[Narcotrend stages and end-tidal desflurane concentrations. An investigation during recovery from desflurane/remifentanil anaesthesia]

Abstract

Objective: [corrected] As indicated by the manufacturer the EEG monitor Narcotrend trade mark (MonitorTechnik, Bad Bramstedt) can be used to analyse EEG effects of volatile anaesthetics, however, published data are missing. This study evaluated the emergence from a desflurane/remifentanil anaesthetic and was designed to investigate the relationship between Narcotrend stages (version 2.0 AF) and end-tidal desflurane concentrations and to identify the pattern of changes of the Narcotrend stages during recovery.

Methods: Adult patients scheduled for orthopaedic surgery were premedicated with 0.15 mg/kg diazepam orally in the evening and on the morning before surgery. Narcotrend EEG electrodes were positioned on the patient's forehead as recommended by the manufacturer. For induction of anaesthesia, remifentanil was infused at 0.4 microgram/kg/min and propofol 2 mg/kg was given for hypnosis. After neuromuscular blockade and orotracheal intubation, remifentanil was reduced to 0.2 microgram/kg/min, and desflurane in O(2)/air was added according to clinical needs. After termination of surgery, administration of anaesthetics was discontinued and simultaneously, the fresh gas flow was increased to 10 l/min of O(2) while the respirator pattern was left unchanged. Narcotrend stages and end-tidal desflurane concentrations were recorded as data pairs at intervals of 1 min during emergence from anaesthesia; data evaluation included the last 7 min before extubation.

Results: A total of 50 patients (mean age +/-SD 44.4+/-13.0 years) were studied and 400 data pairs were obtained. A decreasing depth of anaesthesia as indicated by the Narcotrend was associated with significantly lower end-tidal desflurane concentrations: for E (general anaesthesia with deep hypnosis) 3.6+/-1.0 vol%, for D (general anaesthesia) 1.7+/-0.8 vol%, for C (light anaesthesia) 0.7+/-0.3 vol% and for A and B (awake or sedated) 0.5 vol%. A reduction of end-tidal desflurane concentrations was accompanied by a shift of Narcotrend stages from C/D/E to A/B/C.

Conclusion: During emergence from desflurane/remifentanil anaesthesia, a reduction of end-tidal desflurane concentrations was detected by the EEG monitor Narcotrend and classified as a typical change of distribution of Narcotrend stages.