The renal and neurohumoral effects of the addition of low-dose dopamine in septic critically ill patients

Objectives: Dopamine exerts a complicated action on the cardiovascular-renal and neurohumoral systems. We evaluated the effects of the addition of different doses of dopamine on top of treatment with norepinephrine on the haemodynamics, renal function and neurohormones of septic shock patients. Design: Open, uncontrolled, dosefinding study. Subjects: Dopamine was administered, after fluid resuscitation, to septic shock patients who were more than 2 h haemodynamically and pulmonary stable with the use of a constant dose norepinephrine. Patients with a serum creatinine above 180 μmol·1 were excluded. Methods: Dopamine doses of 0, 2, 4, 6 and 0 μg·kg^-1·min^-1 were given consecutively for 1 h each. Neurohormones were measured hourly after baseline levels had been taken. Systemic haemodynamics were measured using a pulmonary artery (PA) catheter every 30 min, whereas urine collections were examined every hour during the study period. Results and statistical analyses: Eight patients (mean age 46 ± 13 years, M/F 3/5) were included. The median norepinephrine dose at the start of the study was 0.29 μg·kg^-1·min^-1 (range 0.07-0.48 μg·kg^-1·min^-1). Cardiac output (CO) rose during the dopamine infusion for all doses from 7.9 ± 1.74 l/min to a maximum of 10.1 ± 1.71 l/min, achieved at the 4 μg·kg^-1·min^-1 dopamine dose, whereas systemic vascular rate (SVR) decreased slightly for all doses. Heart rate remained unchanged during the 2 μg·kg^-1·min^-1 dose of dopamine but increased for the 4 and 6 μg·kg^-1·min^-1 doses from 108 ± 17 to a maximum of 124 ± 24 beats/min. Filling pressures remained unchanged whereas the mean arterial blood pressure increased (from 83 ± 7 to 93 ± 11 mmHg). Plasma renin activity (PRA) was relatively high (but remained unchanged) as were aldosterone levels. Sodium excretion and diuresis increased for all doses, accompanied by an increase of fractional sodium excretion at the 4 and 6 μg·kg^-1·min^-1 doses of dopamine. Creatinine clearances remained unchanged. All changed values returned to baseline values after cessation of the dopamine administration. Conclusion: During norepinephrine infusion, increasing doses of dopamine from 2 to 6 μg·kg^-1·min^-1 augments CO, diuresis and sodium excretion in patients treated for septic shock, without changes in creatinine clearance. Higher doses of dopamine (4 and 6 μg·kg^-1·min^-1) also induce an increase in heart rate. PRA, aldosterone and norepinephrine levels remain unchanged during dopamine infusion.