Page 57 - Journal of Special Operations Medicine - Spring 2015

Table 5 Completion Pressures when fewer than two windlass turns are used, and the
Base or Ladder ladder of the Tactical RMT has a limited length. The
Completion Strap Completion tourniquet training implications of these combined facts
Pressure, Median, Pressure, Median, are that achieving a high initial strap tension is very de­
Minimum– Minimum– sirable to have the mechanical advantage system work
Tourniquet Maximum mmHg Maximum mmHg properly and quickly achieve arterial occlusion but con­
CAT 423, 255–603 365, 239–552 fers no advantage or disadvantage concerning the skin
Tactical RMT 477, 332–652* 363, 162–534 surface­applied pressure required for arterial occlusion.
Notes: CAT, Combat Application Tourniquet; RMT, Ratcheting Med­
ical Tourniquet. To consistently require two or fewer windlass turns for
*Completion Pressure: CAT Base lower than Tactical RMT Ladder, Completion, a Strap Friction Pressure of 150mmHg
p < .0001. had to be reached. With the CAT strap single threaded
through the friction buckle, it was entirely dependent
Completion Pressures (Table 5). Completion Pressures on the hook­and­loop system not to back slide. Reach­
were not affected by the order of tourniquet use or by ing a Strap Friction Pressure of 150mmHg definitely
Friction Pressures and were not consistently or highly required effort by the applier but was generally manage­
related to windlass turns, ladder distance traveled, or able without help from an additional person. Achiev­
Bunching Index. ing a CAT Strap Friction Pressure of 175mmHg often
required the teamwork of two people, and achieving
Discomfort 200mmHg required teamwork even more frequently.
Recipients found the slightly modified CATs consider­ The teamwork used to reach higher Friction Pressures
ably less unpleasant on bare skin when tightened to consisted of one person holding onto the rod locking
arterial occlusion than was the case for CATs without clip with upward force while the other person used both
the rod locking clip skin­side hook­and­loop covered hands and body position to pull the strap downward
and without the tape over the sharp corners of the base. and around the limb with maximal effort. When the
Discomfort ratings were not statistically significantly re­ CAT hook­and­loop covered strap is double threaded,
lated to Friction Pressure for either tourniquet; however, friction also plays a role in securing the strap. Double
recipients reported that more bunching under the Tacti­ threading the hook­and­loop covered strap increases the
cal RMT was more uncomfortable than was less bunch­ difficulty of achieving a high Friction Pressure. There­
ing. Discomfort ratings were not different between the fore, we think it would be challenging for many appliers
CAT and the Tactical RMT. to reach target Strap Friction Pressures of 150mmHg or
higher during double threaded thigh applications. Previ­
ous observations are consistent with this view.
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Discussion
The key finding of this study is that the skin surface pres­ Despite the relative smoothness of the Tactical RMT
sure exerted prior to engaging the mechanical advantage strap, achieving a Strap Friction Pressure of 100mmHg
system, Friction Pressure, does not affect how much required effort by the applier. With the Tactical RMT,
skin surface pressure must be exerted to reach arterial reaching a Strap Friction Pressure of 125mmHg or
occlusion with either the windlass­tightened CAT or the 150mmHg required teamwork. The only Friction Pres­
ratchet­tightened Tactical RMT. The second important sure with an application that could not reach Occlusion,
finding was a very strong inverse relationship between which was due to insufficient ladder, was a 25mmHg
Friction Pressure and the number of windlass turns or Strap Friction Pressure on a large thigh. Previous ob­
ladder distance needed to reach arterial occlusion. The servations indicate that Strap Friction Pressures above
third important finding was that for individual recipi­ 100mmHg can be reached by individual appliers, but
ents, Occlusion Pressures were similar under the Strap Strap Friction Pressures below 100mmHg are likely to
portion of the CAT and Tactical RMT. be more common. Since ratcheting buckle advancement
5
can become increasingly difficult with greater bunching,
As expected, higher Friction Pressure resulted in less use training appliers to expend the effort to achieve as much
of the mechanical advantage system with fewer windlass initial strap tension as possible is important.
turns or less ladder distance used and less strap bunching
during tightening to arterial occlusion. Contrary to our Regarding the bunching, an interesting finding of this
hypothesis, strap bunching and the accompanying skin study was that strap bunching with the CAT was not at
surface irregularities did not have an effect on the tour­ all circumferentially distributed. Despite both tourniquets
niquet skin surface­applied pressures needed to reach having bunching concentrated in a localized area, the vi­
arterial occlusion. The findings of Kragh et al. indicate sual character of the bunching was quite different (Fig­
9
that battlefield­used CATs suffer the least deformation ure 4): CAT bunching did not involve the same degree of

Initial Tourniquet Pressure Does Not Affect Arterial Occlusion Pressure 47