The enflurane sparing effect of sufentanil in dogs

There is a ceiling to the reduction of enflurane MAC by fentanyl in the dog. Sufentanil (SUF), a more potent narcotic, may be more efficacious in reducing enflurane MAC. To test this hypothesis, 25 mongrel dogs were studied in three groups. Group 1 (n = 8) received SUF in progressively increasing infusion rates from 0.005 micrograms . kg-1 . min-1 to a maximum of 1.215 micrograms . kg-1 . min-1. MAC was determined at stable SUF concentrations in plasma [SUF] during each infusion rate. Group 2 (n = 10) received SUF at a dose rate (0.007 micrograms . kg-1 . min-1) designed to produce approximately 35% MAC reduction, and MAC determinations were made at regular intervals over a mean infusion time of 7.6 +/- 0.43 h (mean +/- SEM). Group 3 (n = 7) received 1.215 micrograms . kg-1 . min-1 and were studied as in group 2 over an infusion time of 6.7 +/- 0.42 h. In group 1, the highest infusion rate (1.215 micrograms . kg-1 . min-1) produced [SUF] = 48 ng/ml and reduced MAC by 71 +/- 6%. This was not statistically different from the reduction which occurred at [SUF] = 0.92 ng/ml (57 +/- 7%; infusion rate 0.015 micrograms . kg-1 . min-1; P = 0.21). In group 2, the degree of MAC reduction achieved by stable [SUF] (0.54 +/- 0.08 ng/ml) declined over time (MAC reduction at start = 34 +/- 2% versus 18 +/- 4.0% at the end of the infusion; P = 0.001), suggesting the development of tolerance.(ABSTRACT TRUNCATED AT 250 WORDS)