AUTOMATED INFUSION OF NITROGLYCERIN TO CONTROL ARTERIAL-HYPERTENSION DURING CARDIAC-SURGERY

Objective: To evaluate the feasibility of closed-loop blood pressure c ontrol during cardiac surgery. Design: A closed-loop system regulated peroperative hypertension by controlling the infusion rate of the vaso dilator nitroglycerin (NTG). The controller consisted of a regulator w hich was monitored by a supervisory computer program. Mean arterial pr essure (MAP) was calculated every 5 s from measurements of the radial artery pressure signal. The regulator calculated an NTG infusion rate with each new MAP measurement. The supervisory computer program monito red the regulator's actions and adapted or overruled the regulator whe n required. Setting: The cardiac surgery operating room. Patients: 46 patients who were scheduled for cardiac Surgery and who developed pero perative hypertension. Interventions: Patients were scheduled for eith er bypass or valve replacement surgery. The closed-loop system was use d to control hypertension before and after cardiopulmonary bypass;The use of the closed-loop system did not require deviation from the proto col normally used during cardiac surgery. All patients received standa rd continuous anaesthesia with opioids. Measurements and results: Init ial automatic control was achieved in 9.4 (4.1 SD) min. The percentage of time that MAP remained in a range around the target MAP of +/- 10 and +/- 20 mmHg was 74 and 94%, respectively. The mean NTG infusion ra te while MAP was within 5 mmHg of target MAP was 1.14 (0.84 SD) mu g k g(-1) min(-1). Target MAP was set between 65 and 90 mmHg. There was a small group of patients (6 out of 46) who did not respond to NTG and r equired alternative drug therapy. Conclusions: The controller provided fast and stable control in all patients. The expert knowledge impleme nted through the supervisory computer program enabled the controller t o respond adequately to the rapid changes in arterial pressures common ly associated with cardiac surgery. We conclude that closed-loop contr ol of arterial pressure is feasible not only in the cardiac surgical c are unit but also during cardiac surgery.