Norepinephrine Versus Dopamine as a First-Line Vasopressor in Dogs with Hypotension: A Pilot Study.

Norepinephrine (NE) and dopamine (DA) are vasopressors used to treat vasodilatory shock for decades, and norepinephrine is considered the preferred first-line vasopressor in human patients. However, there is a dearth of evidence to support specific treatment recommendations for the management of hypotensive, non-anesthetized, fluid-replete dogs. The objective of this study was to compare the effects of NE and DA on systolic blood pressure (SBP), heart rate, and shock index (SI) when used as first-line vasopressors for the treatment of vasodilatory shock in dogs. Twenty-four client-owned canine patients of similar age, sex, and weight with hypotension necessitating vasopressor therapy were randomized to receive NE or DA; attending clinicians were blinded. Twenty-two dogs were included in the final analysis (10 in the NE group and 12 in the DA group). Seventy-seven percent of all dogs achieved normotension. In both groups, SBP increased significantly compared to baseline (p = 0.0004 in the NE group and p = 0.006 in the DA group). The SI also decreased in both groups compared to baseline values (p = 0.01 in the NE group and p = 0.01 in the DA group). The heart rate in the NE group was higher than in the DA group at timepoints 6-10 (p = 0.023). Both NE and DA cause an increase in blood pressure and a decrease in SI in dogs with vasodilatory hypotension. Further investigation is warranted to determine if there are differences between NE and DA or the requirement for a second vasopressor, occurrence of arrhythmias, length of stay, and survival.