Key Takeaways

Chronic severe anemia with a hemoglobin as low as 2 g/dL is compatible with life!

The reduction in hemoglobin results in decreased oxygen content of blood, which in turn decreases oxygen delivery to tissues. However, this effect is partially compensated by optimization of arterial oxygen saturation (from increased ventilation), increased stroke volume and cardiac output (secondary to reduced viscosity), and increased oxygen extraction in the tissues (from a rightward shift in the oxygen dissociation curve owing to increased levels of 2,3-DPG). In addition, there is a redistribution of blood flow to critical organs.

Chronic severe anemia is not associated with significant changes in the heart rate.

Treatment centers around blood transfusion, but efforts should be made to minimize oxygen consumption (for example, with sedation) and to replace missing nutrients (for example iron in iron deficiency).