In an effort to determine the doses of rapacuronium necessary to provide satisfactory conditions for rapid tracheal intubation in infants and children, Meakin et al.  enrolled 165 pediatric patients scheduled for elective surgery in a prospective, randomized, multicenter trial. Sixty-five of the participants were infants less than 1 yr old; 51 were younger children, 1–6 yr old; and 49 were older children, 7–12 yr old.

Anesthesia was induced with 5–8 mg/kg thiopental followed by inhalation of 66% N2O in oxygen. Neuromuscular transmission was monitored using an acceleromyograph. Researchers began train-of-four stimulation of the ulnar nerve as soon as patients were asleep; immediately after the first train-of-four response was recorded, one of five doses of rapacuronium (0.5, 1.0, 1.5, 2.0, or 2.5 mg/kg) was administered by rapid intravenous injection according to a predetermined randomization schedule. Laryngoscopy was started 45–50 s later, followed by intubation at 60 s. Intubating conditions were graded by a blinded observer.

Intubation conditions were good or excellent at 60 s in all infants after doses of 1.5 mg/kg and 2 mg/kg rapacuronium. In all younger and older children, good or excellent intubation conditions were found after doses of 2.0 mg/kg and 2.5 mg/kg. (The 2.5-mg/kg dose of rapacuronium for infants and the 0.5-mg/kg dose for younger and older children were eliminated after an interim analysis of intubation data from the first 35 patients.)

Recovery times were measured from the time of rapacuronium injection to reappearance of the third twitch of the train-of-four. Mean times to T3 recovery were less than 10 min in infants at doses of 1.5 mg/kg or less and in younger and older children at doses of 2.0 mg/kg or less. Recovery of T3 after 1.0 or 2.0 mg/kg rapacuronium was slower in infants compared with younger and older children. Researchers documented five adverse events, ranging from bronchospasm to tachycardia to increased salivation, all of which were related to rapacuronium administration, but none of which were serious.

The authors were able to establish that satisfactory conditions for tracheal intubation in anesthetized infants and children can be produced when giving infants doses of 1.5 mg/kg and children 2.0 mg/kg. In addition, these doses appeared to be well-tolerated and produced few adverse events.