A restrictive approach to blood transfusions is recommended by most current guidelines [1, 2]. Others suggest that in some patients a more liberal transfusion strategy may be beneficial [3]. However, the extensive discussions regarding the appropriate transfusion threshold have not adequately addressed the potential impact of iatrogenic hemodilution on the hemoglobin (Hb) level during dynamic clinical conditions that necessitate fluid administration [4, 5]. This editorial will attempt to describe the frequent occurrence of iatrogenic hemodilution and its potential impact on decisions to transfuse blood.
The effect of fluid administration on the hemoglobin concentration
Fluid administration may result in a beneficial increase in microvascular flow (and perfusion pressure) with a global increase in oxygen delivery (DO2) and cellular oxygenation in conditions of relative volume deficit (e.g., distributive shock in sepsis). Fluid administration may also cause a relative, but not absolute, reduction in hemoglobin (Hb) concentration (“dilutional anemia”). Such iatrogenic hemodilution may cause a paradoxical decrease in DO2 due to the resulting decrease in Hb concentration, as observed in patients who have received more colloids as part of perioperative goal-directed therapy (GDT) [6] and in critically ill patients who did [7] or did not [8] increase their cardiac output following fluid loading. In patients in septic shock who received large amounts of fluids as part of the original early GDT protocol, a decrease of 30% in hematocrit was uniformly observed 3 h into the resuscitation, possibly explaining the very high incidence of blood transfusions in this group of patients [9]. From a very rough analysis of these and other studies in surgical and critically ill patients, it seems that the administration of 500 ml of fluids may acutely decrease the Hb concentration by about 1 g/dl, or about 8% [8]. A similar degree of hemodilution was observed in healthy volunteers in whom sequential Hb measurements were used to assess the impact of crystalloid administration [10]. It should be noted that the microcirculation of healthy individuals may respond differently to macrocirculatory derangements than that of surgical patients, and may differ further in critically ill patients with systemic inflammation.
The potential impact of hemodilution on blood transfusions
It is well established that iatrogenic hemodilution may lead to increased blood transfusion due to dilutional coagulopathy and increased surgical bleeding. However, the resulting decrease in Hb levels may reach values below the acceptable transfusion threshold, and thus prompt clinicians to order blood transfusions in the absence of significant bleeding [4, 5]. This phenomenon should be considered as a potential unintended consequence of the administration of large amounts of fluids. https://pmc.ncbi.nlm.nih.gov/articles/PMC5702064