Feedback-control of muscle relaxation with a varying on-off controller using cisatracurium

Background. Under clinical conditions constant neuromuscular blockade can also be maintained by a simple closed-loop system. However, delayed onset time, non-linearity of the dose-response curve and different sensitivity to muscle relaxants for each patient are limiting factors. Methods. In 20 patients who underwent elective surgical procedures under continuous propofol/alfentanil anaesthesia and relaxation with cisatracurium,the maintenance of an electromyographically controlled cisatracurium block of 90% was achieved by a varying on-off control system. Using an own computer-aided measuring device,the course of the neuromuscular blockade and deviations from the desired neuromuscular block were registered. Results. Over a period of 64.2+/-14.0 min, neuromuscular block could be controlled on average at a T-1-level of 10% (90% block). The mean error of the deviation of the obtained neuromuscular blockade from the set-point was -1.6+/-0.9% on average. To maintain this neuromuscular blockade, a dose rate of 1.4+/-0.9 mug*kg(-1)*min(-1) cisatracurium was necessary. Conclusions. It can be concluded that a simple closed-loop system allows the safe use of the intermediate term muscle relaxant cisatracurium for the performance of surgical procedures.