Page 56 - JSOM Spring 2020

TABLE 1 Linear Response Equations
Bladder Pressure With 95% Confidence Interval 95% Confidence Interval
Chamber Limits of Linearity Linear Response Equation of Slope of y-intercept r 2
Unconstrained
10mmHg y = 0.9916 ✕ x + 0.6539 0.9896 to 0.9937 0.1178 to 1.190 0.9987
100 to 400mmHg
12mmHg y = 0.9901 ✕ x + 0.9413 0.9879 to 0.9923 0.2739 to 1.609 0.9985
150 to 450mmHg
15mmHg
150 to 500mmHg y = 0.9886 ✕ x + 1.612 0.9871 to 0.9902 1.066 to 2.157 0.9993
18mmHg
150 to 500mmHg y = 0.9904 ✕ x + 0.9162 0.9890 to 0.9918 0.4218 to 1.411 0.9993
21mmHg
150 to 550mmHg y = 0.9922 ✕ x + 0.7144 0.9907 to 0.9937 0.1845 to 1.244 0.9992
Constrained
10mmHg y = 0.9931 ✕ x + 0.6257 0.9920 to 0.9943 0.2876 to 0.9639 0.9996
100 to 450mmHg
12mmHg y = 0.9911 ✕ x + 1.305 0.9900 to 0.9922 0.9755 to 1.634 0.9996
100 to 450mmHg
15mmHg
150 to 500mmHg y = 0.9938 ✕ x + 0.3259 0.9925 to 0.9951 -0.1144 to 0.7663 0.9995
18mmHg
150 to 550mmHg y = 0.9940 ✕ x + 0.6073 0.9929 to 0.9950 0.2300 to 0.9845 0.9997
21mmHg
150 to 550mmHg y = 0.9942 ✕ x + 0.3136 0.9931 to 0.9953 -0.07531 to 0.7025 0.9997
The shown linear response equations are for the triplicate for each target bladder inflation pressure.

Constraining the bladder by placement within 1-inch tubu- from 50mmHg or 100mmHg up to 300mmHg. Biehl et al.
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lar webbing may shift the linear response range but does not inflated their “infant blood pressure cuff” to 5mmHg and in-
significantly change the slope or y-intercept within the linear dicated a belief their system could be used to 600mmHg with
response range. High end separation between actual sur- “a reasonable degree of certainty.” Neither reference provided
face-applied pressure and inflated-bladder-measured pressure the dimensions of the bladders used to measure the tourniquet
may be lower with a flatter trajectory and a lower plateau pressures. The measured pressures in their studies ranged
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pressure with the addition of the tubular webbing constraint. from 85 to 497mmHg and approximately 125 to 450mmHg. 7
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The characterized pressure-monitoring system is pliable, costs Based on the systems of Grebing and Coughlin and Biehl
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approximately $500, and allows noninvasive measurement of et al., we first measured under-tourniquet pressures with a
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tourniquet-applied pressures on human limbs. Achieving tar- variant of the system characterized in this study. Namely, the
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get bladder inflation pressures to less than 0.5mmHg accuracy No. 1 sized neonatal blood pressure cuff was inflated to 10 to
and precision is challenging and requires patience and finesse. 15mmHg over atmospheric pressure, and the inflated bladder
We think it would be difficult to routinely use this system as pressure (absolute pressure) was used as the baseline. Like
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an aid for training all individuals in a large setting. However, those 2 groups, we verified our system response using an
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this system is suitable for laboratory use and instructional adult blood pressure cuff. First we verified the Vernier gas
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demonstrations. It may be useful for tourniquet training that pressure sensor against the adult blood pressure cuff’s stan-
is more in-depth than Stop the Bleed, for example: the training dard aneroid manometer. Then we compared the pressure re-
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provided to tourniquet instructors, military medics, and civil- sponses of the No. 1 neonatal blood pressure cuff placed on an
ian first responders. Additionally, until tourniquet certification arm under the adult blood pressure cuff with both cuffs’ pres-
standards exist, some version of the described system might be sures recorded with the Vernier sensors. The verifying pres-
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useful to companies making tourniquets, organizations recom- sure range used was 50 to 300mmHg. We used this variant
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mending specific tourniquets, and decision makers assessing for 4 studies 9-12 then changed to using atmospheric pressure
different tourniquets for large quantity purchases. as baseline rather than inflated bladder pressure plus atmo-
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spheric pressure as baseline.
The characterized pressure-monitoring system is a variation of
the systems used to monitor pressures under Esmark tourni- The starting bladder inflation pressure affects not only the re-
quets by Grebing and Coughlin and Biehl et al. and under a sponse range of linearity but also the size and firmness of the
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surgical glove wrist tourniquet by Guirguis and Bell. Guirguis bleb created by the bladder under a tourniquet. The size and
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and Bell did not verify the accuracy of the pressures from the firmness of the bleb probably affects pressure isobars in the
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size D cuff (no bladder dimensions given but visually appears tissue under the tourniquet, so lower bladder inflation pres-
to be the same width as a standard blood pressure aneroid ma- sures are desirable for fewer potential effects from using the
nometer, approximately 5cm) and aneroid manometer that they system. To accurately measure tourniquet-applied pressures
used to measure overlying “glove tourniquet” pressures, which at occlusion and completion, bladder inflation pressures with
ranged from 110 to 260mmHg. The 2 more recent references higher linear response ranges are desirable; once the bladder is
6,7
used adult blood pressure cuffs attached to standard mercury fully compressed, it can no longer track additional pressure in-
manometers to assess the pressure responses of their systems creases. This study shows that, depending on bladder inflation
52 | JSOM Volume 20, Edition 1 / Spring 2020