Page 51 - JSOM Spring 2020

Characterizing a System for
Measuring Limb Tourniquet Pressures

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Emma Hingtgen, BS ; Piper Wall, DVM, PhD *; Charisse Buising, PhD 3

ABSTRACT
Background: Pressure is an important variable in emergency Most emergency use limb tourniquets do not provide tourni-
use limb tourniquet science. This study characterizes one sys- quet pressure measurements. The characteristics of any sys-
tem for measuring tourniquet-applied pressure. Methods: A tem used to measure tourniquet pressures are important to
neonatal blood pressure cuff bladder was inflated to target understanding how the system being used might influence the
pressures over atmospheric. Unconstrained or constrained measurements obtained and what the obtained measurements
within 1-inch tubular polyester webbing, the neonatal cuff was represent. The purpose of this study is to provide a characteri-
placed in a 500mL Erlenmeyer flask. A 3-hole stopper provided zation of one system for investigating the pressures under limb
connections to flask interior (chamber) and bladder pressure tourniquets.
sensors and a 60mL syringe for altering chamber pressure: at-
mospheric to >1500mmHg absolute to atmospheric. Results: Methods
Within a finite range of chamber pressures, the neonatal cuff-
based system accurately indicates applied pressure (minimum As shown in Figure 1, a No. 1 neonatal blood pressure cuff
and maximum 95% confidence interval linear regression (2.2cm × 6.5cm bladder, single tube) was placed inside a
slopes of 0.9871 to 0.9953 and y-intercepts of –0.1144 to 500mL Erlenmeyer flask (Pyrex ). The neonatal cuff was ei-
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2.157). The visually defined linear response ranges for blad- ther unconstrained (Figure 1A–C) or constrained (Figure 1D)
der inflation pressures were as follows for unconstrained/ by being fully enclosed in 1-inch tubular polyester webbing
constrained: 100 to 400mmHg unconstrained/450mmHg sewn closed at both ends. The Erlenmeyer flask had a size 7
constrained for 10mmHg, 150 unconstrained/100 constrained Twistit 3-hole rubber stopper (The Plasticoid Company, plas-
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to 450mmHg for 12mmHg, 150 to 500mmHg for 15mmHg, ticoid.com). Tight-fitting rigid tubing was forced through 1 of
150 to 500mmHg unconstrained/550mmHg constrained for the holes. Inside the flask, the rigid tubing was connected to the
18mmHg, 150 to 550mmHg for 21mmHg. Below the linear bladder of the neonatal cuff. Outside the flask, the rigid tubing
response range, the inflated bladder system indicated higher was connected by a 4-way stopcock to a gas pressure sensor
pressures than chamber pressures. Above the linear response system (Vernier Gas Pressure Sensor, Vernier LabPro interface,
range, the system indicated progressively lower pressures than and Logger Pro Softwar; Vernier Software and Technology,
chamber pressures. Conclusions: Within the linear response www.vernier.com). The other 2 holes in the rubber stopper
range, the bladder pressure accurately indicates surface-ap- contained tapered valve connectors attached to 4-way stop-
plied pressure. cocks. One stopcock connected the flask interior to a second
Vernier Gas Pressure Sensor for direct chamber pressure mea-
Keywords: pressure; reference standards; tourniquet; hem- surements. The other stopcock connected the flask interior to a
orrhage; first aid; emergency treatment 60mL luer-lock syringe for adding air to or removing air from
the chamber. To avoid air leak during chamber pressurization,
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the stopper was held tightly in the flask via the rope, Parafilm
(Bemis Company, www.bemis.com), and 2 hands.
Introduction
Pressure and time are the major determinants of tissue dam- For each trial, the bladder of the neonatal cuff was inflated to
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age with limb tourniquet use. Pressure and surface area are the following target pressures above atmospheric pressure: 10,
the major determinants of tourniquet-applied force for arte- 12, 15, 18, and 21mmHg. For each target pressure, at least
rial occlusion. Pressure, therefore, is an important variable 3 trials with starting bladder pressures within 0.5mmHg of
in emergency use limb tourniquet science. This means tour- the target pressure and of each other were completed. Because
niquet producers, recommending or certifying organizations, that stringency was not the initial strategy, some target pres-
purchasing decision makers, and potential users should all sures have more than 3 trials. In those instances, data from all
have some interest in and access to information concerning the trials were analyzed and graphed, but only the 3 within
the pressures associated with arterial occlusion and completed 0.5mmHg of the target pressure and of each other were used
application of tourniquets they are considering. as a triplicate for linear and nonlinear regressions.
*Correspondence to piperwall@q.com
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1 Ms Hingtgen is a researcher at Drake University. Dr Wall is a researcher in the Surgery Education Department, UnityPoint Health Iowa Meth-
odist Medical Center, Des Moines, IA. Dr Buising is a professor of biology and the director of the Biochemistry, Cell and Molecular Biology
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Program, Drake University, Des Moines, IA.
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