Auditory evoked response during propofol anaesthesia after pre-induction with midazolam

• Published in: British journal of anaesthesia : BJA Vol. 89; no. 2; pp. 325 - 327
• Main Authors: Brunner, M.D., Nel, M.R., Fernandes, R., Thornton, C., Newton, D.E.F.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01-08-2002; Oxford University Press; Oxford Publishing Limited (England)
• Subjects: Adult; anaesthetics i.v; anaesthetics i.v., propofol; Anesthesia, General; Anesthetics, Intravenous; Anesthetics. Neuromuscular blocking agents; antagonists benzodiazepine; antagonists benzodiazepine, midazolam; Biological and medical sciences; brain; brain, evoked potentials; Confidence Intervals; Drug Administration Schedule; evoked potentials; Evoked Potentials, Auditory - drug effects; Humans; Medical sciences; Midazolam; Middle Aged; monitoring; monitoring, evoked potentials; Neuropharmacology; Pharmacology. Drug treatments; Preanesthetic Medication; Propofol; anaesthetics i.v., propofol; brain, evoked potentials; antagonists benzodiazepine, midazolam; monitoring, evoked potentials; anaesthetics i.v., propofol; antagonists benzodiazepine, midazolam; brain, evoked potentials; monitoring, evoked potentials; Human; Electrodiagnosis; Drug combination; General anesthetic; Auditory evoked potential; General anesthesia; Benzodiazepine derivatives; Drug interaction; Midazolam; Propofol; Sedative; Monitoring
• ISSN: 0007-0912; 1471-6771
• DOI: 10.1093/bja/aef190

In clinical use, midazolam reduces the dose requirement for propofol. We studied the effect of midazolam given before anaesthesia on the amount of propofol needed and the time taken, to achieve loss of consciousness (LOC) in 20 patients.
We compared the auditory evoked responses (AER) in these patients with those in a group of 20 patients who were not given midazolam.
LOC, as defined by a loss of response to verbal command and eyelash reflex, occurred after 113 (95% CI, 99–131) s in the control group and 75 (56–101) s in the midazolam group (P<0.05). In the control group 2.3 (2.0–2.6) mg kg−1 propofol caused LOC compared with 1.3 (1.1–1.5) mg kg−1 in the group pretreated with midazolam (P<0.001). Pa amplitude decreased by 60% in the control group and by 54% in the midazolam group while Nb latency increased by 24% in the control group and by 32% in the midazolam group following LOC. These differences were not significant.
We confirmed that coinduction of anaesthesia with midazolam and propofol reduces the requirement of propofol. We also demonstrated that the AER reflects anaesthetic depth rather than plasma concentrations of anaesthetic drugs.