Perfusing the Cold Brain: Optimal Neuroprotection for Aortic Surgery

Abstract

Selective cerebral perfusion (SCP) may enhance the neuroprotective benefits of hypothermia during aortic surgery. However, despite its widespread adoption, there is no consensus regarding optimal implementation of SCP. We used a survival porcine model to explore the physiologic characteristics and behavioral benefits of various protocols involving hypothermic circulatory arrest (HCA) and SCP. Thirty pigs (26.3 +/- 1.4 kg), cooled to 15 degrees C on cardiopulmonary bypass, using alpha-stat pH management (mean hematocrit 30%), were randomly allocated to differing brain protection strategies: 90 minutes of HCA (group A); 30 minutes of HCA, then 60 minutes of SCP (group B); or 90 minutes of SCP (group C). Using fluorescent microspheres and sagittal sinus sampling, cerebral blood flow (CBF [mL x 100g(-1) x min(-1)]) and cerebral metabolic rate for oxygen (CMRO2 [mL x 100g(-1) x min(-1)]) were assessed at baseline, after cooling, during SCP (where applicable), and for 2 hours after cardiopulmonary bypass. Neurobehavioral scores were assessed blindly from standardized videotaped sessions for 7 days postoperatively. Cerebral blood flow was significantly higher (p = 0.0001) during SCP (60 and 90 minutes) if preceded by HCA. The CMRO2 was also significantly higher in group B versus group C (p = 0.016) at 60 minutes. The CMRO2 in all three groups rebounded promptly toward baseline after weaning from cardiopulmonary bypass. Postoperative neurobehavioral scores were significantly worse in group A. Continuous SCP provides the best brain protection overall. However, an initial period of HCA does not seem to impair late outcome; perhaps the elevated CBF and CMRO2 observed reflect a beneficial cerebral response to a recoverable insult. Clearly, 90 minutes of HCA induces permanent brain injury, even in this carefully controlled setting.