Studies of anaesthesia in relation to hypertension. I. Cardiovascular responses of treated and untreated patients.

The cardiovascular responses to the induction, maintenance, and recovery from anaesthesia with thiopentone, nitrous oxide and halothane, have been studied in seven elderly normotensive patients, seven untreated hypertensive patients, and fifteen patients under treatment with a variety of anti-hypertensive drugs. In five untreated and three treated hypertensive patients, all of whom had high arterial pressures before anaesthesia, severe reduction of arterial pressure occurred during anaesthesia and was associated with electrocardiographic evidence of myocardial ischaemia. Other treated hypertensive patients, whose arterial pressures were well controlled, behaved in a similar manner to the normotensive patients, and gave no ground for concern during anaesthesia. Cardiac output fell to the same extent (30 per cent) in all three groups, and where a great reduction of arterial pressure occurred it was largely due to reduction of initially high systemic vascular resistance. Baroreflex control of heart rate was significantly depressed in hypertensive patients both before and during anaesthesia. It is concluded that untreated high arterial pressure constitutes a serious risk to patients undergoing anaesthesia and surgery, and therefore anti-hypertensive therapy should not be withdrawn prior to anaesthesia without a compelling reason.