Metabolic changes in the brain during transient ischemia measured with microdialysis.

Forty-four patients with severe head injury were monitored for episodes of cerebral ischemia using jugular venous oxygen saturation (sjvO2), brain tissue pO2 (ti-pO2), and a microdialysis probe. The concentration of lactate and glucose were measured in the microdialysate. A total of 10 episodes of global ischemia were observed. The characteristic pattern of a simultaneous decrease in sjvO2 and brain ti-pO2 with an increase in the concentration of lactate occurred in all 10 patients. In addition, 3 episodes of regional ischemia were observed. Although brain ti-pO2 decreased to very low values and the concentration of lactate increased in the microdialysate, sjvO2 remained unchanged. Brain ti-pO2 adds another dimension to our cerebral monitoring by allowing the detection of regional cerebral ischemia.