Isoflurane increases brain oxygen reactivity in dogs.
We tested the possibility that large-dose isoflurane will produce a loss of brain tissue oxygen regulation in dogs. A total of 12 dogs were anesthetized with isoflurane, a craniotomy was performed, and a probe was inserted to measure brain tissue oxygen pressure (PtO(2)), carbon dioxide, and pH. Baseline measures were made during 1.5% end-tidal isoflurane with 30% oxygen ventilation, followed by 95% oxygen ventilation. Six dogs (Group 1) were treated with 3% isoflurane and 30% oxygen, followed by a second oxygen challenge with 95% O(2). Six dogs (Group 2) received propofol to produce a similar suppression of the electroencephalogram as in Group 1, followed by 95% oxygen ventilation. Brain tissue oxygen reactivity was calculated by the increase in PtO(2) divided by the increase in arterial PO(2). During 1.5% isoflurane and propofol anesthesia, PtO(2) increased from 42 to 62 mm Hg with oxygen ventilation, and brain tissue oxygen reactivity was 0.14% per mm Hg(-1). Brain tissue oxygen reactivity did not change during propofol anesthesia. With 3% isoflurane, PtO(2) increased from 52 to 113 mm Hg and brain tissue oxygen reactivity was 0.36% per mm Hg(-1) (P: < 0.05). These results suggest that the cerebrovasodilator and vasoplegic effects of large-dose isoflurane attenuate brain oxygen regulation.


CONCLUSIONS
We evaluated the ability of oxygen ventilation to increase brain tissue oxygen pressure in dogs anesthetized with 1.5% and 3% isoflurane and propofol. Increases in tissue oxygen were significantly greater during 3% isoflurane compared with 1.5% isoflurane and propofol.
Hoffman
W E
WE
Department of Anesthesiology, University of Illinois at Chicago, 60612, USA. whoffman@uic.edu
Edelman
G
G
D000465:Algorithms; D000758:Anesthesia; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D018686:Anesthetics, Intravenous / Q000494:pharmacology; D000818:Animals; D001784:Blood Gas Analysis; D001794:Blood Pressure / Q000187:drug effects; D001923:Brain Chemistry / Q000187:drug effects*; D004285:Dogs; D004569:Electroencephalography / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D007530:Isoflurane / Q000494:pharmacology*; D010101:Oxygen Consumption / Q000187:drug effects*; D015742:Propofol / Q000494:pharmacology
D018685:Anesthetics, Inhalation; D018686:Anesthetics, Intravenous; D007530:Isoflurane; D015742:Propofol