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

Objectives: Dopamine exerts a complicated action on the cardiovascular-rena l and neurohumoral systems. We evaluated the effects of the addition of dif ferent doses of dopamine on top of treatment with norepinephrine on the hae modynamics, renal function and neurohormones of septic shock patients. Design: Open, uncontrolled, dose-finding study. Subjects: Dopamine was administered, after fluid resuscitation, to septic s hock patients who were more than 2 h haemodynamically and pulmonary stable with the use of a constant dose norepinephrine. Patients with a serum creat inine above 180 mu mol.l were excluded. Methods: Dopamine doses of 0, 2, 4, 6 and 0 mug.kg(-1).min(-1) were given c onsecutively for 1 h each. Neurohormones were measured hourly after baselin e levels had been taken. Systemic haemodynamics were measured using a pulmo nary artery (PA) catheter every 30 min, whereas urine collections were exam ined every hour during the study period. Results and statistical analyses: Eight patients (mean age 46 +/- 13 years, M/F 3/5) were included. The media n norepinephrine dose at the start of the study was 0.29 mug.kg(-1).min(-1) (range 0.07-0.48 mug.kg min(-1)). Cardiac output (CO) rose during the dopa mine 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 mug.kg(-1)min(-1) dopamine dose, whereas sy stemic vascular rate (SVR) decreased slightly for all doses. Heart rate rem ained unchanged during the 2 mug.kg(-1)min(-1) dose of dopamine but increas ed for the 4 and 6 mug.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). Plasm a 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 m ug.kg(-1).min(-1) doses of dopamine. Creatinine clearances remained unchang ed. All changed values returned to baseline values after cessation of the d opamine administration. Conclusion: During norepinephrine infusion, increasing doses of dopamine fr om 2 to 6 mug.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 yg kg(-1).min(-1)) also induce an increa se in heart rate. PRA, aldosterone and norepinephrine levels remain unchang ed during dopamine infusion.