Microvascular perfusion upon exchange transfusion with stored red blood cells in normovolemic anemic conditions

A computational study of red blood cell deformability effect on hemodynamic alteration in capillary vessel networks

Capillary blood vessels, the smallest vessels in the body, form an intricate network with constantly bifurcating, merging and winding vessels. Red blood cells (RBCs) must navigate through such complex microvascular networks in order to maintain tissue perfusion and oxygenation. Normal, healthy RBCs are extremely deformable and able to easily flow through narrow vessels. However, RBC deformability is reduced in many pathological conditions and during blood storage. The influence of reduced cell deformability on microvascular hemodynamics is not well established. Here we use a high-fidelity, 3D computational model of blood flow that retains exact geometric details of physiologically realistic microvascular networks, and deformation of every one of nearly a thousand RBCs flowing through the networks. We predict that reduced RBC deformability alters RBC trafficking with significant and heterogeneous changes in hematocrit. We quantify such changes along with RBC partitioning and lingering at vascular bifurcations, perfusion and vascular resistance, and wall shear stress. We elucidate the cellular-scale mechanisms that cause such changes. We show that such changes arise primarily due to the altered RBC dynamics at vascular bifurcations, as well as cross-stream migration. Less deformable cells tend to linger less at majority of bifurcations increasing the fraction of RBCs entering the higher flow branches. Changes in vascular resistance also seen to be heterogeneous and correlate with hematocrit changes. Furthermore, alteration in RBC dynamics is shown to cause localized changes in wall shear stress within vessels and near vascular bifurcations. Such heterogeneous and focal changes in hemodynamics may be the cause of morphological abnormalities in capillary vessel networks as observed in several diseases.

The Acute Effect of Packed Red Blood Cell Transfusion in Mechanically Ventilated Children after the Norwood Operation

Packed red blood cell (PRBC) transfusions are commonly administered in pediatric patients following the Norwood operation. This study was conducted to determine the effect of PRBC transfusions on hemodynamic parameters in pediatric patients with single-ventricle physiology and parallel circulation. A single-center, retrospective chart review was conducted. Pediatric patients admitted to the cardiac intensive care unit after Norwood operation between 2017 and 2018 were identified. Hemodynamic parameters were collected within a four-hour period before and after a PRBC transfusion. Univariate analyses using paired t tests were conducted to compare blood gas values before and after PRBC transfusion. Next, multivariate regression analyses were conducted to model the impact of transfusion volume, change in hemoglobin levels, and change in FiO2 on the change in PaO2 and PaCO2. These analyses included data from 33 eligible patients who received a PRBC transfusion following a Norwood operation. The hemoglobin levels (p < 0.01) and the PaO2/FiO2 ratio (p = 0.04) were significantly increased, while arterial lactate levels (p = 0.03) were significantly decreased following the transfusion. Transfusion for a pre-transfusion hemoglobin of 12.4 g/dL appears to provide greatest reduction in lactate, used as a surrogate marker for systemic oxygen delivery. No significant changes were found in arterial pH, PaO2, and PaCO2. PRBC transfusions following the Norwood operation may be a useful intervention to increase systemic oxygen delivery, improving PaO2/FiO2 ratio and improving serum lactate. The benefits of PRBC transfusions must be weighed against previously identified risks on a patient-specific basis. Further studies are warranted to further delineate the effects of such transfusions in this population.

Prognostic Association Between Perioperative Red Blood Cell Transfusion and Postoperative Cardiac Surgery Outcomes

Objective: To investigate the correlation between red blood cell transfusion and clinical outcome in patients after cardiac surgery.

Methods: Demographic, clinical characteristics, treatment with/without transfusion, and outcomes of patients after cardiac surgery from the Medical Information Mart for Intensive Care—III database were collected. Patients were divided into two groups according to perioperative transfusion. A multivariable logistic regression analysis was utilized to adjust for the effect of red blood cell transfusion on outcomes for baseline and covariates and to determine its association with outcomes.

Results: In total, 6,752 patients who underwent cardiac surgery were enrolled for the analysis. Among them, 2,760 (40.9%) patients received a perioperative transfusion. Compared with patients without red blood cell transfusion, transfused patients demonstrated worse outcomes in inhospital mortality, 1-year mortality, and all-cause mortality. Adjusting odds ratios (ORs) for the significant characteristic, patients with perioperative transfusion remained significantly associated with an increased risk of inhospital mortality [OR = 2.8, 95% confidence interval (CI) 1.5–5.1, P = 0.001], 1-year mortality (OR = 2.0, 95% CI 1.4–2.7, P < 0.001), and long-term mortality (OR = 2.2, 95% CI 1.8–2.8, P < 0.001).

Conclusion: Perioperative red blood cell transfusion is associated with a worse prognosis of cardiac surgery patients. Optimal perioperative management and restricted transfusion strategy might be considered in selected patients.

Perioperative Care of Patients at High Risk for Stroke During or After Non-cardiac, Non-neurological Surgery: 2020 Guidelines From the Society for Neuroscience in Anesthesiology and Critical Care

Perioperative stroke is associated with considerable morbidity and mortality. Stroke recognition and diagnosis are challenging perioperatively, and surgical patients receive therapeutic interventions less frequently compared with stroke patients in the outpatient setting. These updated guidelines from the Society for Neuroscience in Anesthesiology and Critical Care provide evidence-based recommendations regarding perioperative care of patients at high risk for stroke. Recommended areas for future investigation are also proposed.

Microfluidic capillary networks are more sensitive than ektacytometry to the decline of red blood cell deformability induced by storage

Ektacytometry has been the primary method for evaluating deformability of red blood cells (RBCs) in both research and clinical settings. This study was designed to test the hypothesis that the flow of RBCs through a network of microfluidic capillaries could provide a more sensitive assessment of the progressive impairment of RBC deformability during hypothermic storage than ektacytometry. RBC units (n = 9) were split in half, with one half stored under standard (normoxic) conditions and the other half stored hypoxically, for up to 6 weeks. RBC deformability was measured weekly using two microfluidic devices, an artificial microvascular network (AMVN) and a multiplexed microcapillary network (MMCN), and two commercially available ektacytometers (RheoScan-D and LORRCA). By week 6, the elongation indexes measured with RheoScan-D and LORRCA decreased by 5.8–7.1% (5.4–6.9% for hypoxic storage). Over the same storage duration, the AMVN perfusion rate declined by 27.5% (24.5% for hypoxic) and the MMCN perfusion rate declined by 49.0% (42.4% for hypoxic). Unlike ektacytometry, both AMVN and MMCN measurements showed statistically significant differences between the two conditions after 1 week of storage. RBC morphology deteriorated continuously with the fraction of irreversibly-damaged (spherical) cells increasing significantly faster for normoxic than for hypoxic storage. Consequently, the number of MMCN capillary plugging events and the time MMCN capillaries spent plugged was consistently lower for hypoxic than for normoxic storage. These data suggest that capillary networks are significantly more sensitive to both the overall storage-induced decline of RBC deformability, and to the differences between the two storage conditions, than ektacytometry.

Resuscitation After Hemorrhagic Shock in the Microcirculation: Targeting Optimal Oxygen Delivery in the Design of Artificial Blood Substitutes

Microcirculatory preservation is essential for patient recovery from hemorrhagic shock. In hemorrhagic shock, microcirculatory flow and pressure are greatly reduced, creating an oxygen debt that may eventually become irreversible. During shock, tissues become hypoxic, cellular respiration turns to anaerobic metabolism, and the microcirculation rapidly begins to fail. This condition requires immediate fluid resuscitation to promote tissue reperfusion. The choice of fluid for resuscitation is whole blood; however, this may not be readily available and, on a larger scale, may be globally insufficient. Thus, extensive research on viable alternatives to blood has been undertaken in an effort to develop a clinically deployable blood substitute. This has not, as of yet, achieved fruition, in part due to an incomplete understanding of the complexities of the function of blood in the microcirculation. Hemodynamic resuscitation is acknowledged to be contingent on a number of factors other than volume expansion. The circulation of whole blood is carefully regulated to optimize oxygen delivery to the tissues via shear stress modulation through blood viscosity, inherent oxygen-carrying capacity, cell-free layer variation, and myogenic response, among other variables. Although plasma expanders can address a number of these issues, hemoglobin-based oxygen carriers (HBOCs) introduce a method of replenishing the intrinsic oxygen-carrying capacity of blood. There continue to be a number of issues related to HBOCs, but recent advances in the next-generation HBOCs show promise in the preservation of microcirculatory function and limiting toxicities. The development of HBOCs is now focused on viscosity and the degree of microvascular shear stress achieved in order to optimize vasoactive and oxygen delivery responses by leveraging the restoration and maintenance of physiological responses to blood flow in the microcirculation. Blood substitutes with higher viscous properties tend to improve oxygen delivery compared to those with lower viscosities. This review details current concepts in blood substitutes, particularly as they relate to trauma/hemorrhagic shock, with a specific focus on their complex interactions in the microcirculation.

Role of Nitric Oxide Carried by Hemoglobin in Cardiovascular Physiology: Developments on a Three-Gas Respiratory Cycle

A continuous supply of oxygen is essential for the survival of multicellular organisms. The understanding of how this supply is regulated in the microvasculature has evolved from viewing erythrocytes (red blood cells [RBCs]) as passive carriers of oxygen to recognizing the complex interplay between Hb (hemoglobin) and oxygen, carbon dioxide, and nitric oxide-the three-gas respiratory cycle-that insures adequate oxygen and nutrient delivery to meet local metabolic demand. In this context, it is blood flow and not blood oxygen content that is the main driver of tissue oxygenation by RBCs. Herein, we review the lines of experimentation that led to this understanding of RBC function; from the foundational understanding of allosteric regulation of oxygen binding in Hb in the stereochemical model of Perutz, to blood flow autoregulation (hypoxic vasodilation governing oxygen delivery) observed by Guyton, to current understanding that centers on S-nitrosylation of Hb (ie, S-nitrosohemoglobin; SNO-Hb) as a purveyor of oxygen-dependent vasodilatory activity. Notably, hypoxic vasodilation is recapitulated by native S-nitrosothiol (SNO)-replete RBCs and by SNO-Hb itself, whereby SNO is released from Hb and RBCs during deoxygenation, in proportion to the degree of Hb deoxygenation, to regulate vessels directly. In addition, we discuss how dysregulation of this system through genetic mutation in Hb or through disease is a common factor in oxygenation pathologies resulting from microcirculatory impairment, including sickle cell disease, ischemic heart disease, and heart failure. We then conclude by identifying potential therapeutic interventions to correct deficits in RBC-mediated vasodilation to improve oxygen delivery-steps toward effective microvasculature-targeted therapies. To the extent that diseases of the heart, lungs, and blood are associated with impaired tissue oxygenation, the development of new therapies based on the three-gas respiratory system have the potential to improve the well-being of millions of patients.

Effects of blood storage age on immune, coagulation, and nitric oxide parameters in transfused patients undergoing cardiac surgery

BACKGROUND

Retrospective studies suggested that storage age of RBCs is associated with inflammation and thromboembolism. The Red Cell Storage Duration Study (RECESS) trial randomized subjects undergoing complex cardiac surgery to receive RBCs stored for shorter versus longer periods, and no difference was seen in the primary outcome of change in multiple organ dysfunction score.

STUDY DESIGN AND METHODS

In the current study, 90 subjects from the RECESS trial were studied intensively using a range of hemostasis, immunologic, and nitric oxide parameters. Samples were collected before transfusion and on Days 2, 6, 28, and 180 after transfusion.

RESULTS

Of 71 parameters tested, only 4 showed a significant difference after transfusion between study arms: CD8+ T-cell interferon-γ secretion and the concentration of extracellular vesicles bearing the B-cell marker CD19 were higher, and plasma endothelial growth factor levels were lower in recipients of fresh versus aged RBCs. Plasma interleukin-6 was higher at Day 2 and lower at Days 6 and 28 in recipients of fresh versus aged RBCs. Multiple parameters showed significant modulation after surgery and transfusion. Most analytes that changed after surgery did not differ based on transfusion status. Several extracellular vesicle markers, including two associated with platelets (CD41a and CD62P), decreased in transfused patients more than in those who underwent surgery without transfusion.

CONCLUSIONS

Transfusion of fresh versus aged RBCs does not result in substantial changes in hemostasis, immune, or nitric oxide parameters. It is possible that transfusion modulates the level of platelet-derived extracellular vesicles, which will require study of patients randomly assigned to receipt of transfusion to define.

Anemia and acute coronary syndrome: current perspectives

Reference hemoglobin (Hb) values for the definition of anemia are still largely based on the 1968 WHO Scientific Group report, which established a cutoff value of <13 g/dL for adult men and <12 g/dL for adult nonpregnant women. Subsequent studies identified different normal values according to race and age. Estimated prevalence of anemia on admission in the setting of an acute coronary syndrome (ACS) is between 10% and 43% of the patients depending upon the specific population under investigation. Furthermore, up to 57% of ACS patients may develop hospital-acquired anemia (HAA). Both anemia on admission and HAA are associated with worse short- and long-term mortality, even if different mechanisms contribute to their prognostic impact. Baseline anemia can usually be traced back to preexisting disease that should be specifically investigated and corrected whenever possible. HAA is associated with clinical characteristics, medical therapy and interventional procedures, all eliciting cardiovascular adaptive response that can potentially worsen myocardial ischemia. The intrinsic fragility of anemic patients may limit aggressive medical and interventional therapy due to an increased risk of bleeding, and could independently contribute to worse outcome. However, primary angioplasty for ST elevation ACS should not be delayed because of preexisting (and often not diagnosed) anemia; delaying revascularization to allow fast-track anemia diagnosis is usually feasible and justified in non-ST-elevation ACS. Besides identification and treatment of the underlying causes of anemia, the only readily available means to reverse anemia is red blood cell transfusion. The adequate transfusion threshold is still being debated, although solid evidence suggests reserving red blood cell transfusions for patients with Hb level <8 g/dL and considering it in selected cases with Hb levels of between 8 and 10 g/dL. No evidence supports the use of iron supplements and erythropoiesis-stimulating agents in the setting of ACS.

Blood transfusion strategies for acute upper gastrointestinal bleeding: are we back where we started?

Blood transfusion practices for acute upper gastrointestinal hemorrhage have changed over time. Restrictive strategies, which gave way to more liberal approaches for the greater part of the 20^th century, have again gained traction as emerging research suggests restricting transfusion is associated with similar, or possibly better outcomes in UGI bleeding. In a large, retrospective cohort study from an integrated health care system in Taiwan, Chen, et al., report the association between early blood transfusion and clinical outcomes in patients presenting to the emergency department with UGI bleeding, and these findings are discussed in the context of current knowledge and practice.

S-Nitrosohemoglobin Levels and Patient Outcome After Transfusion During Pediatric Bypass Surgery

Banked blood exhibits impairments in nitric oxide (NO)‐based oxygen delivery capability, reflected in rapid depletion of S‐nitrosohemoglobin (SNO‐Hb). We hypothesized that transfusion of even freshly‐stored blood used in pediatric heart surgery would reduce SNO‐Hb levels and worsen outcome. In a retrospective review (n = 29), the percent of estimated blood volume (% eBV) replaced by transfusion directly correlated with ventilator time and inversely correlated with kidney function; similar results were obtained in a prospective arm (n = 20). In addition, an inverse association was identified between SNO‐Hb and postoperative increase in Hb (∆Hb), reflecting the amount of blood retained by the patient. Both SNO‐Hb and ∆Hb correlated with the probability of kidney dysfunction and oxygenation‐related complications. Further, regression analysis identified SNO‐Hb as an inverse predictor of outcome. The findings suggest that SNO‐Hb and ∆Hb are prognostic biomarkers following pediatric cardiopulmonary bypass, and that maintenance of red blood cell‐derived NO bioactivity might confer therapeutic benefit.

Hemorrhagic Shock and the Microvasculature

The microvasculature plays a central role in the pathophysiology of hemorrhagic shock and is also involved in arguably all therapeutic attempts to reverse or minimize the adverse consequences of shock. Microvascular studies specific to hemorrhagic shock were reviewed and broadly grouped depending on whether data were obtained on animal or human subjects. Dedicated sections were assigned to microcirculatory changes in specific organs, and major categories of pathophysiological alterations and mechanisms such as oxygen distribution, ischemia, inflammation, glycocalyx changes, vasomotion, endothelial dysfunction, and coagulopathy as well as biomarkers and some therapeutic strategies. Innovative experimental methods were also reviewed for quantitative microcirculatory assessment as it pertains to changes during hemorrhagic shock. The text and figures include representative quantitative microvascular data obtained in various organs and tissues such as skin, muscle, lung, liver, brain, heart, kidney, pancreas, intestines, and mesentery from various species including mice, rats, hamsters, sheep, swine, bats, and humans. Based on reviewed findings, a new integrative conceptual model is presented that includes about 100 systemic and local factors linked to microvessels in hemorrhagic shock. The combination of systemic measures with the understanding of these processes at the microvascular level is fundamental to further develop targeted and personalized interventions that will reduce tissue injury, organ dysfunction, and ultimately mortality due to hemorrhagic shock. Published 2018. Compr Physiol 8:61-101, 2018.

Iron accelerates hemoglobin oxidation increasing mortality in vascular diseased guinea pigs following transfusion of stored blood

Non-transferrin-bound iron (NTBI) and free hemoglobin (Hb) accumulate in circulation following stored RBC transfusions. This study investigated transfusion, vascular disease, and mortality in guinea pigs after stored RBC transfusion alone and following cotransfusion with apo-transferrin (apo-Tf) and haptoglobin (Hp). The effects of RBC exchange transfusion dose (1, 3, and 9 units), storage period (14 days), and mortality were evaluated in guinea pigs with a vascular disease phenotype. Seven-day mortality and the interaction between iron and Hb as cocontributors to adverse outcome were studied. Concentrations of iron and free Hb were greatest after transfusion with 9 units of stored RBCs compared with fresh RBCs or stored RBCs at 1- and 3-unit volumes. Nine units of stored RBCs led to mortality in vascular diseased animals, but not normal animals. One and 3 units of stored RBCs did not cause a mortality effect, suggesting the concomitant relevance of NTBI and Hb on outcome. Cotransfusion with apo-Tf or Hp restored survival to 100% following 9-unit RBC transfusions in vascular diseased animals. Our data suggest that increases in plasma NTBI and Hb contribute to vascular disease-associated mortality through iron-enhanced Hb oxidation and enhanced tissue injury.

Blood transfusion improves renal oxygenation and renal function in sepsis-induced acute kidney injury in rats

Background

The effects of blood transfusion on renal microcirculation during sepsis are unknown. This study aimed to investigate the effect of blood transfusion on renal microvascular oxygenation and renal function during sepsis-induced acute kidney injury.

Methods

Twenty-seven Wistar albino rats were randomized into four groups: a sham group (n = 6), a lipopolysaccharide (LPS) group (n = 7), a LPS group that received fluid resuscitation (n = 7), and a LPS group that received blood transfusion (n = 7). The mean arterial blood pressure, renal blood flow, and renal microvascular oxygenation within the kidney cortex were recorded. Acute kidney injury was assessed using the serum creatinine levels, metabolic cost, and histopathological lesions. Nitrosative stress (expression of endothelial (eNOS) and inducible nitric oxide synthase (iNOS)) within the kidney was assessed by immunohistochemistry. Hemoglobin levels, pH, serum lactate levels, and liver enzymes were measured.

Results

Fluid resuscitation and blood transfusion both significantly improved the mean arterial pressure and renal blood flow after LPS infusion. Renal microvascular oxygenation, serum creatinine levels, and tubular damage significantly improved in the LPS group that received blood transfusion compared to the group that received fluids. Moreover, the renal expression of eNOS was markedly suppressed under endotoxin challenge. Blood transfusion, but not fluid resuscitation, was able to restore the renal expression of eNOS. However, there were no significant differences in lactic acidosis or liver function between the two groups.

Conclusions

Blood transfusion significantly improved renal function in endotoxemic rats. The specific beneficial effect of blood transfusion on the kidney could have been mediated in part by the improvements in renal microvascular oxygenation and sepsis-induced endothelial dysfunction via the restoration of eNOS expression within the kidney.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-016-1581-1) contains supplementary material, which is available to authorized users.

Blood Transfusion and the Risk of Acute Kidney Injury Among Patients With Acute Coronary Syndrome Undergoing Percutaneous Coronary Intervention

Background—

Acute kidney injury (AKI) complicating percutaneous coronary intervention (PCI) is associated with adverse clinical outcomes. To date, no studies have evaluated the association of blood transfusion with AKI in patients undergoing PCI.

Methods and Results—

We used a retrospective cohort study of all patients with acute coronary syndrome undergoing PCI from CathPCI Registry (n=1 756 864). The primary outcome was AKI defined as the rise in serum creatinine post procedure ≥0.5 mg/dL or ≥25% above baseline values. AKI developed in 9.0% of study sample. Patients with AKI were older, more often women, and had high prevalence of comorbidities, including diabetes mellitus, hypertension, and advanced stages of chronic kidney disease at baseline. Blood transfusion was utilized in 2.2% of patients. In the overall sample, AKI developed in 35.1% of patients who received transfusion versus 8.4% of patients without transfusion (adjusted odds ratio, 4.87 [4.71–5.04]). In the subgroup of patients who sustained bleeding event and received transfusion, the rate of AKI was significantly increased across all preprocedure hemoglobin levels versus no blood transfusion. Similar findings were seen in the subgroup of patients with no bleeding event.

Conclusions—

Blood transfusion is strongly associated with AKI in patients with acute coronary syndrome undergoing PCI. Further investigation is needed to determine whether a restrictive blood transfusion strategy might improve PCI outcomes by reducing the risk of AKI.

Molecular mechanisms of erythrocyte aging

Anemia and hemorrhagic shock are leading causes of morbidity and mortality worldwide, and transfusion of human blood products is the ideal treatment for these conditions. As human erythrocytes age during storage in blood banks they undergo many biochemical and structural changes, termed the red blood cell 'storage lesion'. Specifically, ATP and pH levels decrease as metabolic end products, oxidative stress, cytokines, and cell-free hemoglobin increase. Also, membrane proteins and lipids undergo conformational and organizational changes that result in membrane loss, viscoelastic changes and microparticle formation. As a result, transfusion of aged blood is associated with a host of adverse consequences such as decreased tissue perfusion, increased risk of infection, and increased mortality. This review summarizes current research detailing the known parts of the erythrocyte storage lesion and their physiologic consequences.

The Effect of Patient-Specific Cerebral Oxygenation Monitoring on Postoperative Cognitive Function: A Multicenter Randomized Controlled Trial

BACKGROUND

Indices of global tissue oxygen delivery and utilization such as mixed venous oxygen saturation, serum lactate concentration, and arterial hematocrit are commonly used to determine the adequacy of tissue oxygenation during cardiopulmonary bypass (CPB). However, these global measures may not accurately reflect regional tissue oxygenation and ischemic organ injury remains a common and serious complication of CPB. Near-infrared spectroscopy (NIRS) is a noninvasive technology that measures regional tissue oxygenation. NIRS may be used alongside global measures to optimize regional perfusion and reduce organ injury. It may also be used as an indicator of the need for red blood cell transfusion in the presence of anemia and tissue hypoxia. However, the clinical benefits of using NIRS remain unclear and there is a lack of high-quality evidence demonstrating its efficacy and cost effectiveness.

OBJECTIVE

The aim of the patient-specific cerebral oxygenation monitoring as part of an algorithm to reduce transfusion during heart valve surgery (PASPORT) trial is to determine whether the addition of NIRS to CPB management algorithms can prevent cognitive decline, postoperative organ injury, unnecessary transfusion, and reduce health care costs.

METHODS

Adults aged 16 years or older undergoing valve or combined coronary artery bypass graft and valve surgery at one of three UK cardiac centers (Bristol, Hull, or Leicester) are randomly allocated in a 1:1 ratio to either a standard algorithm for optimizing tissue oxygenation during CPB that includes a fixed transfusion threshold, or a patient-specific algorithm that incorporates cerebral NIRS monitoring and a restrictive red blood cell transfusion threshold. Allocation concealment, Internet-based randomization stratified by operation type and recruiting center, and blinding of patients, ICU and ward care staff, and outcome assessors reduce the risk of bias. The primary outcomes are cognitive function 3 months after surgery and infectious complications during the first 3 months after surgery. Secondary outcomes include measures of inflammation, organ injury, and volumes of blood transfused. The cost effectiveness of the NIRS-based algorithm is described in terms of a cost-effectiveness acceptability curve. The trial tests the superiority of the patient-specific algorithm versus standard care. A sample size of 200 patients was chosen to detect a small to moderate target difference with 80% power and 5% significance (two tailed).

RESULTS

Over 4 years, 208 patients have been successfully randomized and have been followed up for a 3-month period. Results are to be reported in 2015.

CONCLUSIONS

This study provides high-quality evidence, both valid and widely applicable, to determine whether the use of NIRS monitoring as part of a patient-specific management algorithm improves clinical outcomes and is cost effective.

TRIAL REGISTRATION

International Standard Randomized Controlled Trial Number (ISRCTN): 23557269; http://www.isrctn.com/ISRCTN23557269 (Archived by Webcite at http://www.webcitation.org/6buyrbj64).

Deterioration of red blood cell mechanical properties is reduced in anaerobic storage

BACKGROUND

Hypothermic storage of red blood cells (RBCs) results in progressive deterioration of the rheological properties of the cells, which may reduce the efficacy of RBC transfusions. Recent studies have suggested that storing RBC units under anaerobic conditions may reduce this storage-induced deterioration.

MATERIALS AND METHODS

The aim of this study was to compare the rheological properties of conventionally and anaerobically stored RBC and provide a measure of the relationship between oxidative damage to stored RBC and their ability to perfuse microvascular networks. Three different microfluidic devices were used to measure the ability of both types of stored RBC to perfuse artificial microvascular networks. Flow rates of the RBC passing through the entire network (bulk perfusion) and the individual capillaries (capillary perfusion) of the devices were measured on days 2, 21, 42, and 63 of storage.

RESULTS

The bulk perfusion rates for anaerobically stored RBC were significantly higher than for conventionally stored RBCs over the entire duration of storage for all devices (up to 10% on day 42; up to 14% on day 63). Capillary perfusion rates suggested that anaerobically stored RBC units contained significantly fewer non-deformable RBC capable of transiently plugging microfluidic device capillaries. The number of plugging events caused by these non-deformable RBC increased over the 63 days of hypothermic storage by nearly 16- to 21-fold for conventionally stored units, and by only about 3- to 6-fold for anaerobically stored units.

DISCUSSION

The perfusion measurements suggest that anaerobically stored RBC retain a greater ability to perfuse networks of artificial capillaries compared to conventionally (aerobically) stored RBC. It is likely that anaerobic storage confers this positive effect on the bulk mechanical properties of stored RBC by significantly reducing the number of non-deformable cells present in the overall population of relatively well-preserved RBC.

Anemia and Blood Transfusion in Patients with Isolated Traumatic Brain Injury

Rationale. By reducing cerebral oxygen delivery, anemia may aggravate traumatic brain injury (TBI) secondary insult. This study evaluated the impact of anemia and blood transfusion on TBI outcomes. Methods. This was a retrospective cohort study of adult patients with isolated TBI at a tertiary-care intensive care unit from 1/1/2000 to 31/12/2011. Daily hemoglobin level and packed red blood cell (PRBC) transfusion were recorded. Patients with hemoglobin < 10 g/dL during ICU stay (anemic group) were compared with other patients. Results. Anemia was present on admission in two (2%) patients and developed in 48% during the first week with hemoglobin < 7 g/dL occurring in 3.0%. Anemic patients had higher admission Injury Severity Score and underwent more craniotomy (50% versus 13%, p < 0.001). Forty percent of them received PRBC transfusion (2.8 ± 1.5 units per patient, median pretransfusion hemoglobin = 8.8 g/dL). Higher hospital mortality was associated with anemia (25% versus 6% for nonanemic patients, p = 0.01) and PRBC transfusion (38% versus 9% for nontransfused patients, p = 0.003). On multivariate analysis, only PRBC transfusion independently predicted hospital mortality (odds ratio: 6.8; 95% confidence interval: 1.1–42.3). Conclusions. Anemia occurred frequently after isolated TBI, but only PRBC transfusion independently predicted mortality.

Neonatal Transfusion Medicine: Five Major Unanswered Research Questions for the Twenty-First Century

Blood component transfusions are important to the care of preterm neonates; however, their use in clinical practice often is not based on high levels of evidence. Five major questions for neonates are discussed: (1) What is the optimal red blood cell (RBC) transfusion threshold? (2) What is the optimal platelet transfusion threshold? (3) Does the storage age of an RBC unit affect outcomes? (4) Does RBC transfusion contribute to the pathogenesis of necrotizing enterocolitis? and (5) Which new practices should be used to prevent transfusion-transmitted infections? Although definitive answers to these questions do not exist, future research should help answer them.

Harms associated with single unit perioperative transfusion: retrospective population based analysis

OBJECTIVE

To determine whether perioperative transfusion of as little as one unit of packed red blood cells in the operating room or the day after surgery is associated with measurably increased odds for perioperative ischemic stroke and myocardial infarction.

DESIGN

Retrospective cohort study of hospital administrative data.

SETTING

346 hospitals in the United States participating in the claims based Premier Perspective database from 1 January 2009 to 31 March 2012.

PARTICIPANTS

1,583,819 adults who underwent non-cardiac, non-intracranial, non-vascular surgery and required a stay of at least one night in hospital and did not receive packed red blood cells on days two to seven after surgery.

INTERVENTION

Transfusion of packed red blood cells on the day of surgery or one day after by exposure categories (none or one, two, three or four or more units).

MAIN OUTCOME MEASURES

The composite outcome of stroke/myocardial infarction was defined as ischemic stroke, ST elevation myocardial infarction, ventricular tachycardia, or ventricular fibrillation during index admission or as a primary diagnosis for readmission within 30 days. Ventricular tachycardia/ventricular fibrillation were included as a surrogate for myocardial infarction.

RESULTS

41,421 (2.6%) patients received at least one unit of packed red blood cells within 48 hours of surgery, and 8044 (0.51%) experienced the composite outcome of stroke/myocardial infarction. Patients who were transfused were older, more likely to be women, and had more comorbid disease. Hierarchical logistic regression adjusted for comorbidities and demographics with random effects by hospital showed that transfusion of as little as one unit was associated with an odds ratio of 2.33 (95% confidence interval 1.90 to 2.86) for perioperative stroke/myocardial infarction, and the odds of stroke/myocardial infarction markedly increased with transfusion of four or more units. Subgroup analysis limiting the cohort to one of several common surgical procedures, excluding those who received two or more units, or excluding who received transfusion on postoperative day one showed substantially similar results, as did a matched propensity score analysis. Two methods of modeling unmeasured confounders suggest an odds ratio of >10 with imbalance of up to 47% between patients who did and did not receive transfusion would be required to invalidate our results.

CONCLUSIONS

A perioperative transfusion of one unit of packed red blood cells is associated with increased odds of perioperative ischemic stroke and/or myocardial infarction, even after adjustment for a wide range of factors in our data and despite extensive sensitivity analyses.

Anemia and Transfusion in Critical Care

Objective:

The objective of this report is to review the physiology and management of anemia in critical care. Selected publications on physiology and transfusion related to anemia and critical care, including the modern randomized trials of conservative versus liberal transfusion policy, were used. Anemia is compensated and tolerated in most critically ill patients as long as oxygen delivery is at least twice oxygen consumption. There are risks to blood transfusion which can be minimized by blood banking practice. The availability of cultured red cells may allow correction of anemia without significant risk. The benefit of transfusion in anemia must be weighted against the risk in any specific patient.

Conclusion and Recommendation:

In a criticially ill patient, anemia should be managed to avoid oxygen supply dependency (oxygen delivery less than twice comsumption) and to maintain moderate oxygen delivery reserve (DO2/VO2 > 3).

Relationship between Nadir Hematocrit during Cardiopulmonary Bypass and Postoperative Hyperglycemia in Nondiabetic Patients

<p><b>Background:</b> Hyperglycemia is common after cardiac surgery in both diabetic and nondiabetic patients and is associated with increased morbidity and mortality. Association between nadir hematocrit levels on cardiopulmonary bypass (CPB) and postoperative hyperglycemia is not clear. This study was carried out to determine the relationship between nadir hematocrit during CPB and postoperative hyperglycemia in nondiabetic patients.</p><p><b>Methods:</b> Records of 200 nondiabetic patients undergoing coronary artery bypass grafting operation were retrospectively reviewed. In the first analysis, patients were divided into two subgroups according to the presence or absence of hyperglycemia. Further analysis was made after dividing the patients into 3 subgroups according to nadir hematocrit levels on CPB (less than 20%; 20% to 25%; greater than or equal to 25%).</p><p><b>Results:</b> Compared to patients without hyperglycemia, patients with postoperative hyperglycemia had significantly lower preoperative hematocrit levels (p = 0.004) and were associated with lower nadir hematocrit levels during CPB (p= 0.002). Peak intensive care unit blood glucose levels and number of blood transfusions were significantly higher in patients with nadir hematocrit levels less than 20. (p<0.001 and p<0.001 respectively). Logistic regression analysis demonstrated that nadir hematocrit levels less than 20% (OR 2.9, p=0.009) and allogenic blood transfusion (OR 1.5, p=0.003) were independently associated with postoperative hyperglycemia.</p><p><b>Conclusions:</b> Nadir hematocrit levels on CPB less than 20% and allogenic blood transfusions were independently associated with postoperative hyperglycemia in nondiabetic patients. Patients with a nadir hematocrit levels less than 20 % during CPB should be closely monitored for hyperglycemia in the perioperative period.</p>

Red blood cell storage lesion

OBJECTIVE

To summarize current understanding of the mechanisms responsible for changes occurring during red blood cell (RBC) storage, collectively known as the storage lesion, and to review the biological and clinical consequences of increasing storage time of RBCs.

DATA SOURCES

Human and veterinary clinical studies, experimental animal model studies, and reviews of the RBC storage lesion with no date restrictions.

HUMAN DATA SYNTHESIS

Experimental studies have characterized the evolution of human RBC and supernatant changes that occur during storage and form the basis for concern about the potential for harm from long-term storage of RBCs. Although 4 randomized controlled trials of varying sizes failed to find an association between RBC storage time and negative clinical outcomes, a recent meta-analysis and numerous observational clinical studies have demonstrated that transfusion of old versus fresh stored RBCs is associated with an increased risk of morbidity and mortality, particularly among trauma victims and cardiac surgery patients. Potential clinical consequences of RBC transfusion following development of the storage lesion include risk of organ dysfunction, organ failure, infections, and death.

VETERINARY DATA SYNTHESIS

Experimental animal models have contributed to the evidence supporting adverse consequences of the RBC storage lesion. Studies on relevant RBC storage issues such as the effect of different preservative solutions and leukoreduction have been completed. Transfusion with RBCs stored for 42 days increases mortality in dogs with experimental sepsis.

CONCLUSION

Storage of RBCs induces progressive biochemical, biomechanical, and immunologic changes that affect red cell viability, deformability, oxygen carrying capacity, microcirculatory flow, and recipient response. Most reports in the human and veterinary literature support the concept that there are deleterious effects of the RBC storage lesion, but additional studies with improved experimental design are needed to identify compelling reasons to modify current blood banking and transfusion practices.

Transfusion strategy: impact of haemodynamics and the challenge of haemodilution

Blood transfusion is associated with increased morbidity and mortality and numerous reports have emphasised the need for reduction. Following this there is increased attention to the concept of patient blood management. However, bleeding is relatively common following cardiac surgery and is further enhanced by the continued antiplatelet therapy policy. Another important issue is that cardiopulmonary bypass leads to haemodilution and a potential blood loss. The basic role of blood is oxygen transport to the organs. The determining factors of oxygen delivery are cardiac output, haemoglobin, and saturation. If oxygen delivery/consumption is out of balance, the compensation mechanisms are simple, as a decrease in one factor results in an increase in one or two other factors. Patients with coexisting cardiac diseases may be of particular risk, but studies indicate that patients with coexisting cardiac diseases tolerate moderate anaemia and may even benefit from a restrictive transfusion regimen. Further it has been shown that patients with reduced left ventricular function are able to compensate with increased cardiac output in response to bleeding and haemodilution if normovolaemia is maintained. In conclusion the evidence supports that each institution establishes its own patient blood management strategy to both conserve blood products and maximise outcome.

Impaired red blood cell deformability after transfusion of stored allogeneic blood but not autologous salvaged blood in cardiac surgery patients

BACKGROUND

Both cardiopulmonary bypass (CPB) and red blood cell (RBC) storage are associated with detrimental changes in RBC structure and function that may adversely affect tissue oxygen delivery. We tested the hypothesis that in cardiac surgery patients, RBC deformability and aggregation are minimally affected by CPB with autologous salvaged blood alone but are negatively affected by the addition of stored allogeneic blood.

METHODS

In this prospective cohort study, 32 patients undergoing cardiac surgery with CPB were divided into 3 groups by transfusion status: autologous salvaged RBCs alone (Auto; n = 12), autologous salvaged RBCs + minimal (<5 units) stored allogeneic RBCs (Auto+Allo min; n = 10), and autologous salvaged RBCs + moderate (≥5 units) stored allogeneic RBCs (Auto+Allo mod; n = 10). Ektacytometry was used to measure RBC elongation index (deformability) and critical shear stress (aggregation) before, during, and for 3 days after surgery.

RESULTS

In the Auto group, RBC elongation index did not change significantly from the preoperative baseline. In the Auto+Allo min group, mean elongation index decreased from 32.31 ± 0.02 (baseline) to 30.47 ± 0.02 (nadir on postoperative day 1) (P = 0.003, representing a 6% change). In the Auto+Allo mod group, mean elongation index decreased from 32.7 ± 0.02 (baseline) to 28.14 ± 0.01 (nadir on postoperative day 1) (P = 0.0001, representing a 14% change). Deformability then dose-dependently recovered toward baseline over the first 3 postoperative days. Changes in aggregation were unrelated to transfusion (no difference among groups). For the 3 groups combined, mean critical shear stress decreased from 359 ± 174 mPa to 170 ± 141 mPa (P = 0.01, representing a 54% change), with the nadir at the end of surgery and returned to baseline by postoperative day 1.

CONCLUSIONS

In cardiac surgery patients, transfusion with stored allogeneic RBCs, but not autologous salvaged RBCs, is associated with a decrease in RBC cell membrane deformability that is dose-dependent and may persist beyond 3 postoperative days. These findings suggest that autologous salvaged RBCs may be of higher quality than stored RBCs, since the latter are subject to the so-called storage lesions.

Transcutaneous oxygen tension monitoring in critically ill patients receiving packed red blood cells

PURPOSE

Whether transfusions of packed red blood cells (PRBCs) affect tissue oxygenation in stable critically ill patients is still matter of discussion. The microvascular capacity for tissue oxygenation can be determined noninvasively by measuring transcutaneous oxygen tension (tcpO2). The aim of this study was to assess tissue oxygenation by measuring tcpO2 in stable critically ill patients receiving PRBC transfusions.

METHODS

Nineteen stable critically ill patients, who received 2 units of PRBC, were prospectively included into this pilot study. Transcutaneous oxygen tension was measured continuously during PRBC transfusions using Clark's electrodes. In addition, whole blood viscosity and global hemodynamics were determined.

RESULTS

Reliable measurement signals during continuous tcpO2 monitoring were observed in 17 of 19 included patients. Transcutaneous oxygen tension was related to the global oxygen consumption (r=-0.78; P=.003), the arterio-venous oxygen content difference (r=-0.65; P=.005), and the extraction rate (r=-0.71; P=.02). The transfusion-induced increase of the hemoglobin concentration was paralleled by an increase of the whole blood viscosity (P<.001). Microvascular tissue oxygenation by means of tcpO2 was not affected by PRBC transfusions (P=.46). Packed red blood cell transfusions resulted in an increase of global oxygen delivery (P=.02) and central venous oxygen saturation (P=.01), whereas oxygen consumption remained unchanged (P=.72).

CONCLUSIONS

In stable critically ill patients, microvascular tissue oxygenation can be continuously monitored by Clark's tcpO2 electrodes. According to continuous tcpO2 measurements, the microvascular tissue oxygenation is not affected by PRBC transfusions.

Factors Affecting Tissue Oxygenation in Erythrocyte Transfusions

Red blood cell transfusions are used to increase the oxygen-carrying capacity of blood in anemic states. But, because of the changes during storage of blood components and the specifics of preparation, erythrocytes may have controversial effects on tissue oxygenation and microcirculation. Also, the patient situation may play a role in the differing responses in oxygenation and microcirculation. In this review, the studies concerning the effects of banked blood and patient characteristics on microcirculation and tissue oxygenation are summarized.

Aprotinin and transfusion requirements in pediatric craniofacial surgery

OBJECTIVE

To evaluate transfusion requirements in children receiving aprotinin during craniofacial surgery.

BACKGROUND

Pediatric craniofacial procedures may involve massive blood loss. Aprotinin may decrease perioperative blood loss and transfusion requirements.

METHODS

Patients (aged 1 month to 3 years) who had major reconstructive craniofacial surgery received intraoperative aprotinin (13 patients) or placebo (13 patients). Administered colloids and blood products were recorded.

RESULTS

Patients in the aprotinin and placebo groups had similar mean age, body weight, body surface area, operative time, and length of hospital stay. Mean volumes of total colloids (aprotinin group: 70 ± 40 ml; and placebo group: 120 ± 80 ml; P ≤ 0.05) and packed red blood cells (aprotinin group: 380 ± 90 ml; and placebo group: 550 ± 200 ml; P ≤ 0.004) were less in the aprotinin group than in the placebo group. Mean urine output during surgery was greater in the aprotinin group than in the placebo group (320 ± 200 ml vs 150 ± 70 ml, respectively; P ≤ 0.003). Mean blood urea nitrogen and serum creatinine values after surgery were similar between the groups. Complications of aprotinin included anaphylaxis (one patient) and rash (one patient); no deaths occurred.

CONCLUSIONS

Aprotinin was associated with decreased packed red blood cell transfusion requirements in children undergoing craniofacial surgery, with no renal toxicity or death. Aprotinin is no longer available for clinical use in the USA because of adverse effects in adults; re-evaluation of aprotinin is warranted for children scheduled to undergo surgery involving potentially high blood loss.

Microhemodynamic parameters quantification from intravital microscopy videos

Blood flow and blood-endothelium interactions correspond with the genesis of cardiovascular diseases. Therefore, quantitative analysis of blood flow dynamics at the microcirculation level is of special interest. Regulatory mechanisms mediated by blow flow have been studied in detail using in vitro approaches. However, these mechanisms have not been fully validated in vivo due to technical limitations that arise when quantifying microhemodynamics with the required level of detail. Intravital microscopy combined with high-speed video recordings has been used for the analysis of blood flow in small blood vessels of chronic and acute experimental tissue preparations. This tool can be used to study the interaction between the flowing blood and the vessel walls of arterioles and venules with sufficient temporal and spatial resolution. Our objective was to develop a simple and robust cross-correlation algorithm for the automatic analysis of high-speed video recordings of microcirculatory blood flow. The algorithm was validated using in vitro and in vivo systems. Results indicate that the algorithm's ability to estimate the velocity of local red blood cells as a function of blood vessel radius is highly accurate. They thereby suggest that the algorithm could be used to explore dynamic changes in blood flow under different experimental conditions including a wide range of flow rates and hematocrit levels. The algorithm can also be used to measure volumetric flow rates, radial velocity profiles, wall shear rate, and wall shear stress. Several applications are presently explored, including the analysis of velocity profiles in the branches of arterial bifurcations. This work demonstrates the robustness of the cross-correlation technique in various flow conditions and elucidates its potential application for in vivo determination of blood flow dynamics in the microcirculation.

Proinflammatory, immunomodulating, and prothrombotic properties of anemia and red blood cell transfusions

For many years, the traditional treatment for hospitalized patients in the United States who have developed anemia, whether associated with medical illness, surgical procedures or trauma, has been red blood cell transfusion, despite the absence of supporting data in many patient populations. Emerging evidence suggests that transfusions may, in fact, be associated with risk beyond commonly held concerns of microbial transmission and acute antigen-antibody reactions. The following overview represents a biological paradigm for understanding the relationship between medical illness, surgical procedures, inflammatory states, anemia, red blood cell transfusion and immunothrombotic phenomena among hospitalized patients.

Nitric oxide transport in blood: a third gas in the respiratory cycle

The trapping, processing, and delivery of nitric oxide (NO) bioactivity by red blood cells (RBCs) have emerged as a conserved mechanism through which regional blood flow is linked to biochemical cues of perfusion sufficiency. We present here an expanded paradigm for the human respiratory cycle based on the coordinated transport of three gases: NO, O₂, and CO₂. By linking O₂ and NO flux, RBCs couple vessel caliber (and thus blood flow) to O₂ availability in the lung and to O₂ need in the periphery. The elements required for regulated O₂-based signal transduction via controlled NO processing within RBCs are presented herein, including S-nitrosothiol (SNO) synthesis by hemoglobin and O₂-regulated delivery of NO bioactivity (capture, activation, and delivery of NO groups at sites remote from NO synthesis by NO synthase). The role of NO transport in the respiratory cycle at molecular, microcirculatory, and system levels is reviewed. We elucidate the mechanism through which regulated NO transport in blood supports O₂ homeostasis, not only through adaptive regulation of regional systemic blood flow but also by optimizing ventilation-perfusion matching in the lung. Furthermore, we discuss the role of NO transport in the central control of breathing and in baroreceptor control of blood pressure, which subserve O₂ supply to tissue. Additionally, malfunctions of this transport and signaling system that are implicated in a wide array of human pathophysiologies are described. Understanding the (dys)function of NO processing in blood is a prerequisite for the development of novel therapies that target the vasoactive capacities of RBCs.

Interactions of cardiopulmonary bypass and erythrocyte transfusion in the pathogenesis of pulmonary dysfunction in Swine

BACKGROUND

Allogeneic erythrocyte transfusion in cardiac surgical patients is associated with a fourfold increase in pulmonary complications. Our understanding of the processes underlying these observations is poor and there is no experimental model of transfusion-related acute lung injury that shows homology to cardiac surgical patients. Our objective was to develop a novel swine recovery model to determine how two clinical risk factors, allogenic erythrocyte transfusion and cardiopulmonary bypass, interact in the genesis of postcardiac surgery acute lung injury.

METHODS

Thirty-six pigs were infused with allogeneic 14- or 42-day-old erythrocytes or they underwent cardiopulmonary bypass with or without transfusion of 42-day erythrocyte. Controls received saline. All pigs were recovered and assessed for pulmonary dysfunction, inflammation, and endothelial activation at 24 h.

RESULTS

Transfusion of stored allogeneic erythrocytes in pigs compared with sham caused pulmonary dysfunction characterized by reduced lung compliance (mean difference -3.36 [95% CI, -5.31 to -1.42] ml/cm H2O), an increase in protein levels in bronchoalveolar lavage fluid, histological lung injury inflammation, and endothelial activation. Transfusion of blood stored for up to 42 days resulted in greater protein levels in bronchoalveolar lavage fluid, macrophage infiltration, platelet activation, and depletion of T-lymphocytes in recipient lungs versus 14-day-old blood. Transfusion interacted with cardiopulmonary bypass to increase lung injury in the absence of platelet activation.

CONCLUSIONS

In this novel large animal model of allogeneic erythrocyte transfusion, pulmonary dysfunction occurs in the absence of any priming event, is increased when combined with other inflammatory stimuli, and is mediated by monocyte activation and T-lymphocyte depletion.

Microhemodynamic aberrations created by transfusion of stored blood

BACKGROUND

Human red blood cells (RBCs) can be stored for up to 42 days under controlled conditions. Physical and chemical changes occur during RBC storage, altering their function. This study links stored cell mechanical changes with hemodynamic functional alterations upon transfusion.

STUDY DESIGN AND METHODS

Mechanical properties of fresh and stored RBCs were evaluated in vitro. Their transfusion effects were evaluated in vivo using intravital microscopy of the rat's cremaster muscle preparation. Rats were hemodiluted to 30% hematocrit, to mimic an anemic state before transfusion, and then exchange-transfused with fresh or stored cells.

RESULTS

In vitro studies on rheology and oxygen affinity of stored cells confirmed previously published results. Storage was found to modify static and dynamic RBC mechanic behavior. After transfusion, systemic hemodynamics were similar for fresh and stored cells; however, microvascular hemodynamics were drastically affected by stored cells. Stored cells reduced blood flow and oxygen delivery. Additionally, the presence of stored cells in circulation affected cell-to-cell and cell-to-wall interactions and affected cell hydrodynamics. Stored cells disrupted the RBC cell-free layer and wall shear stress signals.

CONCLUSION

The reduced cell deformability due to RBC "storage lesions" caused pathologic changes in microvascular hemodynamics, endothelial cell mechanotransduction, and RBC dynamics. Thus, the mechanical changes of blood-banked cells can limit transfusion ability to achieve its intended goal.

S-nitrosylation therapy to improve oxygen delivery of banked blood

From the perspectives of disease transmission and sterility maintenance, the world's blood supplies are generally safe. However, in multiple clinical settings, red blood cell (RBC) transfusions are associated with adverse cardiovascular events and multiorgan injury. Because ∼85 million units of blood are administered worldwide each year, transfusion-related morbidity and mortality is a major public health concern. Blood undergoes multiple biochemical changes during storage, but the relevance of these changes to unfavorable outcomes is unclear. Banked blood shows reduced levels of S-nitrosohemoglobin (SNO-Hb), which in turn impairs the ability of stored RBCs to effect hypoxic vasodilation. We therefore reasoned that transfusion of SNO-Hb-deficient blood may exacerbate, rather than correct, impairments in tissue oxygenation, and that restoration of SNO-Hb levels would improve transfusion efficacy. Notably in mice, administration of banked RBCs decreased skeletal muscle pO2, but infusion of renitrosylated cells maintained tissue oxygenation. In rats, hemorrhage-induced reductions in muscle pO2 were corrected by SNO-Hb-repleted RBCs, but not by control, stored RBCs. In anemic awake sheep, stored renitrosylated, but not control RBCs, produced sustained improvements in O2 delivery; in anesthetized sheep, decrements in hemodynamic status, renal blood flow, and kidney function incurred following transfusion of banked blood were also prevented by renitrosylation. Collectively, our findings lend support to the idea that transfusions may be causally linked to ischemic events and suggest a simple approach to prevention (i.e., SNO-Hb repletion). If these data are replicated in clinical trials, renitrosylation therapy could have significant therapeutic impact on the care of millions of patients.

Examining and mitigating acellular hemoglobin vasoactivity

SIGNIFICANCE

There has been a striking advancement in our understanding of red cell substitutes over the past decade. Although regulatory oversight has influenced many aspects of product development in this period, those who have approached the demonstration of efficacy of red cell substitutes have failed to understand their implication at the level of the microcirculation, where blood interacts closely with tissue.

RECENT ADVANCES

The understanding of the adverse effects of acellular hemoglobin (Hb)-based oxygen carriers (HBOCs) has fortunately expanded from Hb-induced renal toxicity to a more complete list of biochemical mechanism. In addition, various unexpected adverse reactions were seen in early clinical studies. The effects of the presence of acellular Hb in plasma are relatively unique because of the convergence of mechanical and biochemical natures.

CRITICAL ISSUES

Controlling the variables using genetic engineering and chemical modification to change specific characteristics of the Hb molecule may allow for solving the complex multivariate problems of acellular Hb vasoactivity. HBOCs may never be rendered free of negative effects; however, quantifying the nature and extent of microvascular complications establishes a platform for designing new ameliorative therapies.

FUTURE DIRECTIONS

It is time to leave behind the study of vasoactivity and toxicity based on bench-top measurements of biochemical changes and those based solely on systemic parameters in vivo, and move to a more holistic analysis of the mechanisms creating the problems, complemented with meaningful studies of efficacy.

[Erythrocytes and microvascular tone during acute traumatic haemorrhagic shock]

Haemorrhagic shock remains a leading cause of death in trauma patients. The concept of haematologic damage control is gradually taking place in the management of traumatic haemorrhagic shock. It is based primarily on the early implementation of a quality blood transfusion involving erythrocytes, plasmas and platelets transfusion. Red blood cell transfusion is mainly supported by the oxygen carrier properties of erythrocytes. However, it appears that erythrocytes ability to modulate the bioavailability of nitric oxide (NO) plays a major role in capillary opening and perfusion. Erythrocytes are also actively involved in the processes of hemostasis and coagulation. In this context, it seems difficult to define a threshold of hemoglobin concentration to determine the implementation of a blood transfusion in traumatic haemorrhagic shock.

Resuscitation with aged blood exacerbates liver injury in a hemorrhagic rat model

OBJECTIVE

Blood loss and transfusion are frequent among patients undergoing liver surgery. Concerns have been raised about the safety and efficacy of transfusing stored blood. The influence of transfusing fresh vs. stored blood on the liver has not been studied to date. We tested the hypothesis that transfusion of stored, but not fresh blood, adversely affects liver outcome in vivo following acute hemorrhage. Additionally, possible mechanisms linking adverse liver outcome with increased storage duration were evaluated.

DESIGN

Prospective, controlled, animal study.

SETTING

University research laboratory.

SUBJECTS

Adult male Sprague-Dawley rats

INTERVENTIONS

Anesthetized rats were randomized to control, hemorrhagic and shock group (acute bleeding; HSG), or hemorrhagic and blood resuscitation groups (BR) (with fresh blood [BR-d0], blood stored for 4 [BR-d4] or 7 [BR-d7] days, or packed RBCs stored for 7 days [packed RBC-d7]).

MEASUREMENTS AND MAIN RESULTS

Administration of blood or packed RBC stored for 7 days exacerbated liver injury as reflected by liver necrosis and enhanced apoptosis (p < 0.001). Functional MRI analysis of the liver demonstrated significant improvement in liver perfusion with fresh blood (% change in functional MRI signal intensity due to hyperoxia was 16% ± 3% in BR-d0 vs. 4% ± 3% in hemorrhagic group, p < 0.001) but not with stored blood (12% ± 2% and 9% ± 5% for BR-d4 and BR-d7, respectively). Analysis of stored blood showed reduction in RBC deformability at 7 days of storage, reflecting a five-fold increase in the number of undeformable cells.

CONCLUSION

Liver injury is exacerbated by the transfusion of stored blood, primarily due to the change in the rheological properties of RBC. This data call for clinical studies in patients undergoing liver resection or transplantation.