Differences in need for hemodynamic support in horses anesthetized with sevoflurane as compared to isoflurane.
OBJECTIVE
To study whether hemodynamic function in horses, particularly mean arterial blood pressure (MAP), is better maintained with sevoflurane than isoflurane, thus requiring less pharmacological support.


METHODS
Prospective randomized clinical investigation. Animals Thirty-nine racehorses undergoing arthroscopy in lateral recumbency.


METHODS
Horses were assigned to receive either isoflurane (n = 20) or sevoflurane (n = 19) at 0.9-1.0 minimum alveolar concentration (MAC) for maintenance of anesthesia. Besides routine clinical monitoring, cardiac output (CO) was measured by lithium dilution. Hemodynamic support was prescribed as follows: when MAP decreased to <70 mmHg, patients were to receive infusion of 0.1% dobutamine, which was to be discontinued at MAP >85 mmHg or heart rate >60 beats minute(-1). Statistical analysis of results, given as mean +/- SD, included a clustered regression approach.


RESULTS
Average inhalant anesthetic time [91 +/- 35 (isoflurane group) versus 97 +/- 26 minutes (sevoflurane group)] and dose (in MAC multiples), volume of crystalloid solution infused, and cardiopulmonary parameters including CO were similar in the two groups, except heart rate was 8% higher in isoflurane than sevoflurane horses (p < 0.05). To maintain MAP >70 mmHg, isoflurane horses received dobutamine over a significantly longer period (55 +/- 26 versus 28 +/- 21% of total anesthetic time, p < 0.01) and at a 51% higher dose than sevoflurane horses (41 +/- 19 versus 27 +/- 23 microg kg(-1) MAC hour(-1); p = 0.058), with 14/20 isoflurane animals and only 9/19 sevoflurane horses being infused with dobutamine at >30 microg kg(-1) MAC hour(-1) (p < 0.05). Dobutamine infusion rates were consistently lower in the sevoflurane as compared to the isoflurane group, with differences reaching significance level during the 0-30 minutes (p < 0.01) and 61-90 minutes periods (p < 0.05).


CONCLUSIONS
Horses under sevoflurane anesthesia may require less pharmacological support in the form of dobutamine than isoflurane-anesthetized horses. This could be due to less suppression of vasomotor tone.
Driessen
Bernd
B
Department of Clinical Studies, New Bolton Center, School of Veterinary Medicine, Section of Critical Care/Anesthesia, University of Pennsylvania, PA 19348, USA. driessen@vet.upenn.edu
Nann
Lawrence
L
Benton
Robin
R
Boston
Raymond
R
D000769:Anesthesia, Inhalation / Q000662:veterinary*; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects*; D004280:Dobutamine / Q000008:administration & dosage; D005260:Female; D006339:Heart Rate / Q000187:drug effects*; D006736:Horses / Q000502:physiology*; D007530:Isoflurane / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D008738:Methyl Ethers / Q000008:administration & dosage / Q000494:pharmacology*; D011446:Prospective Studies; D011650:Pulmonary Alveoli / Q000187:drug effects; D000077149:Sevoflurane
D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane; D004280:Dobutamine; D007530:Isoflurane