Cardiovascular function during induced hypotension by fenoldopam or sodium nitroprusside in anesthetized dogs

Fenoldopam, a selective dopamine1 receptor agonist, has been recommended for induced hypotension because it effectively lowers arterial blood pressure and improves renal perfusion. We examined cardiovascular functions during hypotension induced by fenoldopam or sodium nitroprusside. In eight halothane-anesthetized dogs, the left ventricle (LV) was instrumented with pressure and ultrasonic dimension transducers for the assessment of LV contractility using the analysis of the pressure-diameter relationship. Blood flow distribution was measured by radioactive microspheres. Doses of fenoldopam and nitroprusside were titrated to reduce mean arterial blood pressure to 60 mm Hg. After 40 min of hypotension, fenoldopam and nitroprusside caused similar increases in heart rate (17% +/- 4% vs 19% +/- 10%, respectively) and decreases in systemic vascular resistance (-24% +/- 5% vs -27% +/- 4%). Hypotension induced by fenoldopam was associated with higher LV end-diastolic pressure (4.4 +/- 0.6 vs 2.5 +/- 1.1 mm Hg) and end-systolic meridional wall stress (33.0 +/- 4.3 vs 17.8 +/- 2.1 g/cm2) when compared with nitroprusside. There were no significant changes in cardiac output and cardiac contractility as expressed by the slope (Ees) of the LV end-systolic pressure-diameter relationship, velocity of shortening of the diameter, and percentage of wall thickening of the LV. In contrast to nitroprusside, which decreased renal blood flow from 197 +/- 19 to 163 +/- 15 mL/min, renal blood flow increased during fenoldopam-induced hypotension from 187 +/- 20 to 239 +/- 18 mL/min. The increase in renal perfusion was similar in upper, middle, and lower regions of the kidney; however, it was more in the medulla compared with the cortex (37% +/- 17% vs 25% +/- 7%).(ABSTRACT TRUNCATED AT 250 WORDS)