Page 51 - Journal of Special Operations Medicine - Spring 2017

flicker on and off; and the screen may flicker bleeding– the casualty was dead. The setting was Care Under Fire,
not bleeding (stable), which simulates care well if the a setting resembling emergency care when under gunfire
tourniquet use is borderline between inadequate and
adequate. During tourniquet application, rolling of the The manikin settings also included a constant simulated
thigh on the ground or table can add a bit of extra pres- hemorrhage rate (625mL/min). At this rate, the bleed-
sure to the underlying compressed sensors or subtract a out time was 4 minutes (240 seconds); in the absence of
bit when the thigh rolls off the sensors. any hemorrhage control, simulated death would occur
at 240 seconds. If partial hemorrhage control occurred,
The manikin has piezo-electric transducers as pressure then longer survival could occur. The amount of bleed-
sensors under the 8mm-thick silicone skin of the mani- ing required for the casualty status to turn from “bleed-
kin; sensors are arrayed in a line as a flexible strip of ing” to “dead” was 2,500mL, half of the start value of
quarter-sized transducers, which run proximally to dis- 5,000mL. The touchpad reported simulated blood loss
tally along the undersurface of the silicone skin where volume as calculated from arterial flow and number of
the underlying main artery is in anatomic specimens. pulses over time.
A second similar strip is placed diametrically opposite
on the thigh to the other strip to adequately sense pres- Results were summarized by outcome and by models of
sure as an average under the tourniquet on both sides of tourniquet. The primary outcome was effectiveness (yes–
the entire length of the thigh and from the proximal to no, hemorrhage control). Secondary outcomes included
distal edges of the tourniquet (or tourniquets, if more casualty status (alive–dead), tourniquet breakage (yes–
than one tourniquet is applied). The pressure amplitude no; and by degree: major–minor), time to cessation of
is displayed as number (mmHg) on the manikin screen bleeding (seconds), pressure (mmHg) applied to the skin
and is an average value sampled across sensors that are by the tourniquet to achieve hemorrhage control, and
compressed at the time of sampling; sampling of pres- the calculated volume of simulated blood loss (mL). Ef-
sure was made at the time of determination of bleeding fectiveness and pressure were measured by the manikin,
control (i.e., when the button is pushed). while breakage and turn-click numbers were determined
by the user. Major damage of a tourniquet device was
Run-time feedback was on, so limited data during appli- catastrophic disruption of a component of the tourniquet
cation were shown on the touch screen, including a bar such that it was unable to be made effective by the user.
graph of pressure, which was displayed as a short, black
bar, indicating low pressure, or a long, green bar. Such Collected data were used to calculate composite results
feedback was moment to moment in real time when a of five other outcome measures: hemorrhage control,
pressure threshold was achieved in bleeding control; the time to stop bleeding, total trial time (sum of time to
software determined the threshold based on the ampli- stop bleeding, time to secure the tourniquet and assess
tude of the average pressure applied during sampling, its placement, and time to assess the casualty), the pres-
the width of the pressure sensed, and the limb circum- sure exerted under the tourniquet, and the simulated
ference. The pressure is sensed in 1mmHg increments, blood loss volume. Composite results were determined
and the device is recalibrated whenever refurbished. in two ways. The first was a composite score for each
Pressure values do not become uncalibrated; there is no test as a number, the count (0 to 5) of the five possible
artefact such as a drift over time. Touchpad readouts for elements that were satisfactory (i.e., hemorrhage con-
the results of each iteration included hemorrhage con- trol was yes, the time of application was 60 seconds or
trol, the time of application, the pressure exerted under less, the pressure was within 150mmHg and 300 mmHg
the tourniquet, and the simulated blood loss volume. inclusive, blood loss was less than 500mL, and major
damage of any tourniquet component was absent).
The measure of time to determination of hemorrhage The second composite outcome was a binary “good”
control extended from the start of the iteration until or “bad” result for each test of whether every element
the manikin detected that no more blood was lost; if making up the composite result was satisfactory.
the tourniquet broke, then the manikin could determine
that hemorrhage control was not occurring. Effective- Additional results were calculations derived from exist-
ness was determined by the cessation of blood loss (i.e., ing data. “After-time” included time needed to secure
hemorrhage control). the tourniquet, assess its placement, and assess response
of the casualty to its use; after-time was calculated by
Iterations began with a tourniquet laid out flat and un- subtracting time to stop bleeding from total trial time.
done on the benchtop. Iterations ended when the user
touched the touchpad button, determining that the hem- During the data collection, both users recorded their
orrhage was stopped. Users tightened tourniquets until own qualitative assessments of the models of tourniquet
they perceived that simulated bleeding stopped or until to supplement the quantitative assessments.

Tourniquet After Environmental Exposure 29