Effect of buprenorphine delivered by target-controlled infusion on the minimum alveolar concentration of isoflurane in cats.

Objective: To characterize the effect of buprenorphine on the minimum alveolar concentration of isoflurane (MACiso) in cats.

Study Design: Randomized, crossover, experimental study.

Animals: A group of six healthy male neutered cats, aged 2-8 years with body mass 5.0 ± 0.3 kg.

Methods: The MACiso had been determined in each cat in a previous study. Cats were anesthetized with isoflurane in oxygen. Catheters were placed in a medial saphenous vein for drug and fluid administration and in a jugular vein for blood sampling. Buprenorphine was administered intravenously using a target-controlled infusion system to reach and maintain plasma concentrations of 0.5, 1, 2, 4, 8, 16, 32 and 64 ng mL, and MACiso was determined in duplicate at each concentration using the tail clamp technique. Four target plasma buprenorphine concentrations were administered on each study day, with at least 2 weeks between experiments. Blood was sampled after the second MAC determination at each target for determination of plasma buprenorphine concentration.

Results: A significant effect of buprenorphine on MAC was found; however, pairwise comparisons to MACiso without buprenorphine did not reach statistical significance. Maximum reduction in MACiso in individual cats ranged from 2% to 34% at plasma buprenorphine concentrations ranging from 0.25 to 8.15 ng mL.

Conclusions And Clinical Relevance: Although buprenorphine significantly affected MACiso in cats, the magnitude of the effect and the plasma concentration at which the largest effect occurred was highly variable among cats, limiting the clinical usefulness of buprenorphine as an agent to reduce MAC in cats.