Neuromuscular effect of dexmedetomidine on sevoflurane: an open-label, dose-escalation clinical trial.

BACKGROUND: Sevoflurane presents reliable central neuromuscular effects. However, little knowledge is available regarding the interaction between sevoflurane and demedetomidine. We evaluated the neuromuscular effect of dexmedetomidine on sevoflurane in patients with normal neuromuscular transmission and calculated the 50% effective concentration (EC50).

METHODS: One-hundred and forty-four ASA grade I~II patients with normal neuromuscular transmission, aged 20~60 years old, undergoing lower limbs surgery were enrolled in this open-label, dose-escalation clinical trial. Patients were randomly assigned into 12 groups. Each patient received intravenous 0, 0.5, or 1.0 μg/kg dexmedetomidine 15 min after inhaling 0.7, 1.0, 1.4, or 2.0 MAC sevoflurane. Neuromuscular monitoring was recorded from the adductor pollicis muscle by using acceleromyography with train-of-four (TOF) stimulation of the ulnar nerve (2 Hz every 20 s). TOF ratio was recorded before inhaling sevoflurane, 15 min after keeping constant at target MAC of sevoflurane, 30 min after receiving target dose of dexmedetomidine, and 15 min after sevoflurane washing out.

RESULTS: Sevoflurane produced a concentration-dependent decrease in TOF ratio. Mean TOF ratio in 0.7, 1.0, 1.4, and 2.0 MAC groups was 97.9%, 94.9%, 84.7%, and 77.2%, respectively. Neuromuscular EC50 of sevoflurane was 1.31 MAC (95% CI: 1.236~1.388 MAC). Intravenous 0.5 and 1.0 μg/kg dexmedetomidine decreased 3.1% (EC50: 1.27 MAC [95% CI: 1.206~1.327 MAC]) and 10.7% (EC50: 1.17 MAC [95% CI: 1.122~1.217 MAC]) of neuromuscular EC50, respectively.

CONCLUSIONS: Sevoflurane has a concentration-dependent central neuromuscular effect in patients with normal neuromuscular transmission. Intravenous dexmedetomidine dose-dependently decreases the neuromuscular EC50 of sevoflurane.