Page 36 - Journal of Special Operations Medicine - Spring 2014

was statistically significant, but the user, user by posi- stop bleeding results, and the posterior had the longest.
tion, and windlass turn number were not statistically The anterior position had the highest pressures, and the
significant (Table 1). lateral had the lowest pressures. The medial position
had the lowest blood loss volume results, and the lateral
Table 1 Results of Time to Stop Bleeding. had the highest. The differences in times, pressures, and
volumes were small but clinically significant (Figure 1).
Degrees of Sum of
Variable Freedom Squares F Ratio p Value Figure 1 Tourniquet performance by position. Each error
User 1 341.5890 1.3088 .2565 bar is constructed using 1 standard error from the mean.
Position 3 2501.8071 3.1953 .0286
User by 3 336.5819 0.4299 .7322 50
position 40
Turn 1 850.2389 3.2577 .753 Time to Stop Bleeding (s) 30
number 20 10
200
When modeling pressure under the tourniquet, the as- 150
sociation between tourniquet position and pressure un- Pressure (mmHg) 100
der the tourniquet was statistically significant, and the 50
association between user and pressure under the tourni- 250
quet was statistically significant. However, the user-by- 200
position and windlass turn numbers were not statisti- Blood Loss (ml) 150
cally significant (Table 2). 100
Lateral Posterior Medial Anterior
Position
Table 2 Results of Pressure Under the Tourniquet.
Degrees of Sum of Discussion
Variable Freedom Squares F Ratio p Value
User 1 25,075.764 13.4540 .0005 The main finding of the present study was that tourni-
Position 3 22,794.865 4.0767 .0099 quet effectiveness rates were uniformly 100% regardless
of whether the position was medial, lateral, anterior, or
User by 3 12,818.854 2.2926 .0854 posterior. These clinical and statistical results are impor-
position tant because they indicate that users may continue to
Turn 1 3884.272 2.0840 .1532 place the tourniquets as they wish on the proximal thigh
number according to their preference. This finding confirmed
the hypothesis that effectiveness and position are not as-
When modeling blood loss volume, the association be- sociated. However, effectiveness as a yes-no binary vari-
tween tourniquet position and blood loss volume was able is a simple but crude outcome. Other outcomes,
statistically significant (Table 3), the association between such as blood loss volumes, have value also, as discussed
user and blood loss volume was statistically significant, in the following minor findings.
and the association between user-by-position and blood
loss volume was statistically significant. However, the The first minor finding was that several of the hypothesis-
windlass turn number was not statistically significant. generating associations yielded interesting results unex-
pectedly. The experiment was able to detect associations
Table 3 Results of Blood Loss Volume. among outcomes like blood loss volume and technique-
Degrees of Sum of associated variables like turn direction. However, the
Variable Freedom Squares F Ratio p Value design of the experiment was not set up to answer de-
finitively the meaning of such associations.
User 1 23,474.626 9.9458 .0024
Position 3 46,536.196 6.5722 .0006 The second minor finding was that one user turned the
User by 3 31,399.288 4.4345 .0065 windlass in an unexpected direction. Both users were
position right-hand dominant and preferentially used their right
Turn 1 1286.931 0.5453 .4627 hand to turn the windlass, but one turned the windlass
number clockwise and the other counterclockwise. Turning the
windlass is wrist-based, and turning is either with wrist
Excluding effectiveness, the other results indicated that supination or pronation. Supination turns the palm up,
the position had significant associations with perfor- whereas pronation turns the palm down. The two are
mance for time to stop bleeding, pressure, and blood loss performed by muscles of substantially different strength as
volume. The anterior position had the shortest time to supination is stronger. The power supinator is the biceps

28 Journal of Special Operations Medicine Volume 14, Edition 1/Spring 2014