Page 64 - Journal of Special Operations Medicine - Spring 2017

Figure 3 Time- or pressure-based matching of signal presence or absence between the Doppler and each pulse oximeter.
A B

C D

Each panel shows time- or pressure-based matching of the presence or absence of a Doppler signal with that of each pulse oximeter for every
second or every discrete 1mmHg interval from the first Doppler Signal Gone to tourniquet release. Pulse oximeter signals were predominantly not
present when a Doppler signal was absent. However, pulse oximeter signals were absent a significant portion of the tourniqueted time and pres-
sure during which a Doppler signal was present, especially when pulse oximeters were on toes. Blue indicates Pulse Ox 1 versus Doppler. Green
indicates Pulse Ox 2 versus Doppler. Red indicates Pulse Ox 3 versus Doppler. Vertical bars with colored diagonal lines indicate the presence of
the respective pulse oximeter signal. Clear vertical bars indicate the absence of the respective pulse oximeter signal. Vertical bars in the left half
of each graph indicate the pulse oximeter signal status while a Doppler signal was present. Vertical bars in the right half of each graph indicate
the pulse oximeter signal status while a Doppler signal was absent. (A) Thigh tourniquet applications with pulse oximeter sensors on toes: time-
based data. (B) Thigh tourniquet applications with pulse oximeter sensors on toes: pressure-based data. (C) Arm tourniquet applications with
pulse oximeter sensors on fingers: time-based data. (D) Arm tourniquet applications with pulse oximeter sensors on fingers: pressure-based data.

of the pressure points for toes and 13% to 19% of the Discussion
pressure points for fingers.
The key finding of this study is that use of a pulse ox-
imeter to monitor limb tourniquet effectiveness will
Evaluation of the sensitivity and specificity confidence likely result in some instances of an undetected weak
intervals for each toe indicated that, with the pulse ox- arterial pulse being present. This will be true even more
imeter sensors used in this study, some differences in frequently with the use of a standard adult finger sensor
signal detection may exist between the various toes, per- on a toe. These findings leave Doppler ultrasound as the
haps related to toe length. The sensitivity and specificity de facto gold standard for noninvasive monitoring of
confidence intervals for each finger also indicated the tourniquet effectiveness in laboratory studies and offer
possibility of some differences in signal detection be- caution if using pulse oximetry to monitor tourniquet
tween the various fingers. None of the toes, however, effectiveness in a field setting.
had specificities close to the specificities of any of the
fingers.
Some patients with field-placed extremity tourniquets ar-
Discomfort rive at more advanced care locations with distal arterial
The discomfort ratings are shown in Table 4. Most ap- pulses present. Pulse oximetry is an already widespread
3
plications received discomfort ratings of None or Little. monitoring technology that looks at pulsatile blood

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