Evaluation of closed loop control of arterial pressure during hypotensive anaesthesia for local resection of intraocular melanoma.

We have studied 20 patients undergoing local resection of intraocular melanoma during hypotensive anaesthesia, allocated randomly to receive either manual control by an experienced anaesthetist or closed-loop computer control of an infusion of a 5:1 mixture of trimetaphan camsylate (TMP) and sodium nitroprusside (SNP). There were no significant differences in the smallest systolic and diastolic arterial pressures obtained, heart rate or infusion requirements between the two groups, but the duration of both the infusion and the operation were significantly longer in the computer-controlled group (P < 0.05). The quality of control of arterial pressure was assessed by the percentage of time spent at pressures greater and less than the prescribed target values, and was satisfactory in both groups during the critical period of profound hypotension. We conclude that the computer-controlled infusion performed satisfactorily during profound hypotension compared with an experienced anaesthetist.