Page 54 - Journal of Special Operations Medicine - Spring 2017

Blood Loss: Figure 4 Blood loss results by user.*
Results Overall and by Tourniquet Model
For the overall study, 50% of the variance of the blood
loss volume results could be attributed to the users.
Among the 256 effective tests, the mean blood loss for
all three tourniquet models was 163mL. There was no
significant difference between unexposed and exposed
devices in mean blood loss, which were 162mL and
173mL for unexposed and exposed devices, respectively
(p = .15). Results of blood loss by tourniquet model were
three tiered, with each model in its own tier. The C-A-T
was low (mean, 126mL), the SOFTT-W was interme-
diate (mean, 155mL), and the RMT was high (mean,
221mL). All three pairwise comparisons were signifi-
cant (p < .001, all three pairs; Figure 3). Results of mean
blood loss by user were two tiered: user 2 (cadet) was
low (128mL) and user 1 (scientist) was high (207mL). a
Results of mean blood loss by user were two tiered: user 2 (cadet)
The 79mL difference in mean blood loss between users was low (128mL) and user 1 (scientist) was high (207mL). The 79mL
was significant (p < .001; Figure 4). difference in mean blood loss between users was significant (p < .001).
These results are of 256 tests that had a good outcome.
Figure 3 Blood loss results by tourniquet model.*
comparisons, only four were not significant: exposed
SOFTT-W and exposed C-A-T, unexposed SOFTT-W
and exposed C-A-T, exposed and unexposed SOFTT-W,
and exposed and unexposed RMT (p ≥ 0.149, all four
pairs).

Discussion
The main finding of this study was that unexposed de-
vices had significantly better performance than exposed
devices in terms of effectiveness and survival of casual-
ties. Furthermore, unexposed devices had less damage
than exposed devices. The power of the exposure effect
was also seen even if the test of a tourniquet did not fail,
because the results still showed a strongly negative effect
of exposure on other measures of tourniquet function.
C-A-T, Combat Application Tourniquet; RMT, Ratcheting Medical The study results were fairly consistent across the vari-
Tourniquet; SOFTT-W, Special Operations Forces Tactical Tourniquet ous parameters measured, with big differences by ex-
Wide version. posure status. The exposure–dysfunction relationship’s
*ANOVA indicated that blood loss, according to tourniquet model,
was three tiered, with each model in its own tier: C-A-T was low temporal nature, in that the cart came after the horse,
(mean, 126mL), SOFTT-W was intermediate (mean, 155mL), and also included its duration: the long duration made the
RMT was high (mean, 221mL). All three pairwise comparisons were gradient of response large by allowing longer exposure
significant (p <.001, all). These results are of 256 tests that had a good
outcome. The vertical box plots depict the 25th percentile as the box than previous studies, thereby allowing more damage
bottom, 75th percentile as the box top, 5th percentile as the down bar, and dysfunction to accrue and thus be detected. On the
95th percentile as the up bar, the dashed line as the mean, and the solid black nylon band, for example, the dark outline of the
line as the median. Data points beyond bars are dots.
overlying windlass was left shadow-like while surround-
The respective mean volumes of blood loss with the ing nylon was grayed. The specificity (outline size and
unexposed and exposed tourniquets were as follows: shape, and its location underlying an object of similar
C-A-T, 112mL and 140mL; SOFTT-W, 152mL and size and shape) of the outline on exposed tourniquets
159mL; and RMT, 223mL and 219mL. Results of mean indicated that sunlight (responsible components of
blood loss by model and by exposure were three tiered. such light need not be visible) caused this visible effect,
The high tier included unexposed and exposed RMT which may be linked mechanically with the mechanism
devices. The middle tier included exposed and unex- of failure, as outlined next. Altogether, this study offers
posed SOFTT-W, and exposed C-A-T devices. The low evidence that environmental degradation of exposed
tier included unexposed C-A-T devices. Of 15 pairwise tourniquets appears most obviously associated with a

32 Journal of Special Operations Medicine Volume 17, Edition 1/Spring 2017