Abstract： Background:The optimal ventilated status under total intravenous or inhalation anesthesia in neurosurgical patients with a supratentorial tumor has not been ascertained.The purpose of this study was to intraoperatively compare the effects of moderate hyperventilation on the jugular bulb oxygen saturation (SjO2),cerebral oxygen extraction ratio (O2ER),mean arterial blood pressure (MAP),and heart rate (HR) in patients with a supratentorial tumor under different anesthetic regimens.Methods:Twenty adult patients suffered from supratentorial tumors were randomly assigned to receive a propofol infusion followed by isoflurane anesthesia after a 30-min stabilization period or isoflurane followed by propofol.The patients were randomized to one of the following two treatment sequences:hyperventilation followed by normoventilation or normoventilation followed by hyperventilation during isoflurane or propofol anesthesia,respectively.The ventilation and end-tidal CO2 tension were maintained at a constant level for 20 min.Radial arterial and jugular bulb catheters were inserted for the blood gas sampling.At the end of each study period,we measured the change in the arterial and jugular bulb blood gases.Results:The mean value of the jugular bulb oxygen saturation (SjO2) significantly decreased,and the oxygen extraction ratio (O2ER) significantly increased under isoflurane or propofol anesthesia during hyperventilation compared with those during normoventilation (SjO2:t =-2.728,P =0.011 or t =-3.504,P =0.001;O2ER:t =2.484,P =0.020 or t =2.892,P =0.009).The SjO2 significantly decreased,and the O2ER significantly increased under propofol anesthesia compared with those values under isoflurane anesthesia during moderate hyperventilation (SjO2:t =-2.769,P =0.012;O2ER:t =2.719,P =0.013).In the study,no significant changes in the SjO2 and the O2ER were observed under propofol compared with those values under isoflurane during normoventilation.Conclusions:Our results suggest that the optimal ventilated status under propofol or isoflurane anesthesia in neurosurgical patients varies.Hyperventilation under propofol anesthesia should be cautiously performed in neurosurgery to maintain an improved balance between the cerebral oxygen supply and demand.