Page 41 - Journal of Special Operations Medicine - Winter 2016

Figure 6 Pressure-loss curves with and without use of tubular webbing as additional bladder constraint.
(A) (B)

In each panel, individual markers indicate data points at 30 second intervals for each tourniquet application. Lines show the two-phase decay
curves for each tourniquet. The 95% confidence intervals for the two-phase decay curves are also present but are so narrow that they visually
overlap the decay curve. The 301 through 600 second line continuations for thigh two-phase decay curves are calculated from their respective
equations. The pressures shown in the legend are the actual completion-pressures with each application. (A) Pressure-loss curves on 20% ballistic
gel for Combat Application Tourniquet (C-A-T) and Ratcheting Medical Tourniquet (RMT) with and without tubular webbing as additional
bladder constraint. The equation for the C-A-T with tubular webbing is y = −48.6 + 10.7 × e (−0.04578 × x) + 37.9 × e (−0.002389 × x) . The equation for the
RMT with tubular webbing is y = −46.6 + 10.3 × e (−0.04539 × x) + 36.3 × e (−0.002912 × x) . (B) Pressure-loss curves on thigh for C-A-T and RMT with and
without tubular webbing as additional bladder constraint. The equation for the C-A-T with tubular webbing is y = −64.0 + 23.9 × e (−0.08928 × x) +
40.1 × e (−0.006954 × x) . The equation for the RMT with tubular webbing is y = −63.9 + 18.5 × e (−0.07527 × x) + 45.4 × e (−0.006729 × x) .

of tourniquet application, and circumference around One answer to the problem of pressure loss under
which the tourniquet is applied. From a modeling stand- nonelastic tourniquets within minutes after applica-
point, the pressure-loss behavior of neither ballistic gel tion would be to apply such tourniquets some amount
completely matched the pressure-loss behavior of the tighter than needed for initial arterial occlusion. This
thigh. However, the less pliable 20% gel showed less is not a completely useful answer because “the amount
pressure loss than the 10% gel, and both gels and the tighter” is an amorphous amount influenced by tourni-
thigh showed faster and greater pressure losses with quet design, the pressure at which arterial occlusion oc-
nonelastic tourniquets and higher completion-pressures. curs, and limb circumference. Even if the amount could
Circumference as a determinant of the pressure-loss- be specified, most emergency tourniquets do not have
curve profile is supported by comparing the matched- pressure measuring systems. Additionally, the resolution
completion-pressures thigh and arm curves. of possible pressure increases varies with tourniquet me-
chanical advantage systems. Most windlass designs have
The two completion-pressures used were both greater securing options only at 180° increments (large pressure
than needed for the SWATT or adult blood pressure cuff increases). The RMT has much finer pressure increase
to occlude arterial flow through the recipient’s thigh. resolution, so a recommendation of a one or two tooth
Therefore, more appropriate completion-pressure ap- ratchet advancement beyond that needed to reach arte-
plications of the SWATT or blood pressure cuff on the rial occlusion may be wise. Of course, this presupposes
recipient’s thigh would be expected to have slower and the applier has sufficient attention available to deter-
lesser pressure losses. mine just when arterial occlusion was reached.

Both used completion-pressures were also higher than An alternate answer to the pressure-loss problem is to in-
needed to occlude arterial flow through the recipi- clude reassessment of the tourniqueted limb for arterial
ent’s arm with any of the tourniquets. Therefore, all occlusion at a specified time shortly after application.
would be expected to have slower and lesser pressure The nonelastic, 3.8cm-wide C-A-T and RMT required
losses with more arm-appropriate completion-pressure the highest pressures to reach occlusion and had the fast-
applications. est and greatest pressure losses. Within 5 minutes, both

Tourniquet Pressure Loss 25