Compartment syndrome: Evaluation of skeletal muscle ischemia and physiologic biomarkers in controlled conditions within ex vivo isolated muscle bundles.

OBJECTIVES: To identify potential physiologic markers of muscle ischemia to serve as diagnostic indicators of compartment syndrome. We hypothesize that muscle bundles in hypoxic conditions will elicit decreases in potential hydrogen (pH) and increases in lactate and potassium that correlates with decreased muscle twitch forces. METHODS: We performed an ex vivo evaluation of individual skeletal muscle bundles obtained from a swine's diaphragm that were exposed to hypoxic conditions and compared to control groups. Over a four-hour period, we evaluated the following parameters for each muscle bundle: muscle twitch forces and levels of potassium, lactate, and pH. Comparisons betweeen the hypoxic and control groups were calculated at each time point using the two-tailed Wilcoxon rank sum test for non-parametric data. Longitudinal assocations between biomarkers and muscle twitch forces were tested using repeated measures analyses. RESULTS: The hypoxic group elicited more significant decreases in normalized muscle twitch forces than the control group at all time points (0.15 gram versus 0.55 gram at four hours, p<0.001). Repeated measures analyses of the hypoxic group demonstrated a statistically significant association between potassium, lactate, and normalized peak force over time. Potassium demonstrated the strongest association with a 1 millimole/liter unit increase in potassium associated with 2.9 gram decrease in normalized peak force (95% confidence interval -3.3 to -2.4, p<0.001). The pH of all muscle baths increased over time at similar rates between the study groups. CONCLUSIONS: This study utilized an ex vivo ischemic skeletal muscle model as a representation for pathophysiologic pathways associated with compartment syndrome. In this experimental approach we were unable to evaluate the pH of the muscle bundles due to continuous applied gassing. Our findings support further evaluations of potassium and lactate levels as potential diagnostic markers. LEVEL OF EVIDENCE: III.