BRAIN TISSUE METABOLITES IN SUBARACHNOID HEMORRHAGE

S246 INTRODUCTION: Following aneurysmal subarachnoid hemorrhage, patients are at risk to develop cerebral vasospasm and ischemia. However, it is not known if there is a change in brain tissue oxygen pressure (PtO2), carbon dioxide pressure (PtCO2), pH or temperature (Tis Temp) associated with the bleed. We measured these parameters in patients with and without subarachnoid hemorrhage during surgery for cerebral aneurysm clipping. METHODS: This study was approved by the institutional review board for clinical research and patient consent was received. Patients were recruited who were undergoing craniotomy for cerebral aneurysm clipping. These included 26 control patients who had not bled and showed no signs of ischemia and 19 patients who had a subarachnoid hemorrhage 1-8 days before surgery, but patients with angiographic evidence of cerebral vasospasm were excluded. Patients were anesthetized with 10-15 ug/kg fentanyl and 3-5 mg/kg thiopental, paralyzed with vecuronium, intubated and ventilated with 1% isoflurane in oxygen and air (FIO2 = 0.4). Mean arterial pressure (MAP) was measured continuously by a radial artery catheter and esophageal temperature was measured and allowed to decrease to 34[degree sign]C during surgery. Arterial PCO (2) was maintained at 30 - 35 mmHg. Following a pterional craniotomy and dural retraction, a Neurotrend probe (Diametrics, St Paul, MN) was inserted 2 cm into cortex tissue. Care was taken to avoid retractor pressure in the region of the tissue measurement. After a 30 minute equilibration period, a steady state measure of PtO2, PtCO (2), pH and Tis Temp was obtained over a 10 minute period. Measures in each group were compared statistically by student t-test. Spearman Rank Order Correlations were performed. RESULTS: Under baseline conditions, there was no significant difference in MAP, PtO2, PtCO2 or pH between control patients and patients with subarachnoid hemorrhage (Table 1). Brain tissue temperature was significantly higher in patients who had bled compared to controls. Esophageal temperature was 34.5 +/- 1.0 [degree sign]C in controls and 35.4 +/- 0.5 [degree sign]C in patients with subarachnoid hemorrhage and this difference was significant (P < 0.05). The median time of surgery after subarachnoid hemorrhage was 2 days with a range of 1 to 8 days. There was no significant correlation between the time of bleed and any measured parameter. Three patients had Hunt and Hess scores greater than 3 at the time of surgery, but these patients showed no difference in tissue parameters compared to other patients with subarachnoid hemorrhage.Table 1DISCUSSION: These results show that subarachnoid hemorrhage does not significantly change PtO2, PtCO2 or pH compared to patients who have not bled. It is reported that subarachnoid hemorrhage without vasospasm decreases cerebral oxygen metabolic rate 25% [1]. Our results indicate that this decrease in oxygen consumption is not associated with a change in tissue oxygenation or CO2 tension. Brain and esophageal temperature were increased after subarachnoid hemorrhage and many of these patients had temperatures above 37[degree sign]C in spite of the fact that passive cooling was allowed during surgery. This may place the patient at higher risk for ischemic injury.