Automatic control of neuromuscular block with atracurium

We have developed and tested a system for providing automatic control of neuromuscular block with atracurium. The degree of neuromuscular block was monitored in the small muscles of the hand using a Datex Relaxograph, and the signal was used as the controlled variable for a proportional plus integral controller. A preloaded integral was used to shorten the period of stabilization. The system was tested in 36 patients undergoing surgery and found to produce stable block. For a target T1 of 20% of control value, the mean block was 18.7 (SD 1.3) % of baseline T1 and the mean consumption of atracurium was 5.39 (SD 1.23) micrograms kg-1 min-1. The block was sufficiently stable to act as a background for studies of pharmacological and physiological interactions with atracurium.