Objective: During balanced anaesthesia, the degree of neuromuscular block (NMB) must be sufficient to provide adequate surgical conditions but not as excessive as to make it difficult to reverse at the end of surgery. A continuous relaxant infusion is an appropriate technique for long-lasting operations but manuál control of the infusion rate can be time-consuming. We present a device (both hardware and software) for fuzzy control of NMB during generál anaesthesia. Design: Clinical, prospective study. Setting: Department of Anaesthesiology and Intensive Care Medicine, University Hospital. Materials and methods: After local ethics committee approval and informed consent, the Relax 2005 systém was clinically ušed in 80 patients undergoing intracranial neurosurgical intervention to maintain a stable depth of NMB during total i. v. anaesthesia. The degree of block (TOF-ratio, Tt) was determined using a Datex-Ohmeda S/5™ monitor wirelessly interfaced to a PC for data collection; the computer was programmed to ensure a stable level (target T-, = 10% of baseline) of block by controlling the rocuronium (ROC) infusion pump. The effectiveness of regulation was assessed by ROC consumption and root mean square deviation (RMSD) as an index of T-, variation around the přeset NMB level. Results: The mean duration of surgery was 171.7 (SD 81.4) minutes. During the regulation phase the systém automatically maintained a stable degree of NMB with mean T1 error -0.19 (0.26) % and RMSD 1.02 (0.72) %. The ROC consumption was 0.31 (0.23) mg.kg 1.hr1. After discontinuation of the infusion adequate recovery from the block was reached within 15 minutes. Conclusion: Based on mean T-, deviation from the target and RMSD values, the precision of regulation was far beyond the clinical requirements. The ROC consumption was at the lower limit recommended by the manufacturer.

        Key words: neuromuscular block - rocuronium - fuzzy logic - automatic control