Some patients with severe chronic anemia appear to function well at incredibly low hemoglobin levels, especially if the anemia has developed over a long period of time. However, these patients may develop severe heart failure if they receive a blood transfusion.
In severe anemia the heart may develop a hyperkinetic state that is capable of meeting the patient's oxygen delivery needs. However, any increase in blood volume can suddenly precipitate severe heart failure that can take days to resolve.
In developing countries severe vitamin B12 deficiency may present in this manner.
Additional factors affecting risk:
(1) malnutrition, especially if there is risk for the refeeeding syndrome
(2) cardiomyopathy
(3) renal impairment with reduced ability to diurese a fluid load
(4) hypothyroidism and/or adrenal insufficiency
(5) pulmonary disease
When faced with a patient with severe chronic anemia, it is important for the physician to avoid immediate blood transfusion as a knee jerk response. It is important to identify the causes for the anemia first and then to develop a plan to slowly increase the patient's red cell mass.
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