title: Cerebral oxygen saturation-time threshold for hypoxic-ischemic injury in piglets.
abstract: BACKGROUND
  Detection of cerebral hypoxia-ischemia (H-I) and prevention of brain injury remains problematic in critically ill neonates. Near-infrared spectroscopy (NIRS), a noninvasive bedside technology could fill this role, although NIRS cerebral O(2) saturation (Sc(O2)) viability-time thresholds for brain injury have not been determined. We investigated the relationship between H-I duration at Sc(O2) 35%, a viability threshold which causes neurophysiological impairment, to neurological outcome.
  
  
  METHODS
  Forty-six fentanyl-midazolam anesthetized piglets were equipped with NIRS and cerebral function monitor (CFM) to record Sc(O2) and electrocortical activity (ECA). After carotid occlusion, inspired O(2) was adjusted to produce H-I (Sc(O2) 35% with decreased ECA) for 1, 2, 3, 4, 6 or 8 h in different groups, followed by survival to assess neurological outcome by behavioral and histological examination.
  
  
  RESULTS
  For H-I lasting 1 or 2 h, ECA and Sc(O2) during reperfusion rapidly returned to normal and neurological outcomes were normal. For H-I more than 2-3 h, ECA was significantly decreased and Sc(O2) was significantly increased during reperfusion, suggesting continued depression of tissue O(2) metabolism. As H-I increased beyond 2 h, the incidence of neurological injury increased linearly, approximately 15% per h.
  
  
  CONCLUSIONS
  A viability-time threshold for H-I injury is Sc(O2) of 35% for 2-3 h, heralded by abnormalities in NIRS and CFM during reperfusion. These findings suggest that NIRS and CFM might be used together to predict neurological outcome, and illustrate that there is a several hour window of opportunity during H-I to prevent neurological injury.
authors.affiliation: Department of Anesthesiology, Cincinnati Children's Hospital, University of Cincinnati College of Medicine, Cincinnati, Ohio 45229-3039, USA. dean.kurth@cchmc.org
authors.forename: C Dean
authors.initials: CD
authors.lastname: Kurth
authors.forename: John C
authors.initials: JC
authors.lastname: McCann
authors.forename: Jun
authors.initials: J
authors.lastname: Wu
authors.forename: Lili
authors.initials: L
authors.lastname: Miles
authors.forename: Andreas W
authors.initials: AW
authors.lastname: Loepke
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001522:Behavior, Animal; D001930:Brain Injuries / Q000209:etiology* / Q000378:metabolism / Q000503:physiopathology / Q000517:prevention & control; D002470:Cell Survival; D002560:Cerebrovascular Circulation; D004195:Disease Models, Animal; D004569:Electroencephalography; D020925:Hypoxia-Ischemia, Brain / Q000150:complications / Q000175:diagnosis* / Q000378:metabolism / Q000503:physiopathology; D009474:Neurons / Q000378:metabolism / Q000473:pathology; D010100:Oxygen / Q000097:blood*; D011237:Predictive Value of Tests; D019265:Spectroscopy, Near-Infrared; D013552:Swine; D013997:Time Factors
chemical_list: D010100:Oxygen