title: Perfusing the cold brain: optimal neuroprotection for aortic surgery.
abstract: 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.
authors.affiliation: Department of Cardiothoracic Surgery, Division of Biostatistics, Mount Sinai School of Medicine, New York, New York 10029, USA. jameschalstead@yahoo.co.uk
authors.forename: James C
authors.initials: JC
authors.lastname: Halstead
authors.forename: Christian
authors.initials: C
authors.lastname: Etz
authors.forename: D Matthias
authors.initials: DM
authors.lastname: Meier
authors.forename: Ning
authors.initials: N
authors.lastname: Zhang
authors.forename: David
authors.initials: D
authors.lastname: Spielvogel
authors.forename: Donald
authors.initials: D
authors.lastname: Weisz
authors.forename: Carol
authors.initials: C
authors.lastname: Bodian
authors.forename: Randall B
authors.initials: RB
authors.lastname: Griepp
mesh_terms: 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
chemical_list: D010100:Oxygen