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 < 0.001). A similar dose-dependent increase in DO2 was observed (P < 0.001). However, the increase in DO2 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 microgram/kg/min. Minimal advantage to oxygen utilization physiology at low doses of NE and a potential deleterious effect at a dose of 0.04 microgram/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.(ABSTRACT TRUNCATED AT 250 WORDS)