Page 120 - JSOM Summer 2020

FIGURE 3 The SAM-XT is a windlass-type tourniquet with a clip FIGURE 4 The MET is a windlass-type tourniquet that involves
that locks down on the strap to assist with tightening (obtained with feeding the strap through the windlass before twisting to tighten
permission from https://www.sammedical.com). (https://buyhandh.com/products/military-emergency-tourniquet
-met-gen-iii).

of this evaluation, where each volunteer was placed in an en-
vironment that simulated placing each model on during the
had similar success rates, many participants voiced their pref-
erence for the CAT over the SOFT-T as the lack of safety screw night, as well as placing it on a limb soaked with blood. How-
made it easier to use. This concern was also seen by Schreck- ever, while the CAT and SOFTT-W were successful in main-
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engaust et al., who compared the SOFT-T against the CAT in taining 1 minute of occlusion regardless of combat scenario,
Naval corpsmen engaging in simulated combat training ex- the MET’s application design caused more material to bunch
ercises. Here, the SOFT-T was found to be slower to apply up on itself with each rotation, preventing it from successfully
and less effective than the CAT, and many corpsmen disliked locking into the anchoring straps on the baseplate and requir-
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the safety screw for adding an extra step. Therefore, while ing multiple adjustments to achieve occlusion. While this
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direct comparison studies between the CAT and SOFT-T have may seem reassuring for the SOFTT-W, a study by Wall et al.
shown each to perform similarly, the design of the SOFT-T has found that it was not as successful at maintaining occlusion af-
inherent limitation. ter 2 minutes of application, with five failures compared with
the one seen with the CAT. Therefore, while the two models
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can achieve initial occlusion, the layperson should be aware of
However, the SOFTT-W corrects for this by forgoing the screw
and may have some benefit in the pediatric population. El- the increased risk of failure with the SOFTT-W.
Sherif et al. assessed the CAT, SOFT-T, and SOFTT-W in pedi-
atric limb application without slack, which was defined as the The final phase of these studies then compared the CAT against
ability to easily slip more than one adult index finger beneath the Tactical Medical Tourniquet (TMT), another windlass-type
the strap. Using both pediatric mannequins (infant, 1 year old, model that differs from the CAT by having the user first clip a
and 5 years old) and PVC piping to simulate pediatric extrem- black hook on the fastening strap into the bronze loop prior to
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ity circumferences, the SOFTT-W and CAT were more suc- tightening with the strap (Figure 5). Using HapMed trainers
cessful in being tightened to the thigh of the infant mannequin to first instruct participants on proper application, they were
than the SOFT-T. Otherwise, all three could be applied to all then applied to the upper and lower extremities of the vol-
extremities of the 5-year old but only to the lower extremities unteers until occlusion was confirmed by Doppler. Compared
of the 1-year old, which was correlated by all properly fitting with the CAT, the TMT had a slower application time for both
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PVC piping at least 19.7cm in diameter. However, the pres- limbs and caused more excess pressure and discomfort. How-
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ence of slack in a rigid model does not imply occlusion failure ever, the existing literature is conflicting, as a study by Beaven
in an actual limb, especially as the study done by Harcke et et al. revealed similar mid-thigh application times to popliteal
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al. found that if the manufacturer’s instructions were prop- artery occlusion. Additionally, a study by Gibson et al. found
erly followed by bending the baseplate of the windlass prior to that the CAT on average applied more pressure than the TMT
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application, the CAT was effective in occluding blood flow in to their mannequin-model system. This particular finding
both upper and lower pediatric extremities. Therefore, more was also seen in a review conducted by Valliere et al., where
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research is required before officially discounting the use of the CAT applied more baseline circumferential pressure even
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these devices in this population. without the mechanical advantage provided by the windlass.
The SOFTT-W was also compared against the CAT as part FIGURE 5 The TMT is a windlass-style tourniquet that features
of the Joint Operational Evaluation of Field Tourniquets (JO- clipping the fastening strap onto the winding apparatus (obtained
EFT) at the Naval Medical Research Unit in San Antonio. This with permission from https://combatmedical.com/).
three-phase evaluation also considered the Military Emergency
Tourniquet (MET), a model where the free end of the loop is
fed not only through the buckle of the windlass baseplate but
also through the center of the windlass itself before tightening
(Figure 4). Montgomery et al. rated this tourniquet at 28.40
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for decreased occlusion efficacy and slow application speed,
and as such is not recommended by the CoTCCC. In phase
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I of JOEFT, McKeague and Cox found that all windlass-type
tourniquets were successfully applied to HapMed and MATT
tourniquet trainers by study participants, indicating vessel oc-
clusion. This held true for the CAT and SOFTT-W in phase II
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118 | JSOM Volume 20, Edition 2 / Summer 2020