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.

Lung endothelial cells regulate pulmonary fibrosis through FOXF1/R-Ras signaling

Pulmonary fibrosis results from dysregulated lung repair and involves multiple cell types. The role of endothelial cells (EC) in lung fibrosis is poorly understood. Using single cell RNA-sequencing we identified endothelial transcription factors involved in lung fibrogenesis, including FOXF1, SMAD6, ETV6 and LEF1. Focusing on FOXF1, we found that FOXF1 is decreased in EC within human idiopathic pulmonary fibrosis (IPF) and mouse bleomycin-injured lungs. Endothelial-specific Foxf1 inhibition in mice increased collagen depositions, promoted lung inflammation, and impaired R-Ras signaling. In vitro, FOXF1-deficient EC increased proliferation, invasion and activation of human lung fibroblasts, and stimulated macrophage migration by secreting IL-6, TNFα, CCL2 and CXCL1. FOXF1 inhibited TNFα and CCL2 through direct transcriptional activation of Rras gene promoter. Transgenic overexpression or endothelial-specific nanoparticle delivery of Foxf1 cDNA decreased pulmonary fibrosis in bleomycin-injured mice. Nanoparticle delivery of FOXF1 cDNA can be considered for future therapies in IPF.

Normothermic regional perfusion for donation after circulatory death donors

PURPOSE OF REVIEW

This review is intended to provide an update on the logistics, technique, and outcomes associated with normothermic regional perfusion (NRP), as well as provide a discussion of the associated ethical issues.

RECENT FINDINGS

There has been renewed interest in utilizing NRP to increase quality and availability of organs from donation after circulatory death (DCD) donors. Our institution has increasing experience with thoraco-abdominal NRP (TA-NRP) in controlled DCD donors (cDCD), whereas abdominal NRP (A-NRP) has been used with success in both cDCD and uncontrolled DCD (uDCD). There is increasing evidence that NRP can be conducted in a practical and cost-efficient manner, and that the organ yield may be of better quality than standard direct procurement and perfusion (DPP).

SUMMARY

NRP is increasingly successful and will likely prove to be a superior method for cDCD recovery. However, before TA-NRP can be widely accepted the ethical debate surrounding this technique must be settled.

VIDEO ABSTRACT

http://links.lww.com/COOT/A11.

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.

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.

Pathological remodeling of distal lung matrix in end-stage cystic fibrosis patients

BACKGROUND

Manifestations of cystic fibrosis, although well-characterized in the proximal airways, are understudied in the distal lung. Characterization of the cystic fibrosis lung 'matrisome' (matrix proteome) has not been previously described, and could help identify biomarkers and inform therapeutic strategies.

METHODS

We performed liquid chromatography-mass spectrometry, gene ontology analysis, and multi-modal imaging, including histology, immunofluorescence, and electron microscopy for a comprehensive evaluation of distal human lung extracellular matrix (matrix) structure and composition in end-stage cystic fibrosis.

RESULTS

Quantitative proteomic profiling identified sixty-eight (68) matrix constituents with significantly altered expression in end-stage cystic fibrosis. Over 90% of significantly different matrix peptides detected, including structural and basement membrane proteins, were expressed at lower levels in cystic fibrosis. However, the total abundance of matrix in cystic fibrosis lungs was not significantly different from control lungs, suggesting that cystic fibrosis leads to loss of diversity among lung matrix proteins rather than an absolute loss of matrix. Visualization of distal lung matrix via immunofluorescence and electron microscopy revealed pathological remodeling of distal lung tissue architecture and loss of alveolar basement membrane, consistent with significantly altered pathways identified by gene ontology analysis.

CONCLUSIONS

Dysregulation of matrix organization and aberrant wound healing pathways are associated with loss of matrix protein diversity and obliteration of distal lung tissue structure in end-stage cystic fibrosis. While many therapeutics aim to functionally restore defective cystic fibrosis transmembrane conductance regulator (CFTR), drugs that target dysregulated matrix pathways may serve as adjunct interventions to support lung recovery.

Disposable Component Selection in Extracorporeal Life Support: A Cost Analysis

Extracorporeal life support (ECLS) is a resource-intensive technology. Disposable components are modifiable through device selection. Cost analysis tools are needed to inform cost-conscious device selection. We generated a disposable cost analysis to forecast estimated costs of device disposables that included an assumption table, net present value (NPV) analysis, and sensitivity analysis to examine device disposable costs over 5 years with different case volumes and device mixes. To demonstrate the function of the analysis, we included four device options using the following assumptions: 100 cases in year 1, 2.5% case growth rate, 10% discount rate, and $5,000 incremental cost (Device 4 only). Using estimated device costs of $3,000, $12,000, $13,000, and $20,000 and device mix percentages of 65%, 8%, 25%, and 2% for Device 1, 2, 3, and 4, respectively, the 5 year unadjusted and NPV of disposable device costs were $3,691,000 and $2,765,000, respectively. The sensitivity analysis incorporated six separate models with different device mix percentages. The highest and lowest estimated costs were found in Model F (75% Device 3 and 25% Device 4; NPV = $6,64,400) and Model B (100% Device 1; NPV = 1,246,000) respectively. Extracorporeal life support programs may apply this disposable cost analysis tool to reduce programmatic costs.

Left Pulmonary Artery Ligation and Chronic Pulmonary Artery Banding Model for Inducing Right Ventricular-Pulmonary Hypertension in Sheep

Pulmonary hypertension (PH) is a progressive disease that leads to cardiopulmonary dysfunction and right heart failure from pressure and volume overloading of the right ventricle (RV). Mechanical cardiopulmonary support has theoretical promise as a bridge to organ transplant or destination therapy for these patients. Solving the challenges of mechanical cardiopulmonary support for PH and RV failure requires its testing in a physiologically relevant animal model. Previous PH models in large animals have used pulmonary bead embolization, which elicits unpredictable inflammatory responses and has a high mortality rate. We describe a step-by-step guide for inducing pulmonary hypertension and right ventricular hypertrophy (PH-RVH) in sheep by left pulmonary artery (LPA) ligation combined with progressive main pulmonary artery (MPA) banding. This approach provides a controlled method to regulate RV afterload as tolerated by the animal to achieve PH-RVH, while reducing acute mortality. This animal model can facilitate evaluation of mechanical support devices for PH and RV failure.

Curriculum to Introduce Critical Care Nurses to Extracorporeal Membrane Oxygenation

BACKGROUND

Despite the growing use of extracorporeal membrane oxygenation (ECMO) in intensive care units (ICUs), no standardized ECMO training pathways are available for ECMO-naive critical care nurses.

OBJECTIVES

To evaluate a critical care nurse ECMO curriculum that may be reproducible across institutions.

METHODS

An ECMO curriculum consisting of a basic safety course and an advanced user course was designed for critical care nurses. Courses incorporated didactic and simulation components, written knowledge examinations, and electronic modules. Differences in examination scores before and after each course for the overall cohort and for participants from each ICU type were analyzed with t tests or nonparametric equality-of-medians tests. Differences in postcourse scores across ICU types were examined with multiple linear regression.

RESULTS

Critical care nurses new to ECMO (n = 301) from various ICU types participated in the basic safety course; 107 nurses also participated in the advanced user course. Examination scores improved after completion of both courses for overall cohorts (P < .001 in all analyses). Median (interquartile range) individual score improvements were 23.1% (15.4%-38.5%) for the basic safety course and 8.4% (0%-16.7%) for the advanced user course. Postcourse written examination scores stratified by ICU type, compared with the medical ICU/cardiovascular ICU group (reference group), differed only in the neurovascular ICU group for the basic safety course (percent score difference, -3.0; 95% CI, -5.3 to -0.8; P = .01).

CONCLUSIONS

Implementation of an ECMO curriculum for a high volume of critical care nurses is feasible and effective.

A Dual-Lumen Bicaval Cannula for Venovenous Extracorporeal Membrane Oxygenation

BACKGROUND

Single-site, dual-lumen venovenous extracorporeal membrane oxygenation ECMO) facilitates mobilization, reduces recirculation, and mitigates insertion and infectious risks of an additional access site. This study reports the experience with a bicaval dual-lumen cannula that comprises a robust physical design allowing for easy and safe cannulation, precise positioning and monitoring, and appropriate physiologic support for patients with acute respiratory failure.

METHODS

Statistical analysis was performed from data gathered retrospectively from the electronic medical records of 20 adult patients who were cannulated for ECMO with this bicaval dual-lumen cannula from August 2018 through May 2019.

RESULTS

Gas exchange and blood flow were optimized in all patients after cannulation (median pH, 7.42 [interquartile range {IQR}, 7.39, 7.44], ratio of arterial partial pressure of oxygen to fraction of inspired oxygen, 186.5 [Pao₂:Fio₂, 116.5, 247.0]; pump flow, 3.9 L/min [IQR, 3.1, 4.3]). Eleven patients (55%) were able to be freed from mechanical ventilation after cannulation, 9 (45%) patients underwent a tracheostomy procedure while undergoing ECMO, and no patients required reintubation. No morbidity or mortality was related to the cannulation strategy or the catheter. Two patients required cannula repositioning. Survival to decannulation was 90%, and survival to hospital discharge was 80%.

CONCLUSIONS

The bicaval dual-lumen cannula maintains the advantages of upper body single-site configuration to provide the adjunctive respiratory support necessary to facilitate awakening and rehabilitation while minimizing the use of invasive mechanical ventilation. This cannula introduces design qualities that may offer advantages for acute respiratory failure requiring venovenous ECMO.

Multiday maintenance of extracorporeal lungs using cross-circulation with conscious swine

Objectives

Lung remains the least-utilized solid organ for transplantation. Efforts to recover donor lungs with reversible injuries using ex vivo perfusion systems are limited to <24 hours of support. Here, we demonstrate the feasibility of extending normothermic extracorporeal lung support to 4 days using cross-circulation with conscious swine.

Methods

A swine behavioral training program and custom enclosure were developed to enable multiday cross-circulation between extracorporeal lungs and recipient swine. Lungs were ventilated and perfused in a normothermic chamber for 4 days. Longitudinal analyses of extracorporeal lungs (ie, functional assessments, multiscale imaging, cytokine quantification, and cellular assays) and recipient swine (eg, vital signs and blood and tissue analyses) were performed.

Results

Throughout 4 days of normothermic support, extracorporeal lung function was maintained (arterial oxygen tension/inspired oxygen fraction >400 mm Hg; compliance >20 mL/cm H₂O), and recipient swine were hemodynamically stable (lactate <3 mmol/L; pH, 7.42 ± 0.05). Radiography revealed well-aerated lower lobes and consolidation in upper lobes of extracorporeal lungs, and bronchoscopy showed healthy airways without edema or secretions. In bronchoalveolar lavage fluid, granulocyte-macrophage colony-stimulating factor, interleukin (IL) 4, IL-6, and IL-10 levels increased less than 6-fold, whereas interferon gamma, IL-1α, IL-1β, IL-1ra, IL-2, IL-8, IL-12, IL-18, and tumor necrosis factor alpha levels decreased from baseline to day 4. Histologic evaluations confirmed an intact blood–gas barrier and outstanding preservation of airway and alveolar architecture. Cellular viability and metabolism in extracorporeal lungs were confirmed after 4 days.

Conclusions

We demonstrate feasibility of normothermic maintenance of extracorporeal lungs for 4 days by cross-circulation with conscious swine. Cross-circulation approaches could support the recovery of damaged lungs and enable organ bioengineering to improve transplant outcomes.

Outcomes of Extracorporeal Membrane Oxygenation as a Bridge to Lung Transplantation

BACKGROUND

Extracorporeal membrane oxygenation (ECMO) as a bridge to lung transplantation (BTT) has become a critical component of caring for patients with end-stage lung disease. This study examined outcomes of patients who received ECMO as a BTT.

METHODS

Statistical analysis was performed on data gathered retrospectively from the electronic medical records of adult patients who received ECMO as BTT at Columbia University Medical Center from April 2009 through July 2018.

RESULTS

A total of 121 adult patients were placed on ECMO as BTT, and 70 patients (59%) were successfully bridged to lung transplantation. Simplified Acute Physiology Score II, unplanned endotracheal intubation, renal replacement therapy, and cerebrovascular accident were identified as independent predictors of unsuccessful BTT. Ambulation was the only independent predictor of successful BTT (odds ratio, 7.579; 95% confidence interval, 2.158 to 26.615; p = 0.002). Among the 64 patients (91%) who survived to hospital discharge, survival was 88% at 1 year and 83% at 3 years. Propensity matching between BTT and non-BTT lung transplant recipients did not show a significant difference in survival (log-rank = 0.53) despite significant differences in the lung allocation score (median, 92.2 [interquartile range, 89.0 to 94.2] vs 49.6 [interquartile range, 40.6 to 72.3], p < 0.01).

CONCLUSIONS

ECMO can be used successfully to bridge patients with end-stage lung disease to lung transplantation. When implemented by an experienced team with adherence to stringent protocols and patient selection, outcomes in BTT patients were comparable to patients who did not receive pretransplant support.

A decade of interfacility extracorporeal membrane oxygenation transport

OBJECTIVE

Extracorporeal membrane oxygenation (ECMO) is used to provide support for patients with cardiopulmonary failure. Best available medical management often fails in these patients and referring hospitals have no further recourse for escalating care apart from transfer to a tertiary facility. In severely unstable patients, the only option might be to use ECMO to facilitate safe transport. This study aimed to examine the characteristics and outcomes of patients transported while receiving ECMO.

METHODS

Statistical analysis was performed on data gathered retrospectively from the electronic medical records of adult patients transported while receiving ECMO to Columbia University Medical Center between January 1, 2008, and December 31, 2017.

RESULTS

Two hundred sixty five adult patients were safely transported while receiving ECMO with no transport-related complications that adversely affected outcomes. Transport distance ranged from 0.2 to 7084 miles with a median distance of 16.9 miles. One hundred eighty-three (69%) received on veno-venous, 72 (27%) veno-arterial, and 10 (3.8%) veno-venous arterial or veno-arterial venous configurations. Two hundred ten (79%) cannulations were performed at our institution at the referring hospital. Sixty-four percent of patients transported while receiving ECMO survived to hospital discharge.

CONCLUSIONS

Interfacility transport during ECMO was shown to be safe and effective with minimal complications and favorable outcomes when performed at an experienced referral center using stringently applied protocols.