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

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 μg/kg per min) to maintain an adequate cerebral perfusion pressure (> 60 mm Hg). Interventions: Two successive 1-h study periods with NE alone then NE + Dop (2 μg/kg per min). During each period, creatinine (Cl_CREAT), sodium (Cl_Na), potassium (Cl_K), osmolar (Cl_OSM) and free water (Cl_{H2 O}), clearances were measured in all the patients. Effective renal blood flow (ERBF, paraaminohippurate 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 × (Cl_Na/Cl_CREAT) ] and Cl_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. Received: 13 July 1998 Accepted: 7 January 1999