The occurrence of postoperative cognitive dysfunction (POCD) might be related to intraoperative cerebral desaturation. Positioning for neurosurgical procedures are associated with head rotation, elevation, flexion or extention that may affect blood brain inflow and outflow. Anatomical variations of Willis circle could affect the cerebral blood flow in extreme head position with the development of cerebral ischemia or functional changes of brain. Investigators suppose that detection of cerebral tissue desaturation and its prompt correction could modify the occurence of POCD after these procedures.

Standardized anesthesia and perioperative care will be provided to all patiens with positioning for neurosurgical or spinal procedures, where the head is elevated, extended. flected or rotated. In group A before the start of general anesthesia, the baseline level of cerebral tissue oxygenation (rScO2) will be measured using the near-infrared spectroscopy NIRS (Invivo Medtronic) . Continuous measurement of rScO2 will be used for detection of cerebral tissue desaturation. Each desaturation episode will be managed according to a standardized protocol - correction of extreme head position will be followed by optimalisation of mean arterial pressure (MAP), arterial hemoglobin oxygen saturation, end tidal carbon dioxide concentration and a level of hemoglobine concentration. In group B neither measurement of rScO2 nor interventions are provided. Cognitive dysfunction will be assessed by Adenbrooke test before operation and on the fifth postoperative day.

Inclusion Criteria:

• Glasgow Coma Scale 15, American Society of Anaesthesiologists (ASA) Physical Status Classification System Grade I-III, patient positioning with elevation, rotation, flexion or extention of head

Exclusion Criteria:

• Inability to past the Addenbrooke test, postoperative ventilation, awake phase during surgery, lung disease with retention of carbon dioxide, neurological disease before surgery (aphasia, paresis, blindness, deafness)