Cardiovascular Effects of Dobutamine and Norepinephrine Infusion in Healthy, Anesthetized Alpacas
The objective of this study was to characterize the cardiovascular effects of dobutamine and norepinephrine infusion in isoflurane-anesthetized, healthy alpacas.
Eight adult alpacas (3 females, 5 intact males, 4.1 ± 2.7 years) were evaluated. Initial baseline cardiovascular, respiratory and metabolic variables were obtained 30 minutes after induction of isoflurane anesthesia. Four treatments (dobutamine at 4 and 8 µg/kg/min; norepinephrine at 0.3 and 1 µg/kg/min) were administered in random order via constant rate infusion over 15 minutes, followed by repeat measurements of values and a 20 minute washout period. Subsequent baseline and post-treatment measurements were similarly repeated until both drugs and dosages were administered to each animal. Baseline data in awake alpacas was obtained 18-24 hours following recovery from anesthesia.
Both norepinephrine and dobutamine significantly elevated cardiac index and arterial blood pressure from baseline. Similar increases in hemoglobin, oxygen content and oxygen delivery were observed following administration of each drug at either dosage. Only dobutamine, however, reduced relative oxygen consumption while improving overall oxygen balance. Furthermore, heart rate was selectively enhanced by dobutamine and systemic vascular resistance by norepinephrine. Norepinephrine infusion resulted in dose dependent changes in cardiovascular variables.
This study shows that both dobutamine and norepinephrine are appropriate choices to improve cardiac index, mean arterial pressure and thus overall oxygen delivery in alpacas experiencing isoflurane induced hypotension. The lower infusion rates of both dobutamine (4 µg/kg/min) and norepinephrine (0.3 µg/kg/min) are recommended to avoid potential arrhythmogenic effects and excessive vasoconstriction, respectively.