Objectives
The sitting position (SP) or prone position (PP) are used for posterior fossa surgery. The SP induced reduction in cerebral blood flow and cerebral oxygen saturation (rSO2) has been shown in shoulder surgeries, but there is not enough data in intracranial tumor surgery. Studies showed that PP is safe in terms of cerebral oxygen saturation in patients undergoing spinal surgery. Our hypothesis is that the SP may improve cerebral oxygenation in the patients with intracranial pathologies, due to reduction in intracranial pressure. Therefore, we compared the effects of the SP and PP on rSO2 in patients undergoing posterior fossa tumor surgery.

Methods
Data were collected patients undergoing posterior fossa surgery, 20 patients in SP compared to 21 patients in PP. The rSO2 was assessed using INVOS monitor. Heart rate (HR), mean arterial pressure (MAP), EtCO2, BIS, and bilateral rSO2 were recorded preoperatively, and at 5, 8 and 11 minutes after the intubation and every 3 minutes after patient positioning until the initial surgical incision.

Results
Cerebral oxygenation slowly reduced in both the sitting and prone position patients following the positioning (p <  0.002), without any difference between the groups. The HR and MAP were lower in the sitting SP after positioning compared to the PP.

Conclusion
Neurosurgery in the SP and PP is associated with slight reduction in cerebral oxygenation. We speculate that if we rise the lower limit of MAP, we might have showed the beneficial effect of the SP on rSO2.