BACKGROUND: Neurologic and neuropsychologic dysfunction after cardiopulmonary bypass is frequent and can be caused by inadequate cerebral perfusion and oxygenation. A decrease of SjvO2 suggests a situation in which the oxygen supply to the brain is insufficient to meet metabolic demands. This study investigated the effects of normocapnia and hypercapnia on changes in SjvO2 and lactate levels during rewarming from hypothermic cardiopulmonary bypass. METHODS: Anesthesia was induced and maintained with bolus and continuous infusion of fentanyl, midazolam and vecuronium. Patients were assigned to a normocapnic (PaCO2: 35 - 40 mmHg, n = 10) or hypercapnic (PaCO2: 45 50 mmHg, n = 10) group during rewarming. SjvO2 and lactate levels at the jugular bulb were measured at 30, 34 and 37degrees C nasopharyngeal temperature. RESULTS: There was not a reduction in SjvO2 to < 50% in normocapnic and hypercapnic group during the rewarming period, and there was no significant difference in lactate levels at the jugular bulb. However, the hypercapnic group had a higher SjvO2 than the normocapnic group at 30, 34 and 37degrees C nasopharyngeal temperature during rewarming (P<0.05). CONCLUSIONS: Hypercapnia is more effective increasing SjvO2 than normocapnia and may contribute to the prevention of postoperative neurologic dysfunction, especially in patients having a low SjvO2.