Mortality-associated risk factors for transfusion-associated circulatory overload.

BACKGROUND AND OBJECTIVES: Respiratory transfusion reactions associate strongly with morbidity and mortality, and transfusion-associated circulatory overload (TACO) is the leading cause of reaction-related deaths. Risk factors for TACO include transfusion speed and volume and cardiorenal comorbidities. MATERIALS AND METHODS: An academic health network haemovigilance database was interrogated to assess variables associating with 371 cases of TACO and involved-visit outcomes, using univariate and multivariate regression analysis. RESULTS: TACO reactions over 11 years were reported in 179 males and 192 females, median age (interquartile range) 65 (53-75) years. In-hospital and 28-day mortality were 17.5% and 12.9%, respectively. In univariate regression modelling, male sex, injury severity grade, product volume administered, the use of platelets and intensive care admissions were each associated with in-hospital and 28-day mortality (p < 0.05). However, after multivariate regression analysis, only male sex in transfusion recipients independently associated with mortality (p < 0.05). CONCLUSION: In this cohort, male recipient sex and platelet administration were associated with TACO-involving admissions not ending in survival.

Echocardiographic assessment of cardiovascular physiology of preterm miniature piglets supported with a pumped artificial placenta system.

OBJECTIVES: We evaluated fetal cardiovascular physiology and mode of cardiac failure in premature miniature piglets on a pumped artificial placenta (AP) circuit. METHODS: Fetal pigs were cannulated via the umbilical vessels and transitioned to an AP circuit composed of a centrifugal pump and neonatal oxygenator and maintained in a fluid-filled biobag. Echocardiographic studies were conducted to measure ventricular function, umbilical blood flow, and fluid status. In utero scans were used as control data. RESULTS: AP fetuses (n = 13; 102±4d gestational age [term 115d]; 616 ± 139 g [g]; survival 46.4 ± 46.8 h) were tachycardic and hypertensive with initially supraphysiologic circuit flows. Increased myocardial wall thickness was observed. Signs of fetal hydrops were present in all piglets. Global longitudinal strain (GLS) measurements increased in the left ventricle (LV) after transition to the circuit. Right ventricle (RV) and LV strain rate decreased early during AP support compared with in utero measurements but recovered toward the end of the experiment. Fetuses supported for >24 h had similar RV GLS to in utero controls and significantly higher GLS compared to piglets surviving only up to 24 h. CONCLUSIONS: Fetuses on a pump-supported AP circuit experienced an increase in afterload, and redistribution of blood flow between the AP and systemic circulations, associated with elevated end-diastolic filling pressures. This resulted in heart failure and hydrops. These preterm fetuses were unable to tolerate the hemodynamic changes associated with connection to the current AP circuit. To better mimic the physiology of the native placenta and preserve normal fetal cardiovascular physiology, further optimization of the circuit will be required.

Preservation of recipient plasma sphingosine-1-phosphate levels reduces transfusion-related acute lung injury.

Cold-stored (CS) platelets are once again being reintroduced for clinical use. Transfused CS platelets offer benefits over room temperature-stored (RTS) platelets such as increased hemostatic effects and prolongation of shelf-life. Despite these advantages little is known about their association with transfusion-related acute lung injury (TRALI). TRALI is associated with prolonged storage of RTS platelets and has a mortality of >15%. Determining the safety of CS platelets is important considering their proposed use in TRALI-vulnerable populations with inflammation such as surgical patients or patients with trauma. Donor platelet-derived ceramide causes TRALI, whereas donor platelet sphingosine-1-phosphate (S1P) is barrier protective. Females have higher plasma levels of S1P than males. Cold temperatures increase S1P levels in cells. Therefore, we hypothesized that female (donors or recipients) and/or CS platelets would decrease TRALI. To test this, we compared how male and female donor and recipient allogeneic platelet transfusions of CS (4°C) versus RTS (23°C) platelets stored for 5 days influence murine TRALI. Transfusion of CS platelets significantly reduced recipient lung tissue wet-to-dry ratios, bronchoalveolar lavage total protein, lung tissue myeloperoxidase enzyme activity, histological lung injury scores, and increased plasma sphingosine-1-phosphate (S1P) levels compared with RTS platelet transfusions. Female as opposed to male recipients had less TRALI and higher plasma S1P levels. Female donor mouse platelets had higher S1P levels than males. Mouse and human CS platelets had increased S1P levels compared with RTS platelets. Higher recipient plasma S1P levels appear protective considering females, and males receiving platelets from females or male CS platelets had less TRALI.NEW & NOTEWORTHY Transfusion-related acute lung injury (TRALI) though relatively rare represents a severe lung injury. The sphingolipid sphingosine-1-phosphate (S1P) regulates the severity of platelet-mediated TRALI. Female platelet transfusion recipient plasmas or stored platelets from female donors have higher S1P levels than males, which reduces TRALI. Cold storage of murine platelets preserves platelet-S1P, which reduces TRALI in platelet-transfused recipients.

Extracellular vesicles: effectors of transfusion-related acute lung injury.

Respiratory transfusion reactions represent some of the most severe adverse reactions related to receiving blood products. Of those, transfusion-related acute lung injury (TRALI) is associated with elevated morbidity and mortality. TRALI is characterized by severe lung injury associated with inflammation, pulmonary neutrophil infiltration, lung barrier leak, and increased interstitial and airspace edema that cause respiratory failure. Presently, there are few means of detecting TRALI beyond clinical definitions based on physical examination and vital signs or preventing/treating TRALI beyond supportive care with oxygen and positive pressure ventilation. Mechanistically, TRALI is thought to be mediated by the culmination of two successive proinflammatory hits, which typically comprise a recipient factor (1st hit-e.g., systemic inflammatory conditions) and a donor factor (2nd hit-e.g., blood products containing pathogenic antibodies or bioactive lipids). An emerging concept in TRALI research is the contribution of extracellular vesicles (EVs) in mediating the first and/or second hit in TRALI. EVs are small, subcellular, membrane-bound vesicles that circulate in donor and recipient blood. Injurious EVs may be released by immune or vascular cells during inflammation, by infectious bacteria, or in blood products during storage, and can target the lung upon systemic dissemination. This review assesses emerging concepts such as how EVs: 1) mediate TRALI, 2) represent targets for therapeutic intervention to prevent or treat TRALI, and 3) serve as biochemical biomarkers facilitating TRALI diagnosis and detection in at-risk patients.

Detection of clot formation & lysis In-Vitro using high frequency photoacoustic imaging & frequency analysis.

Clotting is a physiological process that prevents blood loss after injury. An imbalance in clotting factors can lead to lethal consequences such as exsanguination or inappropriate thrombosis. Clinical methods to monitor clotting and fibrinolysis typically measure the viscoelasticity of whole blood or optical density of plasma over time. Though these methods provide insights into clotting and fibrinolysis, they require milliliters of blood which can worsen anemia or only provide partial information. To overcome these limitations, a high-frequency photoacoustic (HFPA) imaging system was developed to detect clotting and lysis in blood. Clotting was initiated in vitro in reconstituted blood using thrombin and lysed with urokinase plasminogen activator. Frequency spectra measured using HFPA signals (10-40 MHz) between non-clotted blood and clotted blood differed markedly, allowing tracking of clot initiation and lysis in volumes of blood as low as 25 µL/test. HFPA imaging shows potential as a point-of-care examination of coagulation and fibrinolysis.

Impact of the Addition of a Centrifugal Pump in a Preterm Miniature Pig Model of the Artificial Placenta.

The recent demonstration of normal development of preterm sheep in an artificial extrauterine environment has renewed interest in artificial placenta (AP) systems as a potential treatment strategy for extremely preterm human infants. However, the feasibility of translating this technology to the human preterm infant remains unknown. Here we report the support of 13 preterm fetal pigs delivered at 102 ± 4 days (d) gestation, weighing 616 ± 139 g with a circuit consisting of an oxygenator and a centrifugal pump, comparing these results with our previously reported pumpless circuit (n = 12; 98 ± 4 days; 743 ± 350 g). The umbilical vessels were cannulated, and fetuses were supported for 46.4 ± 46.8 h using the pumped AP versus 11 ± 13 h on the pumpless AP circuit. Upon initiation of AP support on the pumped system, we observed supraphysiologic circuit flows, tachycardia, and hypertension, while animals maintained on a pumpless AP circuit exhibited subphysiologic flows. On the pumped AP circuit, there was a progressive decline in umbilical vein (UV) flow and oxygen delivery. We conclude that the addition of a centrifugal pump to the AP circuit improves survival of preterm pigs by augmenting UV flow through the reduction of right ventricular afterload. However, we continued to observe the development of heart failure within a matter of days.

Perioperative blood conservation strategies for pediatric scoliosis surgery.

PURPOSE: Many pediatric patients with severe scoliosis requiring surgery have baseline anemia. Pediatric scoliosis fusion surgery is associated with perioperative blood loss requiring transfusion. As such, many patients in this surgical population could benefit from a perioperative blood conservation program. METHODS: Here we present a narrative review of perioperative blood conservation strategies for pediatric scoliosis surgery involving nurses, transfusion medicine physicians, anesthesiologists, surgeons, dieticians, perfusionists and neurophysiologists spanning the pre-, intra- and postoperative phases of care. RESULTS: The review highlights how perioperative blood conservation strategies, have the potential to minimize exposures to exogenous blood products. Further, we describe a relevant example of blood conservation related to the care of a Jehovah's Witness patient undergoing staged scoliosis repair. Lastly, we outline areas which would benefit from clinical studies to further elucidate perioperative blood conservation interventions and their outcomes relevant to pediatric scoliosis surgery patients. CONCLUSION: Interdisciplinary communication and meticulous blood conservation strategies are proving to be a means of reducing if not eliminating the need for allogeneic blood products for surgical correction of pediatric scoliosis.

Achieving sustained extrauterine life: Challenges of an artificial placenta in fetal pigs as a model of the preterm human fetus.

Artificial placenta (AP) technology aims to maintain fetal circulation, while promoting the physiologic development of organs. Recent reports of experiments performed in sheep indicate the intrauterine environment can be recreated through the cannulation of umbilical vessels, replacement of the placenta with a low-resistance membrane oxygenator, and incubation of the fetus in fluid. However, it remains to be seen whether animal fetuses similar in size to the extremely preterm human infant that have been proposed as a potential target for this technology can be supported in this way. Preterm Yucatan miniature piglets are similar in size to extremely preterm human infants and share similar umbilical cord anatomy, raising the possibility to serve as a good model to investigate the AP. To characterize fetal cardiovascular physiology, the carotid artery (n = 24) was cannulated in utero and umbilical vein (UV) and umbilical artery were sampled. Fetal UV flow was measured by MRI (n = 16). Piglets were delivered at 98 ± 4 days gestation (term = 115 days), cannulated, and supported on the AP (n = 12) for 684 ± 228 min (range 195-3077 min). UV flow was subphysiologic (p = .002), while heart rate was elevated on the AP compared with in utero controls (p = .0007). We observed an inverse relationship between heart rate and UV flow (r2  = .4527; p < .001) with progressive right ventricular enlargement that was associated with reduced contractility and ultimately hydrops and circulatory collapse. We attribute this to excessive afterload imposed by supraphysiologic circuit resistance and augmented sympathetic activity. We conclude that short-term support of the preterm piglet on the AP is feasible, although we have not been able to attain normal fetal physiology. In the future, we propose to investigate the feasibility of an AP circuit that incorporates a centrifugal pump in our miniature pig model.

General medical publications during COVID-19 show increased dissemination despite lower validation.

BACKGROUND: The COVID-19 pandemic has yielded an unprecedented quantity of new publications, contributing to an overwhelming quantity of information and leading to the rapid dissemination of less stringently validated information. Yet, a formal analysis of how the medical literature has changed during the pandemic is lacking. In this analysis, we aimed to quantify how scientific publications changed at the outset of the COVID-19 pandemic. METHODS: We performed a cross-sectional bibliometric study of published studies in four high-impact medical journals to identify differences in the characteristics of COVID-19 related publications compared to non-pandemic studies. Original investigations related to SARS-CoV-2 and COVID-19 published in March and April 2020 were identified and compared to non-COVID-19 research publications over the same two-month period in 2019 and 2020. Extracted data included publication characteristics, study characteristics, author characteristics, and impact metrics. Our primary measure was principal component analysis (PCA) of publication characteristics and impact metrics across groups. RESULTS: We identified 402 publications that met inclusion criteria: 76 were related to COVID-19; 154 and 172 were non-COVID publications over the same period in 2020 and 2019, respectively. PCA utilizing the collected bibliometric data revealed segregation of the COVID-19 literature subset from both groups of non-COVID literature (2019 and 2020). COVID-19 publications were more likely to describe prospective observational (31.6%) or case series (41.8%) studies without industry funding as compared with non-COVID articles, which were represented primarily by randomized controlled trials (32.5% and 36.6% in the non-COVID literature from 2020 and 2019, respectively). CONCLUSIONS: In this cross-sectional study of publications in four general medical journals, COVID-related articles were significantly different from non-COVID articles based on article characteristics and impact metrics. COVID-related studies were generally shorter articles reporting observational studies with less literature cited and fewer study sites, suggestive of more limited scientific support. They nevertheless had much higher dissemination.

Frequency and timing of all-cause deaths in visits involving suspected transfusion reactions, and the significance of cardiopulmonary disturbances.

BACKGROUND/OBJECTIVES: Transfusion reactions (TRs) may cause or contribute to death. Cardiopulmonary TRs are distressing, and collectively account for most transfusion fatalities, though the degree to which they alter survival more broadly is unclear. Deaths (and their timing) after TRs may provide further insights. MATERIALS/METHODS: Adult (tri-hospital network) haemovigilance data (2013-2016) recorded referrals with conclusions ranging from unrelated to transfusion (UTR) to entities such as: septic TRs, serologic/haemolytic reactions, transfusion-associated circulatory overload (TACO), transfusion-associated dyspnoea (TAD), transfusion-related acute lung injury (TRALI), allergic transfusion reaction (ATR), and others. For (in- or out-patient) visits involving suspected TRs (VISTRs), all-cause mortalities (% [95% confidence interval]) and associated time-to-death (TTD) (median days, [interquartile range]) were compared. Diagnoses were defined inclusively (possible-to-definite) or strictly (probable-to-definite). RESULTS: Of 1144 events, rank order VISTR mortality following (possible-to-definite) TRs, and associated TTDs, were led by: DHTR 33% [6-19], 1 death at 123d; TRALI 32% [15-54], 6 deaths: 3d [2-20]; BaCon 21% [14-31], 17 deaths: 10d [3-28]; TACO 18% [12-26], 23 deaths: 16d [6-28]; TAD 17% [11-26]: 18 deaths, 6d [3-12]. Higher-certainty TRs ranked similarly (DHTR 50% [9-91]; BaCon 29% [12-55], 4 deaths: 12d [3-22]; and TACO 25% [16-38], 15 deaths: 21d [6-28]). VISTR mortality after TACO or TRALI significantly exceeded ATR (3·3% [2·4-5·8], P < 0·00001) but was not different from UTR events (P = 0·3). CONCLUSIONS: Only half of cardiopulmonary TRs constituted high certainty diagnoses. Nevertheless, cardiopulmonary TRs and suspected BaCon marked higher VISTR mortality with shorter TTDs. Short (<1 week) TTDs in TAD, BaCon or TRALI imply either contributing roles in death, treatment refractoriness and/or applicable TR susceptibilities in the dying.

Inflammasome activation in acute lung injury.

Inflammasomes are multiprotein complexes tasked with sensing endogenous or exogenous inflammatory signals and integrating this signal into a downstream response. Inflammasome activation has been implicated in a variety of pulmonary diseases, including pulmonary hypertension, bacterial pneumonia, COPD, and asthma. Of increasing interest is the contribution of inflammasome activation in the context of acute lung injury/acute respiratory distress syndrome (ALI/ARDS). Inflammasome activation in both the lung parenchyma and resident immune cells generates intereukin-1ß (IL-1ß) and IL-18, both of which drive the cascade of lung inflammation forward. Blockade of these responses has been shown to be beneficial in animal models and is a focus of translational research in the field. In this review, we will discuss the assembly and regulation of inflammasomes during lung inflammation, highlighting therapeutically viable effector steps. We will examine the importance of IL-1ß and IL-18, two key products of inflammasome activation, in ALI, as well as the contribution of the pulmonary endothelial cell to this process. Finally, we will explore translational research moving toward anti-inflammasome therapies for ALI/ARDS and speculate toward future directions for the field.

Platelet extracellular vesicles mediate transfusion-related acute lung injury by imbalancing the sphingolipid rheostat.

Transfusion-related acute lung injury (TRALI) is a hazardous transfusion complication with an associated mortality of 5% to 15%. We previously showed that stored (5 days) but not fresh platelets (1 day) cause TRALI via ceramide-mediated endothelial barrier dysfunction. As biological ceramides are hydrophobic, extracellular vesicles (EVs) may be required to shuttle these sphingolipids from platelets to endothelial cells. Adding to complexity, EV formation in turn requires ceramide. We hypothesized that ceramide-dependent EV formation from stored platelets and EV-dependent sphingolipid shuttling induces TRALI. EVs formed during storage of murine platelets were enumerated, characterized for sphingolipids, and applied in a murine TRALI model in vivo and for endothelial barrier assessment in vitro. Five-day EVs were more abundant, had higher long-chain ceramide (C16:0, C18:0, C20:0), and lower sphingosine-1-phosphate (S1P) content than 1-day EVs. Transfusion of 5-day, but not 1-day, EVs induced characteristic signs of lung injury in vivo and endothelial barrier disruption in vitro. Inhibition or supplementation of ceramide-forming sphingomyelinase reduced or enhanced the formation of EVs, respectively, but did not alter the injuriousness per individual EV. Barrier failure was attenuated when EVs were abundant in or supplemented with S1P. Stored human platelet 4-day EVs were more numerous compared with 2-day EVs, contained more long-chain ceramide and less S1P, and caused more endothelial cell barrier leak. Hence, platelet-derived EVs become more numerous and more injurious (more long-chain ceramide, less S1P) during storage. Blockade of sphingomyelinase, EV elimination, or supplementation of S1P during platelet storage may present promising strategies for TRALI prevention.

Association between preoperative hemoglobin levels after iron supplementation and perioperative blood transfusion requirements in children undergoing scoliosis surgery.

BACKGROUND AND AIMS: In this study, we assessed the association between preoperative hemoglobin and red blood cell transfusion in children undergoing spine surgery after the implementation of our preoperative iron supplementation protocol. METHOD: We performed a retrospective analysis of patients who underwent posterior spinal fusion surgery between January 2013 and December 2017 and received preoperative iron supplementation. We used uni- and multivariable logistic regression to determine the association between preoperative hemoglobin level and red blood cell transfusion in patients receiving iron supplementation. RESULTS: A total of 382 patients treated with preoperative oral iron were included. Of these, 175 (45.5%) patients were transfused intraoperatively. Multivariable logistic regression analysis revealed nonidiopathic etiology of the scoliosis (OR 4.178 [95% CI: 2.277-7.668], P < .001), the Cobb angle (OR 1.025 [95% CI: 1.010-1.040], P = .001), and number of vertebrae fused (OR 1.169 [95% CI: 1.042-1.312], P = .008) were associated with red blood cell transfusion. In addition, patients with a preoperative hemoglobin ≥ 140 g/L (OR 0.157 [95% CI: 0.046-0.540], P = .003), and hemoglobin between 130 and 140 g/L (OR 0.195 [95% CI: 0.057-0.669], P = .009) were less likely to be transfused compared with patients with preoperative hemoglobin between 120 and 130 g/L (OR 0.294 [95% CI: 0.780-1.082], P = .066) or <120 g/L (reference). CONCLUSION: Our study suggests that higher preoperative hemoglobin levels (>130 g/L) are associated with a reduced need for red blood cell transfusion in pediatric patients who have received iron supplementation before undergoing posterior spinal fusion in our institution. The effect of iron supplementation, the optimal dosing, and duration of supplemental iron therapy remains unclear at this time.

A regional massive hemorrhage protocol developed through a modified Delphi technique.

BACKGROUND: A massive hemorrhage protocol (MHP) enables rapid delivery of blood components in a patient who is exsanguinating pending definitive hemorrhage control, but there is variability in MHP implementation rates, content and compliance owing to challenges presented by infrequent activation, variable team performance and patient acuity. The goal of this project was to identify the key evidence-based principles and quality indicators required to develop a standardized regional MHP. METHODS: A modified Delphi consensus technique was performed in the spring and summer of 2018. Panellists used survey links to independently review and rate (on a 7-point Likert scale) 43 statements and 8 quality indicators drafted by a steering committee composed of transfusion medicine specialists and technologists, and trauma physicians. External stakeholder input from all hospitals in Ontario was sought. RESULTS: Three rounds were held with 36 experts from diverse clinical backgrounds. Consensus was reached for 42 statements and 8 quality indicators. Additional modifications from external stakeholders were incorporated to form the foundation for the proposed MHP. INTERPRETATION: This MHP template will provide the basis for the design of an MHP toolkit, including specific recommendations for pediatric and obstetrical patients, and for hospitals with limited availability of blood components or means to achieve definitive hemorrhage control. We believe that harmonization of MHPs in our region will simplify training, increase uptake of evidence-based interventions, enhance communication, improve patient comfort and safety, and, ultimately, improve patient outcomes.

Transfusion-related Acute Lung Injury in the Perioperative Patient.

Transfusion-related acute lung injury is a leading cause of death associated with the use of blood products. Transfusion-related acute lung injury is a diagnosis of exclusion which can be difficult to identify during surgery amid the various physiologic and pathophysiologic changes associated with the perioperative period. As anesthesiologists supervise delivery of a large portion of inpatient prescribed blood products, and since the incidence of transfusion-related acute lung injury in the perioperative patient is higher than in nonsurgical patients, anesthesiologists need to consider transfusion-related acute lung injury in the perioperative setting, identify at-risk patients, recognize early signs of transfusion-related acute lung injury, and have established strategies for its prevention and treatment.

Extracellular vesicles in lung health, disease, and therapy.

Both physiological homeostasis and pathological disease processes in the lung typically result from complex, yet coordinated multicellular responses that are synchronized via paracrine and endocrine intercellular communication pathways. Of late, extracellular vesicles have emerged as important information shuttles that can coordinate and disseminate homeostatic and disease signals. In parallel, extracellular vesicles in biological fluids such as sputum, mucus, epithelial lining fluid, edema fluid, the pulmonary circulation, pleural fluid, and lymphatics have emerged as promising candidate biomarkers for diagnosis and prognosis in lung disease. Extracellular vesicles are small, subcellular, membrane-bound vesicles containing cargos from parent cells such as lipids, proteins, genetic information, or entire organelles. These cargos endow extracellular vesicles with biologically active information or functions by which they can reprogram their respective target cells. Recent studies show that extracellular vesicles found in lung-associated biological fluids play key roles as biomarkers and effectors of disease. Conversely, administration of naïve or engineered extracellular vesicles with homeostatic or reparative effects may provide a promising novel protective and regenerative strategy to treat lung disease. To highlight this rapidly developing field, the American Journal of Physiology-Lung Cellular and Molecular Physiology is now launching a special Call for Papers on extracellular vesicles in lung health, disease, and therapy. This review aims to set the stage for this call by introducing extracellular vesicles and their emerging roles in lung physiology and pathobiology.

A suspected case of anesthesia-induced rhabdomyolysis in a child undergoing strabismus surgery.

We report a case of acute rhabdomyolysis following general anesthesia for strabismus surgery in a previously healthy 11-year-old girl. The patient received a depolarizing muscle relaxant (succinylcholine) and halogenated volatile anesthetic agent (sevoflurane) during surgery. In rare cases, these classes of drugs can trigger malignant hyperthermia (MH) or anesthesia-induced rhabdomyolysis (AIR), which can cause significant morbidity and mortality if not recognized and treated promptly. Pathophysiology, early recognition, and special considerations in strabismus patients are discussed.

The Regenerative Potential of Amniotic Fluid Stem Cell Extracellular Vesicles: Lessons Learned by Comparing Different Isolation Techniques.

Extracellular vesicles (EVs) derived from amniotic fluid stem cells (AFSCs) mediate anti-apoptotic, pro-angiogenic, and immune-modulatory effects in multiple disease models, such as skeletal muscle atrophy and Alport syndrome. A source of potential variability in EV biological functions is how EV are isolated from parent cells. Currently, a comparative study of different EV isolation strategies using conditioned medium from AFSCs is lacking. Herein, we examined different isolation strategies for AFSC-EVs, using common techniques based on differential sedimentation (ultracentrifugation), solubility (ExoQuick, Total Exosome Isolation Reagent, Exo-PREP), or size-exclusion chromatography (qEV). All techniques isolated AFSC-EVs with typical EV morphology and protein markers. In contrast, AFSC-EV size, protein content, and yield varied depending on the method of isolation. When equal volumes of the different AFSC-EV preparations were used as treatment in a model of lung epithelial injury, we observed a significant variation in how AFSC-EVs were able to protect against cell death. AFSC-EV enhancement of cell survival appeared to be dose dependent, and largely uninfluenced by variation in EV-size distributions, relative EV-purity, or their total protein content. The variation in EV-mediated cell survival obtained with different isolation strategies emphasizes the importance of testing alternative isolation techniques in order to maximize EV regenerative capacity.