Propofol induction for laryngeal mask airway insertion: dose requirement and cardiorespiratory effects

The dosage, haemodynamic and respiratory effects of propofol for laryngeal mask airway (LMA) insertion were investigated. Fifty patients (ASA I-II) were randomly assigned one of four induction doses of propofol (1.5-2.5 mg/kg) delivered over 30 seconds and the first attempt at LMA insertion was made at 90 seconds. The LMA was inserted at 90 seconds in 35 patients and by 300 seconds in 13 others (mean plasma concentration at 90 seconds was 7.7 mcg/ml (no delay) versus 5.2 mcg/ml (insertion delayed), P < 0.01). Insertion was less successful after 1.5 mcg/kg (failed at 90 seconds in 6 of 12 patients), but did not vary with the other doses. Additional propofol (0.5 mg/kg/30s) was required in 22 patients for LMA insertion or to prevent movement, resulting in propofol concentrations at 120-180 seconds above 7 mcg/ml. Respiratory effects were minor, but MAP decreased by 18 +/- 1.4 mmHg at 90 seconds. Cardiovascular effects did not differ significantly between dosage groups or with the use of additional propofol.