Page 62 - JSOM Fall 2019

than with the thighs of various humans, and possibly automated lack of researcher access to pressure-sensor calibration data
feedback systems that might provide objective measures of the are items that should be kept in mind when considering re-
correctness of tourniquet application technique. search use of this device.

Important concerns with manikins and isolated-limb simula- Discussion
tions are limb circumferences, limb mobility, and how well
the model composition mimics the response of actual tissue Evidence of failures to understand, train, and use up-to-
to force application. Some tourniquet designs involve sections date optimal tourniquet strap-pulling technique exists in the
that do not readily conform, making application difficult on peer-reviewed medical literature and in online tourniquet-
some circumferences. Limb movement affects the best tech- training– related videos. Both the literature and online videos
nique for achieving and the ability to achieve appropriate strap also contain evidence of suboptimal mechanical advantage sys-
tightness, and highly mobile training limbs have considerable tem techniques such as failure to maintain adequate SWATT
inherent bias against success with elastic tourniquets. Un- stretch 5,39 and failure to maintain the slot of the C-A-T wind-
der-tourniquet pressure responses and indentation responses lass rod in a plane parallel to the stabilization plate. 16
differ for cylinders of different materials (unpublished data),
so some models may not provide appliers with tactile or visual Additionally, evidence exists that appliers are likely to achieve
feedback that corresponds well with what would happen if more appropriate pulled-strap pressures when the appliers
applying to a human limb. have high-priority, clear, objective strap-pulling goals to meet
before allowing mechanical advantage use. Evidence also
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Additional important concerns for instrumented models are supports the importance of feedback to appliers regarding
locations and depths of pressure sensors, calibration and drift their application technique and the importance of optimal
5
of sensors, accuracy of sensors, indicators of occlusion, and application technique for achieving arterial occlusion while
pressure choices considered occlusive. An example instru- minimizing the risk of tightening system difficulties. 7–9,60
mented isolated-limb simulation used in many studies is the
HapMed Tourniquet Trainer Leg. Some information necessary Arterial occlusion and the accompanying cessation of bleed-
for its reasonable use as research equipment is present in one ing are the desired endpoints of emergency limb-tourniquet
publication ; however, very little information is available on application. Both are most likely with optimal tourniquet
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1,6
the company website. The circumference is 57cm, bleeding is application techniques, which are more likely to be used when
represented by 26 to 0 lights, and the pressure sensors are two instructional material involves optimal application techniques.
flexible strips of quarter-sized piezo-electric transducers run- Additionally, optimal application techniques are more likely
ning the length of the device, 8mm deep to the silicone skin. when appliers have access to objective information concerning
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The strips are on opposite sides of the device, and shown pres- application technique correctness and high priority is assigned
sure values are an average from both strips from the prox- to application technique correctness.
imal to the distal edges of the tourniquet(s). A conference
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paper regarding pressure choices for occlusion makes use of It is true that some suboptimal tourniquet application tech-
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this device questionable for evaluating tourniquet effective- niques do not always preclude achieving tourniquet success.
ness: “sensors were calibrated from data obtained from surgi- However, using more windlass turns or ratchet advances or a
cal applications of tourniquets (e.g., Klenerman and Hulands second tourniquet to fix the consequences of suboptimal strap
1979).” The “Klenerman and Hulands 1979” reference is a pulling is akin to giving transfusions to fix the consequences of
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two-paragraph note in a “proceedings and reports”; it does suboptimal surgical technique regarding hemorrhage control:
not list thigh circumferences, thigh locations, recipient blood Sometimes it works, but it is not the best solution. Recogniz-
pressures, or the set of pressures used in the pneumatic tour- ing and fixing the problem of suboptimal strap pulling before
niquets (not nonelastic 3.8cm-wide strap tourniquets). In at mechanical advantage engagement is the better solution for
least one HapMed scenario choice, the pressure threshold for tourniquet applications.
occlusion is only 200mmHg, which is below the fifth percen-
19
tile for maintaining thigh occlusion with a nonelastic 3.8cm- The current optimal techniques for all limb tourniquets include
wide tourniquet (250mmHg for 420 thigh applications 24,60–63 ). applying the tourniquet directly on skin unless the application
Additional information to consider regarding HapMed device is occurring in Care Under Fire conditions. Current optimal
1,6
use as a research tool comes from two additional sources. 19,73 techniques for all emergency use limb tourniquets also include
In Baruch et al., the tourniquet appliers were adult male Is- achieving cessation of bleeding and distal pulse and securing
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raeli Defense Forces infantry recruits who had completed a the tourniquet tightening mechanism to maintain that cessa-
17-hour “Life Saver” course that included tourniquet training. tion of bleeding and distal pulse. Current optimal techniques
Using the HapMed as the tourniquet recipient, 67 of the 179 for C-A-T applications include the following:
appliers were reported as “unable to apply any pressure.” We
find it questionable that 67 adult males could not create a cir- (1) Apply the tourniquet directly on skin unless under fire. 1,6
cumferential pressure >0mmHg even if using the suboptimal, (2) Single-route the strap through the redirect buckle. 58
outward-pulling C-A-T application technique shown in the (3) Prevent the tourniquet from sliding around the limb while
paper. In Kragh et al., a change in HapMed devices resulted pulling the strap as tight as possible in a direction tangen-
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in a pressure change from a mean of 233mmHg with the first tial to the limb at the redirect buckle (Figure 1A). 56
device to a mean of 429mmHg with the second device because (4) Prior to windlass use, strap pressure on the limb should
“the software for pressure determination had been redesigned ideally be ≥150mmHg (Figure 1B). Indicators of inad-
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in the second manikin.” With measurement system transpar- equate strap pulls are an absence of tissue indentation
ency and experiment reproducibility being important concerns under the tourniquet, failure to encounter significant
in science, the dramatic device-to-device pressure change and resistance to windlass rotation within the first windlass

60 | JSOM Volume 19, Edition 3 / Fall 2019