Cardiovascular effects of dose escalating of norepinephrine in healthy dogs anesthetized with isoflurane.

Objective: To evaluate the systemic cardiovascular effects of dose escalating administration of norepinephrine in healthy dogs anesthetized with isoflurane.

Study Design: Experimental study.

Animals: A total of six adult laboratory Beagle dogs, 10.5 (9.2-12.0) kg [median (range)].

Methods: Each dog was anesthetized with isoflurane at an end-tidal concentration of 1.7%, mechanically ventilated and administered a continuous rate infusion of rocuronium (0.5 mg kg hour). Each dog was administered incremental dose rates of norepinephrine (0.05, 0.125, 0.25, 0.5, 1.0 and 2.0 μg kg minute), and each dose was infused for 15 minutes. Cardiovascular variables were recorded before administration and at the end of each infusion period.

Results: Norepinephrine infusion increased mean arterial pressure (MAP), cardiac output (CO) and oxygen delivery in a dose-dependent manner. Systemic vascular resistance did not significantly change during the experiment. Stroke volume increased at the lower dose rates and heart rate increased at the higher dose rates. Oxygen consumption and lactate concentrations did not significantly change during infusions.

Conclusions: In dogs anesthetized with isoflurane, norepinephrine increased MAP by increasing the CO. CO increased with a change in stroke volume at lower dose rates of norepinephrine. At higher dosage, heart rate also contributed to an increase in CO. Norepinephrine did not cause excessive vasoconstriction that interfered with the CO during this study.

Clinical Relevance: Norepinephrine can be useful for treating hypotension in dogs anesthetized with isoflurane.