The role of cerebral microdialysis in predicting the outcome after experimental hypothermic circulatory arrest.

ABSTRACT

OBJECTIVE: To evaluate whether and which of the cerebral microdialysis parameters are predictive of postoperative outcome after an experimental 75-min period of hypothermic circulatory arrest (HCA) in a chronic porcine model. DESIGN: Seventy-four juvenile female pigs underwent a 75-min period of HCA at 20 degrees C. A microdialysis catheter was placed into the cortex gray matter and brain extracellular concentrations of glucose, lactate, glycerol and glutamate were measured throughout the experiment by enzymatic methods using a microdialysis analyzer. Surviving animals were sacrificed on the 7th postoperative day and histopathological examination of the brain was performed. RESULTS: Brain glucose concentrations were higher in animals that survived (p = 0.017), especially from the 90-min until the 7-h interval after the start of rewarming. The blood venous concentrations of glucose were also higher among survivors, and correlated significantly with the brain glucose levels at 2-h and 4-h intervals after the start of rewarming. Higher concentrations of brain lactate, glycerol and glutamate were observed throughout the study among animals that died postoperatively. Brain glutamate and glycerol concentrations were significantly, negatively correlated with brain glucose concentrations. The lactate/glucose ratio was significantly lower among survivors during the postoperative period (p=0.014). Furthermore, brain glucose concentrations were higher and brain glycerol concentrations lower among the animals that did not develop brain infarction, but such differences did not reach statistical significance. CONCLUSION: Cerebral microdialysis is a useful tool for cerebral monitoring during experimental HCA. Low brain glucose concentrations and high brain lactate/glucose ratios after HCA are strong predictors of postoperative death. Brain glucose concentrations are negatively correlated with brain glycerol and glutamate concentrations.