title: Effects of isoflurane anesthesia on cerebrovascular autoregulation in horses.
abstract: OBJECTIVE
  To test a hypothesis predicting that isoflurane would interfere with cerebrovascular autoregulation in horses and to evaluate whether increased mean arterial blood pressure (MAP) would increase cerebral blood flow and intracranial pressure (ICP) during isoflurane anesthesia.
  
  
  METHODS
  6 healthy adult horses.
  
  
  METHODS
  Horses were anesthetized with isoflurane at a constant end-tidal concentration sufficient to maintain MAP at 60 mm Hg. The facial, carotid, and dorsal metatarsal arteries were catheterized for blood sample collection and pressure measurements. A sub-arachnoid transducer was used to measure ICP Fluorescent microspheres were injected through a left ventricular catheter during MAP conditions of 60 mm Hg, and blood samples were collected. This process was repeated with different-colored microspheres at the same isoflurane concentration during MAP conditions of 80 and 100 mm Hg achieved with IV administration of dobutamine. Central nervous system tissue samples were obtained after euthanasia to quantify fluorescence and calculate blood flow.
  
  
  RESULTS
  Increased MAP did not increase ICP or blood flow in any of the brain tissues examined. However, values for blood flow were low for all tested brain regions except the pons and cerebellum. Spinal cord blood flow was significantly decreased at the highest MAP.
  
  
  CONCLUSIONS
  Results suggested that healthy horses autoregulate blood flow in the CNS at moderate to deep planes of isoflurane anesthesia. Nonetheless, relatively low blood flows in the brain and spinal cord of anesthetized horses may increase risks for hypoperfusion and neurologic injury.
authors.affiliation: Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616, USA. rjbrosnan@ucdavis.edu
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Brosnan
authors.forename: Eugene P
authors.initials: EP
authors.lastname: Steffey
authors.forename: Richard A
authors.initials: RA
authors.lastname: LeCouteur
authors.forename: Alejandro
authors.initials: A
authors.lastname: Esteller-Vico
authors.forename: Betsy
authors.initials: B
authors.lastname: Vaughan
authors.forename: Irwin K M
authors.initials: IK
authors.lastname: Liu
mesh_terms: D000768:Anesthesia, General / Q000662:veterinary*; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D001783:Blood Flow Velocity / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects; D002560:Cerebrovascular Circulation / Q000187:drug effects*; D005260:Female; D006706:Homeostasis / Q000187:drug effects*; D006736:Horses / Q000502:physiology*; D007530:Isoflurane / Q000494:pharmacology*; D008297:Male
chemical_list: D018685:Anesthetics, Inhalation; D007530:Isoflurane