Effects of dexmedetomidine on the minimum alveolar concentration and its derivatives in sevoflurane-anesthetized cats.

OBJECTIVE

To evaluate the effects of dexmedetomidine on the sevoflurane minimum alveolar concentration (SEVMAC), minimum alveolar concentration (MAC) for blocking adrenergic responses (SEVMAC-BAR), and MAC for tracheal extubation (SEVMAC-Extubation).

STUDY

DESIGN

Prospective randomized, crossover experimental study.

ANIMALS: Six healthy adult neutered cats [one female and five males; weighing 4.8 ± 1.1 kg (mean ± standard deviation)].

METHODS

Cats were anesthetized with sevoflurane in oxygen. After endotracheal intubation, anesthesia was maintained with sevoflurane and mechanical ventilation was performed. Each cat was given all six treatments in a random order, which were saline or dexmedetomidine infusions at maintenance doses of 0.15, 0.3, 0.6, 1.5, or 6.0 μg kg-1 hour-1, following respective loading doses of 1, 2, 4, 10, and 40 μg kg-1 over 20 minutes, designed to achieve an estimated plasma concentration of 0.5-20.0 ng mL-1. SEVMAC-BAR, SEVMAC and SEVMAC-Extubation were measured in this order. Plasma dexmedetomidine concentrations were determined using liquid chromatography-tandem mass spectrometry. A linear regression analysis was used to assess the plasma concentration-response relationships and estimate the half-maximal inhibitory concentration (IC50), defined as the plasma dexmedetomidine concentration producing a 50% reduction from the control value, separately for SEVMAC-BAR, SEVMAC, and SEVMAC-Extubation.

RESULTS

The baseline SEVMAC-BAR, SEVMAC and SEVMAC-Extubation were 2.79 ± 0.86%, 2.65 ± 0.32%, and 1.60 ± 0.64%, respectively. These values significantly decreased in a plasma dexmedetomidine concentration-dependent manner. The IC50 values for SEVMAC-BAR, SEVMAC and SEVMAC-Extubation were 1.90 ng mL-1 [95% confidence interval (CI): 0.51-6.99 ng mL-1], 1.38 ng mL-1 (95% CI: 0.35-5.39 ng mL-1), and 2.24 ng mL-1 (95% CI: 0.67-7.50 ng mL-1), respectively.

CONCLUSIONS

Dexmedetomidine reduced the MAC and MAC derivatives in a plasma dexmedetomidine concentration-dependent manner in sevoflurane-anesthetized cats.

CLINICAL RELEVANCE: Dexmedetomidine could be effective in suppressing motor and sympathetic responses accompanied by noxious stimulation and maintaining endotracheal intubation in cats.