Details are as follows. • Monitoring: SctO2 monitored using two probes placed on left and right forehead. SstO2 monitored using one probe placed over the forearm brachioradialis muscle on the arm not used for non-invasive blood pressure monitoring.

• Baseline: The first baseline is measured 12-48 hours before surgery, with the patient supine, awake, calm, eyes closed, and breathing room air or oxygen that is equivalent to the home oxygen rate for patients using home oxygen.

• Goals: Maintain both SctO2 and SstO2 within 90-110% of the baseline level.
• Trigger of intervention: SctO2/SstO2 outside of the 90-110% baseline range.
• Diagnosis:
• Care team: The caregivers providing SctO2/SstO2-guided care will be trained and given the opportunity to use the intervention protocol in at least 20 patients before the formal study.
• Treatments: Refer to the algorithm to restore SctO2/SstO2 within 90-110% baseline range.

Patients in the control group will be managed by clinical staff according to usual care. Patients in this group will be monitored using the same tissue oximeter used in the intervention group; however, the screen will be covered by an opaque cloth to prohibit the care givers seeing the monitoring data. The same baseline measurements will be performed in patients allocated to the usual care group.

The following intervention algorithm is intended to be used as a guidance only. We emphasize the different aspects that can cause changes in SctO2/SstO2 in a systematic approach. We avoid recommending a concrete drug and method of dosing for a specific condition.

Manage tissue perfusion Preload: overall picture including direct observation of the heart, findings of echocardiography, urine output, blood loss, labs results, HR, BP, PPV, SVV, fluid responsiveness (SV increase >/= 10% following 250 ml fluid bolus) Contractility: direct observation of the heart, findings of echocardiography Stroke volume and heart rate: important determinants of CO Systemic vascular resistance: important determinant of BP Regional vascular resistance: important determinant of tissue perfusion along with perfusion pressure Maintain autoregulation: normalize CO2, avoid potent vasodilators

Manage arterial blood oxygen content

Manage tissue metabolic activity

The primary outcome is a collapsed (one or more) composite of the following complications with a Clavien-Dindo grade II or greater arising within 30 days of randomization (randomization and surgery are performed on the same day). The patient is regarded as having the event of composite complications if any of the following complications occur (i.e., yes); otherwise, the patient is regarded as not having the event of composite complications. The percentage of patients having the event of composite complications will be used in the primary analysis.

• Brain complications (delirium, cognition decline, stroke);
• Cardiac complications (non-fatal cardiac arrest, myocardial injury, heart failure, new-onset symptomatic ventricular arrhythmia);
• Respiratory failure;
• Renal complications (AKI stages II and III);
• Infectious complications;
• Death.

Atrial fibrillation

A new diagnosis of AF per the current standard.

Postoperative delirium (assessed using CAM-ICU Worksheet for patients in PACU and ICU, or CAM for patients on the floor). The validated Chinese version will be used for assessment.

Delirium will be formally assessed as early in the morning as practical and early evening for the initial five postoperative days while patients remain hospitalized because this approach will detect nearly all postoperative delirium. Observed daytime delirium will be recorded and considered as an outcome. Delirium will not be evaluated the evening after surgery because confusion might result from residual anesthetic effects.