Fatigue during acute isovolemic anemia in healthy, resting humans

BACKGROUND: Transfusion guidelines recommend that clinicians assess patient s 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 reducti on of Hb concentration to 5 g per dL would result in fatigue, tachycardia, or hypotension in resting, young, healthy, isovolemic humans, and whether c hanges were reversible with RBC transfusion. STUDY DESIGN AND METHODS: Conscious, resting, healthy adults less than 35 y ears old (n = 8) underwent acute isovolemic hemodilution to Hb of 5 g per d L and self-scored their energy level at various Hb concentrations. Heart ra te and blood pressure were also measured. For controls, measurements of eac h subject were made during a comparable period of rest without hemodilution . RESULTS: During acute isovolemic hemodilution, energy levels decreased prog ressively 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. CONCLUSION: In resting, young, healthy humans, acute isovolemic anemia to H b levels of 7, 6, and 5 g per dL results in decreased self-scored energy le vels and in an increase in heart rate but not in hypotension. Changes in en ergy and heart rate are reversible with the transfusion of autologous RBCs.