The effect of norepinephrine infusion on oxygen delivery and consumption in the canine model.

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)

Prophylactic administration of tranexamic acid preserves platelet numbers during extracorporeal circulation in rabbits.

Neonatal extracorporeal life support is associated with platelet consumption and hemostatic disorders. This study in rabbits was undertaken to evaluate the effect of heparin coating and of the plasminogen and plasmin inhibitor, tranexamic acid on platelet consumption during extracorporeal circulation. Fibrinogen consumption was prevented by heparin coating, but platelet consumption was only prevented after the prophylactic administration of tranexamic acid. The authors concluded that inhibition of the fibrinolytic system had a specific effect on preserving platelet numbers, rather than improving the thromboresistance of the artificial surface. The main advantage of a heparin coating is the anticoagulant activity of the surface. Thus systemic heparinization can be reduced or omitted.