[Effects of pregnancy on the onset time of rocuronium]

Rapid onset of a muscle relaxant is required for general anesthesia with rapid sequence induction technique. Although a high dose of rocuronium was demonstrated to achieve the rapid onset in non-pregnant persons, it is still unknown whether this is true in women during late pregnancy. The purpose of this study is to compare the onset time of high dose rocuronium between pregnant and non-pregnant women.

Ten pregnant women undergoing cesarean delivery and 10 age, height, and body weight-matched non-pregnant women were enrolled in the study. Neuromuscular function was continuously assessed by twitch response with acceleromyography immediately after induction of general anesthesia with intravenous injection of thiopental (4-5 mg x kg(-1)) and rocuronium (0.9 mg x kg(-1)). Onset time of muscle relaxation, defined by the time from rocuronium bolus injection to complete absence of twitch height, was measured.

The onset time of rocuronium in pregnant women was significantly shorter than that in non-pregnant women (42 +/- 9 seconds vs. 56 +/- 10 seconds; P = 0.0039. unpaired t-test).

The onset time of high dose of rocuronium in pregnant women was significantly shorter than that of non-pregnant women.