Effects of adenosine infusion on the minimum alveolar concentration of isoflurane in dogs

OBJECTIVE: To determine the effects of adenosine infusion on the minimum alveolar concentration (MAC) of isoflurane in dogs. STUDY DESIGN: Prospective, randomized crossover study. ANIMALS: Seven adult male and female Beagles weighing 10.9 (7.5, 13.6) kg median (minimum, maximum)]. METHODS: Each dog was anesthetized with isoflurane in oxygen and randomly assigned to receive either an intravenous (IV) adenosine (0.3 mg kg(-1) minute(-1)) or saline (6 mL kg(-1) hour(-1) IV) infusion. After an interval of 7 days or more, each dog was re-anesthetized and treated with the alternative infusion. Using a tail-clamp technique, MAC was determined before (pre-infusion), during (infusion), and 2 hours after the infusions (post-infusion). RESULTS: The pre-infusion MAC of isoflurane was 1.25 (1.15, 1.35) median (minimum, maximum)] vol.% for the saline treatment group and 1.25 (1.05, 1.45) vol.% for the adenosine treatment group, and did not differ significantly between the two treatments. The infusion MAC values were not significantly different (p = 0.16) and were 1.25 (0.95, 1.35) vol.% and 1.05 (1.00, 1.25) vol.%, respectively. The post-infusion MAC values differed significantly (p = 0.016); MAC was 1.15 (1.15, 1.35) vol.% and 1.05 (1.05, 1.25) vol.% for the saline and adenosine treatment groups, respectively. During infusion, mean arterial blood pressure decreased significantly (p = 0.008) during adenosine treatment compared with the saline 66 mmHg (52, 72) and 91 mmHg (68, 110), respectively. End-tidal CO2 (Pe'CO2), urine production, hematocrit, and plasma total solids did not differ significantly between the two treatments at any time (all p > 0.05). CONCLUSION: Although the MAC of isoflurane in dogs was not decreased significantly during infusion with adenosine (0.3 mg kg(-1) minute(-1)), it was significantly decreased post-infusion, but only by 0.1 vol.%, an amount not considered clinically important. Adenosine infusion decreased mean arterial pressure by 27% and did not adversely affect renal function.