Cardiopulmonary effects of three concentrations of isoflurane with or without mechanical ventilation and supramaximal noxious stimulation in New Zealand white rabbits.
OBJECTIVE
To determine the cardiopulmonary effects of 3 doses of isoflurane, with and without controlled mechanical ventilation and noxious stimulation, in healthy adult New Zealand white rabbits.


METHODS
6 adult female rabbits.


METHODS
Each rabbit was administered isoflurane in oxygen at each of 3 anesthetic doses (1.0, 1.5, or 2.0 times the published minimum alveolar concentration of 2.07%). At each anesthetic dose, blood gas and cardiopulmonary measurements were obtained before and during application of a supramaximal noxious stimulus. Effects of spontaneous and mechanical ventilation were assessed during separate anesthetic episodes.


RESULTS
Mean ± SEM isoflurane concentrations used were 2.11 ± 0.04%, 3.14 ± 0.07%, and 4.15 ± 0.06%. During spontaneous ventilation, the rabbits' Paco2 and mixed venous Pco2 significantly increased with concomitant reductions in both arterial and mixed venous pH as isoflurane concentration increased. Cardiac output and vascular resistance did not change significantly. Noxious stimulation minimally affected measured cardiopulmonary variables. During mechanical ventilation, significant reductions in arterial blood pressures and cardiac output occurred with increasing isoflurane dose. Systemic vascular resistance index at the highest anesthetic dose was significantly lower than the value at the lowest anesthetic dose. During noxious stimulation, systolic arterial blood pressure and cardiac output significantly increased at the 2 lower isoflurane concentrations, but not at the highest concentration.


CONCLUSIONS
In rabbits, isoflurane-induced dose-dependent cardiopulmonary depression was attributable to vasodilation and negative inotropy. At an isoflurane concentration of 4.15% with mechanical ventilation, cardiovascular depression was severe; use of unnecessarily high isoflurane concentrations in this species should be avoided.
Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California-Davis, Davis, CA 95616.
Linda S
LS
Barter
Steven E
SE
Epstein
D000704:Analysis of Variance; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D001784:Blood Gas Analysis / Q000662:veterinary; D001794:Blood Pressure / Q000187:drug effects; D001798:Blood Proteins / Q000032:analysis; D002302:Cardiac Output / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005260:Female; D006400:Hematocrit / Q000662:veterinary; D006439:Hemodynamics / Q000187:drug effects*; D007530:Isoflurane / Q000494:pharmacology*; D019344:Lactic Acid / Q000097:blood; D011817:Rabbits; D012121:Respiration, Artificial / Q000662:veterinary*; D014655:Vascular Resistance / Q000187:drug effects; D014664:Vasodilation / Q000187:drug effects
D018685:Anesthetics, Inhalation; D001798:Blood Proteins; D019344:Lactic Acid; D007530:Isoflurane