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USAFSAM-TR-90-13 


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AD-A227 317 


EVALUATION OF SIX CHEST DRAINAGE UNITS FOR 
USE IN AEROMEDICAL EVACUATION 


Susan K. Nagel, Captain, USAF, BSC 


July 1990 


Final Report lor Period September 1988- April 1990 




DT1C 


ELECTE 
OCT 0 5 sac 


I 


Approved for public release; distribution is unlimited. 


USAF SCHOOL OF AEROSPACE MEDICINE 
Human Systems Division (AFSC) 

Brooks Air Force Base, TX 78235-5301 












NOTICES 


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. 

This report was prepared as an account of work sponsored by an agency of the United 
States Government. Neither the United States Government nor any agency thereof, nor any of 
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completeness, or usefulness of any information, apparatus, product, or process disclosed, or 
represents that its use would not infringe privately owned rights. Reference herein to any specific 
commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, 
does not necessarily constitute or imply its endorsement, recommendation, or favoring by the 
United States Government or any agency, contractor, or subcontractor thereof. The views and 
opinions of the authors expressed herein do not necessarily state or reflect those of the United 
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Technical Information Service, where it will be available to the general public, including foreign 
nationals. 

This report has been reviewed and is approved for publication. 








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Evaluation of Six Chest Drainage Units For Use in Aeromedical Evacuation 


12. PERSONAL AUTHOR(S) 

Nage1, Susan K. 


13*. TYPE OF REPORT 13b TIME COVEREO 14 DATE OF REPORT (Y»tr. Month. Day) IS. PAGE COUNT 

Final _ from 88709 tq 9Q/Q4 1990. July 19 


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CODES 

FIELD 

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18. SUBJECT T1RMS (Continue on reverye if ntcttssry tnd idtntify by block numb*') 

Test and Evaluation; Chest Drainage Unit; 

Aeromedical Evacuation 


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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EVALUATION OF SIX CHEST DRAINAGE UNITS 
FOR USE IN AEROMEDICAL EVACUATION 


BACKGROUND 

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 
aeromedical evacuation. 

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 
this test. 

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 


1 




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 & 
ATMOSPHERIC VENT 
TO SUCTION PUMP 


COLLECTION 

CHAMBER 


WATER SEAL SUCTION CONTROL 

CHAMBER CHAMBER 


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 


2 
















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. 


METHODS 


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 
configurations: 


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. 

Initial Inspection 

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. 


4 



This test was not performed because CDUs do not have any electrical 
components. 


In-flight Feasibility 

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. 

Vibration 

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. 

Environmental 

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 


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 

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.) 

RESULTS 
Initial Inspection 

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. 


6 







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. 

In-flight Feasibility 

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. 

Environmental 

All the units successfully passed the environmental tests. 


7 


Vibration 


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 
the test. 


Altitude 

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 


8 



10 . 000 ' 


CRUISE 



Figure 2. Flight profile and typical CDU reaction 
during the altitude test. 

- Altitude Profile 

-Measured Pressure 


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. 


9 










For all of the units tested, the addition of the Heimlich valve did not have a 
significant effect on the measured pressure. 

Rapid Decompression 

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. 


CONCLUSIONS 

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 


10 







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. 


ACKNOWLEDGMENTS 


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. 


12 




APPENDIX A 


FUNDAMENTALS OF UNOERWATER SEAL CHEST DRAINAGE 

Normal Operation 


AIR & LIQUID 

FROM PATENTS CHEST TUBE 



AIR MIX FROM 
PATENTS CHEST 4 
ATMOSPHERIC VENT 
TO SUCTION PUMP 


COLLECTION WATER SEAL SUCTION CONTROL 

CHAMBER CHAMBER CHAMBER 


Figure A-1 
Normal Operation 


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 
tube. 


13 







APPENDIX B 


FUNDAMENTALS OF UNDERWATER SEAL CHEST DRAINAGE 

Ascent 


AIR a LIQUID 

FROM PATENTS CHEST TUBE 



COLLECTION WATER SEAL SUCTION CONTROL 

CHAMBER CHAMBER CHAMBER 


Figure B 1 
Ascent 

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. 


15 






APPENDIX C 


FUNDAMENTALS OF UNDERWATER SEAL CHEST DRAINAGE 

Descent 


PATIENTS CHEST TUBE 



COLLECTION 

CHAMBER 


WATER SEAL SUCTION CONTROL 

CHAM8ER CHAMBER 


Figure C-1 

Descent 

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. 


« u. a. cove emit nr put urine office: i#*u-«T*i-o5i/aoina 


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