The Effect of Norepinephrine Infusion on Oxygen Delivery and Consumption in the Canine Model

Abstract

Norepinephrine (NE) is used clinically to increase oxygen delivery (DO2) by increasing cardiac output (CO). The rate of administration of NE is usually based on frequent measurements of blood pressure (BP) and infrequent measurements of CO with little regard for oxygen delivery or consumption dynamics. Although the ultimate goal of an inotropic drug is to increase DO2 in excess of metabolic requirements (VO2), the effect of NE on the DO2/VO2 ratio has not been previously studied. In the present investigation, healthy anesthetized dogs were infused with various doses of intravenous NE. These dosages were chosen to span the range used clinically. NE administration caused a significant primary increase in VO2 which was dose dependent (P 2 was observed (P 2 minimally exceeded the increase in VO2 at lower doses of NE and the relative increase in VO2 exceeded the change in DO2 at a dose of 0.04 [mu]g/kg/min. Minimal advantage to oxygen utilization physiology at low doses of NE and a potential deleterious effect at a dose of 0.04 [mu]g/kg/min were observed, therefore, despite associated increases in mean systemic blood pressure. The effectiveness of NE administration could be most effectively monitored by the mixed venous oxygen saturation (SVO2), rather than by intermittent assessment of BP, CO, or DO2. Even though values for SVO2 and CO do track closely for the dose of drug administered, SVO2 is a more accurate summation of all components of oxygen consumption and delivery and can be easily and continuously monitored.