Feed-back monitoring in anaesthesia. IV. The indirect measurement of arterial pressure and its use for the control of halothane administration.

A technique of indirect determination of arterial systolic pressure using a photoelectric pulse monitor signal to indicate arterial occlusion has been applied to the feed-back control of halothane administration. In normotensive patients, the inspired halothane concentration had little influence on arterial pressure; in about 25% of patients a periodic pattern between the low and medium outputs of the vaporizer occurred. In hypertensive patients, the arterial pressure was more sensitive to the depressant effects of halothane and the concentration administered was reduced automatically as the operation proceeded.