Cerebral metabolism and intracranial hypertension in high grade aneurysmal subarachnoid haemorrhage patients

We evaluated the effect of intracranial hypertension on cerebral metabolism in patients with high grade aneurysmal subarachnoid hemorrhage (SAH) using bedside cerebral microdialysis (MD). Thirty-six patients with SAH were studied and classified into two groups (intracranial pressure, ICP > 20 mmHg, n = 25) and (ICP < 20 mmHg, n = 11). ICP was monitored hourly using an intraventricular drainage (n = 36). The MD catheter was placed after aneurysm clipping into the vascular territory of interest and was perfused with Ringer's Solution (0.3 mu l/min). The MD samples were collected hourly for measurements of glucose, lactate, and glutamate (CMA 600, Sweden). Lactate/pyruvate ratio was also calculated. To calculate group specific differences, the 24 hours median values of the first 7 days after SAH were compared. Differences were considered statistically significant at P < 0.05. Patient groups were comparable for age, severity of SAH, Fisher's grade and duration of MD sampling. In patients with ICP > 20 mmHg from day 1 to 7 after SAH, extracellular concentrations of glucose were significantly lower, while the lactate/pyruvate ratio was higher compared to SAH patients with normal ICP values. The differences between groups in glutamate levels was only significant on day 1 after SAH due to high inter-individual differences. We concluded that intracranial hypertension in associated with an anaerobic cerebral metabolism indicated cerebral ischemia in high grade SAH patients.