Effects of norepinephrine and combined norepinephrine and fenoldopam infusion on systemic hemodynamics and indices of renal function in normotensive neonatal foals

Background: Norepinephrine increases arterial blood pressure but may have adverse effects on renal blood flow. Fenoldopam, a dopamine-1 receptor agonist, increases urine output in normotensive foals. The combination of norepinephrine and fenoldopam may lead to improved renal perfusion compared with an infusion of norepinephrine alone. The combined effects of these drugs have not been reported in the horse.
Hypothesis: Norepinephrine will alter the hemodynamic profile of foals without affecting renal function. Addition of fenoldopam will change the renal profile during the infusions without changing the hemodynamic profile.
Animals: Five conscious pony foals.
Methods: Each foal received norepinephrine (0.3 μg/kg/min), combined norepinephrine (0.3 μg/kg/min) and fenoldopam (0.04 μg/kg/min), and a control dose of saline in a masked, placebo-controlled study. Heart rate (HR), arterial blood pressure (direct), and cardiac output (lithium dilution) were measured, and systemic vascular resistance (SVR), stroke volume, cardiac index (CI), and stroke volume index were calculated. Urine output, creatinine clearance, and fractional excretion of electrolytes were measured.
Results: Norepinephrine and a combined norepinephrine and fenoldopam infusion increased arterial blood pressure, SVR, urine output, and creatinine clearance and decreased HR and CI compared with saline. The combination resulted in higher HR and lower arterial blood pressure than norepinephrine alone.
Conclusions and Clinical Importance: Norepinephrine might be useful for hypotensive foals, because in normal foals, this infusion rate increases SVR without negatively affecting renal function (creatinine clearance increased). Fenoldopam does not provide additional benefit to renal function. These findings warrant further investigation.