![]() ![]() In previous experimental studies, Hb crit was found at values between 2 and 3 g/dL. In a standardised experimental protocol, it could be demonstrated that the persistence of DO 2crit without any treatment leads to death within less than 3 hours 33.īoth DO 2crit and Hb crit vary within and between individuals and are influenced by different physiological circumstances ( Table I). The haemoglobin value that corresponds to the inflection of VO 2 is called the “critical haemoglobin” (Hb crit) and reflects the physiological limit of dilutional anaemia. This indirectly indicates the onset of tissue hypoxia. The amount of oxgyen delivered to the tissues becomes insufficient to meet their oxygen demand and VO 2 starts to decline (oxygen supply dependency of VO 2, cf. The present article reviews: (i) physiological principles of oxygen transport, including compensatory mechanisms of acute anaemia and limits of anaemia tolerance, (ii) clinical evidence regarding the effects of RBC transfusion on mortality and morbidity, and (iii) the effects of such transfusions on oxygen transport and tissue oxygenation.Īt extreme degrees of dilutional anaemia, the DO 2 falls below a critical value (DO 2crit). Whether a RBC transfusion may be effective or not remains an individual decision based on a thorough analysis of the patient’s risk/benefit ratio and the identification of an appropriate transfusion trigger. ![]() Irrespective of the final outcome, the efficacy of blood transfusions may be higher in patients who immediately need allogeneic blood transfusions, while the benefit of a RBC transfusion may be more difficult to assess in stable patients. However, patients having required blood transfusions were usually more critically ill as documented by higher illness and organ failure scores at baseline. Patients requiring allogeneic blood are commonly reported to have worse outcomes than those who do not 10, 22, 53. The most relevant clinical studies report inconsistent effects of blood transfusion on morbidity and mortality as primary outcome parameters. Nevertheless, systematic evidence about the clinical effectiveness of blood transfusions is still difficult to obtain. those with profound anaemia or circulatory shock. To this end, RBC transfusions have undoubtedly been proven effective in many medical and surgical conditions, thereby particularly improving the survival of patients with critical impairment of tissue oxygenation, i.e. Generally, RBC transfusions are performed with the intention to increase arterial oxygen content and thus oxygen delivery to the tissues. The transfusion of allogeneic red blood cell (RBC) concentrates is common practice in critical care medicine: up to 45% of critically ill patients are transfused during their stay in an intensive care unit (ICU) 10, 53.
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