Changes in serum S100beta protein and Mini-Mental State Examination after cold (28oC) and warm (34oC) cardiopulmonary bypass using different blood gas strategies (alpha-stat and pH-stat)

Perioperative hypothermia: use and therapeutic implications

Perioperative cerebral ischemic insults are common in some surgical procedures. The notion that induced hypothermia can be employed to improve outcome in surgical patients has persisted for six decades. Its principal application has been in the context of cardiothoracic and neurosurgery. Mild (32-35 degrees C) and moderate (26-31 degrees C) hypothermia have been utilized for numerous procedures involving the heart, but intensive research has found little or no benefit to outcome. This may, in part, be attributable to confounding effects associated with rewarming and lack of understanding of the mechanisms of injury. Evidence of efficacy of mild hypothermia is absent for cerebral aneurysm clipping and carotid endarterectomy. Deep hypothermia (18-25 degrees C) during circulatory arrest has been practiced in the repair of congenital heart disease, adult thoracic aortas, and giant intracranial aneurysms. There is little doubt of the protective efficacy of deep hypothermia, but continued efforts to refine its application may serve to enhance its utility. Recent evidence that mild hypothermia is efficacious in out-of-hospital cardiac arrest has implications for patients incurring anoxic or global ischemic brain insults during anesthesia and surgery, or perioperatively. Advances in preclinical models of ischemic/anoxic injury and cardiopulmonary bypass that allow definition of optimal cooling strategies and study of cellular and subcellular events during perioperative ischemia can add to our understanding of mechanisms of hypothermia efficacy and provide a rationale basis for its implementation in humans.

Cardiopulmonary bypass temperature and brain function

A debate has emerged in recently published studies about the optimum cardiopulmonary bypass temperature for good neurological outcome - warm vs. cold, i.e. normothermic vs. hypothermic. Although many comparative studies have been performed, the results of these studies are inconclusive and are difficult to interpret. Brain function has been studied in terms of neurological and neuropsychological outcome, protein S100beta levels as a marker of brain damage, and cerebral oxygenation using jugular bulb oximetry and near-infrared spectroscopy. The studies produce no conclusive proof of the superiority of warm or cold cardiopulmonary bypass. However, it appears that any degree of bypass hypothermia (< 35 degrees C) may protect the brain. On the other hand, even a slight increase in bypass temperature to > 37 degrees C may cause marked brain injury.

A pilot study of evaluation of cerebral function by S100? protein and near-infrared spectroscopy during cold and warm cardiopulmonary bypass in infants and children undergoing open-heart surgery

Cerebral injury in children undergoing cardiopulmonary bypass (CPB) remains a major source of morbidity. The effect of cardiopulmonary bypass temperature on cerebral function in terms of serum S100beta protein level and cerebral oxygenation monitored by near infrared spectroscopy (NIRO-300) in children is not known. In this study, 18 children undergoing open-heart surgery at the Hospital for Sick Children in London were equally assigned by minimisation to warm (35 +/- 1 degrees C) or cold (25 +/- 1 degrees C) CPB. Changes in S100beta protein and cerebral oxygenation were studied in both groups. S100beta protein serum level increased significantly after CPB in both groups. There was no significant difference in serum S100beta protein concentrations between the two groups. However, cerebral oxygenation in terms of tissue oxygen index (TOI) was significantly impaired during rewarming from cold CPB. Five patients were desaturated (TOI < 50%) during rewarming in the cold bypass group compared to two in the warm patients. This study supports the use of warm CPB in children undergoing open-heart surgery, although further studies recruiting more patients are warranted.