Local changes in cerebral energy metabolism due to brain retraction during routine neurosurgical procedures

Patients and Interventions. Tissue damage caused by brain retraction was evaluated utilizing intracerebral microdialysis in six patients operated on subfrontally for pituitary adenoma. The microdialysis probes (membrane length 10 mm, cut-off 20 kDalton) were placed in cerebral cortex beneath the brain retractor and perfused with Ringer solution at 0.3 mul/min. The microdialysis vials were changed at intervals of 30 minutes and analysed for glucose, pyruvate, lactate, glutamate and glycerol. Results. During brain retraction regional intracerebral glucose was within normal range in cortical tissue and the levels of lactate, glutamate, and glycerol as well as the lactate/pyruvate ratio were considerably above normal range. Conclusion. The biochemical analysis shows a pronounced incomplete cerebral ischemia due to brain retraction. The increases in glutamate and glycerol indicate tissue damage and degradation of cell membranes. Intracerebral microdialysis may be a valuable tool in the development of optimal techniques for brain retraction during neurosurgical procedures

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 frontal cerebral cortex in nine patients who were undergoing surgery to treat benign lesions of the posterior fossa. The perfusion rate was 1.0 microl/min during anesthesia/neurosurgery and the early postoperative course and 0.3 microl/min during the later course. Bedside biochemical analyses of glucose, pyruvate, lactate, glycerol, glutamate, and urea were performed before, during, and after neurosurgery. After the bedside analyses, all samples were frozen for subsequent high-performance liquid chromatographic analyses of amino acids. RESULTS: The following baseline values were obtained during wakefulness (perfusion rate, 0.3 microl/min): glucose, 1.7+/-0.9 mmol/L; lactate, 2.9+/-0.9 mmol/L; pyruvate, 166+/-47 micromol/L; lactate/pyruvate ratio, 23+/-4; glycerol, 82+/-44 micromol/L; glutamate, 16+/-16 mmol/L; urea, 4.4+/-1.7 mmol/L. Marked increases in the levels of all chemical markers were observed at the beginning and end of anesthesia/surgery. CONCLUSION: The study provides human baseline levels for biochemical markers that can presently be measured at the bedside during neurointensive care. In addition, some changes that occurred under varying physiological conditions are described