Renal hemodynamics during norepinephrine and low-dose dopamine infusions in man

Objectives: To characterize the effects of presser doses of norepinephrine and low dose dopamine (3 mu g/kg/min) on renal hemodynamics in man, as well as to determine the clinical relevance of combining dopamine with norepinephrine. Design: Prospective, single-blind, randomized study, Setting: CLinical research unit of a tertiary care hospital. Subjects: Six healthy male volunteers ranging in age between 20 and 28 yrs, Interventions: The subjects were assigned randomly to four treatments (1 wk apart) in which renal hemodynamics and electrolyte excretion were assessed. Treatments consisted of 180-min infusions of the following: a) 0.9% sodium chloride (control); b) presser doses of norepinephrine; c) dopamine at 3 mu g/kg/min; and d) presser doses of norepinephrine and dopamine at 3 mu g/kg/min. Presser doses of norepinephrine were defined as doses required to increase mean arterial pressure (MAP) by 20 mm Hg. Measurements and Main Results: Glomerular filtration rate and renal blood flow were derived from inulin and paraaminohippurate clearances, respectively. Urine output and urine solute excretion were also determined, The mean norepinephrine dose required to increase MAP by 22 +/- 2 mm Hg was 118 +/- 30 ng/kg/min (range 76 to 164). After the addition of dopamine, similar doses of norepinephrine resulted in an MAP increase of 15 +/- 4 mm Hg. Glomerular filtration rate and urine output were comparable under all conditions, The infusion of norepinephrine decreased renal blood flow from 1241 +/- 208 to 922 +/- 143 mL/min/1.73 m(2) (p = .03). The addition of dopamine returned renal blood flow to baseline values, The clearance of urine sodium increased significantly with the infusion of dopamine alone (p = .03). All subjects completed the four treatment periods, Adverse events, manifested mostly as palpitations and flushing, were rare and self-limiting, Conclusions: The addition of dopamine (3 mu g/kg/min) to presser doses of norepinephrine normalized renal blood flow in healthy volunteers, These hemodynamic changes were not reflected in urine output and glomerular filtration rate; hence, these monitoring parameters may be unreliable indicators of renal function in the setting of vasopressor therapy, In addition, systemic effects were observed with dopamine (3 mu g/kg/min), as indicated by a decrease in MAP.