The correlation between P_(ET)CO_2 and cerebral blood flow, cerebral metabolism and intracranial pressure in neurosurgical patients / 中华麻醉学杂志

ABSTRACT

Objective To investigate the correlation between PaCO2 and cerebral blood flow (CBF), cerebral metabolism of oxygen (CMRO2), glucose (CMRglu) and lactate (CMRlact) and intracranial pressure during intracranial surgery. Methods Twenty ASA Ⅰ - Ⅱ patients (6 male, 6 female), aged between 26-54yr, weighing (65 ? 11) kg scheduled for elective intracranial surgery were studied. The patients were unpremedicated. Before general anesthesia radial artery was cannulated and a catheter was inserted into internal jugular vein and advanced cranially until jugular bulb. Lumber puncture was performed at L3-4 and a catheter was inserted into subarachnoid space for 3 cm, for pressure monitoring and CSF sampling. Anesthesia was induced with diazepam 10mg, fentanyl 3-4?g?kg-1, propofol 2mg?kg-1 and vecuronium 0.08mg?kg-1 iv. The patients were mechanically ventilated with a mixture of oxygen and argon (O2 argon = 3 1) after tracheal intubation. Anesthesia was maintained with sevoflurane and intermittent iv boluses of vecuronium. Arterial and cerebral venous blood gases, glucose and lactate levels, CBF, ICP and CSF level of lactate were determined before anesthesia when patients were awake(Ⅰ) and during anesthesia when PETCO2 = 40, 30, 20 mm Hg (Ⅱ,Ⅲ,Ⅳ). CBF was measured by modified Kety-Schmidt inert gas saturation technique with argon. CMRO2 and CMRglu were calculated based on the difference in their arterial -cerebral venous blood levels. Results At PETCO2 20mm Hg (Ⅳ) CBF decreased by 57.75% and CMRO2 by 58.70% as compared with the baseline; CMRglu decreased by 46.93% as compared with the baseline. There was no significant change in lactate level, jugular venous blood O2 saturation and pH. ICP decreased from (22.14 ? 7.88)mm Hg( Ⅰ) to (17.57?5.03)mm Hg( Ⅱ ),(13.43?4.89)mm Hg(Ⅲ) and (10.00? 2.31)mm Hg(Ⅳ) and the differences were significant. All measurements were done when MAP and HR were stable. PET CO2 was (10? 2) mm Hg lower than PaCO2 . Conclusions Cerebral blood flow, cerebral oxygen and glucose metabolism and intracranial pressure change with changes in PET CO2 . Cerebral vascular reactivity to CO2 is not impaired by 1.3 MAC sevoflurane. Mild hypocapnia is necessary during neurosurgery.