Page 45 - Journal of Special Operations Medicine - Fall 2016

pressure–width relationship, which is often unknown meant to replace windlass-and-band tourniquets but to
to tourniquet users, resulted in numerous and increas- supplement them. Windlass-and-band tourniquets can
ingly harder pumps by hand to inflate at ever-increasing be applied faster with less blood loss than pneumatic
pressures needed to attain effectiveness, and so required tourniquets, but conversion of a windlass-and-band
more time and effort. If the user stops early, time may be tourniquet to a pneumatic tourniquet is considered a
saved yet pressure is not sufficient, whereas if the user common medic task.
continues, it takes longer to attain effectiveness with re-
liable pressures at or above 180mmHg. In contradistinc- The inner cover of the TPT is mainly made of the pneu-
tion to the narrowest model (TPT2), the widest model matic bladder, which is rectangular, and wrapping it
(the 3.5-inch EMT) yielded reliable effectiveness at the straight around the limb circumferentially leads to an
lowest mean pump counts. The EMT has a record of imperfect fit because the limb is not cylindrical; wrap-
superior performance in healthcare and research 6,8,12–14 ; ping it straight makes the proximal edge of the TPT snug
no other field tourniquet, pneumatic or nonpneumatic, but makes the distal edge loose. If the TPT is wrapped
has a record of performance comparable to the EMT. to fit snug to the limb, which resembles a conic section
where the distal end is smaller than the proximal end,
The second minor finding was of mixed results among then the rectangular cover spirals to diverge in each cir-
the new metrics tracked, including rate of bleeding, cumferential wrap, because each new wrap does not lie
composite outcomes, total time, and after time. The rate squarely atop the previous one. Thus, the inner cover’s
of bleeding (mL/s) was a calculation based on the total two ends eventually overlay each other only partly and
blood loss and the time to stop bleeding. Therefore, this not fully. Maximal divergence occurs at the last wrap
rate was an average during that time, and the less time at the cover’s end, the nonpneumatic extension end of
required to achieve effectiveness with EMT during fast the inner cover. The magnitude of the divergence may
bleeding led to the higher calculated rate of bleeding, be mitigated, but not eliminated, by the user by bending
whereas with the TPTs, the longer it took to reach effec- the cover in the opposite (i.e., proximal) direction dur-
tiveness led to lower bleeding rates. In other words, par- ing the process of wrapping; such a bend permits more
tial hemorrhage control early slowed the rate but took area for contact between Velcro surfaces but also makes
longer to become fully effective with high loss of blood; the distal edge of the cover less snug in its fit to the limb.
the TPT models had longer periods of partial control, The outer cover is longer than the inner cover, so the
whereas EMT had shorter periods. outer cover has more divergence.

The value of the percentage of good results with com- The TPT3 is 50% wider than the TPT2, and it has com-
posite outcomes by model was expected because this mensurately greater divergence, although the angles of
was the reason these metrics were invented: to perform a divergence are the same. The EMT is simpler in design
logic function of existing data to improve stratification than the TPTs as it has only one band, not two; the se-
of results. For example, some but not all readers realize curing mechanism allows no divergence (the bladder is
that a mean difference of 147mL blood loss by model routed through the clamp, which is as wide as the blad-
is an important factor, but all readers innately under- der); and the user does not need to have any awareness
stand that 90% good results versus 13% good results is of divergence or its countermeasures. The circumferen-
a significant difference, with 77% improvement in the tial wrap of the EMT bladder lies flat and snug by itself
outcome. Overall, the results were consistent: the EMT without specific intent of the user, slack removal slides
outperformed the other models in most of the param- the clamp to the limb such that the clamp tensions prox-
eters, and neither TPT model outperformed the EMT on imal and distal edges of the bladder equally, and both
any parameter. edges are snug. Such use, which is in accordance with
the instructions for use, makes the bladder nearly the
Total time (the sum of time to stop bleeding and the shape of a conic section, to fit the limb well.
time spent after stopping the bleeding for assessing the
effectiveness of the bleeding control) is a topic of im- The TPTs have bladders of fixed length, and they inflate
portance to medics that, heretofore, has been neglected the entire length irrespective of the limb size or even
as a metric and topic of study. By directly measuring of which portion of the limb (proximal, middle, dis-
total time and after time, awareness of techniques and tal) to which the bladder is applied. The bladder, when
their assessment by metric analysis may improve user wrapped around a limb, will overlap itself to a degree
performance through improved understanding. For ex- on most limbs, and the degree of overlap is greater in
ample, after time includes the assessment time but also smaller limbs. Overlap of pneumatic bladders increases
includes extra time to apply pumps to attain goals be- pressure underneath overlapped portions and makes
yond effectiveness, such as attaining desired pressures. pressure applied over the limb surface asymmetric, and
The reader should make no mistake: the EMT is not such asymmetry increases shear in tissue to increase risk

Evaluation of Pneumatic-Tourniquet Models 27