THE EFFECT OF NOREPINEPHRINE INFUSION ON OXYGEN DELIVERY AND CONSUMPTION IN THE CANINE MODEL

Norepinephrine (NE) is used clinically to increase oxygen delivery (DO ,) 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 o r consumption dynamics. Although the ultimate goal of an inotropic dru g is to increase DO, in excess of metabolic requirements (VO2), the ef fect of NE on the DO2/VO2 ratio has not been previously studied. In th e present investigation, healthy anesthetized dogs were infused with v arious doses of intravenous NE. These dosages were chosen to span the range used clinically. NE administration caused a significant primary increase in VO, which was dose dependent (P < 0.001). A similar dose-d ependent increase in DO, was observed (P < 0.001). However, the increa se in DO, minimally exceeded the increase in VO, at lower doses of NE and the relative increase in VO, exceeded the change in DO, at a dose of 0.04 mu g/kg/min. Minimal advantage to oxygen utilization physiolog y 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 administrati on could be most effectively monitored by the mixed venous oxygen satu ration (SVO2), rather than by intermittent assessment of BP, CO, or DO 2. Even though values for SVO, and CO do track closely for the dose of drug administered, SVO, is a more accurate summation of all component s of oxygen consumption and delivery and can be easily and continuousl y monitored. (C) 1994 Academic Press, Inc.