Renal effects of low-dose dopamine during vasopressor therapy for posttraumatic intracranial hypertension.

ABSTRACT

OBJECTIVE: To investigate the effects of low-dose dopamine (Dop) on renal hemodynamics and function in patients with brain trauma receiving norepinephrine (NE). DESIGN: Prospective clinical study. SETTING: Surgical intensive care unit of a university hospital. PATIENTS 20 stable, non-septic, mechanically ventilated, sedated patients with brain trauma and normal renal function treated with intravenous NE (0.11-0.65 microg/kg per min) to maintain an adequate cerebral perfusion pressure (> 60 mmHg). INTERVENTIONS: Two successive 1-h study periods with NE alone then NE + Dop (2 microg/kg per min). During each period, creatinine (Cl(CREAT)), sodium (Cl(Na)), potassium (Cl(K)), osmolar (Cl(OSM)) and free water (Cl(H2O)), clearances were measured in all the patients. Effective renal blood flow (ERBF, para-aminohippurate clearance) and glomerular filtration rate (GFR, inulin clearance) were measured in 7 of the 20 patients. RESULTS: Dop during NE infusion induced increases in urine flow and natriuresis which were not correlated with possible changes in arterial pressure. Cl(CREAT), GFR and their difference remained unchanged, whereas ERBF tended to increase. Fractional sodium excretion [100 x (Cl(Na)/Cl(CREAT)] and C1(K) increased during Dop infusion. CONCLUSION: The mechanism of Dop-induced natriuresis during NE infusion in brain trauma patients seems mainly related to a direct tubular effect of the drug.