CORTICAL BRAIN MICRODIALYSIS AND TEMPERATURE MONITORING DURING HYPOTHERMIC CIRCULATORY ARREST IN HUMANS

Objectives-Critical vascular surgery of the brain or the heart occasio nally requires total cessation of the circulatory system. Profound hyp othermia is used to protect the brain from ischaemic injury. This stud y explores the use of microdialysis to measure metabolic indices of is chaemia: glutamate, lactate, and pH, and cerebral temperature during p rofound hypothermia and circulatory arrest. Methods-Effluent from a mi crodialysis catheter placed in the cerebral cortex of three patients u ndergoing complete circulatory arrest was continuously sampled. Sample s were pooled over 10 minute periods and glutamate and lactate concent rations were measured postoperatively. Brain temperature and pH were m easured on line intraoperatively. Electroencephalography and monitorin g of somatosensory evoked potentials and brainstem auditory evoked pot entials were simultaneously carried out. Results-Patient 1 had normal glutamate and lactate. PH was 6.75 to 6.85 and increased to 6.9 after warming ensued. Patient 2 had raised glutamate and lactate during most measurements. The glutamate concentrations peaked at 305 mu M/l at th e start of the measurements and fell below 20 mu M/l after warming. Th e lactate concentrations peaked at 680 mu M/l before cooling, rose to 1040 mu M/l during the cooling process, decreased to 212 mu M/l during circulatory arrest, and rose again to 620 mu M/l after warming. The p H started at 7.06 and continued a downward course until stabilising at a pH of 6.5 after circulatory arrest. Patient 3 had a transient, mild increase in glutamate and lactate during the cooling and warming peri od. pH was stable throughout. Conclusion-Microdialysis combined with t emperature and pH measurements of the cerebral cortex promises to be a n important tool in detecting cerebral ischaemia. Further studies are needed to validate our findings and test the feasibility of modifying ischaemic changes.