's
atmosphere. As soon as possible, reestablish the water levels and continue to
operate the unit as normal.
I would like to thank die following people for their help and advice during the
evaluation of the chest drainage units: Majs. Garye D. Jensen and Mark G.
Swedenburg; Capt. Theresa R. Lewis; Lt. Rebecca B. Schultz; MSgt. Thomas E.
Philbeck; TSgts. Gary L. Jenkins, Rufino U. Navalta, Ernest G. Roy, and Robert J.
Van Oss; and SSgt. Thomas W. Waters.
FUNDAMENTALS OF UNOERWATER SEAL CHEST DRAINAGE
AIR & LIQUID
FROM PATENTS CHEST TUBE
AIR MIX FROM
PATENTS CHEST 4
TO SUCTION PUMP
COLLECTION WATER SEAL SUCTION CONTROL
CHAMBER CHAMBER CHAMBER
Air and liquid from the patient's pleural cavity move from a region of high pressure to a
region of lower pressure. Liquid remains at the bottom of the Collection Clumber while air
is forced out through the connecting tube, released under the water seal, and bubbles into the
Water Seal Chamber. The air is forced out through the second connecting tube into the
Suction Control Chamber. Here the air from the pleural cavity mixes with cabin air which
bubbles through the suction control water level from the atmospheric vent The air mixture is
forced out through the last tube into the suction pump. In the gravity drain configuration, the
Suction Control Chamber is not filled with water, air forced from the Water Seal Chamber
exhausts into the atmosphere through the atmospheric vent and suction pump connection
FUNDAMENTALS OF UNDERWATER SEAL CHEST DRAINAGE
AIR a LIQUID
FROM PATENTS CHEST TUBE
COLLECTION WATER SEAL SUCTION CONTROL
CHAMBER CHAMBER CHAMBER
Figure B 1
Air and liquid from the patient's pleural cavity continue to drain into the Collection
Chamber. During ascent, air in the chambers expands causing a slight increase in the
measured pressure. The expanding air in the Collection Chamber is forced through the
connecting tube and bubbles out from the water seal into the Water Seal Chamber. The air
is then forced out through the second connecting tube into the Suction Control Chamber.
From there, it is forced out of the unit into the suction pump. The air in the chest drainage
unit is expanding in response to the decreasing cabin pressure. Little or no cabin air enter
the unit through the atmospheric vent during descent At the cruising altitude, the pressure
within the unit equalizes and the drainage system operates as it did on the ground.
FUNDAMENTALS OF UNDERWATER SEAL CHEST DRAINAGE
PATIENTS CHEST TUBE
WATER SEAL SUCTION CONTROL
During descent, air inside the unit contracts causing a decrease in the measured pressure.
To equalize the pressure, cabin air enters the unit through the atmospheric vent and bubbles
through the suction control water level. From the Suction Control Chamber some air is
drawn into the suction pump. Air is also forced backwards through the connecting tube into
the Water Seal Chamber. As the air pressure increases above the water seal, it forces the
water up the connecting tube and into the Collection Chamber. Soon the water level is
reduced so that it is equal with the tube's opening. Now water and air bubble into the
Collection Chamber. After enough cabin air either works its way into, or is manually
vented into the Collection Chamber, the pressure equalizes and the unit begins to operate
like it did prior to ascent The only difference is that the water seal level may be reduced and
is not effective.
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