Rapacuronium for modified rapid sequence induction in elective Caesarean section: neuromuscular blocking effects and safety compared with succinylcholine, and placental transfer

We have compared rapacuronium 2.5 mg kg(-1) (n=20) with succinylcholine 1.5 mg kg(-1) (n=22) in a multicentre, blinded, randomized study in full-term parturients undergoing elective Caesarean section under general anaesthesia . Thiopental 5 mg kg(-1) was given i.v. followed by the neuromuscular block ing agent Sixty seconds later intubation was performed. Intubating conditio ns, evaluated as excellent, good or poor, were good to excellent in 95% and 91% in the intent-to-treat patients after rapacuronium and succinylcholine , respectively (ns). Mean onset times at the adductor pollicis muscle for r apacuronium and succinylcholine were 80.4 (SEM 14.4) s and 63.9 (5.6) s (ns ) while maximum block was 96 (1.9)% and 99 (0.4)%, respectively (ns). Rate of recovery was significantly longer after rapacuronium; times for return o f TI to 25% were 16.9 (1.5) min and 9.6 (1.1) min for rapacuronium and succ inylcholine, respectively (P=0.0004). Maternal side effects included more t achycardia and skin erythema with rapacuronium; no maternal mortality or mo rbidity, including bronchospasm, occurred in either group. There were no ne onatal adverse effects in either group based on: Apgar scores at 1 and 5 mi n; times to sustained respiration; neuroadaptive capacity scores at 15 min, 2 h and 24 h; and umbilical venous and arterial blood-gas values and acid- base status. At delivery (17.7 (3.2) min), mean maternal plasma concentrati ons of rapacuronium were 9041.4 (1259.1) ng ml(-1) and 506.4 (24.9) ng ml(- 1) for Org 9488 (the main metabolite). Corresponding values for umbilical v enous plasma were 808.0 (92.1) ng ml(-1) and 59.1 (6.5) ng ml(-1), and for umbilical arterial plasma, 361.4 (56.4) ng ml(-1) and 29.7 (4.6) ng ml(-1), respectively, Umbilical venous to maternal venous ratios for rapacuronium and Org 9488 were 8.8% (1.3)% and 10.2 (1.7)%, respectively.