Lactic acidosis and oxygen debt in African children with severe anaemia

A syndrome of severe anaemia (Hb less than or equal to 5 g/dl), particularly severe malarial anaemia (SMA), remains a major cause of childhood mortality in sub-Saharan Africa. We hypothesized that the lactic acidosis which identifies those at the greatest risk of death often represents an oxygen debt incurred as a result of inadequate tissue perfusion. To examine this hypothesis, we measured oxygen consumption (VO2) using a portable metabolic monitor. Blood lactate and acid-base status were also determined. Pretransfusion data on 44 children (28 with mild symptoms, 7 with respiratory distress and 9 controls) demonstrated very close dependence of VO2 on body surface area (BSA, R-2 = 0.86, P < 0.001). After correcting for BSA, no significant differences were observed in mean VO2 values of the three clinical groups, indicating that a critical reduction in oxygen delivery is not the sole explanation for the development of a lactic acidosis and severe symptoms. Nine children (including five of the original 44) were monitored duping transfusion. In four of the five with SMA, severe symptoms and severe lactic acidosis, transfusion produced a marked, transient increase in VO2 (maximum 30-41 %), with a marked fall in blood lactate and clinical improvement. These data suggest that some children with SMA and respiratory distress accumulate an oxygen debt when a relatively high oxygen demand outstrips supply, this debt being repaid when supply is increased during transfusion. However, in the remaining one of these five children, an increase in VO2 (maximum 20%), was accompanied by a rise in blood lactate and clinical deterioration, suggesting that more pathophysiologically complex mechanisms, which may predominate in some children.