The purpose of this nine-centre study in 602 patients was to show that the frequency of acceptable intubating conditions after rapacuronium 2.0 or 2.5 mg kg(-1) is not more than 10% lower than the frequency after succinylcholine 1.0 mg kg(-1) during rapid-sequence induction of anaesthesia with fentanyl 1-2 mug kg(-1) and thiopental 2-7 mg kg(-1). Laryngoscopy and intubation were carried out 60 s after administration of muscle relaxant by an anaesthetist blinded to its identity. Intubating conditions were clinically acceptable (excellent or good) in 91.8% of patients given succinylcholine and in 84.1 and 87.6% of patients given rapacuronium 2.0 and 2.5 mg kg(-1) respectively. With respect to the percentage of clinically acceptable intubating conditions, the estimated difference (and the upper limit of the one-sided 97.5% confidence interval) between succinylcholine and rapacuronium 2.0 mg kg(-1) was 7.8 (14.4)% and between succinylcholine and rapacuronium 2.5 mg kg(-1) it was 4.0 (10.2)%. For both comparisons, the upper limit of the one-sided confidence interval exceeded the predefined 10% difference. Hence, it could not be demonstrated that the intubating conditions with either of the two doses of rapacuronium were not inferior to those with succinylcholine 1.0 mg kg(-1). The increase in heart rate was significantly greater during the first 5 min in the rapacuronium groups, but the arterial pressure increased significantly only in the succinylcholine group (P<0.001). Respiratory side-effects were observed in 4.0, 13.5 and 18.5% of patients after succinylcholine and rapacuronium 2.0 and 2.5 mg kg(-1) respectively (P<0.05). As the non-inferiority of intubating conditions after rapacuronium 2.0 and 2.5 mg kg(-1) could not be proven, succinylcholine should be considered the neuromuscular blocking agent that provides better intubating conditions for rapid-sequence induction.
