A portable self-learning fuzzy logic control system for muscle relaxation.

We have assessed the practicality and performance of the Vital Signs Paragraph neuromuscular blockade monitor as part of a 'self-learning' fuzzy logic control feedback system used to administer atracurium to a required depth of neuromuscular blockade. Fifteen patients undergoing surgery expected to last longer than 90 min entered the study. A Vital Signs Paragraph was used to measure the degree of neuromuscular blockade and control it such that the first twitch of the train-of-four was kept at 10% of its baseline value. The controller instructed a Graseby Medical 3400 infusion pump to administer an atracurium infusion to maintain this level of blockade. Five patients (33%) were withdrawn from the study due to inadequate piezo-electric sensor function. In the remaining 10 patients, the system achieved stable control of neuromuscular blockade with a mean (range) error for the first twitch of the train-of-four of -0.45 (-1.06 to 0.13)%. The mean atracurium infusion rate ranged from 0.13 to 0.67 mg.kg-1.h-1. These results compare reasonably well with previous results using the Datex Relaxograph, whilst the system itself was portable and easy to use. However, the reliability of the system was limited due to variability in the sensitivity of piezoelectric sensors.