Fatigue during acute isovolemic anemiain healthy, resting humans

Transfusion guidelines recommend that clinicians assess patients for signs and symptoms of anemia before the transfusion of RBCs. However, studies of signs and symptoms associated with acute isovolemic anemia are limited. The objective of this study was to determine whether acute reduction of Hb concentration to 5 g per dL would result in fatigue, tachycardia, or hypotension in resting, young, healthy, isovolemic humans, and whether changes were reversible with RBC transfusion.

Conscious, resting, healthy adults less than 35 years old (n = 8) underwent acute isovolemic hemodilution to Hb of 5 g per dL and self-scored their energy level at various Hb concentrations. Heart rate and blood pressure were also measured. For controls, measurements of each subject were made during a comparable period of rest without hemodilution.

During acute isovolemic hemodilution, energy levels decreased progressively and were lower at Hb of 7, 6, and 5 g per dL than at baseline (p<0.01) or in control sessions (p<0.05). The energy level was lower at Hb 7 g per dL than at 14 ( p = 0.005), lower at Hb 6 g per dL than at 7 (p = 0.01), and lower at Hb 5 g per dL than at 6 (p =0.01). Energy levels rose and were not different from baseline or control levels after transfusion of all autologous RBCs. Similarly, median heart rate increased with hemodilution to Hb of 7, 6, and 5 g per dL and decreased with transfusion of autologous RBCs. Supine blood pressure did not decrease with isovolemic hemodilution.

In resting, young, healthy humans, acute isovolemic anemia to Hb levels of 7, 6, and 5 g per dL results in decreased self-scored energy levels and in an increase in heart rate but not in hypotension. Changes in energy and heart rate are reversible with the transfusion of autologous RBCs.