SummaryWe have compared, in 40 healthy patients, the cardiovascular responses induced by laryngoscopy and intubation with those produced by insertion of a laryngeal mask. Anaesthesia was induced with thiopentone and maintained with enjlurane and nitrous oxide in oxygen; vecuronium was used for muscle relaxation. Arterial pressure was measured with a Finapres monitor. The mean maximum increase in systolic arterial pressure after laryngoscopy and tracheal intubation was 51.3% compared with 22.9% for laryngeal mask insertion ( p < 0.01). Increases in maximum heart rate were similar, (26.6% v 25.7%) although heart rate remained elevated for longer after tracheal intubation. We conclude that insertion of the laryngeal mask airway is accompanied by smaller cardiovascular responses than those after laryngoscopy and intubation and that its use may be indicated in those patients in whom a marked pressor response would be deleterious.

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Using a fibreoptic laryngoscope, we have recorded on video tape the movements of the vocal cords after induction of anaesthesia with either propofol or thiopentone. The angle formed by the vocal cords decreased after induction of anaesthesia in both groups. This reduction in angle was significantly greater in the thiopentone group. The vocal cords closed completely in four patients in the thiopentone group and one patient in the propofol group. This difference may be explained by greater depression of laryngeal reflexes by propofol and this may account for the lower incidence of laryngospasm after induction of anaesthesia with propofol in comparison with thiopentone.

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We have studied the effect of varying the timing of a prior dose of intravenous lignocaine 1.5 mg/kg on the cardiovascular and catecholamine responses to tracheal intubation. Forty healthy patients were given an intravenous injection of either placebo or lignocaine 2, 3 or 4 minutes before tracheal intubation. There was a significant increase in heart rate of 21-26% in all groups. There was no significant increase in mean arterial pressure in response to intubation in any group of patients given lignocaine before intubation, but in the placebo group, mean arterial pressure increased by 19.1% compared to baseline values (p less than 0.05).