Determination of end-tidal sevoflurane concentration for tracheal intubation in children with the rapid method

Using the conventional method of determining the end-tidal concentration of inhalational anaesthetic for tracheal intubation, a constant end-tidal anaesthetic concentration is maintained for at least 15 min. As sevoflurane has a low tissue/gas partition coefficient, it seems possible in paediatric patients to determine end-tidal concentrations for tracheal intubation more rapidly by using a high inspired concentration. We determined ED50 and ED95 of sevoflurane for tracheal intubation, the end-tidal concentrations that prevented 50% and 95% of patients from coughing and gross purposeful muscular movements after intubation.

Twenty-nine, ASA 1, unpremedicated patients, aged two to eight years, were enrolled. Anaesthesia was induced using a mask and 5% sevoflurane, inspired, in oxygen. When end-tidal sevoflurane concentration attained a predetermined value, laryngoscopy and tracheal intubation were performed using an uncuffed tracheal tube without neuromuscular relaxants or adjuvants. Each concentration at which laryngoscopy and tracheal intubation were attempted was randomly predetermined (with 0.5% as a step size). When tracheal intubation was accomplished without gross purposeful muscular movements, it was considered a smooth tracheal intubation.

The ED50 end-tidal sevoflurane concentration for tracheal intubation was 3.10% (95% confidence limits: 2.43% and 3.78%), and the ED95 was 4.68% (95% confidence limits: 3.91% and 12.74%). The times to end-tidal sevoflurane concentrations of 3.0% and 4.5% were 149 +/- 15 sec (mean +/- SD) and 213 +/- 23 sec.

In paediatric patients, this method enabled determination of ED50 and ED95 end-tidal sevoflurane concentrations for tracheal intubation without obtaining a long stabilization period.