Oxygen consumption-oxygen delivery relationship in children.

We examined the relationship between oxygen consumption (VO2) and oxygen delivery (DO2) over a range of metabolic demand in two groups of children. We studied 15 children after cardiac surgery (plasma lactate levels < 2.2 mmol/L, VO2 < 6 ml/min per kilogram, oxygen extraction ratio < 25%); 8 were given transfusions with erythrocytes, 10 to 15 ml/kg, and 7 received adrenaline infusions (0.05 to 0.3 micrograms/kg per minute). Blood transfusions significantly increased DO2 (20.5 +/- 6.4 to 26.2 +/- 7.1 ml/min per kilogram; p < 0.05) but did not alter VO2. Adrenaline increased DO2 (19.9 +/- 5.0 to 25.9 +/- 6.1 ml/min per kilogram; p < 0.05) and VO2 (4.3 +/- 0.8 to 5.5 +/- 1.2 ml/min per kilogram; p < 0.05), but the oxygen excretion ratio and the mixed venous oxygen saturation were unchanged. We also measured VO2 and Doppler-derived DO2 in 25 normal children during exercise. The relationship during exercise is given by the following equation: VO2 index (in milliliters per minute per kilogram) = 0.88 x DO2 index - 6.95. Adrenaline infusions, but not blood transfusions, increased VO2 and DO2 together. This effect may be due to increased demand, analogous to exercise, and probably does not represent improved perfusion. We also found significant measurement error in DO2 and spontaneous variation in VO2. We believe that the concept of supply-dependent VO2 is based on a number of methodologic and measurement errors. It should not be used to justify potentially dangerous therapies in sick children.