British journal of anaesthesia
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Comparative Study
Analysis of the EEG bispectrum, auditory evoked potentials and the EEG power spectrum during repeated transitions from consciousness to unconsciousness.
We have compared the auditory evoked potential (AEP) index (a numerical index derived from the AEP), 95% spectral edge frequency (SEF), median frequency (MF) and the bispectral index (BIS) during alternating periods of consciousness and unconsciousness produced by target-controlled infusions of propofol. We studied 12 patients undergoing hip or knee replacement under spinal anaesthesia. During periods of consciousness and unconsciousness, respective mean values for the four measurements were: AEP index, 60.8 (SD 13.7) and 37.6 (6.5); BIS, 85.1 (8.2) and 66.8 (10.5); SEF, 24.2 (2.2) and 18.7 (2.1); and MF, 10.9 (3.3) and 8.8 (2.0). ⋯ There was no recorded value for MF that was 100% specific for unconsciousness. Of the four measurements, only AEP index demonstrated a significant difference (P < 0.05) between all mean values 1 min before recovery of consciousness and all mean values 1 min after recovery of consciousness. Our findings suggest that of the four electrophysiological variables, AEP index was best at distinguishing the transition from unconsciousness to consciousness.
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We describe the successful use of methadone in the restoration of sedation and provision of analgesia in two morphine-tolerant, paediatric patients who had suffered significant thermal injuries and were undergoing mechanical ventilation. Both patients had exhibited escalating requirements for sedative drugs while undergoing ventilation yet remained inadequately sedated. ⋯ Hyperalgesia and morphine tolerance appear to be associated; it is proposed that methadone acts primarily, under these circumstances, by re-establishing the analgesic state. Such use of methadone in the morphine-tolerant patient also afforded a concomitant sedative-sparing effect.
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We have measured the performance of 10 trainee anaesthetists during a single simulated anaesthetic during which there was a complex critical incident. Errors in the recording on the anaesthetic charts of the "patient's" oxygen saturation, heart rate, systolic and diastolic arterial pressures and end-tidal carbon dioxide concentrations were used as a measure of mental workload and hence performance. The critical incident was designed to be stressful and contained, in sequence, episodes of hypotension, arrhythmia and bronchospasm. ⋯ There was no evidence of a tendency to consistently underestimate the magnitude of abnormal values. This method is appropriate for assessing the performance of groups of anaesthetists during simulated critical incidents. It also raises questions on the accuracy of anaesthetic record charts when recording critical incidents.