Page 24 - Journal of Special Operations Medicine - Winter 2016

To explore such measures of learning, the present study (one turn equaled one 180-degree revolution), and pres-
was performed with the purpose of generating hypotheses sure under the tourniquet (mmHg). Effectiveness, time
about tourniquet learning curves from existing data of to effectiveness, and pressure were measured by the
two users with three models of tourniquets. manikin, while windlass turn number and pulse cessa-
tion were measured by the user.
Methods
The investigators used tourniquets on a HapMed Leg
™
The current study was designed from an existing dataset Tourniquet Trainer (CHI Systems, http://www.chisystems
23
from a previous experiment. The dataset was a conve- .com/); a simulated right-thigh body segment (leg num-
nient sample that could be used to assess repetitions of ber 000F) with an amputation injury just proximal to
tourniquet use. The prior experiment used of two tour- the knee was selected as the testing apparatus. 21,22 The
niquet appliers who used three models of tourniquets; manikin was designed to train users by providing dif-
the experiment was designed to compare the function ferential performance feedback; in the present study,
of tourniquets exposed to heat to those not exposed to investigators used the manikin as a tool to measure
heat. The prior experiment was approved within a labo- learning of multiple aspects of tourniquet application.
ratory protocol (USAISR Regulatory Office, Practical The manikin was placed on a bench in the laboratory
Biomedical Engineering Research of Tourniquet Appli- and was operated in accordance with the manufacturer’s
cation and Use, L-12-009). The current study was con- instructions. The medial hip–pelvic area had an embed-
ducted under this protocol and was not designed to test ded smartphone-like touchpad. Software (CHI Systems,
a hypothesis but to generate hypotheses after attempting version 1.9) internal to the manikin allowed the leg to
discovery of new ways to measure learning in a first-aid be used independently and to be operated by user input
task. through finger touch on the pad. The manikin simu-
lated bleeding with red lights that transilluminated the
The two users of tourniquets included a physician assis- wound. The number of lights illuminated represented
tant who was training as a fellow at a military medical bleeding intensity: all 26 lights illuminated meant no
center; the fellow had military experience with tourni- control of bleeding; no lights on meant bleeding had
quet use in medical training. The second user was an stopped. A few lights blinking on and off indicated in-
experienced orthopedic surgeon (a military clinician- termediate control. Distal arterial pulse was noted when
scientist) with extensive experience with tourniquet use palpable in the popliteal area. The proximal arterial
including care, teaching, research, and development. pulse was palpable in the groin.

The three models of tourniquet included were the Combat For each test, the touchpad’s readout included (1) the
Application Tourniquet (C-A-T, Generation 6; Composite effectiveness of bleeding control, (2) the time to effec-
Resources, http://combattourniquet.com/), Special Oper- tiveness, (3) the pressure exerted under the tourniquet,
ations Forces Tactical Tourniquet Wide (SOFTT-W; Tac- and (4) the blood loss volume. The measurement of the
tical Medicine Solutions, https://www.tacmedsolutions time to effectiveness started when the test began and
.com/), and the Ratcheting Medical Tourniquet (RMT; stopped when the manikin sensed that the thigh was los-
M2 Inc., https://www.ratchetingbuckles.com/). ing no more blood. Effectiveness was a determination
of the cessation of blood loss. Tests began with a tour-
There were 840 tests conducted that were divided into niquet device laid flat and undone (strap unhooked or
two parts; the first part had 240 tests, and the second unrouted through the buckle) on the bench and not yet
part had 600 tests. There were 10 tourniquet devices per applied to the thigh. Tests ended when the user pressed
model and three models of tourniquet, for 30 devices in the touchpad button, assessing that hemorrhage was
all. One set of uses with each of the three models of 40 stopped. The casualty had a medium build, and the set-
tests (iterations) per model was intended in the previous ting was Care Under Fire, a setting of emergency care
study to have each of the two users become expert in associated with either gunfire or a similar danger. The
use. Beyond the original 240 tests, there were also 10 system reported the blood loss volume, calculated by us-
additional tests per device per user for another 600 tests ing an equation from the arterial flow and time before
(10 iterations, three models, 10 devices, two users). The hemorrhage control. The manikin had a constant hem-
840 tests were conducted over 48 days in January and orrhage rate (635mL/min), which was chosen by the
February 2014. maker; the resulting bleed-out time in this testing was 4
minutes, giving the user 240 seconds (assuming no hem-
Outcomes were summarized by tourniquet model and by orrhage control) to successfully apply the tourniquet;
user. Outcomes included effectiveness (a yes-no determi- with no control of hemorrhage, the casualty died at this
nation of hemorrhage control), pulse cessation (yes-no), time limit. Tourniquet devices, users, test iterations, and
time to effectiveness (seconds), windlass turn number outcomes were uniquely identified.

8 Journal of Special Operations Medicine Volume 16, Edition 4/Winter 2016