EEG arousal during laryngoscopy and intubation: comparison of thiopentone or propofol supplemented with nitrous oxide.

We studied EEG arousal after laryngoscopy and intubation with standardized bolus induction of anaesthesia. Twenty patients were prospectively allocated randomly to induction with propofol 3 mg kg-1 (n = 10) or thiopentone (6 mg kg-1 (n = 10) and 50% nitrous oxide in oxygen. Neuromuscular block was produced with vecuronium 0.2 mg kg-1 given 30 s after induction. Three minutes after induction, laryngoscopy was performed for 60 s, with intubation at 3 min 30 s, and study end at 5 min. Nociception to laryngoscopy and intubation was followed by loss of low (relative delta activity change: thiopentone -30%, propofol -7%; P < 0.05) and a shift to higher frequency EEG activity (beta activity change: thiopentone +647%, propofol +61%; P < 0.05). This EEG arousal was greater in the thiopentone group, despite the fact that EEG depression was similar to that produced by propofol before laryngoscopy and intubation. Propofol and thiopentone in combination with nitrous oxide had similar cortical depressant effects, but propofol appeared to depress subcortical nociceptive processing more than thiopentone. While the degree of cortical EEG depression seems less useful for predicting reaction to subsequent nociception, EEG arousal reactions may prove suitable for monitoring intra-anaesthetic nociception and its modulation.