Final answer:
In the seriously ill or injured child, the arterial lactate level can increase as a result of tissue hypoxia and anaerobic metabolism, indicating that tissues are not receiving enough oxygen.
Step-by-step explanation:
In the seriously ill or injured child, the arterial lactate level can increase as a result of tissue hypoxia and anaerobic metabolism. When there is insufficient oxygen, tissues rely on anaerobic metabolism for energy, which leads to the production of lactate as a by-product.
This lactate can accumulate, especially in conditions where the circulatory or respiratory function is compromised, indicating that the tissue is not receiving enough oxygen. Over time, an increase in circulating erythrocytes can occur as a compensatory mechanism in response to chronic hypoxia, through the release of erythropoietin (EPO) that stimulates red blood cell production.
However, during an acute illness or injury, there may not be sufficient time for this compensatory mechanism to take effect, and an increase in lactate levels can be one of the first indicators of tissue hypoxia before changes in the number of erythrocytes could occur.