Background

When appropriately applied to massive extremity hemorrhages, tourniquets have become an irrefutable life-saving intervention. ^{Reference Butler1–Reference Kragh, Dubick and Aden4} For this reason, tourniquets have become the standard of care for civilian and military prehospital treatment of massive extremity hemorrhages. ^5–10 A properly applied tourniquet stops all blood flow distal of the device via circumferential pressure. Multiple retrospective studies have been conducted examining the military’s use of tourniquets in the last 17 years, demonstrating minimal complications related to tourniquet usage. Rare complications of tourniquet use in military populations include neuropathy, decreased limb function, amputation, and impaired kidney function. ^{Reference Butler1–Reference Kotwal, Montgomery and Kotwal3,Reference Kragh, O’Neill and Walters11–Reference Lakstein, Blumenfeld and Sokolov17} Studies within military populations may not translate well to civilian populations due to differences in age, fitness, and baseline health. This disparity may apply to the most foundational of military research.

There have been civilian case reports of acute kidney injury (AKI) after tourniquet usage during surgical cases and experimental studies in which mice experience renal pathology. ^{Reference Orsi, Brunelli and Zorzi18–Reference Vold and Weiss23} Additionally, more recent studies have demonstrated increased rates of post-traumatic AKIs in rats with obesity and increased oxidative stress, both of which can be found in the civilian population. ^{Reference Mittwede, Xiang, Lu, Clemmer and Hester24–Reference Xiang, Thompson, Clemmer, Mittwede, Khan and Hester28} Important health-related characteristics of the military population found within the previously mentioned studies that demonstrated minimal to no complications related to tourniquet usage may not reflect the population in which prehospital tourniquets are applied within the civilian sectors. ^{Reference Hoerster, Lehavot, Simpson, McFall, Reiber and Nelson29} When prehospital tourniquets are applied to a civilian population with increased underlying risk factors such as obesity and medical illness, the complication rate could exceed studies in military populations. Specifically, the rates of associated AKI could be increased due to pre-existing renal stressors such as hypertension and diabetes mellitus in a population already prone to AKI due to injury-related hypovolemia and the need for necessary interventions that may adversely affect the kidneys. ^{Reference Hsu, Ordonez, Chertow, Fan, McCulloch and Go30–Reference Bargman and Skorecki32} If pre-existing conditions increased the risk of AKI after the use of a prehospital tourniquet, this would be of importance to clinical decision making as AKIs increase the likelihood of death up to four-times the baseline in hospitalized and critically injured patients. ^{Reference Bihorac, Delano and Schold33,Reference Ulger, Pehlivanlar Kucuk and Kucuk34}

Two recently published retrospective chart reviews by Inaba, et al and Scerbo, et al documented incidental AKIs in trauma patients who received civilian prehospital tourniquets at a frequency of less than 3.2%. ^{Reference Inaba, Siboni and Resnick35,Reference Scerbo, Mumm and Gates36} After aggregating the incidence of AKI found by Inaba, et al (two out of 87; 2.3%) and Scerbo, et al (three out of 105; 2.9%), there was an aggregated incidence of five AKIs out of 192 (2.6%) civilian trauma patients. ^{Reference Inaba, Siboni and Resnick35,Reference Scerbo, Mumm and Gates36} Inaba, et al and Scerbo, et al did not examine patient characteristics that may increase tourniquet-associated complications, nor did they imply causation between tourniquet usage and AKI. ^{Reference Inaba, Siboni and Resnick35,Reference Scerbo, Mumm and Gates36} Yet, they provide an associated incidence of AKI with civilian tourniquet usage that surpassed previous results in the military population published by Kragh, et al (seven out of 427; 1.6%). ^{Reference Kragh, O’Neill and Walters11}

Harrois, et al provided significant insight into the multifactorial pathophysiology of AKIs in trauma patients. ^{Reference Harrois, Libert and Duranteau37} Iodinated contrast, inflammation, hemorrhagic shock, rhabdomyolysis, abdominal compartment syndrome, and fluid excess all increased the chances of an AKI. ^{Reference Harrois, Libert and Duranteau37} Tourniquet usage could increase rhabdomyolysis and inflammation, which Harrois, et al further delineated as occurring at significantly higher levels during ischemia-reperfusion events. ^{Reference Harrois, Libert and Duranteau37} In theory, tourniquet-related inflammation and muscular apoptosis with subsequent myoglobinemia could tip the scales into an AKI, even if neither event would cause an AKI when experienced in isolation. This additive and deleterious effect could be further increased in patients with renally-injurious comorbidities such as diabetes mellitus or hypertension.

This cross-sectional study aimed to provide descriptive data concerning AKI incidence and relative risk amongst civilian patients treated with at least one prehospital tourniquet. This study is not meant to affect the usage of tourniquets for massive extremity hemorrhages, nor imply causation, but to investigate a potential increased association demonstrated by Inaba, et al and Scerbo, et al that warrants further investigation. ^{Reference Inaba, Siboni and Resnick35,Reference Scerbo, Mumm and Gates36} The study hypothesized that renal comorbidities, such as diabetes mellitus and hypertension, would increase the incidence of associated AKIs in patients treated with a prehospital tourniquet.