title: Effects of hypercapnia, hypocapnia, and hyperoxemia on brain morphometrics determined by use of T1-weighted magnetic resonance imaging in isoflurane-anesthetized dogs.
abstract: OBJECTIVE
  To evaluate the effects of various combinations of PaCO2 and PaO2 values on brain morphometrics.
  
  
  METHODS
  6 healthy adult dogs.
  
  
  METHODS
  A modified Latin square design for randomization was used. Dogs were anesthetized with propofol (6 to 8 mg/kg, IV), and anesthesia was maintained with isoflurane (1.7%) and atracurium (0.2 mg/kg, IV, q 30 min). Three targeted values of PaCO2 (20, 40, and 80 mm Hg) and 2 values of PaO2 (100 and 500 mm Hg) were achieved in each dog, yielding 6 combinations during a single magnetic resonance (MR) imaging session. When the endpoints were reached, dogs were given at least 5 minutes for physiologic variables to stabilize before T1-weighted MR images were obtained. Total brain volume (TBV) and lateral ventricular volume (LVV) were calculated from manually drawn contours of areas of interest by use of a software program, with each dog serving as its own control animal. Three blinded investigators subjectively evaluated the lateral ventricular size (LVS) and the cerebral sulci width (CSW). Brain morphometric values were compared among the target blood gas states.
  
  
  RESULTS
  No significant differences in TBV were found among target states. The LVV was significantly greater during hypocapnia, compared with hypercapnia at the same PaO2 value. With regard to the subjective evaluations, there were no significant differences among evaluators or among combinations of PaO2 and PaCO2 values.
  
  
  CONCLUSIONS
  The changes observed in LVV during hypocapnia and hypercapnia may serve as a potential confounding factor when neuromorphometric evaluations are performed in anesthetized dogs.
authors.affiliation: Department of Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, ON N1G 2W1, Canada. eva.riojagarcia@up.ac.za
authors.forename: Eva
authors.initials: E
authors.lastname: Rioja
authors.forename: Wayne N
authors.initials: WN
authors.lastname: McDonell
authors.forename: Carolyn L
authors.initials: CL
authors.lastname: Kerr
authors.forename: Howard
authors.initials: H
authors.lastname: Dobson
authors.forename: Norman B
authors.initials: NB
authors.lastname: Konyer
authors.forename: Roberto
authors.initials: R
authors.lastname: Poma
authors.forename: Heather J
authors.initials: HJ
authors.lastname: Chalmers
authors.forename: Michael D
authors.initials: MD
authors.lastname: Noseworthy
mesh_terms: D000758:Anesthesia / Q000379:methods / Q000662:veterinary; D000818:Animals; D001783:Blood Flow Velocity; D001810:Blood Volume; D001921:Brain / Q000033:anatomy & histology / Q000502:physiology* / Q000503:physiopathology; D002245:Carbon Dioxide / Q000097:blood; D002560:Cerebrovascular Circulation / Q000502:physiology; D004285:Dogs; D006935:Hypercapnia / Q000503:physiopathology / Q000662:veterinary*; D018496:Hyperoxia / Q000503:physiopathology / Q000662:veterinary*; D016857:Hypocapnia / Q000503:physiopathology / Q000662:veterinary*; D008279:Magnetic Resonance Imaging; D010092:Oximetry / Q000379:methods / Q000662:veterinary; D010100:Oxygen / Q000097:blood; D015742:Propofol
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen; D015742:Propofol