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- Author or Editor: Michael D. Noseworthy x
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Objective—To assess the effects of alterations in PaCO 2 and PaO 2 on blood oxygenation level–dependent (BOLD) signal intensity determined by use of susceptibility-weighted magnetic resonance imaging in brains of isoflurane-anesthetized dogs.
Animals—6 healthy dogs.
Procedures—In each dog, anesthesia was induced with propofol (6 to 8 mg/kg, IV) and maintained with isoflurane (1.7%) and atracurium (0.2 mg/kg, IV, q 30 min). During 1 magnetic resonance imaging session in each dog, targeted values of PaCO 2 (20, 40, or 80 mm Hg) and PaO 2 (100 or 500 mm Hg) were combined to establish 6 experimental conditions, including a control condition (PaCO 2, 40 mm Hg; PaO 2, 100 mm Hg). Dogs were randomly assigned to different sequences of conditions. Each condition was established for a period of ≥ 5 minutes before susceptibility-weighted imaging was performed. Signal intensity was measured in 6 regions of interest in the brain, and data were analyzed by use of an ANCOVA and post hoc Tukey-Kramer adjustments.
Results—Compared with control condition findings, BOLD signal intensity did not differ significantly in any region of interest. However, signal intensities in the thalamus and diencephalic gray matter decreased significantly during both hypocapnic conditions, compared with all other conditions except for the control condition.
Conclusions and Clinical Relevance—In isoflurane-anesthetized dogs, certain regions of gray matter appeared to have greater cerebrovascular responses to changes in PaCO 2 and PaO 2 than did others. Both PaO 2 and PaCO 2 should be controlled during magnetic resonance imaging procedures that involve BOLD signaling and taken into account when interpreting findings.
Objective—To evaluate the effects of various combinations of Paco2 and Pao2 values on brain morphometrics.
Animals—6 healthy adult dogs.
Procedures—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 and Clinical Relevance—The changes observed in LVV during hypocapnia and hypercapnia may serve as a potential confounding factor when neuromorphometric evaluations are performed in anesthetized dogs. (Am J Vet Res 2010;71:1011–1018)