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Tins STUDY evolved from two recent developments at the Hospital for Sick Children, Toronto. The first was the avoidance of explosive anaesthetic agents for routine clinical practice. The second was the introduction into clinical use of a new endotracheal aerosol with a metering system which could deliver accurate doses of lidocaine. 1Previously, 4 per cent lidocaine was administered to the glottic and tracheal regions from a Macintosh spray. With this method, toxic blood levels could readily be reached in small infants from rapid absorption or from overdose. Foldes et aI. 2 investigated the acute toxicity of lldocahae following intravenous infusion. Objective signs of toxicity developed after an average dose of 6.4 mg/kg with a corresponding serum concentration of 5.29 -+-0.55 ftg/ml.Using 4 per cent lidocaine, Bromage et al? showed that the rate of absorption from the larynx and trachea varied. Following a dose of 3.5 to 10.5 mg/kg, peak blood concentrations occurred in 5 to 25 minutes. Bromage observed no toxic signs, although serum concentration did reach 10 ftg/ml in one case. He stated that statistically there is one chance in 20 that the concentration will reach 10 /zg/ml when a dose of 6 mg/kg is given jntratracheally. Therefore, he recommended that the dosage should be below this amount. METHODS

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