Theoretical framework:

Hypotension during surgery directly impacts patients' postoperative outcomes and complications. Decrease in blood pressure measurements secondary to anesthetic drugs is an expected scenario in most surgical cases. Moreover, hypovolemia secondary to fast pre-operative period may facilitate post-induction hypotension which can be compensated by fluid bolus pre-operatively.

Objectives:

The purpose of the study is to conduct a randomized intervention cohort study using pre-operative fluid therapy to assess its effect on blood pressure during the post-induction period. The investigators are testing the hypothesis that preoperative Crystalloid bolus decreases the risk of post-induction hypotension, specifically the time-weighted average (TWA) mean arterial pressure (MAP) under 65 mmHg during the first 20 minutes after anaesthetic induction or until surgical incision, whichever is first, compared to standard of care, which is minimal fluid administration in the pre-operative period.

Methods:

The investigators will conduct a randomized intervention cohort study using pre-operative fluid therapy to assess its effect on blood pressure during the post-induction period. The intervention group will receive a bolus of a balanced crystalloid solution within 60 ± 15 minutes before induction of anaesthesia. The control group will be treated according to the current clinical standard of care. The investigators will compare the time-weighted average (TWA) mean arterial pressure (MAP) under 65 mmHg during the first 20 minutes after anaesthetic induction or until surgical incision (whichever comes first).

Inclusion Criteria:

1. Scheduled for major non-cardiac surgery

2. Having general anaesthesia

3. Are designated ASA physical status ≥2 (ranging from mild systemic disease through severe systemic disease that is a constant threat to life)

4. Subject to at least one of the following risk factors:

   1. Age ≥ 65 years
   2. History of peripheral arterial surgery
   3. History of coronary artery disease
   4. History of stroke or transient ischemic attack
   5. Serum creatinine >175 µmol/L (>2.0 mg/dl)
   6. Diabetes requiring medication
   7. Current smoking or 15 pack-year history of smoking tobacco
   8. Preoperative high-sensitivity troponin T >14 ng/L or troponin I equivalent, defined as ≥15 ng/L (Abbott assay),75 19 ng/L (Siemens assay, [Borges, unpublished]), or 25% of the 99% percentile for other assays;
   9. B-type natriuretic protein (BNP) ≥ 80 ng/L or N-terminal B-type natriuretic protein (NT-ProBNP) ≥ 200 ng/L.76,77
   10. History of atrial fibrillation
   11. Chronically taking at least one anti-hypertensive medication

Exclusion Criteria:

1. Are scheduled for carotid artery surgery
2. Are scheduled for intracranial surgery
3. Are scheduled for pheochromocytoma surgery
4. Require preoperative intravenous vasoactive medications
5. Active decompensated congestive heart failure (documented EF < 30%)
6. Chronic Kidney Disease (eGFR< 30 mL/min)
7. History of organ transplantation
8. Rectal surgical procedures
9. Patients receiving preoperative bowel preparation
10. Severe pulmonary edema

For electronic data management we will use the CLINCASE software (Quadratek, Berlin, Germany). Data storage and back up will be provided by IT Systems & Communications (ITSC) - IT4Science (Medical University of Vienna). Access to data is strictly controlled and will only be provided to the Sponsor (Medical University of Graz and the Medical University of Vienna), the study investigators and the ethic commission (Ethic commission of the Medical University of Vienna).

All entries and changes in the CLINCASE software will be tracked.

The data will be transferred immediately after patient's enrolment and will be available until the end of the study for both sponsors (Medical University of Graz, Medical University of Vienna)

Access will only be provided to the Sponsor (Medical University of Graz and the Medical University of Vienna), the study investigators and the ethic commission (Ethic commission of the Medical University of Vienna).