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Comparison Of Non-clinical Tourniquet Research for Appliance Superiority & Tolerance (CONTRAST)

BACKGROUND: 
Tourniquets are effective tools to manage life-threatening extremity hemorrhage. Commercial devices are recommended over improvised ones; however, mass casualty incidents and austere environments may prevent access to commercial devices. The aim of this review is to systematically search and meta-analyze commercial and improvised tourniquets: arterial occlusion, application speed, and patient tolerance.  
METHODS:
We searched MEDLINE, Embase, CINAHL, Cochrane Library, SPORTDiscus, and ProQuest Dissertations & Theses Global using controlled terms; without date limits. Manikin, animal, and operative studies were excluded. Tourniquet devices were pooled by design and compared. Data regarding provider training and experience, recipient anthropometrics, application site, ease of application, speed, tolerance, and device efficacy were examined.
RESULTS:
5169 studies were screened. The 36 included studies were prospective trials on healthy volunteers and published between 2000 and 2021. There were 8205 unique tourniquet applications to 1921 subjects using 23 unique commercial and improvised devices. Median sample size of included studies was 20 (IQR 26) participants, ranging from 1 to 773 participants; and 102 (IQR=152) applications ranging from 20 individual applications to 1546 unique applications. The most commonly assessed outcomes were: effectiveness (n=30), pain (n=18), speed of application (n=13), and amount of mechanical advantage (ex. Windlass turns) required (n=13). Male participants outnumbered females 1,414 to 169, mean age ranged from 21 to 45 years of age. Devices were pooled into 5 categories according to mechanical advantage mechanism: elastic, friction, mechanical, pneumatic, and windlass. Initial hemostasis was achieved in 95% of upper extremity placements (CI=0.89-0.98, p= 0.02), and 88% of mid-thigh applications (CI=0.78-0.94, p>0.01), in both groups pneumatic and mechanical tourniquet devices had the highest rates of success, with friction and elastic devices having the lowest rates of success. Meta-analysis showed that mechanical and pneumatic advantage systems had superior rates of hemostasis, ease of use, and pain tolerance scores. Due to study heterogeneity, we could not determine which devices were the fastest to apply. The overall risk of bias assessment for included studies found the certainty of studies ranged from moderate to critical.
CONCLUSION:
In pre-clinical studies mechanical and pneumatic advantage systems appear to be the superior tourniquet design. Due to the low certainty of evidence and non-randomizable nature of traumatic injury, pre-clinical tourniquet devices will likely continue to be tested on well volunteers. Adoption of a minimum data set, agreed upon definitions for testable metrics, and a standardized experimental design could improve the comparability and quality of future tourniquet device studies.