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Cardiopulmonary effects of sevoflurane, compared with halothane, enflurane, and isoflurane, in dogs.

OBJECTIVE
To evaluate cardiopulmonary effects of sevoflurane (Sevo), compared with halothane (Hal), enflurane (Enf), and isoflurane (Iso).


ANIMALS
24 healthy Beagles, randomly assigned to 4 groups of 6 dogs each.


PROCEDURE
Dogs under spontaneous ventilation were anesthetized with Sevo, Hal, Enf, or Iso. After minimum elveolar concentration (MAC) of each anesthetic was determined, anesthesia was maintained at light (1 MAC), moderate surgical (1.5 MAC), and deep (2 MAC), stages and cardiopulmonary variables at conscious state (baseline) and each anesthesia stage were measured.


RESULTS
In dogs of the Sevo group, heart rate increased significantly from the baseline value at all anesthesia stages. Systemic vascular resistance during Sevo anesthesia decreased gradually with increasing anesthesia stage, which was accompanied by dose-dependent decreases in systolic, mean, and diastolic arterial blood pressures. At 1.5 and 2 MAC Sevo, stroke index decreased slightly but significantly from the baseline value; however, cardiac index was unchanged because of the significant increase in heart rate. Respiratory rate decreased significantly at 2 MAC from that at 1 MAC Sevo. Tidal volume and dead space-to-tidal volume ratio were unchanged at all anesthesia stages of Sevo, resulting in significantly decreased expired and alveolar ventilation at 2 MAC, compared with values at 1 and 1.5 MAC Sevo. PaCO2 increased and pHa decreased significantly, depending on anesthesia stage; PaO2, increased significantly from baseline values, and remained constant because of inhalation of 100% O2.


CONCLUSION
Cardiovascular effects of Sevo were greater than those of Hal, similar to those of Iso, and less than those of Enf. Respiratory effects of Sevo were similar to those of Iso at all anesthesia stages, greater than those of Hal at 2 MAC, and less than those of Enf at 1.5 and 2 MAC. Up to the moderate surgical anesthesia stage, Sevo can be used safely in dogs undergoing spontaneous ventilation.