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Mechanical ventilation with positive end-expiratory pressure (PEEP) can impair renal hemodynamics. Fenoldopam, a dopamine receptor agonist, has been shown, in animal experiments, to improve renal perfusion. The purpose of the current study was to examine the effects of this agent on altered renal hemodynamics secondary to positive pressure ventilationTwelve patients requiring mechanical ventilation of their lungs and PEEP for the treatment of hypoxemia after multiple trauma or visceral surgery were studied. Hemodynamic variables, renal vascular resistance, urine flow, creatinine, inulin and PAH clearance, and excretion of sodium and potassium (NaE and KE) were measured before and after Introduction of a level of PEEP high enough to decrease urine flow rate by 25% or more, and after administration of intravenous fenoldopam.No hemodynamic effect resulted from 0.1 μg · kg−1, but 0.2 μg · Kg−1 · min−1 fenoldopam decreased both diastolic and mean arterial blood pressure from 66 ± 37 (mean ± SEM) to 57 ± 21 mmHg, and from 83 ± 3 to 74 ± 4 mmHg, respectively. Renal vascular resistance was reduced from 54 ± 12 to 19 ± 5 dynes · s · cm-5 at 0.2 μg · kg−1 · min−1. Fenoldopam produced a dose-related Increase in renal blood flow and PAH clearance. With 0.2 μg · kg−1 · min−1 fenoldopam, urine flow increased from 81 ± 25 to 116 ± 29 ml/h, NaE from 28 ± 7 to 85 ± 70 μM/min, and KE from 65 ± 12 to 109 ± 16 μM/min.The results of the current study indicate that intravenous fenoldopam at a dose of 0.2 μg · kg−1 · min−1 improves renal hemodynamics and increases Na and K excretion in patients requiring mechanical ventilation of their lungs and PEEP. These effects are probably caused by an increased kidney perfusion secondary to renal artery vasodilation.