RESUMEN
BACKGROUND: The cerebral vascular response to CO2 has been reported to be preserved during isoflurane and propofol anesthesia. This study compared the cerebral oxygen extraction ratio during normoventilation versus hyperventilation in propofol anesthesia and isoflurane anesthesia. METHODS: 28 patients undergoing cerebral aneurysmal surgery were studied following informed consent. In the isoflurane group (n = 14), anesthesia was induced with thiopental 5 mg/kg, and maintained with isoflurane and nitrous oxide (N2O) in oxygen (FiO2 0.33). In the propofol group (n = 14), anesthesia was induced with propofol 2 mg/kg, and maintained by infusion of propofol and N2O-O2 (FiO2 0.33). Monitoring included measurement of mean arterial blood pressure, heart rate, body temperature, end-tidal CO2 (PetCO2), jugular bulb O2 saturation (SjO2) and arterial O2 saturation (SaO2). Mechanical ventilation was adjusted to achieve PetCO2 levels of 40 and 25 mmHg. Ten minutes of equilibration were allowed at each PetCO2 level. Blood was sampled from the jugular bulb and radial artery at each PetCO2 level (40 and 25 mmHg). The cerebral oxygen extraction ratio was calculated as (CaO2 CjO2) / CaO2 (CaO2; arterial oxygen content, CjO2; jugular bulb oxygen content). RESULTS: The cerebral oxygen extraction ratio was higher in hyperventilation (PetCO2 25 mmHg) compared to normoventilation (PetCO2 40 mmHg) in each group (P < 0.05) and higher in the propofol group compared to the isoflurane group (P < 0.05). CONCLUSIONS: The increased cerebral oxygen extraction ratio in hyperventilation during both isoflurane and propofol anesthesia showed that cerebral vascular CO2 reactivity was maintained during both isoflurane anesthesia and propofol anesthesia. The cerebral oxygen extraction ratio was higher during propofol anesthesia compared to isoflurane anesthesia in both normoventilation and hyperventilation, therefore this data showed that cerebral blood flow was lower during propofol anesthesia compared to isoflurane anesthesia.