The GUARDIAN Trial

Inclusion Criteria:

1. At least 45 years old;
2. Scheduled for major noncardiac surgery expected to last at least 2 hours;
3. Having general anesthesia, neuraxial anesthesia, or the combination;
4. Expected to require at least overnight hospitalization (planned ICU admission is acceptable);
5. Are designated ASA physical status 2-4 (ranging from mild systemic disease through severe systemic disease that is a constant threat to life);
6. Expected to have direct intraoperative blood pressure monitoring with an arterial catheter;
7. Cared for by clinicians willing to follow the GUARDIAN protocol;
8. Subject to at least one of the following risk factors:

   1. Age \>65 years;
   2. History of peripheral arterial disease;
   3. History of coronary artery disease;
   4. History of stroke or transient ischemic attack;
   5. Serum creatinine \>175 μmol/L (\>2.0 mg/dl) within 6 months;
   6. Diabetes requiring medication;
   7. Current smoking or 15 pack-year history of smoking tobacco;
   8. Scheduled for major vascular surgery;
   9. Body mass index ≥35 kg/m2;
   10. 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14 ng/L or troponin I equivalent, defined as ≥15 ng/L (Abbott assay), 19 ng/L (Siemens assay, \[Borges, unpublished\]), or 25% of the 99% percentile for other assays - all within 6 months;
   11. B-type natriuretic protein (BNP) \>80 ng/L or N-terminal B-type natriuretic protein (NTProBNP) \>200 ng/L within six months.

Exclusion Criteria:

1. Are scheduled for carotid artery surgery;
2. Are scheduled for intracranial surgery;
3. Are scheduled for partial or complete nephrectomy;
4. Are scheduled for pheochromocytoma surgery;
5. Are scheduled for liver or kidney transplantation;
6. Require preoperative intravenous vasoactive medications;
7. Have a condition that precludes routine or tight blood pressure management such as surgeon request for relative hypotension;
8. Require beach-chair positioning;
9. Have a documented history of dementia;
10. Have language, vision, or hearing impairments that may compromise cognitive assessments;
11. Have contraindications to norepinephrine or phenylephrine per clinician judgement;
12. Have previously participated in the GUARDIAN trial.