title: Cerebral blood flow and cerebrovascular autoregulation in a swine model of pediatric cardiac arrest and hypothermia.
abstract: OBJECTIVE
  Knowledge remains limited regarding cerebral blood flow autoregulation after cardiac arrest and during postresuscitation hypothermia. We determined the relationship of cerebral blood flow to cerebral perfusion pressure in a swine model of pediatric hypoxic-asphyxic cardiac arrest during normothermia and hypothermia and tested novel measures of autoregulation derived from near-infrared spectroscopy.
  
  
  METHODS
  Prospective, balanced animal study.
  
  
  METHODS
  Basic physiology laboratory at an academic institution.
  
  
  METHODS
  Eighty-four neonatal swine.
  
  
  METHODS
  Piglets underwent hypoxic-asphyxic cardiac arrest or sham surgery and recovered for 2 hrs with normothermia followed by 4 hrs of either moderate hypothermia or normothermia. In half of the groups, blood pressure was slowly decreased through inflation of a balloon catheter in the inferior vena cava to identify the lower limit of cerebral autoregulation at 6 hrs postresuscitation. In the remaining groups, blood pressure was gradually increased by inflation of a balloon catheter in the aorta to determine the autoregulatory response to hypertension. Measures of autoregulation obtained from standard laser-Doppler flowmetry and indices derived from near-infrared spectroscopy were compared.
  
  
  RESULTS
  Laser-Doppler flux was lower in postarrest animals compared to sham-operated controls during the 2-hr normothermic period after resuscitation. During the subsequent 4-hr recovery, hypothermia decreased laser-Doppler flux in both the sham surgery and postarrest groups. Autoregulation was intact during hypertension in all groups. With arterial hypotension, postarrest, hypothermic piglets had a significant decrease in the perfusion pressure lower limit of autoregulation compared to postarrest, normothermic piglets. The near-infrared spectroscopy-derived measures of autoregulation accurately detected loss of autoregulation during hypotension.
  
  
  CONCLUSIONS
  In a pediatric model of cardiac arrest and resuscitation, delayed induction of hypothermia decreased cerebral perfusion and decreased the lower limit of autoregulation. Metrics derived from noninvasive near-infrared spectroscopy accurately identified the lower limit of autoregulation during normothermia and hypothermia in piglets resuscitated from arrest.
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA. jklee@jhmi.edu
authors.forename: Jennifer K
authors.initials: JK
authors.lastname: Lee
authors.forename: Ken M
authors.initials: KM
authors.lastname: Brady
authors.forename: Jennifer O
authors.initials: JO
authors.lastname: Mytar
authors.forename: Kathleen K
authors.initials: KK
authors.lastname: Kibler
authors.forename: Erin L
authors.initials: EL
authors.lastname: Carter
authors.forename: Karen G
authors.initials: KG
authors.lastname: Hirsch
authors.forename: Charles W
authors.initials: CW
authors.lastname: Hogue
authors.forename: Ronald B
authors.initials: RB
authors.lastname: Easley
authors.forename: Lori C
authors.initials: LC
authors.lastname: Jordan
authors.forename: Peter
authors.initials: P
authors.lastname: Smielewski
authors.forename: Marek
authors.initials: M
authors.lastname: Czosnyka
authors.forename: Donald H
authors.initials: DH
authors.lastname: Shaffner
authors.forename: Raymond C
authors.initials: RC
authors.lastname: Koehler
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001794:Blood Pressure; D002560:Cerebrovascular Circulation / Q000502:physiology*; D006439:Hemodynamics; D006706:Homeostasis / Q000502:physiology*; D007036:Hypothermia, Induced / Q000379:methods*; D007427:Intracranial Pressure / Q000502:physiology; D017078:Laser-Doppler Flowmetry; D008297:Male; D009203:Myocardial Infarction / Q000503:physiopathology* / Q000628:therapy*; D015427:Reperfusion Injury / Q000503:physiopathology; D019265:Spectroscopy, Near-Infrared; D013552:Swine