Bedside Detection of Brain Ischemia Using Intracerebral Microdialysis: Subarachnoid Hemorrhage and Delayed Ischemic Deterioration

Objective: Intracerebral microdialysis has been demonstrated to be a useful method for detection of brain ischemia in experimental models and in patients. We have applied new mobile microdialysate analysis equipment that allows a bedside comparison of changes in neurochemistry with the neurological status of the patient. Ten patients with severe aneurysmal subarachnoid hemorrhage (that is, with a high risk of vasospasm and a high risk of subsequent ischemic deficits) were selected.

Methods: Microdialysis catheters were inserted into the temporal and subfrontal cortex at the end of aneurysm surgery. Samples, collected hourly for 4 to 11 days, were analyzed immediately at the bedside for glucose, lactate, and glycerol and later for pyruvate and glutamate. The patients' neurological status was monitored constantly, and daily recordings of blood flow velocities were performed using transcranial Doppler sonography.

Results: Concentrations of the measured substances varied widely. Individual analyses revealed that patients with uneventful clinical courses generally demonstrated low and stable levels of the different metabolites, and those with signs of cerebral ischemia demonstrated various patterns of neurochemical changes. Lactate and glutamate seemed to be sensitive markers of impending ischemia, and increased glycerol levels were associated with severe ischemic deficits. Obtaining the microdialysis data directly at the bedside seemed to be of great advantage when relating the values to other clinical findings.

Conclusion: Bedside intracerebral microdialysis monitoring of patients with subarachnoid hemorrhage and signs of delayed ischemia revealed dramatic changes in extracellular concentrations of glucose, lactate, and glycerol that could be directly correlated to the clinical status of the patients. These findings emphasize the potential of microdialysis in neurosurgical intensive care patients.