Adaptive feedback-controlled infusion versus repetitive injections of vecuronium in patients during isoflurane...

To compare vecuronium requirements using repetitive injections and a model-based, closed-loop, feedback-controlled infusion during isoflurane anesthesia.

Randomized open study.

Departments of Anesthesiology and Ear, Nose, and Throat Surgery at a university hospital.

Twenty-two patients of ASA physical status I or II undergoing elective otolaryngological surgery requiring general anesthesia.

Vecuronium was used for muscle relaxation. The desired level of neuromuscular transmission was set to 10% of control. All patients received vecuronium 0.08 mg/kg for intubation. Thereafter, vecuronium was injected repetitively in 11 patients (Group 1) whenever spontaneous recovery had reached the 10% level. In the other group of 11 patients (Group 2), relaxation was maintained by an adaptive closed-loop feedback system, which was based on a pharmacokinetic-dynamic model.

Neuromuscular transmission was quantified by the evoked electromyogram of the hypothenar muscles. In Group 1, the first repetition of 0.02 mg/kg had to be administered after 27.0 +/- 5.5 minutes, followed by repetitions of the same dose every 16.3 +/- 3.0 minutes. The induced neuromuscular block ranged from 83% to 100%. The mean vecuronium demand was 0.123 +/- 0.018 mg/kg/h. In Group 2, stable relaxation of 90% +/- 2% was achieved within 19.2 +/- 7.5 minutes after a period of damped oscillations. The mean offset from the target value of 90% blockade was 0.65% +/- 0.32%. The average vecuronium requirement was 0.056 +/- 0.021 mg/kg/h during steady state. The difference between the groups in muscle relaxant demand was statistically significant.

The model-based adaptive feedback system proved to be useful in maintaining a stable degree of paralysis, adjusting relaxant input to individual demand, and minimizing drug requirement, as compared with repetitive injections.