[Effect of sevoflurane on the neuromuscular blockade produced by continuous mivacurium infusion ]

To evaluate the effect of sevoflurane on a neuromuscular block from mivacurium in continuous infusion.

Fourteen ASA I-II patients receiving general anesthesia for orthopedic procedures on the knee. The neuromuscular block was monitored by acceleromyography in the adductor pollicis muscle after stimulation of the cubital nerve. Anaesthesia was induced with propofol and remifentanil. After orotracheal intubation, mivacurium was given in continuous infusion adjusted to obtain a stable submaximal block defined as a variation in the block of 3% more or less for 10 minutes (first response on a train of four [T1] between 40% and 60% of the calibrated value). Values for T1, the T4/T1 ratio (TR) and temperature over the thenar eminence were recorded at 3 moments: control moment (infusion of mivacurium and sevoflurane at an expired fraction of 1.5% for 30 minutes) and post-sevoflurane moment (perfusion of mivacurium and sevoflurane at an expired fraction of 0% for 15 minutes). Statistical analysis was by analysis of variance and post-hoc contrast (Tukey).

Results are expressed as means with standard error between parentheses. We found that values at T1(%) and TR(%) were significantly lower at the sevoflurane moments (T1 = 43.11 [1]; TR = 25.68 [1]) and the post-sevoflurane moment (T1 = 36.29 [2]; TR = 25.06 [2]) than at the control moment (T1 = 53.18 [1]; TR = 38.93 [1]) (P < .05). T1 was significantly lower at the post-sevoflurane moment than at the sevoflurane moment (P < .05) but TR did not differ significantly.

Sevoflurane causes a significant increase in the neuromuscular block maintained by mivacurium in continuous infusion and the increase lasts at least 15 minutes after the halogenated agent is cleared from blood.