At what point does hemodilution harm the brain?

摘要

HEMODILUTION has been strongly associated with neurological injury in patients with cardiovascular disease. This phenomenon is best characterized in patients undergoing cardiopulmonary bypass (CPB) during heart surgery when the additional stresses of laminar circulation and co-morbid vascular disease are present. In other clinical settings, patients undergoing major surgery also share the risk of exposure to acute hemodilution and the associated cerebrovascular consequences. In critical care units, current clinical transfusion thresholds demand that patients be maintained at hemoglobin concentrations near 70 g-L (hematocrit ~ 25%) which place them at risk for tissue ischemia and end-organ injury.6'7 Despite failure in earlier clinical trials,8 hemodilution is currently under re-assessment as a therapy to minimize cerebral injury following an acute stroke.9 The frequency with which cardiovascular patients are exposed to acute hemodilution emphasizes the need for a more complete understanding of the adaptive regulatory mechanisms which maintain cerebral homeostasis during acute hemodilution.