ORIGINAL ARTICLE The Combined Influence of Hemorrhage and Tourniquet Application on the Recovery of Muscle Function in Rats Thomas J. Walters, PhD,* John F. Kragh, MD,*† David S. Kauvar, MD,* and David G. Baer, PhD* Objective: The objective of this study was to compare the effect of tourniquet-induced ischemia/reperfusion (I/R) injury on the recovery of muscle function with and without prior hemorrhage. Methods: Male Sprague-Dawley rats (initially 400–450 g) were randomly assigned to 1 of 4 groups (n = 8 per group): (1) hemorrhage (33% of estimated blood volume) plus tourniquet +H/+TK; (2) tour- niquet alone (2H/+TK); (3) hemorrhage alone (+H/2TK); and (4) surgical control (2H/2TK). A pneumatic tourniquet was applied to the upper leg for 4 hours, followed by 2 weeks of recovery. For +H animals, tourniquets were applied at the conclusion of blood with- drawal. The predominantly fast-twitch plantaris and the predomi- nantly slow-twitch soleus muscles were examined using in situ isometric muscle function 2 weeks following treatment. Results: Tourniquet application resulted in significantly greater loss of force production [peak tetanic force (Po)] in the plantaris compared with the soleus. The decrease in Po was a result of both a loss of muscle mass and a reduction in specific force [force per unit weight; Po (n/g)]. Hemorrhage prior to tourniquet application significantly increased the extent of functional loss compared with tourniquet alone in the plantaris but not the soleus. Hemorrhage prior to tour- niquet application significantly reduced the rate of postsurgical recov- ery of body weight. Conclusion: The functional loss resulting from tourniquet appli- cation is exacerbated by the superimposition of hemorrhage in the predominantly fast-twitch plantaris but not the predominantly slow- twitch soleus. This was likely a result of metabolic derangement resulting from the combination of hemorrhage and tourniquet appli- cation. The development of interventions designed to attenuate the loss of muscle mass and function following complex trauma is nec- essary for optimal patient recovery. Key Words: fiber type, healing, ischemia reperfusion injury, rat, regeneration, repair, skeletal muscle (J Orthop Trauma 2008;22:47–51) INTRODUCTION Wounds to the extremities are the most frequently encountered in combat, accounting for between 60% and 80% of injuries on the modern battlefield. 1–5 These injuries are frequently severe and often accompanied by major vascular damage, making them a leading contributor to preventable battlefield mortality. 6,7 Tourniquets are the most effective way of treating severe arterial trauma in extremities under emer- gency combat conditions and have saved countless lives in the current wars in Iraq and Afghanistan (personal communica- tions Col. John Holcomb, MC, and Col. John F. Kragh, MC). Furthermore the liberalization of tourniquet use 8–10 and the availability of effective, easy-to-use, combat tourniquets have greatly increased tourniquet use. 8,9 Regardless of how rapidly a tourniquet is applied, considerable blood loss can occur before control of hemorrhage is achieved. Tourniquet-induced ischemia/reperfusion (I/R) injury results in a complex cascade of responses that can lead to muscle degeneration and loss of muscle function. 11–13 Severe hemorrhage results in global I/R, which can lead to multiorgan system failure; even in less severe cases these organ systems undergo some degree of I/R. 14 It is unknown whether the combinations of these 2 physiologic stressors interact to worsen muscle injury. Previous studies from our laboratory have shown that hemorrhage (33% estimated blood volume) combined with tourniquet application paradoxically reduces muscle edema and reduces loss of viability acutely (2 hour and 48 hour) as assessed by histology and vital staining. 15 However, it is unknown whether this acute beneficial effect translates to greater return of muscle function during recovery at later time points. Here we report the combined impact of hemorrhage and tourniquet application on the rate of recovery of muscle function. METHODS Male Sprague-Dawley rats were obtained from the colonies of the Charles River (Wilmington, Massachusetts). At the time of the experiment rats weighed between 400 and 450 g. Rats were randomly assigned to 1 of 4 treatment groups (n = 8 rats/group): (1) hemorrhage (H) and tourniquet Accepted for publication August 31, 2007. From the *United States Army Institute of Surgical Research; and †Brooke Army Medical Center, Fort Sam Houston, Texas. The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or reflecting the views of the Department of Defense or United States government. The authors are employees of the U.S. government and this work was prepared as part of their official duties. All work supported by U.S. Army Medical Research and Material Command. The authors would like to thank Ms. Heather Gooden, Ms. Rosalinda Fernandez-Rivera, and Ms. Angelica Torres for their technical support. Reprints: Thomas J. Walters, PhD, USAISR, 3400 Rawley E. Chambers Avenue, Fort Sam Houston, Texas 78234 (e-mail: thomas.walters@ amedd.army.mil). Copyright Ó 2008 by Lippincott Williams & Wilkins J Orthop Trauma  Volume 22, Number 1, January 2008 47