The Association of Tourniquet Usage and Change in Postoperative Intramuscular pH after Ankle Fracture Surgery

Research Type: Level 1 - Randomized controlled trial (RCT), Meta-analysis of randomized trials with homogeneous results Introduction/Purpose: Tourniquets are widely used in lower extremity surgery. They are generally considered safe for up to two hours, after which the risk of tourniquet ischemia is thought to rise. Literature to support this practice remains sparse and inconsistent, primarily based on decades-old animal studies citing irreversible muscle damage and cellular derangements at a pH below 7.0. Clinical outcomes including postoperative pain and swelling have been more recently studied, but evidence-based recommendations regarding proper tourniquet use remain lacking. Our novel pilot study examines the effect of tourniquet use on intramuscular pH and venous pH, via a continuous intramuscular pH monitoring in isolated ankle fractures undergoing surgical fixation. Methods: This is a prospective, randomized trial of patients with isolated ankle fractures undergoing ankle surgery between 2021-2024 at two metropolitan hospitals. Patients 18 years or older at time of evaluation for an acute fibular, bimalleolar, or trimalleolar ankle fracture were included. Participants were randomized to tourniquet or a non-tourniquet group using a random number generator. Those presenting with concomitant metabolic derangements, bleeding disorders, or other significant traumatic injuries were excluded. For all patients, a VersaFlex® pH catheter was placed in the anterior compartment musculature and continuous intramuscular pH was measured from the start of surgery until 2 hours postoperatively. Primary outcomes assessed included pre-, intra-, and 2 hours post-operative intramuscular pH and venous pH. Bivariate and multivariate linear regression models were run using STATA based on average intraoperative and postoperative pH values. PROs and functional outcomes were collected but not reported in this abstract due to sample size. Results: Eleven patients were included for analysis. The sample was 36.4% male with a mean age of 41.2 years. 63.6% of ankle fractures were trimalleolar and the mean surgical duration was 134.4 minutes. The average intraoperative intramuscular pH was more alkalotic in the tourniquet group than non-tourniquet group: 7.01 versus 6.85, respectively. The change in postoperative peripheral venous pH was –1.05 in the tourniquet group and 0.00 in the non-tourniquet group (p=0.445). The intramuscular compartment was more acidic two hours postoperatively after tourniquet release (mean pH=6.78, SD=0.18) compared to the non-tourniquet group (pH=7.00, SD=0.36); this pH change was significant (β=-0.36, 95% CI=-0.59, -0.13, p=0.009). Multicollinearity was not present. The final model explained 75.6% of the variation in change in two hours postoperative intramuscular pH. Conclusion: Our study demonstrates the effect of tourniquets on intramuscular and peripheral venous pH in the intraoperative through postoperative period of ankle fracture surgery. Intramuscular pH was more alkalotic in the tourniquet group intraoperatively, suggesting the body may self-regulate pH during temporary exsanguination. Two hours postoperatively, intramuscular pH became more acidic in the tourniquet group. Although non-significant, peripheral venous pH also decreased postoperatively after tourniquet application. To our knowledge, this is the first randomized trial to assess continuous intramuscular pH variation in patients during surgery. Future work includes correlating metabolic changes after tourniquet use with functional outcomes in a larger sample.