Impact of anticoagulation intensity on blood transfusion for venoarterial extracorporeal membrane oxygenation during lung transplantation.

Venoarterial extracorporeal membrane oxygenation is increasingly used for mechanical circulatory support during lung transplant. Optimal intensity of intraoperative anticoagulation would be expected to mitigate thromboembolism without increasing bleeding and blood product transfusions. Yet, the optimal intensity of intraoperative anticoagulation is unknown. We performed a retrospective cohort study of 163 patients who received a bilateral lung transplant at a single center. We categorized the intensity of anticoagulation into 4 groups (very low to high) based on the bolus dose of unfractionated heparin given during lung transplant and compared the rates of intraoperative blood transfusions and the occurrence of thromboembolism between groups. When compared to the very low-intensity group, each higher intensity group was associated with higher red blood cell, fresh frozen plasma, and platelet transfusions. The occurrence of thromboembolism was similar across groups. These preliminary data suggest that lower intensity anticoagulation may reduce the rate of intraoperative blood transfusions, although further study is needed.

Ambulatory 7-day mechanical circulatory support in sheep model of pulmonary hypertension and right heart failure.

BACKGROUND: Right heart failure is the major cause of death in pulmonary hypertension. Lung transplantation is the only long-term treatment option for patients who fail medical therapy. Due to the scarcity of donor lungs, there is a critical need to develop durable mechanical support for the failing right heart. A major design goal for durable support is to reduce the size and complexity of devices to facilitate ambulation. Toward this end, we sought to deploy wearable mechanical support technology in a sheep disease model of chronic right heart failure. METHODS: In 6 sheep with chronic right heart failure, a mechanical support system consisting of an extracorporeal blood pump coupled with a gas exchange unit was attached in a right atrium-to-left atrium configuration for up to 7 days. Circuit performance, hematologic parameters, and animal hemodynamics were analyzed. RESULTS: Six subjects underwent the chronic disease model for 56 to 71 days. Three of the subjects survived to the 7-day end-point for circulatory support. The circuit provided 2.8 (0.5) liter/min of flow compared to the native pulmonary blood flow of 3.5 (1.1) liter/min. The animals maintained physiologically balanced blood gas profile with a sweep flow of 1.2 (1.0) liter/min. Two animals freely ambulated while wearing the circuit. CONCLUSIONS: Our novel mechanical support system provided physiologic support for a large animal model of pulmonary hypertension with right heart failure. The small footprint of the circuit and the low sweep requirement demonstrate the feasibility of this technology to enable mobile ambulatory applications.

Xenogeneic cross-circulation for physiological support and recovery of ex vivo human livers.

BACKGROUND AND AIMS: The scarcity of suitable donor livers highlights a continuing need for innovation to recover organs with reversible injuries in liver transplantation. APPROACH AND RESULTS: Explanted human donor livers (n = 5) declined for transplantation were supported using xenogeneic cross-circulation of whole blood between livers and xeno-support swine. Livers and swine were assessed over 24 hours of xeno-support. Livers maintained normal global appearance, uniform perfusion, and preservation of histologic and subcellular architecture. Oxygen consumption increased by 75% ( p = 0.16). Lactate clearance increased from -0.4 ± 15.5% to 31.4 ± 19.0% ( p = 0.02). Blinded histopathologic assessment demonstrated improved injury scores at 24 hours compared with 12 hours. Vascular integrity and vasoconstrictive function were preserved. Bile volume and cholangiocellular viability markers improved for all livers. Biliary structural integrity was maintained. CONCLUSIONS: Xenogeneic cross-circulation provided multisystem physiological regulation of ex vivo human livers that enabled functional rehabilitation, histopathologic recovery, and improvement of viability markers. We envision xenogeneic cross-circulation as a complementary technique to other organ-preservation technologies in the recovery of marginal donor livers or as a research tool in the development of advanced bioengineering and pharmacologic strategies for organ recovery and rehabilitation.

Immune characterization of a xenogeneic human lung cross-circulation support system.

Improved approaches to expanding the pool of donor lungs suitable for transplantation are critically needed for the growing population with end-stage lung disease. Cross-circulation (XC) of whole blood between swine and explanted human lungs has previously been reported to enable the extracorporeal recovery of donor lungs that declined for transplantation due to acute, reversible injuries. However, immunologic interactions of this xenogeneic platform have not been characterized, thus limiting potential translational applications. Using flow cytometry and immunohistochemistry, we demonstrate that porcine immune cell and immunoglobulin infiltration occurs in this xenogeneic XC system, in the context of calcineurin-based immunosuppression and complement depletion. Despite this, xenogeneic XC supported the viability, tissue integrity, and physiologic improvement of human donor lungs over 24 hours of xeno-support. These findings provide targets for future immunomodulatory strategies to minimize immunologic interactions on this organ support biotechnology.

Area Deprivation Index and Distress Community Index Scores Are Not Associated With Short-Term and Long-Term Extracorporeal Life Support Outcomes.

Distressed Communities Index (DCI) and Area Deprivation Index (ADI) are two composite ranking scores that report community level socioeconomic status (SES) by ZIP codes. The objective of this study was to evaluate the impact of SES as estimated by DCI and ADI scores on short-term and long-term outcomes after extracorporeal life support (ECLS) at a quaternary medical center. All patients on ECLS between January 1, 2015 and August 31, 2020 (N = 428) at Vanderbilt University Medical Center in Nashville, Tennessee, had their ADI and DCI scores calculated. Primary outcome was mortality during index hospitalization, and secondary outcome was survival to end of study follow-up. There was no significant difference in primary outcome between the top 25% ADI vs . bottom 75% ADI (53.8% vs . 50.6%; p = 0.56) or between top 25% DCI vs . bottom 75% DCI (56.1 vs . 49.2; p = 0.21). Adjusted odds ratio for the primary outcome with ADI and DCI was 1.13 (95% CI, 0.63-2.0; p = 0.67) and 1.28 (95% CI, 0.70-2.34; p = 0.41), respectively. Additionally, there was no significant difference in long-term survival curves based on their ADI or DCI scores. In conclusion, SES as estimated by baseline DCI and ADI scores does not appear to impact short- or long-term survival post-ECLS at a large volume center. http://links.lww.com/ASAIO/A951.

Large animal preclinical investigation into the optimal extracorporeal life support configuration for pulmonary hypertension and right ventricular failure.

INTRODUCTION: Right ventricular failure (RVF) is a major cause of mortality in pulmonary hypertension (PH). Mechanical circulatory support holds promise for patients with medically refractory PH, but there are no clinical devices for long-term right ventricular (RV) support. Investigations into optimal device parameters and circuit configurations for PH-induced RVF (PH-RVF) are needed. METHODS: Eleven sheep underwent previously published chronic PH model. We then evaluated a low-profile, ventricular assist device (VAD)-quality pump combined with a novel low-resistance membrane oxygenator (Pulmonary Assist Device, PAD) under one of four central cannulation strategies: right atrium-to-left atrium (RA-LA, N = 3), RA-to-pulmonary artery (RA-PA, N=3), pumpless pulmonary artery-to-left atrium (PA-LA, N = 2), and RA-to-ascending aorta (RA-Ao, N = 3). Acute-on-chronic RVF (AoC RVF) was induced, and mechanical support was provided for up to 6 hours at blood flow rates of 1 to 3 liter/min. Circuit parameters, physiologic, hemodynamic, and echocardiography data were collected. RESULTS: The RA-LA configuration achieved blood flow of 3 liter/min. Meanwhile, RA-PA and RA-Ao faced challenges maintaining 3 liter/min of flow due to higher circuit afterload. Pumpless PA-LA was flow-limited due to anatomical limitations inherent to this animal model. RA-LA and RA-Ao demonstrated serial RV unloading with increasing circuit flow, while RA-PA did not. RA-LA also improved left ventricular (LV) and septal geometry by echocardiographic assessment and had the lowest inotropic dependence. CONCLUSION: RA-LA and RA-Ao configurations unload the RV, while RA-LA also lowers pump speed and inotropic requirements, and improves LV mechanics. RA-PA provide inferior support for PH-RVF, while an alternate animal model is needed to evaluate PA-LA.

Technique for xenogeneic cross-circulation to support human donor lungs ex vivo.

BACKGROUND: Xenogeneic cross-circulation (XC) is an experimental method for ex vivo organ support and recovery that could expand the pool of donor lungs suitable for transplantation. The objective of this study was to establish and validate a standardized, reproducible, and broadly applicable technique for performing xenogeneic XC to support and recover injured human donor lungs ex vivo. METHODS: Human donor lungs (n = 9) declined for transplantation were procured, cannulated, and subjected to 24 hours of xenogeneic XC with anesthetized xeno-support swine (Yorkshire/Landrace) treated with standard immunosuppression (methylprednisolone, mycophenolate mofetil, tacrolimus) and complement-depleting cobra venom factor. Standard lung-protective perfusion and ventilation strategies, including periodic lung recruitment maneuvers, were used throughout xenogeneic XC. Every 6 hours, ex vivo donor lung function (gas exchange, compliance, airway pressures, pulmonary vascular dynamics, lung weight) was evaluated. At the experimental endpoint, comprehensive assessments of the lungs were performed by bronchoscopy, histology, and electron microscopy. Student's t-test and 1-way analysis of variance with Dunnett's post-hoc test was performed, and p < 0.05 was considered significant. RESULTS: After 24 hours of xenogeneic XC, gas exchange (PaO2/FiO2) increased by 158% (endpoint: 364 ± 142 mm Hg; p = 0.06), and dynamic compliance increased by 127% (endpoint: 46 ± 20 ml/cmH2O; p = 0.04). Airway pressures, pulmonary vascular pressures, and lung weight remained stable (p > 0.05) and within normal ranges. Over 24 hours of xenogeneic XC, gross and microscopic lung architecture were preserved: airway bronchoscopy and parenchymal histomorphology appeared normal, with intact blood-gas barrier. CONCLUSIONS: Xenogeneic cross-circulation is a robust method for ex vivo support, evaluation, and improvement of injured human donor lungs declined for transplantation.

Extracorporeal Membrane Oxygenation Selection by Multidisciplinary Consensus: The ECMO Council.

Coronavirus disease 2019 (COVID-19) has increased the demand for extracorporeal membrane oxygenation (ECMO) and introduced distinct challenges to patient selection for ECMO. Standardized processes for patient selection amidst resource limitations are lacking, and data on ECMO consults are underreported. We retrospectively reviewed consecutive adult ECMO consults for acute respiratory failure received at a single academic medical center from April 1, 2020, to February 28, 2021, and evaluated the implementation of a multidisciplinary selection committee (ECMO Council) and standardized framework for patient selection for ECMO. During the 334-day period, there were 202 total ECMO consults; 174 (86.1%) included a diagnosis of COVID-19. Among all consults, 157 (77.7%) were declined and 41 (20.3%) resulted in the initiation of ECMO. Frequent reasons for decline included the presence of multiple relative contraindications (n = 33), age greater than 60 years (n = 32), and resource limitations (n = 27). The ECMO Council deliberated on every case in which an absolute contraindication was not present (n = 96) via an electronic teleconference platform. Utilizing multidisciplinary consensus together with a standardized process for patient selection in ECMO is feasible during a pandemic and may be reliably exercised over time. Whether such an approach is feasible at other centers remains unknown.

Extracorporeal membrane oxygenation circuits in parallel for refractory hypoxemia in patients with COVID-19.

OBJECTIVES: Refractory hypoxemia can occur in patients with acute respiratory distress syndrome from COVID-19 despite support with venovenous (VV) extracorporeal membrane oxygenation (ECMO). Parallel ECMO circuits can be used to increase physiologic support. We report our clinical experience using ECMO circuits in parallel for select patients with persistent severe hypoxemia despite the use of a single ECMO circuit. METHODS: We performed a retrospective cohort study of all patients with COVID-19-related acute respiratory distress syndrome who received VV-ECMO with an additional circuit in parallel at Vanderbilt University Medical Center between March 1, 2020, and March 1, 2022. We report demographic characteristics and clinical characteristics including ECMO settings, mechanical ventilator settings, use of adjunctive therapies, and arterial blood gas results after initial cannulation, before and after receipt of a second ECMO circuit in parallel, and before removal of the circuit in parallel, and outcomes. RESULTS: Of 84 patients with COVID-19 who received VV-ECMO during the study period, 22 patients (26.2%) received a circuit in parallel. The median duration of ECMO was 40.0 days (interquartile range, 31.6-53.1 days), of which 19.0 days (interquartile range, 13.0-33.0 days) were spent with a circuit in parallel. Of the 22 patients who received a circuit in parallel, 16 (72.7%) survived to hospital discharge and 6 (27.3%) died before discharge. CONCLUSIONS: In select patients, the additional use of an ECMO circuit in parallel can increase ECMO blood flow and improve oxygenation while allowing for lung-protective mechanical ventilation and excellent outcomes.

Extracorporeal Membrane Oxygenation Circuits in Parallel for Refractory Hypoxemia in COVID-19: A Case Series.

Refractory hypoxemia despite the use of extracorporeal membrane oxygenation (ECMO) for coronavirus disease 2019 (COVID-19)-related acute respiratory distress syndrome remains a challenging problem. A single ECMO circuit may not provide adequate physiologic support in the setting of an elevated cardiac output, physiologic demand, and impaired gas exchange. In select patients with refractory hypoxemia, addition of a second ECMO circuit in parallel can improve oxygenation, facilitate lung protective ventilation, awakening, and physical rehabilitation. We report the largest case series to date of patients receiving ECMO circuits in parallel and the first to report this approach in COVID-19.

Bridge to Transplant: Central Extracorporeal Membrane Oxygenation With Pulmonary Artery Drainage.

Providing optimal support in patients with concomitant cardiac and pulmonary failure presents multiple challenges. We report a novel approach to central extracorporeal membrane oxygenation support using a minimal access approach to successfully bridge a patient to heart-lung transplant.

Simulation Versus Interactive Mobile Learning for Teaching Extracorporeal Membrane Oxygenation to Clinicians: A Randomized Trial.

OBJECTIVES: Extracorporeal membrane oxygenation has become integral to critical care. Data informing optimal extracorporeal membrane oxygenation education modalities are lacking. We aimed to compare the effect of high-fidelity simulation versus interactive mobile learning on extracorporeal membrane oxygenation knowledge acquisition and retention among clinicians. DESIGN: Observer-blinded, randomized controlled trial. SETTING: A single academic medical center. SUBJECTS: Forty-four critical care clinicians with limited extracorporeal membrane oxygenation experience. INTERVENTIONS: Participants were randomized to receive: 1) simulation: three high-fidelity training scenarios, 2) QuizTime: 15 total multiple-choice questions delivered over 3 weeks via mobile device, or 3) experiential: no formal training. Participants completed a survey, written knowledge examination, and simulation assessment prior to randomization, immediately following the intervention, and 4 month postintervention. MEASUREMENTS AND MAIN RESULTS: The primary outcome was knowledge about extracorporeal membrane oxygenation assessed by score on the immediate postintervention written examination. Secondary outcomes included performance in extracorporeal membrane oxygenation simulation postintervention and 4 months later assessed by a rater blinded to group assignment. Clinicians randomized to simulation (n = 15), QuizTime (n = 14), and experiential (n = 15) had similar baseline characteristics. Adjusting for baseline knowledge, postintervention examination scores were higher in the simulation group (90.0%; interquartile range, 85.0-90.0%) than the QuizTime group (70.0%; interquartile range, 65.0-80.0%; p = 0.0003) and the experiential group (75.0%; interquartile range, 65.0-80.0%; p = 0.001). Scores did not differ between the groups at 4 months (p > 0.05 in all analyses). In postintervention extracorporeal membrane oxygenation simulations, the simulation group demonstrated shorter time to critical action compared with QuizTime (80.0 s [interquartile range, 54.0-111.0 s] vs 300.0 s [interquartile range 85.0-300.0 s]; p = 0.02) and compared with both QuizTime (45.0 s [interquartile range, 34.0-92.5 s] vs 255.5 s [interquartile range, 102.0-300.0 s]; p = 0.008) and experiential (300.0 s [interquartile range, 58.0-300.0 s]; p = 0.009) at 4 months. CONCLUSIONS: Simulation was superior to QuizTime and experiential learning with regard to extracorporeal membrane oxygenation knowledge acquisition. Further studies are needed to ascertain the effect of these interventions on knowledge retention, clinical performance, and patient outcomes.

Clinician Ethical Perspectives on Extracorporeal Membrane Oxygenation in Practice.

PURPOSE: Extracorporeal membrane oxygenation (ECMO) is an expensive and scarce life sustaining treatment provided to certain critically ill patients. Little is known about the informed consent process for ECMO or clinician viewpoints on ethical complexities related to ECMO in practice. METHODS: We sent a cross-sectional survey to all departments providing ECMO within 7 United States hospitals in January 2021. One clinician from each department completed the 42-item survey representing their department. RESULTS: Fourteen departments within 7 hospitals responded (response rate 78%, N = 14/18). The mean time spent consenting patients or surrogate decision-makers for ECMO varied, from 7.5 minutes (95% CI 5-10) for unstable patients to 20 minutes (95% CI 15-30) for stable patients (p = 0.0001). Few clinician respondents (29%) report patients or surrogate decision-makers always possess informed consent for ECMO. Most departments (92%) have absolute exclusion criteria for ECMO such as older age (43%, cutoffs ranging from 60-75 years), active malignancy (36%), and elevated body mass index (29%). A significant minority of departments (29%) do not always offer the option to withdraw ECMO to patients or surrogate decision-makers. For patients who cannot be liberated from ECMO and are ineligible for heart or lung transplant, 36% of departments would recommend the patient be removed from ECMO and 64% would continue ECMO support. CONCLUSION: Adequate informed consent for ECMO is a major ethical challenge, and the content of these discussions varies. Use of categorical exclusion criteria and withdrawal of ECMO if a patient cannot be liberated from it differ among departments and institutions.

Cross-Circulation for Extracorporeal Liver Support in a Swine Model.

Although machine perfusion has gained momentum as an organ preservation technique in liver transplantation, persistent organ shortages and high waitlist mortality highlight unmet needs for improved organ salvage strategies. Beyond preservation, extracorporeal organ support platforms can also aid the development and evaluation of novel therapeutics. Here, we report the use of veno-arterial-venous (V-AV) cross-circulation (XC) with a swine host to provide normothermic support to extracorporeal livers. Functional, biochemical, and morphological analyses of the extracorporeal livers and swine hosts were performed over 12 hours of support. Extracorporeal livers maintained synthetic function through alkaline bile production and metabolic activity through lactate clearance and oxygen consumption. Beyond initial reperfusion, no biochemical evidence of hepatocellular injury was observed. Histopathologic injury scoring showed improvements in sinusoidal dilatation and composite acute injury scores after 12 hours. Swine hosts remained hemodynamically stable throughout XC support. Altogether, these outcomes demonstrate the feasibility of using a novel V-AV XC technique to provide support for extracorporeal livers in a swine model. V-AV XC has potential applications as a translational research platform and clinical biotechnology for donor organ salvage.

Progression Toward Decompensated Right Ventricular Failure in the Ovine Pulmonary Hypertension Model.

Decompensated right ventricular failure (RVF) in patients with pulmonary hypertension (PH) is fatal, with limited treatment options. Novel mechanical circulatory support systems have therapeutic potential for RVF, but the development of these devices requires a large animal disease model that replicates the pathophysiology observed in humans. We previously reported an effective disease model of PH in sheep through ligation of the left pulmonary artery (PA) and progressive occlusion of the main PA. Herein, we report a case of acute decompensation with this model of chronic RVF. Gradual PA banding raised the RV pressure (maximum RV systolic/mean pressure = 95 mmHg/56 mmHg). Clinical findings and laboratory serum parameters suggested appropriate physiologic compensation for 7 weeks. However, mixed venous saturation declined precipitously on week 7, and creatinine increased markedly on week 9. By the 10th week, the animal developed dependent, subcutaneous edema. Subsequently, the animal expired during the induction of general anesthesia. Post-mortem evaluation revealed several liters of pleural effusion and ascites, RV dilatation, eccentric RV hypertrophy, and myocardial fibrosis. The presented case supports this model's relevance to the human pathophysiology of RVF secondary to PH and its value in the development of novel devices, therapeutics, and interventions.