Impact of Red Blood Cell Transfusion on Global and Regional Measures of Oxygenation

Abstract

Anemia is common in critically ill patients. While the goal of transfusion of red blood cells (RBCs) is to increase oxygen carrying capacity, there are contradictory results about whether RBC transfusion to treat moderate anemia (e.g. hemoglobin 7–10 g/dL) improves tissue oxygenation or changes outcomes. While increasing levels of anemia eventually lead to a level of critical oxygen delivery (DO2), increased cardiac output and oxygen extraction are homestatic mechanisms the body uses to prevent a state of dysoxia in the setting of diminished DO2 due to anemia. In order for cardiac output to increase in the face of anemia, normovolemia must be maintained. Transfusion of RBCs increases blood viscosity which may actually decrease cardiac output (barring a state of hypovolemia prior to transfusion). Studies have generally shown that transfusion of RBCs fails to increase oxygen uptake (VO2) unless VO2/DO2 dependency exists, e.g., severe anemia or strenuous exercise. Recently near-infrared spectroscopy (NIRS), which approximates the hemoglobin saturation of venous blood, has been used to investigate whether transfusion of RBCs increases NIRS measurements of tissue oxygenation in regional tissue beds (e.g., brain, peripheral skeletal muscle). These studies have generally shown increases in NIRS derived measurements of tissue oxygenation following transfusion. Studies evaluating the effect of transfusion on the microcirculation have shown that transfusion increases the functional capillary density. This article will review fundamental aspects of oxygen delivery and extraction, and the effects of RBC transfusion on tissue oxygenation as well as the effects of RBC transfusion on the microcirculation.

Transfusion Decision Making in Pediatric Critical Illness

“…Much of the uncertainty in RBC transfusion stems from the fact that it is not currently possible to quantify anemia risk and balance that against risk of donor RBCs. There are many technologies attempting to infer risk of anemia, but to date we lack biomarkers that fulfill Prentice criteria (9, 65–67). As such, there is a plurality of perspectives and clinical practice regarding RBC transfusion (64), (54).…”

Red Cell Transfusion Triggers and Postoperative Outcomes After Major Surgery

“…transfusion can also result in a diminished immune response and transfusion-related acute lung injury. 4,[8][9][10] Our group and others have also noted that transfusion can possibly be related to worse long-term oncological outcomes. 11,12 As such, there is an increasing interest in trying to minimize patient exposure to unnecessary transfusions.…”

Anemia and Oxygen Delivery

“…However, increasing the inspired concentration of oxygen can enhance DO 2 by increasing the amount of dissolved oxygen in the plasma. 54 Per Equation 3, in an animal breathing 100% oxygen with a [Hb] of 6 g/dL and PaO 2 of 450 mm Hg, dissolved oxygen can account for more than 20% of overall DO 2 . This effect was shown clearly in a human study of severe normovolemic anemia in which an increase in PaO 2 to 400 mm Hg was associated with hemodynamic improvements equivalent to 3 g/dL of circulating Hb.…”