Manual vs Closed-loop Control of Mean Arterial Pressure

Intraoperative hypotension can impact patient outcome. Vasopressors are usually used to correct hypotension and ensure adequate organ perfusion. The investigators have recently developed an automated system (closed-loop system) to titrate vasopressor agents in surgical and intensive care patients. The purpose of this study is to compare two strategies to correct hypotension based on an individual definition of hypotension (therefore, the target MAP used to define hypotension will differ for each patient (individualized approach): 1. Control group = standard practice ( manually adjusted norepinephrine infusion to correct hypotension and keep MAP within 90% of patient's baseline MAP 2. Intervention group = closed-loop (automated) vasopressor administration system will deliver norepinephrine using feedback from standard operating room hemodynamic monitor (EV1000 Monitor-Flotrac, Edwards Lifesciences, IRVINE, USA) to correct hypotension and keep MAP within 90% of patient's baseline MAP