Page 47 - Journal of Special Operations Medicine - Spring 2016

buckle that permits slack removal from the strap before but bleeding was represented by red lights that transil-
turning of the windlass. The C-A-T strap is 39mm wide. luminated the wound. The number of lights illuminated
At the time of assessment, the C-A-T had been registered represented the bleeding rate: all 26 lights illuminated
for years with the FDA (Figure 3). indicated uncontrolled bleeding; few lights blinking indi-
cated intermediate control; and no lights illuminated indi-
Figure 3 The Combat Application Tourniquet is a US cated bleeding had stopped. Arterial pulses were palpable
military, standard-issue tourniquet.
in the popliteal area. Touchpad readouts for each itera-
tion included hemorrhage control, the time of use, the
pressure exerted under the tourniquet, and the simulated
blood loss volume.

The measure of time to determination of hemorrhage
control extended from the start of the iteration until
the manikin detected that no more blood was lost; if
the tourniquet broke, then the manikin could determine
that hemorrhage control had not occurred and the user
could stop the test iteration by touching the pad. Ef-
fectiveness was determined by the cessation of blood
loss (i.e., hemorrhage control). Iterations began with a
tourniquet laid out flat and undone on the benchtop.
Iterations ended when the user touched the touchpad
button, assessing that the hemorrhage was stopped. Us-
ers tightened tourniquets until they perceived that simu-
lated bleeding stopped or until a tourniquet broke. The
There were two tourniquet users: a female undergradu- casualty had a medium build and the setting was CUF, a
ate student and a male clinician-scientist. Both had fa- setting resembling emergency care when under gunfire.
miliarization training in use of the manikin. The student
was relatively inexperienced in tourniquet use, whereas The manikin settings also included a constant simulated
the clinician-scientist was a tourniquet expert and had hemorrhage rate (635mL/min). With such a rate, the re-
tourniquet experience in trauma care. The clinician- sulting bleed-out time was 4 minutes (240 seconds), and
scientist trained himself on the new tourniquets and in the absence of any hemorrhage control, simulated
had formal military training on the standard-issue tour- death would occur at 240 seconds. If partial hemor-
niquet (i.e., the C-A-T). The clinician-scientist trained rhage control occurred, then longer survival could oc-
the student. Training included reading the instructions cur. The touchpad reported simulated blood loss volume
for use, handling of the device, and one or two practice as calculated from arterial flow and time. Tourniquets,
uses for each tourniquet model on the manikin before users, tests, and outcomes were uniquely identified.
testing began. The clinician-scientist tested before the
student; the control tourniquet was tested by each user Results were summarized by outcome and by tourniquet
before the study tourniquets. There were 10 tests per models. The critical, or primary, outcome was effective-
tourniquet model per user; hence, both users performed ness (hemorrhage control, yes/no). Another important
30 tests. The overall number of tests performed for the outcome was absence of palpable pulse distal to the
experiment was 60 replicates. tourniquet (yes/no). Secondary outcomes included time
to cessation of bleeding (seconds); pressure (mmHg) ap-
The tourniquets were tested on a laboratory manikin that plied to the skin by the tourniquet to achieve hemor-
was designed to train users by providing feedback on user rhage control, and the calculated volume of simulated
™
performance. The investigators used a HapMed Leg blood loss (mL). Turn numbers were the number of
Tourniquet Trainer (CHI Systems; http://www.chisystems windlass turns (180° was a turn for C-A-T and TMT) or
.com/p_medicaltrain.html); a simulated right thigh with wraps around the circumference of a limb (RATS). Ef-
an above-knee amputation injury was the testing appa- fectiveness and pressure were measured by the manikin,
ratus. 19,20 The medial hip had an embedded computer while breakage, turn numbers, and pulse stoppage were
and a smartphone-like touchpad. Software (version 1.9; determined by the user.
CHI Systems) integral to the thigh allowed the manikin
to stand alone and be operated by user input by finger Descriptive statistics were used to portray results.
touch on the pad. The thigh was placed on a laboratory Categorical data (hemorrhage control and pulse stop-
benchtop and was operated in accordance with the page in 2-by-2 contingency tables) were analyzed with
manufacturer’s instructions. The thigh did not bleed, a chi-square test and the likelihood ratio p values were

Comparison of Tactical Tourniquets 31