Inclusion Criteria:  ≥45 years old Scheduled for major noncardiac surgery expected to last at least 2 hours; Having general endotracheal, neuraxial anesthesia, or the combination; Expected to require at least overnight hospitalization; Are designated ASA physical status 2-4 (ranging from mild systemic disease through severe systemic disease that is a constant threat to life); Chronically taking at least one anti-hypertensive medication; Expected to have direct blood pressure monitoring with an arterial catheter; Cared for by clinicians willing to follow the GUARDIAN protocol; Subject to at least one of the following risk factors: History of peripheral arterial disease; History of coronary artery disease; History of stroke or transient ischemic attack; Serum creatinine >175 µmol/L (>2.0 mg/dl); Diabetes requiring medication; Current smoking or 15 pack-year history of smoking tobacco; Scheduled for major vascular surgery; Body mass index ≥35 kg/m2; Preoperative high-sensitivity troponin T >14 ng/L or troponin I equivalent; defined as ≥15 ng/L (Abbott assay),73 19 ng/L (Siemens assay, [Borges, unpublished]), or 50% of the 99% percentile for other assays; B-type natriuretic protein (BNP) >80 ng/L or N-terminal B-type natriuretic protein (NT-ProBNP) >200 ng/L  Exclusion Criteria:  Are scheduled for carotid artery surgery; Are scheduled for intracranial surgery; Are scheduled for partial or complete nephrectomy; Are scheduled for pheochromocytoma surgery; Are scheduled for liver or kidney transplantation; Require preoperative intravenous vasoactive medications; Have a condition that precludes routine or tight blood pressure management such as surgeon request for relative hypotension; Require beach-chair positioning; Have a documented history of dementia; Have language, vision, or hearing impairments that may compromise cognitive assessments; Have contraindications to norepinephrine or phenylephrine per clinician judgement; Have previously participated in the GUARDIAN trial.