Postoperative neurocognitive disorders (NCD) are of high priority in perioperative management. The risk of suffering from NCD after surgery may be increased due to perioperative impairment of cerebrovascular autoregulation and thereby inadequate cerebral perfusion. Cerebrovascular autoregulation refers to the ability of cerebral arterioles to ensure constant cerebral blood flow independently of fluctuations in systemic blood pressure.

Cerebrovascular autoregulation can be measured based on mean arterial pressure (MAP) and a surrogate for cerebral blood flow using the correlation method. Until today, measurement of cerebral blood flow velocity assessed with transcranial Doppler sonography (TCD) is most commonly used as a non-invasive surrogate for cerebral blood flow. Alternatively, cerebral oxygenation measured with near-infrared spectroscopy (NIRS) can be used as another surrogate.

The study includes three substudies:

1. To compare NIRS and TCD for the assessment of perioperative cerebrovascular autoregulation in patients undergoing major non-cardiac surgery with an increased risk of bleeding.
2. To compare MAP for optimal cerebrovascular autoregulation before induction of general anesthesia with MAP for optimal cerebrovascular autoregulation during or after general anesthesia.
3. To analyze the association between the time-weighted average MAP below the MAP for optimal cerebrovascular autoregulation and postoperative NCD.

Inclusion Criteria:

• Age ≥ 18 years
• Elective surgery with a minimum duration of 120 minutes
• General anesthesia
• expected blood loss > 500 ml

Exclusion Criteria:

• Temporal bone window failure (substudy 1)
• Cerebrovascular disease
• Cardiac surgery
• Neurosurgery

Patients scheduled for non-cardiac surgery with general anesthesia at a tertiary care hospital