Page 55 - JSOM Fall 2022

34
compressive forces on the treated limb. The general con­ Implications of ST Findings in
sensus amongst a majority of leading trauma researchers is Context of Wrap-Based Tourniquets
that the benefits of prehospital tourniquet use far outweigh The findings of this study demonstrate the functional feasibil­
the risks of tourniquet­associated sequelae. 2,3,6,35 Nonetheless, ity of the minimally elastic, wrap­based ST tourniquet design.
decreasing the risk of those sequelae is desirable for improving While both ST and Esmarch tourniquets are tightened around
patient outcomes. The finding that the 10.2­cm­wide, mini­ a limb by successive circumferential wraps while stretched
mally elastic, adhesive wrap–based ST can deliver quick, effec­ under pull­tension, there are important differences between
tive arterial occlusion with completion pressures lower than these devices. Beyond the presence of an adhesive and release
the windlass­based CAT addresses an important concern asso­ coating on its opposing surfaces, the ST most notably differs
ciated with emergency­use tourniquets. from the Esmarch tourniquet in that it is minimally elastic.
This structural difference is important as a study on canines
While the 10.2­cm­wide ST was found to deliver mid­thigh of a 8.5­cm­wide, shape­stabilized pneumatic cuff and an
tourniquet completion pressures lower than the 3.8­cm­wide 8­cm­wide Esmarch tourniquet reported that the tissue pres­
CAT, the data from this study do not provide direct evidence sure profile decreases from the midpoint outward to the edges
about the origin(s) of this phenomenon. The characterization of a tourniquet, but to a substantially greater extent in the
of the relationship between tourniquet width and delivered Esmarch device. Furthermore, the Esmarch tourniquet was
39
limb compression, occlusion pressure, tissue pressure profile, observed to show pressure concentration at the center of the
and other parameters has been an active area of research for limb, and such a pressure concentration is expected to increase
many years. 15,28,33,36,37 Some progress has been made in this area risk of tourniquet­associated tissue damage. Thus, while
through the use of pneumatic tourniquet pressure data, but a wider, elastic wrap might be presumed to present a lower
a mathematical relationship which accurately predicts occlu­ risk of tissue injury than a narrower non­elastic tourniquet,
sion pressures for nonpneumatic designs remains elusive. 28,37 this may not be the case. The laboratory validation of the ST
For example, a study by Wall et al. reported a 3.8­cm­width, suggests the feasibility of future studies investigating the lo­
nonelastic strap, rachet­based tourniquet achieving comple­ cal tissue pressure profiles of similarly sized, minimally elastic
tion pressures similar to a 10.2­cm­width, elastic, wrap­based and elastic wrap–based tourniquets. Such studies may provide
tourniquet in certain cases, while the 3.8­cm­wide, nonelastic a better understanding of the complex interplay between the
15
strap CAT generally achieved occlusion at higher pressures. width and elasticity of tourniquets and their resulting capacity
Therefore, attributing the observed differences between ST to safely distribute pressure while delivering arterial occlusion.
and CAT completion pressures specifically to their differing
widths without additional supporting data is inadvisable. This Limitations
is because these two tourniquets also differ meaningfully in The mid­thigh tourniquet application site was selected based
their structure and composition as well as how each is tight­ on the expectation that it would require greater pressures to
ened and secured. achieve arterial occlusion than an alternate site of smaller limb
circumference, and thus the mid­thigh was also expected to
Tourniquet Application and allow for greater experimental resolution of any differences
Human Use Factors in occlusion pressures, and by extension, completion pres­
Despite substantial differences between the design, composi­ sures. However, the pressure required for a given tourniquet
tion, and application process for the ST and CAT, it is im­ to achieve occlusion is known to be impacted not only by
portant to note that no statistically significant differences tourniquet configuration and limb circumference, but also by
were observed in their times to occlusion and completion or hemorrhage location, muscle tension, arterial depth, and other
in their ease­of­use ratings. This finding suggests that the ad­ anatomical characteristics which were not explored in this
hesive wrap–based design of the ST does not negatively impact study. 15,28,33,40 Thus, it is unknown if an analogous difference
its ability to efficiently deliver hands­free hemorrhage control would be observed between the completion pressures of the
relative to the CAT. CAT and ST if the study were repeated at another limb site.

While the physical design of a tourniquet can provide a lower This study was conducted in a controlled laboratory setting
limit for the time and number of steps required for it to be on perfused cadavers with similar demographics and not on
effectively deployed, human factors such as intuitiveness of living patients. While the CAT and ST were applied at an ap­
design, ease of handling, and the complexity of each appli­ propriate, limb extremity site in a process similar to how each
cation and adjustment step can critically influence how effi­ might be used on live patients, differences remain between the
ciently a tourniquet delivers hemostasis for a real­world user. cardiovascular output and tissue response of a living patient
This aspect of tourniquet use was highlighted by Baruch et al. compared with that of a perfused cadaver. As a result, a future
who reported that a user’s ability to effectively apply a tourni­ study of the pressure required for the CAT and ST to deliver ar­
quet to a mannequin limb model can be impacted by the user’s terial occlusion in the limbs of healthy human volunteers would
level of understanding of a specific tourniquet’s mechanism of provide valuable context for the findings reported herein.
38
action. While the CAT and several similar, windlass­based
tourniquets have been widely used for many years, the same While the experimental protocol for this study was designed
cannot be said of the minimally elastic, adhesive wrap­based to simulate the emergency treatment of serious arterial hem­
ST tourniquet. Therefore, while the ST somewhat resembles orrhage, it nonetheless did not fully replicate the real­world
an Esmarch tourniquet, experienced tourniquet users who are conditions in which a tourniquet is typically used. As previ­
unfamiliar with the ST would be expected to require practice ously noted, the efficacy of a tourniquet is a function of both
to achieve occlusion times, application speeds, and success its inherent operational capabilities as well as user­related fac­
rates at parity with more familiar tourniquets. tors such as intuitiveness of design, complexity of application,
and ease of adjustment. Therefore, a focused investigation of

Solo-T and the Combat Application Tourniquet Evaluation | 53