Intracerebral microdialysis in clinical practice: Baseline values for chemical markers during wakefulness, anesthesia, and neurosurgery

OBJECTIVE: The study was undertaken to measure baseline values for chemical markers in human subjects during wakefulness, anesthesia, and neurosurgery , using intracerebral microdialysis. METHODS: Microdialysis catheters were inserted into normal posterior fronta l cerebral cortex in nine patients who were undergoing surgery to treat ben ign lesions of the posterior fossa, The perfusion rate was 1.0 mu l/min dur ing anesthesia/neurosurgery and the early postoperative course and 0.3 mu l /min during the later course. Bedside biochemical analyses of glucose, pyru vate, lactate, glycerol, glutamate, and urea were performed before, during, and after neurosurgery. After the bedside analyses, all samples were froze n for subsequent high-performance liquid chromatographic analyses of amino acids. RESULTS: The following baseline Values were obtained during wakefulness (pe rfusion rate, 0.3 mu l/min): glucose, 1.7 +/- 0.9 mmol/L; lactate, 2.9 +/- 0.9 mmol/L; pyruvate, 166 +/- 47 mu mol/L; lactate/pyruvate ratio, 23 +/- 4 ; glycerol, 82 +/- 44 mu mol/L; glutamate, 16 +/- 16 mmol/L; urea, 4.4 +/- 1.7 mmol/L. Marked increases in the levels of all chemical markers were obs erved at the beginning and end of anesthesia/surgery. CONCLUSION: The study provides human baseline levels for biochemical marker s that can presently be measured at the bedside during neurointensive care. In addition, some changes that occurred under varying physiological condit ions are described.