The effects of fenoldopam on renal blood flow and tubular function during aortic cross-clamping in anaesthetized dogs

Abstract

Postoperative renal impairment is a recognized complication of infrarenal aortic cross-clamping. Fenoldopam, a selective dopamine agonist, may increase renal blood flow and decrease tubular oxygen consumption. The objective of this study was to quantify the effects of fenoldopam (0.1 μg kg⁻¹ min⁻¹) on renal blood flow and renal tubular function in anaesthetized dogs that have undergone aortic cross clamping. Eight labrador dogs were selected to receive either saline or fenoldopam (0.1 μg kg⁻¹ min⁻¹) intravenously. Arterial pressure, heart rate, renal blood flow, urinary output, fractional excretion of sodium, creatinine clearance and lithium clearance were measured (a) prior to infusions of saline or fenoldopam (b) 1 h after commencing the infusion (c) during a 90 min period of infrarenal aortic cross-clamping with concurrent infusion of fenoldopam or saline and (d) for 1 h after simultaneous aortic declamping and discontinuation of the infusions. There was no haemodynamic instability upon commencing the infusion of fenoldopam (0.1 μg kg⁻¹ min⁻¹). Creatinine clearance (2.03±0.5–2.45±0.3 mL min⁻¹ kg⁻¹ (mean±SD)), urine output (0.23±0.16–0.35±0.23 mL min⁻¹ (mean±SD)), and fractional excretion of sodium (0.7±0.52–1.3±0.73% (mean±SD)) increased (P < 0.05), following commencement of the fenoldopam infusion. Fractional excretion of sodium (1.2±0.7% (mean±SD)) and urine output (0.36±0.21 mL min⁻¹ (mean±SD)) were maintained during the aortic cross-clamp period (P < 0.05). Renal blood flow increased when the fenoldopam infusion was commenced (145±43.3–161±39.2 mL min⁻¹ (mean±SD)) and remained greater than baseline during the aortic cross-clamping period (152±44 mL min⁻¹ (mean±SD)), although these increases did not reach statistical significance. The most striking abnormalities observed by electron microscopy were marked disruption of the microvillus brush border in proximal tubules, vacuolation and separation of epithelial cells on basolateral infolds. The changes were similar in the two groups. In conclusion fenoldopam (0.1 μg kg⁻¹ min⁻¹) may have renoprotective effects which persist during infrarenal aortic cross clamping.