(Table 16-4: Equations for Tissue Oxygenation)
- The clinical justification for RBC transfusion assumes that increasing the hemoglobin will improve oxygen-carrying capacity and therefore avoid tissue hypoxia. However, given the ability of the body to compensate for anemia, it is unclear whether increasing hemoglobin in a stable anemic patient actually improves tissue oxygenation.
- Compensatory mechanisms for anemia include (i) increased cardiac output, (ii) altered microcirculatory blood flow, and (iii) improved tissue oxygen extraction from hemoglobin.
- These physiologic changes in conjunction with the detrimental impact of RBC storage limit the therapeutic effects of transfusion (see Table 16-4: Equations for Tissue Oxygenation).
- There continues to be controversy about RBC transfusion given the lack of evidence to support a universal transfusion threshold.
- Despite the wealth of literature documenting the potential harm, transfusion continues to be the mainstay of treatment for acute and chronic anemia (Table 16-5: Clinical Indications of Tissue Hypoxia).
- In stable patients without ongoing bleeding, the hemoglobin should rise 1g/dL with an approximate 3% rise in hematocrit for each unit of packed RBCs given.
- In the case of uncompensated blood loss, hemoglobin levels may be normal or misleadingly high. In these situations, the clinician must estimate blood loss from the patient's hemodynamic picture and assessment of the operative field to guide their transfusion management.