DISSOCIATION BETWEEN THE EFFECTS OF FENTANYL AND ALFENTANIL ON SPONTANEOUS AND REFLEXLY EVOKED CARDIOVASCULAR RESPONSES IN THE DOG

Abstract

Observations were made for 3 h in 10 anaesthetized dogs on the effects of alfentanil 500 μg kg ⁻ andfentanyl 100 μg kg⁻¹ on resting heart rate (HR) and mean arterial pressure (MAP), and on the changes evoked in heart rate and mean arterial pressure (Δ HR and Δ MAP) by stimulation of a cutaneous nerve. Both drugs caused similar decreases in the resting HR (43%44%) and MAP (28–31%), which returned to baseline within lgOmin following alfentanil but not fentanyl. Fentanyl decreased the somato - cardiovascular reflexes by 73% and 82% compared with a significantly smaller reduction of 54% and 55% (P< 0.05) with alfentanil. Following nlffntanilj Δ MAP had recovered by 15 min and Δ HR by 70 min compared with 70 and 90 nun respectively for fentanyl. In conclusion, there was a dissociation between the maximum effect of alfentanil and fentanyl on the resting circulation and on the evoked cardiovascular reflexes. With both drugs a dissociation was observed between the durations of their effect on the resting cardiovascular system and on the evoked cardiovascular responses