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Despite its many disadvantages ketamine may offer a partial answer to the problems of pollution of the operating theatre by gases and vapours. It is a relatively long-acting drug with a good analgesic action and does not require supplementation with nitrous oxide. The problems of emergence delirium and postoperative dreams have been overcome by lorazepam premeditation'** which has made continued studies with ketamine not only ethically justified, but also desirable.Ketamine infusion would appear to offer many advantages and this is a report on its use in over 200 major surgical procedures.This study was carried out in patients undergoing body surface operations not requiring tracheal intubation (varicose veins, mastectomy, skin grafts, etc.) or abdominal surgery (mostly gynaecological) where a long acting neuromuscular blocking drug and controlled ventilation were needed. The only contraindications to the use of the technique were hypertension, a history of a cerebrovascular accident or a known history of psychiatric upset. Although over 200 patients have been anaesthetised with a ketamine infusion, the detailed analysis of dosage and cardiovascular effects is limited to 70 in whom the minimum operating time was 30 minutes. MethodAll patients were premedicated with lorazepam (4 mg). Initially this was given intravenously 30-40 min before induction, but it was found that oral administration of the same dose 90-120 min before operation gave equally good protection against emergence delirium and unpleasant sequelae from ketamine. Either method of administration is equally acceptable in this respect. The absence of an antisialagogue in the premedication led to no problems during ketamine anaesthesia.Anaesthesia was induced with 1 mg/kg ketamine and maintained with an infusion containing 1 mg/ml in 5% dextrose or balanced salt solution. The dosage of ketamine sufficient to maintain sleep and adequate operating conditions was measured by a paediatric burette in the infusion system. No supplementary general anaesthesia was given, but when the infusion did not provide an adequate depth of anaesthesia additional ketamine in doses of approximately 0.25 mg/kg was given.The initial cases in this study were undergoing body surface operation and neuromuscular blocking drugs were not needed. On giving a paralysing dose of a muscle relaxant theobvious signs of adequate depth of anaesthesia are abolished and there is a danger of a return of consciousness when supplementary inhalational drugs are not given. For this reason a detailed analysis of average dosage in twenty-five spontaneously breathing patients was carried out before embarking on the ketamine-relaxant

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