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Ann Thorac Surg 2007;84:768-774
© 2007 The Society of Thoracic Surgeons

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Original Articles: Cardiovascular

Perfusing the Cold Brain: Optimal Neuroprotection for Aortic Surgery

^a Department of Cardiothoracic Surgery, Division of Biostatistics, Mount Sinai School of Medicine, New York, New York
^b Department of Neurosurgery, Division of Biostatistics, Mount Sinai School of Medicine, New York, New York
^c Department of Anesthesiology, Division of Biostatistics, Mount Sinai School of Medicine, New York, New York

Accepted for publication April 13, 2007.

^_* Address correspondence to Dr Halstead, Department of Cardiothoracic Surgery, Mount Sinai School of Medicine, One Gustave L. Levy Place, New York, NY 10029 (Email: jameschalstead{at}yahoo.co.uk).

Presented at the Forty-second Annual Meeting of The Society of Thoracic Surgeons, Chicago, IL, Jan 30–Feb 1, 2006.

Background: 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.

Methods: Thirty pigs (26.3 ± 1.4 kg), cooled to 15°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 · 100g^–1 · min^–1]) and cerebral metabolic rate for oxygen (CMRO₂ [mL · 100g^–1 · 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.

Results: 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.

Conclusions: 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.