The use of sodium nitroprusside as a hypotensive agent in plastic surgery.

THE use of sodium nitroprusside for hypotension during plastic surgical operations has been investigated at the Queen Victoria Hospital, East Grinstead, in a series of twelve cases. An attempt has been made to compare its effectiveness with that of the pharmacological blockers, and to determine whether controls such as posture and respiration are similarly responsible for its hypotensive action. The series consisted of six male and six female patients whose ages ranged from 23 to 65 years. They were all normotensive pre-operatively and no patient had a history of cardiac, cerebral or chest disease. The operations performed were four nasal reductions, one abdominal reduction, two operations on the buttock and back for an extensive naevus, one facial hair transplant and four operations on the extremities. All operations on the head and neck and abdomen were performed in the foot down position, with an angle of tilt of approximately 20-30o. The naevus operation was in the prone position, whilst those on the extremities were performed under tourniquet, and hypotension induced immediately before its release. All patients were premedicated with levorphan 1-1 5 mg, phenergan 25 mg and hyoscine 04 mg I hr pre-operatively. Anaesthesia was induced with thiopentone 2-5 %, and intubation performed under suxamethonium together with decamethonium 5 mg to facilitate controlled ventilation. Maintenance was with oxygen, 30-50% nitrous oxide, and halothane 1-2 %. Two cases also received methoxyflurane. Those patients below 40 years of age were given a small dose of a ,B-adrenergic blocker, either propranolol (1>0-1 5 mg), or practolol (5-8 mg). Intermittent positive pressure ventilation was maintained in all cases using a semi-closed circle absorber system. An intravenous infusion of 5% dextrose was then commenced in all patients. In eight of these 5-10 ml of 1% sodium nitroprusside was added to 500 ml dextrose. In the remaining four patients intermittent injections of a dilute solution of sodium nitroprusside (0 5 mg/ml) were made from a 20 ml syringe. The sodium nitroprusside infusion was started just before surgery, and maintained until the desired level of blood pressure was obtained, this being estimated on a Boulitte Oscillometer. An attempt was then made to maintain a constant hypotension by adjustment of drip rate. When this had been achieved the effects of varying halothane concentrations, alterations of the angle of table tilt, and variations in airway pressure were performed in order to determine their effects on blood pressure. After surgery the patients were extubated and returned to the recovery ward, where the dextrose drip was maintained until the circulation was stable. In practice this was for a brief period of 15-30 min only, but blood pressure and pulse rate were observed for 3 hr thereafter.