Page 162 - JSOM Fall 2020

casualty the greatest chance of survival. When assessing key seal with a goal of further minimizing risk to the patient when
design inputs, there are many different aspects to consider, treated for an open pneumothorax.
from stability of the product to chemical and biological safety,
ease and intuitive use by the care provider, performance, and Human Physiological Data Review
compliance by the casualty. Each of these different aspects Human physiological data are available for lung capacity and
may affect the outcome of the casualty either alone or in breathing rate, but the pressure in the pleural cavity is de-
combination. scribed as “slightly higher/lower than atmospheric pressure.”
Reviewing the available animal model data gives the follow-
8,9
This review will focus on the performance of a newly devel- ing physiological data, which can be used to set the perfor-
oped vented chest seal. Assessment of the literature 7–10 and mance requirements for a chest seal (Table 2).
market available data identify the following key requirements
for an effective vented chest seal: TABLE 2 Human Physiological Data
Property Value
1. Adhesion to skin in different conditions Inspiration intrapleural pressure –5 → –8mmHg
2. Conformability around the chest area Exhalation intrapleural pressure ~0mmHg
3. Ability to maintain clear vents to allow release of air/gas
from the pleural cavity throughout the wear time Blood flow in hemopneumothorax 25mL/min (max of 226mL)
4. Prevent ingress of air from the external environment into Airflow through the chest seal 200mL/5 min
the pleural cavity Respiration rate 22–41 breaths/min
5. Wear time of several days if needed
6. Ability to perform as per points 1 to 5 on concave and In the presence of a nonvented chest seal, the interpleural pres-
convex anatomy sure rises with air accumulation in the chest cavity. As the level
7. Work under armor or clothing without be occluded of pneumothorax increases, the pressures for inhalation and
8. Fit easily within IFAK and medical kits, potentially folded. expiration become closer and higher. When the quantity of air
is equivalent to the total lung capacity, tension pneumothorax
is developed and the mean exhalation intrapleural pressure
Analysis of the currently available vented chest seal dressings
identifies different designs aimed at treating open pneumotho- reaches ~10mmHg. Acceptance criteria for a vented chest seal
rax. The different design features include different adhesive can therefore be defined as shown in Table 3.
formulations, different number of valves/vents available, soft
or hard valves/vents, location of vents/valves, and various Animal models have been used to test occlusive and vented
shapes. There are several “film valve”–type chest seals. These chest seals for some time. The original models used involved
are referred to by different names, such as flutter valves, vents, measuring hemodynamic stats as an indication of pneumotho-
vented, etc. These all work via a similar action relying on a rax presence. More recent testing has included measurement
pressure differential to lift/collapse a thin plastic film. There of the intrapleural pressure as a direct indicator of pneumo-
are slight variations in the design of these valve systems; some thorax. In all cases, the air used to create pneumothorax and
are bonded around the periphery and have remote holes in the the blood used to create hemopneumothorax is artificially
8,9
valve film, and others have incomplete bonding and the edge introduced.
of the film is used as the outlet. Typically, these types of seal
use a hole in the main seal with the valve part mounted to the Many methods have been developed for testing the vent func-
outer face. tion of vented chest seals in a laboratory environment. These
methods simulate flow of both air and fluid through the chest
seal at variable rates and then subsequently test for valve func-
“Hard valves” are typically premolded valve units that are
bonded into the dressing. The mechanism of action of these tion. Consequently, all parameters required for the chest seal
valves varies with valve type. For example, one chest seal uses dressing are available to test in the laboratory or have been
a duck bill–type valve where the pressure is controlled via the previously tested.
flexibility of the rubber valve, whereas an alternative chest seal Methods
uses three valves that work via displacement of an internal disc
(Table 1). Adhesion
Both in vitro and in vivo studies were designed to challenge the
The described commercially available vented chest seal de- adhesion properties of the dressing in extreme conditions in
signs were reviewed during the design of a new vented chest which the military are expected to operate. The environments

TABLE 1 Comparison of Different Commercially Available Vented Chest Seal Dressings
Chest Seal Number of Potential
Currently on Market Vents Type of Vent Burp Tab Air Pathways Vent Location Design
Chest seal 1 3 Soft Yes 3 Edge of dressing Square/rectangle
Chest seal 2 3 Hard Yes 3 Centre of dressing Circular
Chest seal 3 4 Soft Yes 4 Edge of dressing Oval
Chest seal 4 1 Hard Yes 1 Centre of dressing Circular
Chest seal 5 1 Hard Yes 1 Centre of dressing Oval
Chest seal 6 4 Soft No 4 Midway from center to edge Square/rectangle
Chest seal 7 4 Soft Yes 4 Midway from center to edge Circular

160 | JSOM Volume 20, Edition 3 / Fall 2020