Stored blood transfusion induces transient pulmonary arterial hypertension without impairing coagulation in an ovine model of nontraumatic haemorrhage

Experimental Models of Traumatic Injuries: Do They Capture the Coagulopathy and Underlying Endotheliopathy Induced by Human Trauma?

Trauma-induced coagulopathy (TIC) is a major cause of morbidity and mortality in patients with traumatic injury. It describes the spectrum of coagulation abnormalities that occur because of the trauma itself and the body's response to the trauma. These coagulation abnormalities range from hypocoagulability and hyperfibrinolysis, resulting in potentially fatal bleeding, in the early stages of trauma to hypercoagulability, leading to widespread clot formation, in the later stages. Pathological changes in the vascular endothelium and its regulation of haemostasis, a phenomenon known as the endotheliopathy of trauma (EoT), are thought to underlie TIC. Our understanding of EoT and its contribution to TIC remains in its infancy largely due to the scarcity of experimental research. This review discusses the mechanisms employed by the vascular endothelium to regulate haemostasis and their dysregulation following traumatic injury before providing an overview of the available experimental in vitro and in vivo models of trauma and their applicability for the study of the EoT and its contribution to TIC.

Large Animal Models for Simulating Physiology of Transfusion of Red Cell Concentrates-A Scoping Review of The Literature

Background and Objectives: Transfusion of red cell concentrates is a key component of medical therapy. To investigate the complex transfusion-associated biochemical and physiological processes as well as potential risks for human recipients, animal models are of particular importance. This scoping review summarizes existing large animal transfusion models for their ability to model the physiology associated with the storage of erythrocyte concentrates. Materials and Methods: The electronic databases PubMed, EMBASE, and Web of Science were systematically searched for original studies providing information on the intravenous application of erythrocyte concentrates in porcine, ovine, and canine animal models. Results: A total of 36 studies were included in the analysis. The majority of porcine studies evaluated hemorrhagic shock conditions. Pig models showed high physiological similarities with regard to red cell physiology during early storage. Ovine and canine studies were found to model typical aspects of human red cell storage at 42 days. Only four studies provided data on 24 h in vivo survival of red cells. Conclusions: While ovine and canine models can mimic typical human erythrocyte storage for up to 42 days, porcine models stand out for reliably simulating double-hit pathologies such as hemorrhagic shock. Large animal models remain an important area of translational research since they have an impact on testing new pharmacological or biophysical interventions to attenuate storage-related adverse effects and allow, in a controlled environment, to study background and interventions in dynamic and severe disease conditions.

Autologous red blood cell transfusion does not result in a more profound increase in pulmonary capillary wedge pressure compared to saline in critically ill patients: A randomized crossover trial

Background and Objectives

Transfusion‐associated circulatory overload (TACO) is a major cause of severe transfusion‐related morbidity. Transfusion of red blood cells (RBCs) has been shown to induce hydrostatic pressure overload. It is unclear which product‐specific factors contribute. We set out to determine the effect of autologous RBC transfusion versus saline on pulmonary capillary wedge pressure (PCWP) change.

Materials and Methods

In a randomized crossover trial, patients who had undergone coronary bypass surgery were allocated to treatment post‐operatively in the intensive care unit with either an initial 300 ml autologous RBC transfusion (salvaged during surgery) or 300 ml saline infusion first, followed by the other. Primary outcome was the difference in PCWP change. Secondary outcome measures were the difference in extra‐vascular lung water index (EVLWI) and pulmonary vascular permeability index (PVPI).

Results

Change in PCWP was not higher after autologous RBC transfusion compared to saline (ΔPCWP 0.3 ± 0.4 vs. 0.1 ± 0.4 mmHg). ΔEVLWI and ΔPVPI were significantly decreased after autologous RBC transfusion compared to saline (ΔEVLWI −1.6 ± 0.6 vs. 0.2 ± 0.4, p = 0.02; ΔPVPI −0.3 ± 0.1 vs. 0.0 ± 0.1, p = 0.01). Haemodynamic variables and colloid osmotic pressure were not different for autologous RBC transfusion versus saline.

Conclusion

Transfusion of autologous RBCs did not result in a more profound increase in PCWP compared to saline. RBC transfusion resulted in a decrease of EVLWI and PVPI compared to saline. Our data suggest that transfusing autologous RBCs may lead to less pulmonary oedema compared to saline. Future studies with allogeneic RBCs are needed to investigate other factors that may mediate the increase of PCWP, resulting in TACO.

An Ovine Model of Hemorrhagic Shock and Resuscitation, to Assess Recovery of Tissue Oxygen Delivery and Oxygen Debt, and Inform Patient Blood Management

BACKGROUND

Aggressive fluid or blood component transfusion for severe hemorrhagic shock may restore macrocirculatory parameters, but not always improve microcirculatory perfusion and tissue oxygen delivery. We established an ovine model of hemorrhagic shock to systematically assess tissue oxygen delivery and repayment of oxygen debt; appropriate outcomes to guide Patient Blood Management.

METHODS

Female Dorset-cross sheep were anesthetized, intubated, and subjected to comprehensive macrohemodynamic, regional tissue oxygen saturation (StO2), sublingual capillary imaging, and arterial lactate monitoring confirmed by invasive organ-specific microvascular perfusion, oxygen pressure, and lactate/pyruvate levels in brain, kidney, liver, and skeletal muscle. Shock was induced by stepwise withdrawal of venous blood until MAP was 30 mm Hg, mixed venous oxygen saturation (SvO2) < 60%, and arterial lactate >4 mM. Resuscitation with PlasmaLyte® was dosed to achieve MAP > 65 mm Hg.

RESULTS

Hemorrhage impacted primary outcomes between baseline and development of shock: MAP 89 ± 5 to 31 ± 5 mm Hg (P < 0.01), SvO2 70 ± 7 to 23 ± 8% (P < 0.05), cerebral regional tissue StO2 77 ± 11 to 65 ± 9% (P < 0.01), peripheral muscle StO2 66 ± 8 to 16 ± 9% (P < 0.01), arterial lactate 1.5 ± 1.0 to 5.1 ± 0.8 mM (P < 0.01), and base excess 1.1 ± 2.2 to -3.6 ± 1.7 mM (P < 0.05). Invasive organ-specific monitoring confirmed reduced tissue oxygen delivery; oxygen tension decreased and lactate increased in all tissues, but moderately in brain. Blood volume replacement with PlasmaLyte® improved primary outcome measures toward baseline, confirmed by organ-specific measures, despite hemoglobin reduced from baseline 10.8 ± 1.2 to 5.9 ± 1.1 g/dL post-resuscitation (P < 0.01).

CONCLUSION

Non-invasive measures of tissue oxygen delivery and oxygen debt repayment are suitable outcomes to inform Patient Blood Management of hemorrhagic shock, translatable for pre-clinical assessment of novel resuscitation strategies.

Incompatible erythrocyte transfusion with lipopolysaccharide induces acute lung injury in a novel rat model

Acute transfusion reactions can manifest in many forms including acute hemolytic transfusion reaction, allergic reaction and transfusion-related acute lung injury. We previously developed an acute hemolytic transfusion reaction rat model mediated by transfusion of incompatible human erythrocytes against which rats have preexisting antibodies resulting in classical complement pathway mediated intravascular hemolysis. In this study, the acute hemolytic transfusion reaction model was adapted to yield an acute lung injury phenotype. Adolescent male Wistar rats were primed in the presence or absence of lipopolysaccharide followed by transfusion of incompatible erythrocytes. Blood was collected at various time points during the course of the experiment to determine complement C5a levels and free DNA in isolated plasma. At 4 hours, blood and lung tissue were recovered and assayed for complete blood count and histological acute lung injury, respectively. Compared to sham animals or animals receiving increasing amounts of incompatible erythrocytes (equivalent to a 15–45% transfusion) in the absence of lipopolysaccharide, lungs of animals receiving lipopolysaccharide and a 30% erythrocyte transfusion showed dramatic alveolar wall thickening due to neutrophil infiltration. C5a levels were significantly elevated in these animals indicating that complement activation contributes to lung damage. Additionally, these animals demonstrated a significant increase of free DNA in the blood over time suggestive of neutrophil extracellular trap formation previously associated with transfusion-related acute lung injury in humans and mice. This novel ‘two-hit’ model utilizing incompatible erythrocyte transfusion in the presence of lipopolysaccharide yields a robust acute lung injury phenotype.

Activation of the protein C pathway and endothelial glycocalyx shedding is associated with coagulopathy in an ovine model of trauma and hemorrhage

INTRODUCTION

Acute traumatic coagulopathy (ATC) is an endogenous coagulopathy that develops following tissue injury and shock. The pathogenesis of ATC remains poorly understood, with platelet dysfunction, activation of the protein C pathway, and endothelial glycocalyx shedding all hypothesized to contribute to onset. The primary aim of this study was to develop an ovine model of traumatic coagulopathy, with a secondary aim of assessing proposed pathophysiological mechanisms within this model.

METHODS

Twelve adult Samm-Border Leicester cross ewes were anesthetized, instrumented, and divided into three groups. The moderate trauma group (n = 4) underwent 20% blood volume hemorrhage, bilateral tibial fractures, and pulmonary contusions. The severe trauma group (n = 4) underwent the same injuries, an additional hamstring crush injury, and 30% blood volume hemorrhage. The remaining animals (n = 4) were uninjured controls. Blood samples were collected at baseline and regularly after injury for evaluation of routine hematology, arterial blood gases, coagulation and platelet function, and factor V, factor VIII, plasminogen activator inhibitor 1, syndecan 1, and hyaluranon levels.

RESULTS

At 4 hours after injury, a mean increase in international normalized ratio of 20.50% ± 12.16% was evident in the severe trauma group and 22.50% ± 1.00% in the moderate trauma group. An increase in activated partial thromboplastin time was evident in both groups, with a mean of 34.25 ± 1.71 seconds evident at 2 hours in the severe trauma animals and 34.75 ± 2.50 seconds evident at 4 hours in the moderate trauma animals. This was accompanied by a reduction in ROTEM EXTEM A10 in the severe trauma group to 40.75 ± 8.42 mm at 3 hours after injury. Arterial lactate and indices of coagulation function were significantly correlated (R = -0.86, p < 0.0001). Coagulopathy was also correlated with activation of the protein C pathway and endothelial glycocalyx shedding. While a significant reduction in platelet count was evident in the severe trauma group at 30 minutes after injury (p = 0.018), there was no evidence of altered platelet function on induced aggregation testing. Significant fibrinolysis was not evident.

CONCLUSIONS

Animals in the severe trauma group developed coagulation changes consistent with current definitions of ATC. The degree of coagulopathy was correlated with the degree of shock, quantified by arterial lactate. Activation of the protein C pathway and endothelial glycocalyx shedding were correlated with the development of coagulopathy; however, altered platelet function was not evident in this model.

Diverse coagulopathies in a rabbit model with different abdominal injuries

BACKGROUND

Although coagulopathy can be very common in severe traumatic shock patients, the exact incidence and mechanism remain unclear. In this study, a traumatic shock rabbit model with special abdomen injuries was developed and evaluated by examining indicators of clotting and fibrinolysis.

METHODS

Forty New Zealand white rabbits were randomly divided into four groups: group 1 (sham), group 2 (hemorrhage), group 3 (hemorrhage-liver injury), and group 4 (hemorrhage-liver injury/intestinal injury-peritonitis). Coagulation was detected by thromboelastography before trauma (T₀), at 1 hour (T₁) and 4 hours (T₂) after trauma.

RESULTS

Rabbits that suffered from hemorrhage alone did not differ in coagulation capacity compared with the sham group. The clot initiations (R times) of group 3 at T₁ and T₂ were both shorter than those of groups 1, 2, and 4 (P<0.05). In group 4, clot strength was decreased at T₁ and T₂ compared with those in groups 1, 2, and 3 (P<0.05), whereas the R time and clot polymerization were increased at T₂ (P<0.05). The clotting angle significantly decreased in group 4 compared with groups 2 and 3 at T₂ (P<0.05).

CONCLUSION

This study suggests that different abdominal traumatic shock show diverse coagulopathy in the early phase. Isolated hemorrhagic shock shows no obvious effect on coagulation. In contrast, blunt hepatic injury with hemorrhage shows hypercoagulability, whereas blunt hepatic injury with hemorrhage coupled with peritonitis caused by a ruptured intestine shows a tendency toward hypocoagulability.

Effects of volume resuscitation on the microcirculation in animal models of lipopolysaccharide sepsis: a systematic review

Background

Recent research has identified an increased rate of mortality associated with fluid bolus therapy for severe sepsis and septic shock, but the mechanisms are still not well understood. Fluid resuscitation therapy administered for sepsis and septic shock targets restoration of the macro-circulation, but the pathogenesis of sepsis is complex and includes microcirculatory dysfunction.

Objective

The objective of the study is to systematically review data comparing the effects of different types of fluid resuscitation on the microcirculation in clinically relevant animal models of lipopolysaccharide-induced sepsis.

Methods

A structured search of PubMed/MEDLINE and EMBASE for relevant publications from 1 January 1990 to 31 December 2015 was performed, in accordance with PRISMA guidelines.

Results

The number of published papers on sepsis and the microcirculation has increased steadily over the last 25 years. We identified 11 experimental animal studies comparing the effects of different fluid resuscitation regimens on the microcirculation. Heterogeneity precluded any meta-analysis.

Conclusions

Few animal model studies have been published comparing the microcirculatory effects of different types of fluid resuscitation for sepsis and septic shock. Biologically relevant animal model studies remain necessary to enhance understanding regarding the mechanisms by which fluid resuscitation affects the microcirculation and to facilitate the transfer of basic science discoveries to clinical applications.

The influence of the storage lesion(s) on pediatric red cell transfusion

PURPOSE OF REVIEW

This article will analyze and evaluate the current evidence regarding the use of older, longer-stored red blood cells (RBCs) for transfusion in pediatric patients and will examine some of the postulated mechanisms of injury related to prolonged refrigerated storage of RBCs and studies reporting clinical outcomes.

RECENT FINDINGS

Three randomized controlled trials and seven observational studies have been conducted entirely in pediatric patients. The outcomes, mortality and morbidity in critically ill patients and children undergoing cardiac surgery, and necrotizing enterocolitis in premature infants, have been inconsistent. However, many of these studies have been confounded by study design, mixed patient populations, red cell preparation, and other factors.

SUMMARY

Further exploration into the possible deleterious effects of older, longer-stored RBC transfusions on mortality and morbidity in different pediatric populations is merited. Understanding the potential mechanisms of injury should help explain the clinical findings.

Fetal Anemia With Persistent Pulmonary Hypertension: A Report of 3 Cases

Fetal anemia may cause tissue hypoxia and hence has the potential to predispose to persistent pulmonary hypertension of the newborn (PPHN). Review articles and textbooks do not include severe anemia as a cause of PPHN. We report 3 cases of fetal anemia complicated by severe PPHN.

Optimal management of the critically ill: anaesthesia, monitoring, data capture, and point-of-care technological practices in ovine models of critical care

Animal models of critical illness are vital in biomedical research. They provide possibilities for the investigation of pathophysiological processes that may not otherwise be possible in humans. In order to be clinically applicable, the model should simulate the critical care situation realistically, including anaesthesia, monitoring, sampling, utilising appropriate personnel skill mix, and therapeutic interventions. There are limited data documenting the constitution of ideal technologically advanced large animal critical care practices and all the processes of the animal model. In this paper, we describe the procedure of animal preparation, anaesthesia induction and maintenance, physiologic monitoring, data capture, point-of-care technology, and animal aftercare that has been successfully used to study several novel ovine models of critical illness. The relevant investigations are on respiratory failure due to smoke inhalation, transfusion related acute lung injury, endotoxin-induced proteogenomic alterations, haemorrhagic shock, septic shock, brain death, cerebral microcirculation, and artificial heart studies. We have demonstrated the functionality of monitoring practices during anaesthesia required to provide a platform for undertaking systematic investigations in complex ovine models of critical illness.

Does prolonged storage of red blood cells cause harm?

Red blood cells (RBCs) degrade progressively during the weeks of refrigerated storage. No universally accepted definition of 'fresh' or 'old' RBCs exists. While practices vary from country to country, preservative solutions permitting shelf life as long as 7 weeks have been licenced. Transfusion of stored RBCs, particularly those at the end of the approved shelf life, has been implicated in adverse clinical outcomes. The results of observational analyses, animal models and studies in volunteers have proved provocative, controversial and contradictory. A recently completed randomized controlled trial (RCT) in premature infants exemplifies the difficulties with moderately sized clinical studies. Several other RCTs are in progress. The effect of RBC storage may well vary according to the clinical setting. Resolution of the importance of the storage lesion may require large pragmatic clinical trials. In the meantime, institutions involved in blood collection and transfusion should explore strategies that assure blood availability, while limiting the use of the oldest RBCs currently approved by regulation.

A comprehensive ovine model of blood transfusion

BACKGROUND

The growing awareness of transfusion-associated morbidity and mortality necessitates investigations into the underlying mechanisms. Small animals have been the dominant transfusion model but have associated limitations. This study aimed to develop a comprehensive large animal (ovine) model of transfusion encompassing: blood collection, processing and storage, compatibility testing right through to post-transfusion outcomes.

MATERIALS AND METHODS

Two units of blood were collected from each of 12 adult male Merino sheep and processed into 24 ovine-packed red blood cell (PRBC) units. Baseline haematological parameters of ovine blood and PRBC cells were analysed. Biochemical changes in ovine PRBCs were characterized during the 42-day storage period. Immunological compatibility of the blood was confirmed with sera from potential recipient sheep, using a saline and albumin agglutination cross-match. Following confirmation of compatibility, each recipient sheep (n = 12) was transfused with two units of ovine PRBC.

RESULTS

Procedures for collecting, processing, cross-matching and transfusing ovine blood were established. Although ovine red blood cells are smaller and higher in number, their mean cell haemoglobin concentration is similar to human red blood cells. Ovine PRBC showed improved storage properties in saline-adenine-glucose-mannitol (SAG-M) compared with previous human PRBC studies. Seventy-six compatibility tests were performed and 17·1% were incompatible. Only cross-match compatible ovine PRBC were transfused and no adverse reactions were observed.

CONCLUSION

These findings demonstrate the utility of the ovine model for future blood transfusion studies and highlight the importance of compatibility testing in animal models involving homologous transfusions.

Transfusion of 28-day-old leucoreduced or non-leucoreduced stored red blood cells induces an inflammatory response in healthy dogs

BACKGROUND AND OBJECTIVES

Studies in mice suggest that rapid transfusions of red blood cells (RBCs), refrigerator stored for longer durations, induce a pro-inflammatory cytokine response. Studies in human neonates confirm these findings; however, to date, adult human studies have failed to replicate these findings. We used healthy research dogs to begin to examine the factors affecting the cytokine response to transfusion.

MATERIALS AND METHODS

In a prospective study, healthy dogs were randomized for two autologous packed RBC transfusions after 7 (i.e. 'fresh') and 28 (i.e. 'old') days of storage, or after 28 and 7 days of storage, with or without prestorage leucoreduction (LR).

RESULTS

No significant differences were observed between LR and non-LR transfusions for all circulating analytes measured following transfusion. A pro-inflammatory cytokine response, exemplified by monocyte chemoattractant protein-1, was observed 6 h after only old RBC transfusions, irrespective of infusion rate (P < 0·001). This response was accompanied by increased neutrophil counts (P < 0·001) and decreased platelet counts (P < 0·001).

CONCLUSION

In healthy dogs, old RBC transfusions induce inflammation, which is unaffected by infusion rate.