Detomidine reduces isoflurane anesthetic requirement (MAC) in horses.

OBJECTIVE

To quantitate the dose- and time-related magnitude of the anesthetic sparing effect of, and selected physiological responses to detomidine during isoflurane anesthesia in horses.

STUDY DESIGN

Randomized cross-over study.

ANIMALS

Three, healthy, young adult horses weighing 485 ± 14 kg.

METHODS

Horses were anesthetized on two occasions to determine the minimum alveolar concentration (MAC) of isoflurane in O and then to measure the anesthetic sparing effect (time-related MAC reduction) following IV detomidine (0.03 and 0.06 mg kg). Selected common measures of cardiopulmonary function, blood glucose and urinary output were also recorded.

RESULTS

Isoflurane MAC was 1.44 ± 0.07% (mean ± SEM). This was reduced by 42.8 ± 5.4% and 44.8 ± 3.0% at 83 ± 23 and 125 ± 36 minutes, respectively, following 0.03 and 0.06 mg kg, detomidine. The MAC reduction was detomidine dose- and time-dependent. There was a tendency for mild cardiovascular and respiratory depression, especially following the higher detomidine dose. Detomidine increased both blood glucose and urine flow; the magnitude of these changes was time- and dose-dependent CONCLUSIONS: Detomidine reduces anesthetic requirement for isoflurane and increases blood glucose concentration and urine flow in horses. These changes were dose- and time-related.

CLINICAL RELEVANCE

The results imply potent anesthetic sparing actions by detomidine. The detomidine-related increased urine flow should be considered in designing anesthetic protocols for individual horses.