• At least 45 years old;

• Scheduled for major noncardiac surgery expected to last at least 2 hours;

• Having general anesthesia, neuraxial anesthesia, or the combination;

• Expected to require at least overnight hospitalization (planned ICU admission is acceptable);

• Are designated ASA physical status 2-4 (ranging from mild systemic disease through severe systemic disease that is a constant threat to life);

• Expected to have direct intraoperative 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:

‣ Age \>65 years;

⁃ 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) within 6 months;

⁃ 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14 ng/L or troponin I equivalent, defined as ≥15 ng/L (Abbott assay), 19 ng/L (Siemens assay, \[Borges, unpublished\]), or 25% of the 99% percentile for other assays - all within 6 months;

‣ B-type natriuretic protein (BNP) \>80 ng/L or N-terminal B-type natriuretic protein (NTProBNP) \>200 ng/L within six months.