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 (DO2crit) 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.
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