Page 59 - Journal of Special Operations Medicine - Spring 2017

finer-resolution pressure control than can be achieved LabPro interface, and Logger Pro Software; Vernier
with current commercially available windlass systems. Software and Technology, www.vernier.com). Pressure
The study used two different RMT designs: the Tactical was continuously displayed graphically with numeric
RMT (November 2014 manufacturing lot) and the Pe- values displayed every second. This system provided
diatric RMT (November 2014 manufacturing lot). The the Doppler and pressure timeline for each experiment.
two designs differed only in ladder composition and lad- Each tourniquet application’s data were saved as com-
der length: the Tactical RMT ladder had a higher tooth- plete, combined graphic and numeric data. An example
load failure rating, and the Tactical ladder was 22.4cm pressure trace is shown in Figure 1.
long whereas the Pediatric ladder was 10.0cm long. Both
tourniquet designs consisted of a fabric strap; a friction Friction-Pressure
buckle composed of two overlapping, 4.0cm-diameter Friction-pressure was taken when the strap secured
metal rings with a rough, friction-enhancing coating with the friction buckle was pulled tightly around the
to secure the correctly routed strap around the limb; a limb and all hands were off the tourniquet. Obtaining
thermoplastic polyamide ladder (linear rack with teeth); a friction-pressure greater than 100mmHg was an ap-
and a ratcheting buckle. The strap width was 3.8cm, plication goal, and the person collecting the pressure
the ladder width was 1.9cm with 2.5 teeth/cm, and the data with the computer was to alert the appliers of inad-
ratcheting buckle was 3.0cm wide by 4.5cm long with a equate friction-pressures.
0.762cm-long slot to allow the cam action of the pawl
when ratcheting. Signal Gone Definitions
The Doppler signal was defined as “Signal Gone” when
The Tactical RMT was used on all thighs and most up- no audible distal arterial Doppler pulse signal could be
per arms. The Pediatric RMT was used only on upper heard with the ratcheting buckle returned to its rest po-
arms of small enough circumference that the pressure- sition and the applier’s hands off the tourniquet. Each
measuring system could be affected by the Tactical pulse oximeter signal was defined as Signal Gone when
RMT ladder length. the assigned rater(s) determined that a pulsatile plethys-
mographic waveform was no longer present.
Doppler and Pulse Oximeters
The Doppler monitor used was an Ultrasonic Doppler Signal Return Definitions
Flow Detector Model 811 with 9.5MHz adult flat probe The Doppler signal was defined as “Signal Return”
(Parks Medical Electronics; www.parksmed.com). The when the distal arterial Doppler pulse signal again be-
three pulse oximeters used were a Nellcor OxiMax N- came audible. Each pulse oximeter signal was defined
600x (assigned the name Pulse Ox 1; Medtronics, www as Signal Return when the assigned rater(s) determined
.medtronic.com), a more than 17-years-old Nellcor mod- that a pulsatile plethysmographic waveform was again
ule inside its Spacelabs Medical multiparameter monitor present.
(assigned the name Pulse Ox 2; Spacelabs Healthcare,
www.spacelabshealthcare.com), and a Masimo Radical Signal Monitoring
(assigned the name Pulse Ox 3; Masimo, www.masimo. The Doppler pulse signal monitoring locations were the
com). Each pulse oximeter was set to its fastest avail- radial artery in the wrist, the dorsal pedal artery on the
able signal averaging; those modes were “Fast mode” top of the foot, or the posterior tibial artery at the ankle.
for Pulse Ox 1 (2 to 3 second averaging), “4 second The pulse oximeter monitoring locations were the in-
averaging” for Pulse Ox 2, and “2 second averaging” dex, middle, or ring finger or the first, second, or third
with “Fast Sat = No” for Pulse Ox 3. toe. The pulse oximeter locations for each experiment
were predetermined by drawing labeled slips of paper
Pressure Measurements from a box in a randomized block design (each pulse
Pressures under each tourniquet were measured using oximeter was used at each location five times). The
a No. 1 neonatal blood pressure cuff (2.2cm × 6.5cm pulse oximeter sensors were the reusable, spring-hinged
bladder, single tube). The cuff bladder was inflated to style designed for use on adult fingers, and each had a
10mmHg to 15mmHg above atmospheric pressure to small sheet of matte black paper shielding it from the
avoid complete collapse of the bladder during tourni- adjacent sensor.
quet applications. Atmospheric pressure was used as
baseline pressure. The cuff was taped to the tourniquet Time and Pressure Determinations
under the strap just beyond the ratcheting buckle at- The time and pressure for each Signal Gone and each
tachment rivet. Signal Return were recorded. The determinations of Sig-
nal Gone and Signal Return were by consensus of three
The inflated bladder was connected to a gas pressure listeners for the Doppler and by one or two independent
sensor system (Vernier Gas Pressure Sensor, Vernier raters for each pulse oximeter.

Tourniquet Effectiveness Monitoring 37