Influence of preoperative oral rehydration on arterial plasma rocuronium concentrations and neuromuscular blocking effects

BACKGROUND The influence of preoperative rehydration on the action of rocuronium has not yet been investigated. OBJECTIVE The objective is to evaluate the hypothesis that preoperative rehydration lowers arterial rocuronium plasma concentrations and changes its associated neuromuscular blocking effects during induction of anaesthesia. DESIGN Randomised, single-blinded study. SETTING A secondary hospital from October 2013 to July 2014. PATIENTS In total, 46 men undergoing elective surgery were eligible to participate and were randomly allocated into two groups. Exclusion criteria were severe hepatic, renal or cardiovascular disorder; neuromuscular disease; history of allergy to rocuronium; BMI more than 30 kg m−2; receiving medication known to influence neuromuscular function. INTERVENTION Participants received 1500 ml of oral rehydration solution (rehydration group) or none (control group) until 2 hours before anaesthesia. Arterial blood samples were obtained 60, 90 and 120 s and 30 min after rocuronium (0.6 mg kg−1) administration during total intravenous anaesthesia. Responses to 0.1-Hz twitch stimuli were measured at the adductor pollicis muscle using acceleromyography. MAIN OUTCOME MEASURES Arterial plasma rocuronium concentrations. RESULTS Arterial plasma rocuronium concentrations at 60, 90 and 120 s in the rehydration and control groups were 9.9 and 13.7, 6.8 and 9.5 and 6.2 and 8.1 μg ml−1, respectively (P = 0.02, 0.003 and 0.02, respectively); the onset times in the rehydration and control groups were 92.0 and 69.5 s (P = 0.01), and the times to twitch re-appearance were 25.3 and 30.4 min (P = 0.004), respectively. CONCLUSION Preoperative rehydration significantly reduces arterial plasma rocuronium concentrations in the first 2 minutes after administration, prolonging the onset time and shortening the duration of effect. A higher dose or earlier administration should be considered for patients who receive preoperative rehydration. TRIAL REGISTRATION Umin identifier: UMIN000011981.