Effect of muscle relaxation on the oxygenation of human skeletal muscle: a prospective in-vivo experiment using an isolated forearm technique

BACKGROUND: Total oxygen consumption has been found to be reduced under deep neuromuscular blockade due to a lower rate of metabolism of skeletal muscles. However, the magnitude of this effect in individual muscles has not been investigated. Thus the aim of this study was to compare the oxygenation of paralyzed versus non-paralyzed forearm muscle under tourniquet-provoked ischemia. METHODS: After ethics approval and written informed consent, 30 patients scheduled for elective hand and wrist surgery were included. Ischemia was provoked by inflation of bilateral upper arm tourniquets and muscle relaxation was achieved via intravenous administration of rocuronium 0.9 mg/kg. Bilateral tourniquets were applied to both upper arms before induction of anesthesia and near infrared spectrometry (NIRS) electrodes applied on both forearms. Muscular ischemia in an isolated (= non-paralyzed, NP) as well as a paralyzed forearm (P) was created by sequential inflation of both tourniquets before and after intravenous administration of rocuronium. Muscle oxygen saturations (S(m)O(2)) of NIRS in both forearms and their changes were determined and compared. RESULTS: Data of 30 patients (15 male, 15 female; 41.8 ± 14.7 years) were analyzed. The speed of S(m)O(2) decrease (50% decrease of S(m)O(2) from baseline (median [percentiles]: NP 210 s [180/480s] vs. P 180 [180/300]) as well as the maximum decrease in S(m)O(2) (minimum S(m)O(2) in % (median [percentiles]: NP 20 [19/24] vs. P 21 [19/28]) were not significantly affected by neuromuscular paralysis. CONCLUSIONS: No significant effect of muscle relaxation on NIRS-assessed muscle oxygenation under tourniquet-induced ischemia was found in human forearm muscles.