Physiological determinants and the red blood cells transfusion decision-making process in non-bleeding critically ill patients: a comprehensive narrative review

Purpose There is a willingness to move towards a more personalised medicine; however, the red blood cells’ (RBC) transfusion decision-making process remains a one-size-fits-all practice in most non-bleeding critically ill patients. This narrative review describes the limitations of a transfusion decision-making process based only on haemoglobin (Hb) threshold and the potential physiological triggers of RBC transfusion with the clinical evidence investigating their implementation in routine. Results Hb does not reflect tissue oxygenation and anaemia tolerance, and applying the same Hb threshold throughout the ICU stay neither prevents unnecessary transfusion nor insufficient transfusion. Central venous oxygen saturation (ScvO2) and oxygen extraction ratio (O2ER) are accessible at the bedside and display significant changes after RBC transfusion when in abnormal ranges. Although they have been prospectively investigated in the transfusion decision process, there is a need for more evidence to definitely implement them in routine. The arterial–venous difference in oxygen (A–VO2diff) might be another useful bedside RBC transfusion trigger. Microcirculatory markers are also promising candidates for physiological determinants for RBC transfusion. Conclusions There is a need for additional determinants in the RBC transfusion decision process to offset the limitations of RBC transfusion based only on Hb level in non-bleeding critically ill patients. A multimodal strategy, including comorbidities, underlying diseases, clinical signs, ECG changes, biochemical markers, and microcirculatory assessment, may optimise transfusion timing and avoid unnecessary red blood cell administration. However, further research is warranted to determine the potential benefit of integrating tissue oxygenation and microcirculatory parameters in the transfusion decision-making process.