Perfusing the cold brain: optimal neuroprotection for aortic surgery.
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 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.


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.
Halstead
James C
JC
Department of Cardiothoracic Surgery, Division of Biostatistics, Mount Sinai School of Medicine, New York, New York 10029, USA. jameschalstead@yahoo.co.uk
Etz
Christian
C
Meier
D Matthias
DM
Zhang
Ning
N
Spielvogel
David
D
Weisz
Donald
D
Bodian
Carol
C
Griepp
Randall B
RB
D000818:Animals; D001011:Aorta / Q000601:surgery*; D001921:Brain / Q000378:metabolism; D002315:Cardiopulmonary Bypass; D002560:Cerebrovascular Circulation; D005260:Female; D006324:Heart Arrest, Induced; D007427:Intracranial Pressure; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption; D013552:Swine
D010100:Oxygen