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 patie nts. We have applied new mobile microdialysate analysis equipment that allo ws a bedside comparison of changes in neurochemistry with the neurological status of the patient. Ten patients with severe aneurysmal subarachnoid hem orrhage (that is, with a high risk of vasospasm and a high risk of subseque nt ischemic deficits) were selected. METHODS: Microdialysis catheters were inserted into the temporal and subfro ntal 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' neurologi cal status was monitored constantly, and daily recordings of blood flow vel ocities were performed using transcranial Doppler sonography. RESULTS: Concentrations of the measured substances varied widely. individua l analyses revealed that patients with uneventful clinical courses generall y demonstrated low and stable levels of the different metabolites, and thos e with signs of cerebral ischemia demonstrated various patterns of neuroche mical changes. Lactate and glutamate seemed to be sensitive markers of impe nding ischemia, and increased glycerol levels were associated with severe i schemic 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 ch anges in extracellular concentrations of glucose, lactate, and glycerol tha t could be directly correlated to the clinical status of the patients. Thes e findings emphasize the potential of microdialysis in neurosurgical intens ive care patients.