Pathological supply dependence of O2 uptake during bacteremia in dogs

Abstract

When systemic delivery of O2 [QO2 = cardiac output X arterial O2 content (CaO2)] is reduced, the systemic O2 extraction ratio [(CaO2-concentration of O2 in venous blood/CaO2] increases until a critical limit is reached below which O2 uptake (VO2) becomes limited by delivery. Many patients with adult respiratory distress syndrome exhibit supply dependence of VO2 even at high levels of QO2, which suggests that a peripheral O2 extraction defect may be present. Since many of these patients also suffer from serious bacterial infection, we tested the hypothesis that bacteremia might produce a similar defect in the ability of tissues to maintain VO2 independent of QO2, as QO2 reduced. The critical O2 delivery (QO2crit) and critical extraction ratio (ERcrit) were compared in a control group of dogs and a group receiving a continuous infusion of Pseudomonas aeruginosa (5 x 10(7) organisms/min). Dogs were anesthetized, paralyzed, and ventilated with room air. Systemic QO2 was reduced in stages by hemorrhage as hematocrit was maintained. At each stage, systemic VO2 and QO2 were measured, and the critical point was determined from a plot of VO2 vs. QO2. The mean QO2crit and ERcrit of the bacteremic group (11.4 +/- 2.2 ml.min-1.kg-1 and 0.51 +/- 0.09) were significantly different from control (7.4 +/- 1.2 and 0.71 +/- 0.10) (P less than 0.05). These results suggest that bacterial infection can reduce the ability of peripheral tissues to extract O2 from a limited supply, causing VO2 to become limited by O2 delivery at a stage when a smaller fraction of the delivered O2 has been extracted.(ABSTRACT TRUNCATED AT 250 WORDS)