One of the main goals during anesthesia practice is to provide adequate tissue oxygenation. For this purpose, many parameters such as ECG, blood pressure, blood gas, and urine monitoring are monitored. However, it is a serious deficiency that the brain, which is the most sensitive organ to ischemia, is not monitored in intracranial surgeries . Trying to keep the intraoperative blood gas parameters and cerebral blood flow at normal values in order to overcome this deficiency brings along serious problems in proportion to the frequency of the measurement interval. For this reason, evaluation of tissue oxygenation with the Near Infrared Spectroscopy (NIRS) method has come to the fore in recent years, and especially cerebral regional oxygen saturation (rSo2) follow-ups have begun to be performed more frequently. The values obtained by this method represent 75% venous, 20% arterial and 5% capillary compartment of the measurement area .

While deciding on the positions applied in intracranial surgery, it may be necessary to apply modifications by keeping the surgical application site in the foreground. The preferred patient position in the operation can help prevent complications and serious side effects. Although each position applied in intracranial operations has advantages and disadvantages, the surgeon should choose the most suitable position for the patient and pathology. The "park bench" position is widely used in posterior fossa operations and has replaced the sitting position for most neurosurgical procedures . However, since the advantages of the sitting position could not be obtained, this position was also changed and the modified Park bench position with 30 degrees upside tilt was used. This position can provide similar advantages with the sitting position and also reduces the risk of venous air embolism and hypotension . The modified sitting position for posterior fossa surgery versus the semi-sitting or "beach chair" position retains many of the advantages and provides a rapid trendelenburg in case of air embolism. The classical sitting position causes postural hypotension in approximately 1/3 of the patients and severe hypotension is seen in 2-5% of the patients. Excellent surgical intervention, drier area and less blood loss, reduced facial swelling are the advantages of the sitting position. However, the risk of venous air embolism and increased pneumocephalus should not be ignored.

In addition to the hemodynamic changes due to all these known positions, there is no follow-up of cerebral regional oxygen saturation (rSo2) monitoring depending on the position, which we could not detect in the literature. This monitoring can contribute to the optimal continuation of cerebral blood flow while deciding on the appropriate position of the patients. In this case, the postoperative mortality and morbidity of the patients can be reduced. In addition, intraoperative cerebral oxygenation monitoring is critical for predicting delirium in the postoperative period.

Our aim in this study is to investigate the effects of the positions applied in Intracranial Surgery on Cerebral Oxygenation and to evaluate the superiority of the patient positions used to each other.