Extracorporeal Membrane Oxygenation for Respiratory Failure: A Narrative Review.

Extracorporeal membrane oxygenation support for respiratory failure in the intensive care unit continues to have an expanded role in select patients. While acute respiratory distress syndrome remains the most common indication, extracorporeal membrane oxygenation may be used in other causes of refractory hypoxemia and/or hypercapnia. The most common configuration is veno-venous extracorporeal membrane oxygenation; however, in specific cases of refractory hypoxemia or right ventricular failure, some patients may benefit from veno-pulmonary extracorporeal membrane oxygenation or veno-venoarterial extracorporeal membrane oxygenation. Patient selection and extracorporeal circuit management are essential to successful outcomes. This narrative review explores the physiology of extracorporeal membrane oxygenation, indications and contraindications, ventilator management, extracorporeal circuit management, troubleshooting hypoxemia, complications, and extracorporeal membrane oxygenation weaning in patients with respiratory failure. As the footprint of extracorporeal membrane oxygenation continues to expand, it is essential that clinicians understand the underlying physiology and management of these complex patients.

Percutaneous decannulation reduces procedure length and rates of groin wound infection in patients on venoarterial extracorporeal membrane oxygenation.

Objective: Open decannulation from femoral venoarterial extracorporeal membrane oxygenation (VA-ECMO) carries high risk of morbidity, including groin wound infection. This study evaluated the impact of percutaneous decannulation on rates of groin wound infection in patients decannulated from femoral VA-ECMO. Methods: Between January 1, 2022, and April 30, 2023, 47 consecutive patients received percutaneous femoral VA-ECMO and survived to decannulation. A percutaneous suture-mediated closure device was used for decannulation in patients with relatively smaller arterial cannulas. Patients with larger arterial cannulas or unsuccessful percutaneous closures underwent surgical cutdown and repair of the femoral artery. The primary outcome was arterial site wound infection following decannulation. Results: Among the 47 patients who survived to decannulation from VA-ECMO, 21 underwent percutaneous decannulation and 27 underwent surgical cutdown. One patient underwent 2 VA-ECMO runs, one with percutaneous decannulation and one with surgical cutdown. Percutaneous decannulation was attempted in 22 patients, with 21 of 22 (95.5%) success rate. Decannulation procedure length was significantly shorter in the percutaneous group (79 minutes vs 148 minutes, P = .0001). The percutaneous group had significantly reduced rates of groin wound complications (0% vs 40.7%, P = .001) and groin wound infections (0% vs 22.2%, P = .03) when compared with the surgical cutdown group. Three patients (14.3%) in the percutaneous group experienced vascular complications, including pseudoaneurysm at the distal perfusion catheter site and nonocclusive thrombus of the common femoral artery. Conclusions: Percutaneous decannulation may reduce decannulation procedure length and rate of groin wound infection in patients who survive to decannulation from VA-ECMO.

Physiologic benefits of veno-pulmonary extracorporeal membrane oxygenation for COVID-19 ARDS: A single center experience.

BACKGROUND: A subset of patients with COVID-19 acute respiratory distress syndrome (ARDS) require extracorporeal membrane oxygenation (ECMO). Veno-pulmonary (VP) ECMO provides support to the right ventricle and decreased risk of recirculation. METHODS: A retrospective analysis of patients with COVID-19 ARDS and VP ECMO was performed. Patients were separated into groups by indication (1) "right ventricular (RV) failure," (2) "refractory hypoxemia," and (3) "recurrent suck-down events (SDEs)." Pre- and post-configuration vasoactive inotropic scores (VIS), fraction of inspired oxygen (FIO2), and resolution of SDEs were reported. A 90-day mortality was computed for all groups. Patients were also compared to those who underwent conventional venovenous (VV) ECMO. RESULTS: Forty-seven patients underwent VP ECMO configuration, 18 in group 1, 16 in group 2, and 8 in group 3. Ninety-day mortality was 66% for the entire cohort and was 77.8%, 81.3% and 37.5% for groups 1, 2, and 3, respectively. Mean VIS decreased in group 1 (8.3 vs 2.9, p = 0.005), while mean FIO2 decreased in the group 2 and was sustained at 72 h (82.5% vs 52.5% and 47.5%, p < 0.001). Six of the eight (75%) of patients with recurrent SDEs had resolution of these events after configuration to VP ECMO. Patients with VP ECMO spent more days on ECMO (33 days compared to 18 days, p = 0.004) with no difference in mortality (66% compared to 55.1%, p = 0.28). CONCLUSION: VP ECMO in COVID-19 ARDS improves hemodynamics in patients with RV failure, improves oxygenation in patients with refractory hypoxemia and improves the frequency of SDEs.

Venovenous extracorporeal membrane oxygenation after cardiac arrest for acute respiratory distress syndrome caused by Legionella: a case report.

BACKGROUND: Legionella remains underdiagnosed in the intensive care unit and can progress to acute respiratory distress syndrome (ARDS), multiorgan failure and death. In severe cases, venovenous extracorporeal membrane oxygenation (VV-ECMO) allows time for resolution of disease with Legionella-targeted therapy. VV-ECMO outcomes for Legionella are favorable with reported survival greater than 70%. Rapid molecular polymerase chain reaction (PCR) testing of the lower respiratory tract aids in diagnosing Legionella with high sensitivity and specificity. We present a unique case of a patient with a positive COVID-19 test and ARDS who suffered a cardiac arrest. The patient was subsequently cannulated for VV-ECMO, and after lower respiratory tract PCR testing, Legionella was determined to be the cause. She was successfully treated and decannulated from VV-ECMO after eight days. CASE PRESENTATION: A 53-year-old female presented with one week of dyspnea and a positive COVID-19 test. She was hypoxemic, hypotensive and had bilateral infiltrates on imaging. She received supplemental oxygen, intravenous fluids, vasopressors, broad spectrum antibiotics, and was transferred to a tertiary care center. She developed progressive hypoxemia and suffered a cardiac arrest, requiring ten minutes of CPR and endotracheal intubation to achieve return of spontaneous circulation. Despite mechanical ventilation and paralysis, she developed refractory hypoxemia and was cannulated for VV-ECMO. Dexamethasone and remdesivir were given for presumed COVID-19. Bronchoscopy with bronchoalveolar lavage (BAL) performed with PCR testing was positive for Legionella pneumophila and negative for COVID-19. Steroids and remdesivir were discontinued and she was treated with azithromycin. Her lung compliance improved, and she was decannulated after eight days on VV-ECMO. She was discharged home on hospital day 16 breathing room air and neurologically intact. CONCLUSIONS: This case illustrates the utility of rapid PCR testing to diagnose Legionella in patients with respiratory failure and the early use of VV-ECMO in patients with refractory hypoxemia secondary to Legionella infection. Moreover, many patients encountered in the ICU may have prior COVID-19 immunity, and though a positive COVID-19 test may be present, further investigation with lower respiratory tract PCR testing may provide alternative diagnoses. Patients with ARDS should undergo Legionella-specific testing, and if Legionella is determined to be the causative organism, early VV-ECMO should be considered in patients with refractory hypoxemia given reported high survival rates.

Point-of-Care Echocardiography in the Difficult-to-Image Patient in the ICU: A Narrative Review.

OBJECTIVES: The objective of this narrative review was to address common obstacles encountered in the ICU to acquiring quality and interpretable images using point-of-care echocardiography. DATA SOURCES: Detailed searches were performed using PubMed and Ovid Medline using medical subject headings and keywords on topics related to patient positioning, IV echo contrast, alternative subcostal views, right ventricular outflow tract (RVOT) hemodynamics, and point-of-care transesophageal echocardiography. Articles known to the authors were also selected based on expert opinion. STUDY SELECTION: Articles specific to patient positioning, IV echo contrast, alternative subcostal views, RVOT hemodynamics, and point-of-care transesophageal echocardiography were considered. DATA EXTRACTION: One author screened titles and extracted relevant data while two separate authors independently reviewed selected articles. DATA SYNTHESIS: Impediments to acquiring quality and interpretable images in critically ill patients are common. Notably, body habitus, intra-abdominal hypertension, dressings or drainage tubes, postoperative sternotomies, invasive mechanical ventilation, and the presence of subcutaneous emphysema or lung hyperinflation are commonly encountered obstacles in transthoracic image acquisition in the ICU. Despite these obstacles, the bedside clinician may use obstacle-specific maneuvers to enhance image acquisition. These may include altering patient positioning, respiratory cycle timing, expanding the subcostal window to include multilevel short-axis views for use in the assessment of RV systolic function and hemodynamics, coronal transhepatic view of the inferior vena cava, and finally point-of-care transesophageal echocardiography. CONCLUSIONS: Despite common obstacles to point-of-care echocardiography in critically ill patients, the beside sonographer may take an obstacle-specific stepwise approach to enhance image acquisition in difficult-to-image patients.

Advanced Respiratory Support Days as a Novel Marker of Mortality in COVID-19 Acute Respiratory Distress Syndrome Requiring Extracorporeal Membrane Oxygenation.

Emerging evidence suggests prolonged use of noninvasive respiratory support may increase mortality of patients with coronavirus disease 2019 (COVID-19)-associated acute respiratory distress syndrome who require extracorporeal membrane oxygenation (ECMO). Using a database of adults receiving ECMO for COVID-19, we calculated survival curves and multivariable Cox regression to determine the risk of death associated with pre-ECMO use of high-flow nasal oxygen (HFNO), noninvasive ventilation (NIV), and invasive mechanical ventilation (IMV) days. We investigated the performance of a novel variable, advanced respiratory support days (composite of HFNO, NIV, and IMV days), on Respiratory ECMO Survival Prediction (RESP) score. Subjects (N = 146) with increasing advanced respiratory support days (<5, 5-9, and ≥10) had a stepwise increase in 90 day mortality (32.2%, 57.7%, and 75.4%, respectively; p = 0.002). Ninety-day mortality was significantly higher in subjects (N = 121) receiving NIV >4 days (81.8% vs. 52.4%, p < 0.001). Each additional pre-ECMO advanced respiratory support day increased the odds of right ventricular failure (odds ratio [OR]: 1.066, 95% confidence interval [CI]: 1.002-1.135) and in-hospital mortality (1.17, 95% CI: 1.08-1.27). Substituting advanced respiratory support days for IMV days improved RESP score mortality prediction (area under the curve (AUC) or: 0.64 vs. 0.71). Pre-ECMO advanced respiratory support days were associated with increased 90 day mortality compared with IMV days alone. Adjusting the RESP score for advanced respiratory support days improved mortality prediction.

Management of severe acute respiratory distress syndrome: a primer.

This narrative review explores the physiology and evidence-based management of patients with severe acute respiratory distress syndrome (ARDS) and refractory hypoxemia, with a focus on mechanical ventilation, adjunctive therapies, and veno-venous extracorporeal membrane oxygenation (V-V ECMO). Severe ARDS cases increased dramatically worldwide during the Covid-19 pandemic and carry a high mortality. The mainstay of treatment to improve survival and ventilator-free days is proning, conservative fluid management, and lung protective ventilation. Ventilator settings should be individualized when possible to improve patient-ventilator synchrony and reduce ventilator-induced lung injury (VILI). Positive end-expiratory pressure can be individualized by titrating to best respiratory system compliance, or by using advanced methods, such as electrical impedance tomography or esophageal manometry. Adjustments to mitigate high driving pressure and mechanical power, two possible drivers of VILI, may be further beneficial. In patients with refractory hypoxemia, salvage modes of ventilation such as high frequency oscillatory ventilation and airway pressure release ventilation are additional options that may be appropriate in select patients. Adjunctive therapies also may be applied judiciously, such as recruitment maneuvers, inhaled pulmonary vasodilators, neuromuscular blockers, or glucocorticoids, and may improve oxygenation, but do not clearly reduce mortality. In select, refractory cases, the addition of V-V ECMO improves gas exchange and modestly improves survival by allowing for lung rest. In addition to VILI, patients with severe ARDS are at risk for complications including acute cor pulmonale, physical debility, and neurocognitive deficits. Even among the most severe cases, ARDS is a heterogeneous disease, and future studies are needed to identify ARDS subgroups to individualize therapies and advance care.

Timing of Intubation in COVID-19: When It Is Too Early and When It Is Too Late.

The timing of initiating mechanical ventilation in patients with acute respiratory distress syndrome due to COVID-19 remains controversial. At the outset of the pandemic, "very early" intubation was recommended in patients requiring oxygen flows above 6 L per minute but was followed closely thereafter by avoidance of invasive mechanical ventilation (IMV) due to a perceived (yet over-estimated) risk of mortality after intubation. While the use of noninvasive methods of oxygen delivery, such as high-flow nasal oxygen (HFNO) or noninvasive positive pressure ventilation (NIV), can avert the need for mechanical ventilation in some, accumulating evidence suggests delayed intubation is also associated with an increased mortality in a subset of COVID-19 patients. Close monitoring is necessary in COVID-19 patients on HFNO or NIV to identify signs of noninvasive failure and ensure appropriate provision of IMV.

Bronchopleural Fistula in the Mechanically Ventilated Patient: A Concise Review.

OBJECTIVE: To describe the physiology of air leak in bronchopleural fistula in mechanically ventilated patients and how understanding of its physiology drives management of positive-pressure ventilation. To provide guidance of lung isolation, mechanical ventilator, pleural catheter, and endobronchial strategies for the management of bronchopleural fistula on mechanical ventilation. DATA SOURCES: Online search of PubMed and manual review of articles (laboratory and patient studies) was performed. STUDY SELECTION: Articles relevant to bronchopleural fistula, mechanical ventilation in patients with bronchopleural fistula, independent lung ventilation, high-flow ventilatory modes, physiology of persistent air leak, extracorporeal membrane oxygenation, fluid dynamics of bronchopleural fistula airflow, and intrapleural catheter management were selected. Randomized trials, observational studies, case reports, and physiologic studies were included. DATA EXTRACTION: Data from selected studies were qualitatively evaluated for this review. We included data illustrating the physiology of driving pressure across a bronchopleural fistula as well as data, largely from case reports, demonstrating management and outcomes with various ventilator modes, intrapleural catheter techniques, endoscopic placement of occlusion and valve devices, and extracorporeal membrane oxygenation. Themes related to managing persistent air leak with mechanical ventilation were reviewed and extracted. DATA SYNTHESIS: In case reports that demonstrate different approaches to managing patients with bronchopleural fistula requiring mechanical ventilation, common themes emerge. Strategies aimed at decreasing peak inspiratory pressure, using lower tidal volumes, lowering positive end-expiratory pressure, decreasing the inspiratory time, and decreasing the respiratory rate, while minimizing negative intrapleural pressure decreases airflow across the bronchopleural fistula. CONCLUSIONS: Mechanical ventilation and intrapleural catheter management must be individualized and aimed at reducing air leak. Clinicians should emphasize reducing peak inspiratory pressures, reducing positive end-expiratory pressure, and limiting negative intrapleural pressure. In refractory cases, clinicians can consider lung isolation, independent lung ventilation, or extracorporeal membrane oxygenation in appropriate patients as well as definitive management with advanced bronchoscopic placement of valves or occlusion devices.

Cardiogenic Auto-Triggering as a Consequence of Hemoperitoneum.

A 70-year-old woman presented with hemorrhagic shock secondary to hemoperitoneum following a paracentesis. On hospital day 3, she developed respiratory alkalosis and increased respiratory rates observed on the ventilator despite no spontaneous inspiratory effort. Converting to pressure support mode uncovered a cardiogenic oscillatory flow that had been auto-triggering the ventilator. This cardiogenic auto-triggering resolved with large-volume paracentesis. Cardiogenic auto-triggering leads to patient-ventilator dyssynchrony, respiratory alkalosis, lung distension, and difficulty with weaning from the ventilator, and it may be unrecognized in ICUs.

Emergency physician performed tricuspid annular plane systolic excursion in the evaluation of suspected pulmonary embolism.

OBJECTIVES: The primary objectives were to describe the diagnostic characteristics tricuspid annular plane systolic excursion (TAPSE) for pulmonary embolism (PE) and to optimize the measurement cutoff of TAPSE for the diagnosis of PE. Secondary objectives included assessment of interrater reliability and the quantitative visual estimation of TAPSE. METHODS: This is a prospective observational cohort study involving a convenience sample of patients at an urban academic emergency department. Patients underwent focused right heart echocardiogram (FOCUS) before computed tomographic angiography (CTA) for suspected PE. RESULTS: A total of 150 patients were enrolled, 32 of whom (21.3%) were diagnosed as having a PE. A receiver operating characteristic curve analysis yielded 2.0 cm as the optimal cutoff for TAPSE in the diagnosis of PE, with a sensitivity of 72% (95% confidence interval [CI], 53-86), a specificity of 66% (95% CI, 57-75), and an area under the curve of 0.73 (95% CI, 0.65-0.83). In patients with tachycardia or hypotension, post hoc analysis demonstrated that FOCUS is 100% (95% CI, 80-100) sensitive for PE, whereas TAPSE is 94% (95% CI, 71-99) sensitive for PE. The intraclass correlation coefficient was 0.87 (95% CI, 0.79-0.93). Emergency physicians with training in echocardiography accurately visually estimated TAPSE, with a κ statistic of 0.94 (95% CI, 0.87-0.98). CONCLUSIONS: Emergency physicians with training in echocardiography can reliably measure TAPSE and are able to accurately visually estimate TAPSE as either normal or abnormal. When using an abnormal cutoff of less than 2.0 cm, TAPSE has moderate diagnostic value in patients with suspected PE. On post hoc analysis, TAPSE and FOCUS appear to be highly sensitive for PE in patients with tachycardia or hypotension.

Thermally oxidized titania nanotubes enhance the corrosion resistance of Ti6Al4V.

The negative impact of in vivo corrosion of metallic biomedical implants remains a complex problem in the medical field. We aimed to determine the effects of electrochemical anodization (60V, 2h) and thermal oxidation (600°C) on the corrosive behavior of Ti-6Al-4V, with serum proteins, at physiological temperature. Anodization produced a mixture of anatase and amorphous TiO2 nanopores and nanotubes, while the annealing process yielded an anatase/rutile mixture of TiO2 nanopores and nanotubes. The surface area was analyzed by the Brunauer-Emmett-Teller method and was estimated to be 3 orders of magnitude higher than that of polished control samples. Corrosion resistance was evaluated on the parameters of open circuit potential, corrosion potential, corrosion current density, passivation current density, polarization resistance and equivalent circuit modeling. Samples both anodized and thermally oxidized exhibited shifts of open circuit potential and corrosion potential in the noble direction, indicating a more stable nanoporous/nanotube layer, as well as lower corrosion current densities and passivation current densities than the smooth control. They also showed increased polarization resistance and diffusion limited charge transfer within the bulk oxide layer. The treatment groups studied can be ordered from greatest corrosion resistance to least as Anodized+Thermally Oxidized > Anodized > Smooth > Thermally Oxidized for the conditions investigated. This study concludes that anodized surface has a potential to prevent long term implant failure due to corrosion in a complex in-vivo environment.

A microfluidic model to study fluid dynamics of mucus plug rupture in small lung airways.

Fluid dynamics of mucus plug rupture is important to understand mucus clearance in lung airways and potential effects of mucus plug rupture on epithelial cells at lung airway walls. We established a microfluidic model to study mucus plug rupture in a collapsed airway of the 12th generation. Mucus plugs were simulated using Carbopol 940 (C940) gels at concentrations of 0.15%, 0.2%, 0.25%, and 0.3%, which have non-Newtonian properties close to healthy and diseased lung mucus. The airway was modeled with a polydimethylsiloxane microfluidic channel. Plug motion was driven by pressurized air. Global strain rates and shear stress were defined to quantitatively describe plug deformation and rupture. Results show that a plug needs to overcome yield stress before deformation and rupture. The plug takes relatively long time to yield at the high Bingham number. Plug length shortening is the more significant deformation than shearing at gel concentration higher than 0.15%. Although strain rates increase dramatically at rupture, the transient shear stress drops due to the shear-thinning effect of the C940 gels. Dimensionless time-averaged shear stress, T xy , linearly increases from 3.7 to 5.6 times the Bingham number as the Bingham number varies from 0.018 to 0.1. The dimensionless time-averaged shear rate simply equals to T xy /2. In dimension, shear stress magnitude is about one order lower than the pressure drop, and one order higher than yield stress. Mucus with high yield stress leads to high shear stress, and therefore would be more likely to cause epithelial cell damage. Crackling sounds produced with plug rupture might be more detectable for gels with higher concentration.