While complex physiological mechanisms exist to regulate and optimize tissue oxygenation under various conditions, clinical and experimental evidence indicates that anaemia, unchecked, is associated with organ injury and unfavourable outcomes. More data (especially from human studies) are needed to answer questions regarding the optimal approaches to the treatment of acute and chronic anaemia. Meantime, allogeneic blood transfusions remain the most common treatment, particularly in surgical/trauma patients and those with moderate-to-severe anaemia. Clinical studies emphasize the paradox that both anaemia and transfusion are associated with organ injury and increased morbidity and mortality across a wide span of disease states and surgical interventions. Further characterization of the mechanisms of injury is needed to appropriately balance these risks and to develop novel treatment strategies that will improve patient outcomes. Here, we present the current understanding of the physiological mechanisms of tissue oxygen delivery, utilization, adaptation, and survival in the face of anaemia and current evidence on the independent (and often, synergistic) deleterious impact of anaemia and transfusion on patient outcomes. The risks of anaemia and transfusion in the light of substantial variations in transfusion practices, increasing costs, shrinking pool of donated resources, and ambiguity about actual clinical benefits of banked allogeneic blood demand better management strategies targeted at improving patient outcomes.
Many strategies to improve outcome while reducing allogeneic blood transfusions are available. These strategies rely on approaches to optimize haematopoiesis, minimize blood loss, and use and manipulate physiological responses to anaemia while treating this condition with minimal or no use of allogeneic blood transfusion. The concept encompassing these interventions is collectively known as patient blood management.183–185 Emerging evidence supports the efficacy of these strategies in managing various patients, including those known to be exposed to a high risk of blood loss, anaemia, and transfusion.69 186–188 Using these strategies, it is possible to detect and treat anaemia in a timely manner and mitigate the risk of allogeneic blood Anaemia Other causes of anaemia: nutritional deficiencies, blood loss, increased destruction,etc. Allogeneic blood transfusion Chronic iIIness/ inflammation Unfavourable outcomes Fig 3 Causal pyramid depicting the theoretical relationship of anaemia and its accomplices in causing unfavourable outcomes. Positive causal links are denoted by solid arrows and indicate that the first node (or increase in its severity or dose in the case of transfusions) would cause the second node (or increase in its severity or dose in the case of transfusions). A negative causal link denoted by dashed arrow exists between transfusion and anaemia as the former is expected to reduce the severity of the latter (albeit temporarily), but the effectiveness of this measure in terms of improving oxygen delivery and consumption is debated. Unfavourable outcomes can include occurrence of new morbid events or exacerbation of pre-existing ones, which could lead to increased chronic illness/inflammation burden and further reinforce the loop. Dangers of anaemia and transfusion BJA i53 transfusions and their associated negative outcomes. Untreated anaemia and inappropriate transfusions are both deleterious to patients in addition to being significant burdens to the healthcare system. Therefore, clinicians should remain vigilant and apply evidence-based best clinical practices to save patients from the long list of adverse outcomes associated with allogeneic transfusion.
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