A large individual variation in both the infusion rate and the blood concentration of rocuronium necessary for obtain adequate surgical muscle relaxation during total intravenous anesthesia with propofol and remifentanil.

BACKGROUND

Rocuronium (Rb) is ideal for continuous infusion but has a widely variable duration of action. We investigated the distribution of Rb infusion in a steady state of optimal muscle relaxation and the relationship between the measured and predicted blood Rb concentrations in laparoscopic surgery.

METHODS

Seventeen patients were anesthetized with propofol. Continuous Rb infusion was commenced at 7.5 µg/kg/min from 15 min after an initial Rb injection (0.6 mg/kg) and adjusted every 15 min to keep T1 within 3-10 %. Blood concentration was measured at the first onset of steady state, predicted concentration was calculated pharmacokinetically, and 25 % recovery time was measured. The distribution of the predicted concentration and infusion rate was plotted by histogram, the median value and 95th percentile were calculated, and the relationship between measured and predicted concentrations was analyzed by regression analysis.

RESULTS

The rate during the stable state was 7.3 ± 2.1 µg/kg/min on average, 4 at minimum, 12 at maximum, and 12 at the 95th percentile. The predicted concentration was 1.7 ± 0.5 µg/ml on average, 0.8 at minimum, and 2.9 at maximum. The mean measured concentration was 1.4 ± 0.4 µg/ml. The predicted concentration was proportional to the measured concentration (y = 0.91x, r = 0.475; p < 0.001). A significant linear relationship was observed between the measured concentration and infusion rate (y = 0.64 + 0.11x, r = 0.618; p < 0.05).

CONCLUSION

The measured blood concentration of Rb was comparable to the predicted value. Anesthesiologists can avoid overdose and attain a reliable muscle relaxant effect by maintaining a continuous dose by titration according to individual differences under muscle relaxant monitoring.