pH-Stat Versus α-Stat Acid–Base Management Strategy During Hypothermic Circulatory Arrest Combined With Embolic Brain Injury

There is some evidence of beneficial metabolic effects associated with the pH-stat than with α-stat perfusion strategy, but this is tempered by a likely increased risk of embolism to the brain, especially in adult patients. We investigated this possible adverse effect in an experimental model that combined hypothermic circulatory arrest (HCA) and embolic brain injury. Twenty-four female juvenile pigs undergoing 25 minutes of HCA at a brain temperature of 18°C were assigned to either α-stat (n = 12) or pH-stat (n = 12) strategy during cardiopulmonary bypass. Before the initiation of HCA, the descending aorta was clamped and 200 mg of albumin-coated polystyrene microspheres (250 to 750 μm in diameter) were injected into the isolated aortic arch in both groups. The 7-day survival rate was 75% in the pH-stat group and 50% in the α-stat group (p = 0.40). The pH-stat group had significantly better behavioral scores on postoperative days 5 (p = 0.03) and 6 (p = 0.04). The pH-stat strategy was associated with better postoperative intracranial pressures and histopathologic scores, but such differences did not reach statistical significance. The α-stat group had lower brain glucose concentrations postoperatively as well as higher brain lactate/glucose and lactate/pyruvate ratios These results suggest that pH-stat strategy does not cause any worse brain injury than the α-stat strategy. Indeed, the pH-stat strategy is associated with a slightly better outcome compared with the α-stat strategy, even in the setting of cerebral embolization. This observation suggests that the pH-stat strategy could also be used in adults during deep hypothermic cardiopulmonary bypass despite the increased risk of intraoperative cerebral embolization.