Cardiovascular Effects of Sustained Norepinephrine Infusions. I. Hemodynamics

Abstract

Norepinephrine (NE) in graded doses of 1, 2, and 4 µg/kg/min was infused for four hours into 14 dogs; 5 dogs served as controls. The systemic pressure and flow, blood volume, hematocrit, arterial blood pH, and oxygen saturation were measured at selected intervals throughout the infusion period. Cardiovascular performance was augmented during the first 15 minutes of the NE infusions, but this effect was not sustained. Thereafter, there was a dose-related decline in cardiac output, systemic pressure and left ventricular work, and an increase in the calculated peripheral vascular resistance. At the highest NE dose rate employed, significant left ventricular failure developed by the second hour of NE administration. The hematocrit increased during the first 15 minutes of NE infusion and remained elevated throughout the infusion period. Sustained hypovolemia was not found during the prolonged NE administration, and severe acidosis (pH < 7.20) was inconstant. The processes which lead to cardiovascular dysfunction during prolonged NE infusion are discussed.