Effect of nitrous oxide on pain due to rocuronium injection: A randomised, double-blind, controlled clinical trial

A prospective, randomised, double-blind, placebo-controlled study was carried out to determine the effect of nitrous oxide (N2O) on the frequency and severity of pain and withdrawal reactions after injection of rocuronium. Eighty ASA physical status I and II patients undergoing general anaesthesia for elective surgery were enrolled. The patients were randomised to receive 100% oxygen (O-2), or 50% N2O in O-2 for 3 minutes followed by a subparalysing dose of rocuronium 0.06 mg/kg. After induction of anaesthesia with thiopentone 5 mg/kg, an intubating dose of rocuronium 0.6 mg/kg was given. The patients were observed after injection of rocuronium 0.06 mg/kg, and asked to rate pain in the arm on a 4-point (0-3) verbal rating scale (none, mild, moderate or severe). After the intubating dose of rocuronium, withdrawal reactions were recorded. Thirty-six patients (90%) in the group N2O and 15 patients (37.5%) in the group O-2 reported no pain (P < 0.001). The pain was mild in 1 (2.5%) and 9 (22.5%) patients in N2O and O-2 groups, respectively (P = 0.006). Moderate pain occurred in 2 (5%) patients in group N2O and 15 (37.5%) patients in group O-2 (P = 0.001). Severe pain was reported by one patient in each group (P = 0.47). Withdrawal response after an intubating dose of rocuronium was observed in 6 (15%) and 18 (45%) patients in the N2O and O-2 groups, respectively (P < 0.05). Inhalation of 50% N2O in O-2 reduces the incidence and severity of pain and the withdrawal reactions associated with rocuronium injection.