NO supplementation for transfusion medicine and cardiovascular applications

A model of anemic tissue perfusion after blood transfusion shows critical role of endothelial response to shear stress stimuli

Although some of the cardiovascular responses to changes in hematocrit (Hct) are not fully quantified experimentally, available information is sufficient to build a mathematical model of the consequences of treating anemia by introducing RBCs into the circulation via blood transfusion. We present such a model, which describes how the treatment of normovolemic anemia with blood transfusion impacts oxygen (O₂) delivery (DO₂, the product of blood O₂ content and arterial blood flow) by the microcirculation. Our analysis accounts for the differential response of the endothelium to the wall shear stress (WSS) stimulus, changes in nitric oxide (NO) production due to modification of blood viscosity caused by alterations of both hematocrit (Hct) and cell free layer thickness, as well as for their combined effects on microvascular blood flow and DO₂. Our model shows that transfusions of 1- and 2-unit of blood have a minimal effect on DO₂ if the microcirculation is unresponsive to the WSS stimulus for NO production that causes vasodilatation increasing blood flow and DO₂. Conversely, in a fully WSS responsive organism, blood transfusion significantly enhances blood flow and DO₂, because increased viscosity stimulates endothelial NO production causing vasodilatation. This finding suggests that evaluation of a patients' pretransfusion endothelial WSS responsiveness should be beneficial in determining the optimal transfusion requirements for treating patients with anemia.NEW & NOTEWORTHY Transfusion of 1 or 2 units of blood accounts for about 3/4 of the world blood consumption of 119 million units per year, whereas a current world demand deficit is on the order of 100 million units. Therefore, factors supporting the practice of transfusing 1 unit instead of 2 are of interest, given their potential to expand the number of interventions without increasing blood availability. Our mathematical model provides a physiological support for this practice.

Impact of anemia on outcomes in on-pump coronary artery bypass surgery patients

Aim    To study the contribution of preoperative anemia to the prognosis of adverse clinical events (mortality, complications, transfusion) in patients with ischemic heart disease (IHD) after myocardial revascularization in the conditions of artificial circulation.Material and methods    This retrospective cohort study included 1 133 patients with IHD who had undergone isolated myocardial revascularization in the conditions of artificial circulation in 2019. The primary endpoints were mortality and a composite endpoint that included, in addition to mortality, cases of acute coronary syndrome, heart, respiratory and renal failure, neurological deficit, and infectious complications. The secondary endpoints were duration of artificial ventilation of more than 12 h, duration of stay in the resuscitation and intensive care unit (RICU) of more than one day, and duration of postoperative inpatient treatment of more than 7 days. Results    Preoperative anemia was found in 196 (17.3 %) patients. The anemia was not associated with mortality but increased the risk of the composite endpoint, prolonged artificial ventilation, stay in RICU for more than one day, and red blood cell transfusion. Despite the absence of a relationship between red blood cell transfusion and mortality, the use of transfusion was associated with increased risks of the composite endpoint and prolonged stay in the RICU and hospital.Conclusion    Preoperative anemia is a risk factor for adverse outcomes of myocardial revascularization in the conditions of artificial circulation. Timely treatment of preoperative anemia may improve outcomes of the treatment.

Old, older, the oldest: red blood cell storage and the potential harm of using older red blood cell concentrates

PURPOSE OF REVIEW

Over the last decades, clinical studies have suggested that transfusion of red blood cells (RBCs) might negatively impact patient outcomes. Even though large randomized clinical trials did not show differences in mortality when transfusing fresh versus standard-issue RBC units, data imply that RBCs at the very end of storage could elicit negative effects.

RECENT FINDINGS

Certain alterations of RBCs during cold storage -- such as an increase of potassium and lactate in the storage solution -- have been discovered a century ago. In recent years, proteomic and metabolomic studies have shed more light into pathophysiological changes of RBCs during storage and have helped to specify the definition of old blood. These advancements are now utilized to increase the quality of stored RBCs and devise therapeutic strategies (e.g. nitric oxide, haptoglobin, or reduction of the iron load) when transfusing old blood.

SUMMARY

Further research to improve the quality of RBC units and to study populations potentially at risk is warranted. Until the question whether transfusion of old blood is detrimental for specific patient populations has been answered, a deliberate use of RBC transfusion should be implemented.

Red blood cell storage time and transfusion: current practice, concerns and future perspectives

Red blood cells (RBCs) units are the most requested transfusion product worldwide. Indications for transfusion include symptomatic anaemia, acute sickle cell crisis, and acute blood loss of more than 30% of the blood volume, with the aim of restoring tissue oxygen delivery. However, stored RBCs from donors are not a qualitative equal product, and, in many ways, this is a matter of concern in the transfusion practice. Besides donor-to-donor variation, the storage time influences the RBC unit at the qualitative level, as RBCs age in the storage bag and are exposed to the so-called storage lesion. Several studies have shown that the storage lesion leads to post-transfusion enhanced clearance, plasma transferrin saturation, nitric oxide scavenging and/or immunomodulation with potential unwanted transfusion-related clinical outcomes, such as acute lung injury or higher mortality rate. While, to date, several studies have claimed the risk or deleterious effects of "old" vs "young" RBC transfusion regimes, it is still a matter of debate, and consideration should be taken of the clinical context. Transfusion-dependent patients may benefit from transfusion with "young" RBC units, as it assures longer inter-transfusion periods, while transfusion with "old" RBC units is not itself harmful. Unbiased Omics approaches are being applied to the characterisation of RBC through storage, to better understand the (patho)physiological role of microparticles (MPs) that are found naturally, and also on stored RBC units. Perhaps RBC storage time is not an accurate surrogate for RBC quality and there is a need to establish which parameters do indeed reflect optimal efficacy and safety. A better Omics characterisation of components of "young" and "old" RBC units, including MPs, donor and recipient, might lead to the development of new therapies, including the use of engineered RBCs or MPs as cell-based drug delivering tools, or cost-effective personalised transfusion strategies.