Low oxygen delivery produced by anemia, hypoxia, and low cardiac output

In pentobarbital-anesthetized dogs, oxygen delivery (DO₂) was measured by thermodilution cardiac output and cooximeter determined oxygen content, while oxygen consumption (VO₂) was measured independently by spirometry. Oxygen delivery was decreased by isovolemic dilutional anemia, breathing hypoxic gas mixtures, or cardiac tamponade to reduce cardiac output. Baseline VO₂ (cc/kg/min) for the three groups was 5.9 ± 0.7 (anemia), 5.4 ± 0.4 (hypoxia), and 5.6 ± 0.1 (low C.O.) (NS). A critical level of oxygen delivery (DO_2crit) was found at 9-10 cc/kg/min (anemia), 10-11 cc/kg/min (hypoxia), and 9-10 cc/kg/min (low C.O.) (NS.). Below this level, VO₂ fell (became supply dependent) and lactic acidosis occurred, regardless of the mechanism of impaired oxygen delivery.