Extracorporeal techniques in acute respiratory distress syndrome

Outcomes following additional drainage during veno-venous extracorporeal membrane oxygenation: A single-center retrospective study

Refractory hypoxemia during veno-venous (V-V) extracorporeal membrane oxygenation (ECMO) may require an additional cannula (VV-V ECMO) to improve oxygenation. This intervention includes risk of recirculation and other various adverse events (AEs) such as injury to the lung, cannula malpositioning, bleeding, circuit or cannula thrombosis requiring intervention (i.e., clot), or cerebral injury. During the study period, 23 of 142 V-V ECMO patients were converted to VV-V utilizing two separate cannulas for bi-caval drainage with an additional upper extremity cannula placed for return. Of those, 21 had COVID-19. In the first 24 h after conversion, ECMO flow rates were higher (5.96 vs 5.24 L/min, p = .002) with no significant change in pump speed (3764 vs 3630 revolutions per minute [RPMs], p = .42). Arterial oxygenation (PaO2) increased (87 vs 64 mmHg, p < .0001) with comparable pre-oxygenator venous saturation (61 vs 53.3, p = .12). By day 5, flows were similar to pre-conversion values at lower pump speed but with improved PaO2. Unadjusted survival was similar in those converted to VV-V ECMO compared to V-V ECMO alone (70% [16/23] vs 66.4% [79/119], p = .77). In a mixed effect regression model, any incidence of AEs, demonstrated a negative impact on PaO2 in the first 48 h but not at day 5. VV-V ECMO improved oxygenation with increasing flows without a significant difference in AEs or pump speed. AEs transiently impacted oxygenation. VV-V ECMO is effective and feasible strategy for refractory hypoxemia on VV-ECMO allowing for higher flow rate and unchanged pump speed.

Neutrophil-to-Lymphocyte Ratio as a Predictor of Mortality for COVID-19-Related Acute Respiratory Distress Syndrome (ARDS) Patients Requiring Extracorporeal Membrane Oxygenation Therapy

BACKGROUND

The neutrophil-to-lymphocyte ratio (NLR) has been studied as an indicator of systemic inflammation and as a prognostic tool in multiple areas of medicine. Previous research has suggested that higher NLR and rapid increase to peak NLR are associated with poorer outcomes in patients with coronavirus disease 2019 (COVID-19), particularly in those experiencing acute respiratory distress syndrome (ARDS). Within vascular surgery, there is data to suggest a positive correlation between elevated pre-extracorporeal membrane oxygenation (ECMO) NLR and higher rates of mortality following major procedures. This study explores the prognostic value of peri-ECMO NLR in patients requiring veno-venous ECMO (VV-ECMO) therapy for COVID-19-related ARDS. The objective of this study was to explore the utility of pre-ECMO NLR as an easily accessible prognostic factor for patients suffering from COVID-19-associated ARDS that require VV-ECMO.

METHODS

This was a retrospective cohort study within a tertiary care hospital conducted between April 2020 and January 2021. Patients requiring VV-ECMO therapy for COVID-19-associated ARDS were included. Peri-ECMO NLR values, length of stay (LOS), duration on VV-ECMO, and discharge status were recorded. Receiver operating characteristic (ROC) curve analysis and Youden's J statistics were performed to calculate a cut-off value of 11.005 for pre-ECMO NLR and 17.616 for on-ECMO NLR. Pre-ECMO and on-ECMO Kaplan-Meyer curves were generated for two groups of patients, those above and below NLR cutoff thresholds. Two-sample T-test was performed to test for significant differences in LOS and duration on VV-ECMO.

RESULTS

Twenty-six patients were included in the study for final analyses. There was an overall mortality of 39% (n = 10). ROC curve analysis and Youden's J statistic revealed an optimal cut-off value of pre-ECMO NLR = 11.005 and on-ECMO NLR = 17.616. Results showed that the patient group placed on VV-ECMO with a pre-ECMO NLR less than 11.005 experienced no mortality (n = 7) and a median LOS of 28 days (IQR = 14.5-64.5 days). The patient group on VV-ECMO with a pre-ECMO NLR greater than 11.005 (n = 19) included all mortality (n = 10) and had a median LOS of 49 days (IQR = 25.5-63.5 days). The patient group with on-ECMO NLR less than 17.616 also conferred a survival advantage. There was no significant difference in LOS or duration on VV-ECMO between the two groups, pre-ECMO or on-ECMO.

CONCLUSIONS

 A pre-ECMO NLR cutoff was identified and offered statistically significant prognostic value in predicting mortality. A lower on-ECMO NLR value also indicated a survival advantage. Future studies should include NLR within multivariate models to better discern the effect of NLR and elucidate how it can be factored into clinical decision-making. Importantly, this data can be expanded to assess the predictive value of NLR pertaining to the COVID-19-induced ARDS population and matched cohorts.

Comparison of Blood and Blood Product Transfusion in COVID-19 and Non-COVID-19 Patients Requiring Extracorporeal Membrane Oxygenation for Severe Respiratory Failure

COVID-19 has resulted in an exponential increase in patients with severe respiratory failure requiring extracorporeal membrane oxygenation (ECMO). Patients on ECMO regularly require high volumes of blood and blood products but, so far, there has been no comparison of transfusion requirements between COVID-19 and non-COVID-19. Using electronic patient records at two major UK ECMO centres, Royal Papworth Hospital and University Hospital South Manchester, we reviewed the transfusion requirements of patients requiring ECMO between January 2019 to December 2021. A total of 271 patients, including 168 COVID-19 patients were available for analysis. Since COVID-19 patients spent almost twice as long on ECMO (27.1 vs. 14.16 days, p ≤ 0.0001) we indexed transfusion in both groups to days on ECMO to allow comparison. COVID-19 patients required less red blood cells (RBC) per day (0.408 vs. 0.996, p = 0.0005) but more cryoprecipitate transfusions (0.117 vs. 0.106, p = 0.022) compared to non-COVID-19 patients. COVID-19 patients had more than double the mortality of non-COVID-19 patients (47% vs. 20.4%, p = 0.0001) and those who died during the study period had higher platelet transfusion requirements (p = 0.007) than their non-COVID-19 counterparts. Transfusion requirements and coagulopathy differ between COVID-19 and non-COVID-19 patients. The distinctly different transfusion patterns between the two groups remain difficult to interpret, but further investigations may help explain the haematological aspects of severe COVID-19 infection.

A descriptive evaluation of causes of death in venovenous extracorporeal membrane oxygenation

Veno-venous extracorporeal membrane oxygenation (VV ECMO) has become an important support modality for patients with acute respiratory failure refractory to optimal medical therapy, such as low tidal volume mechanical ventilator support, early paralytic infusion, and early prone positioning. The objective of this cohort study was to investigate the causes and timing of in-hospital mortality in patients on VV ECMO. All patients, excluding trauma and bridge to lung transplant, admitted 8/2014-6/2019 to a specialty ICU for VV ECMO were reviewed. Two hundred twenty-five patients were included. In-hospital mortality was 24.4% (n = 55). Most non-survivors (46/55, 84%) died prior to lung recovery and decannulation from VV ECMO. Most common cause of death (COD) for patients who died on VV ECMO was removal of life sustaining therapy (LST) in setting of multisystem organ failure (MSOF) (n = 24). Nine patients died a median of 9 days [6, 11] after decannulation. Most common COD in these patients was palliative withdrawal of LST due to poor prognosis (n = 3). Non-survivors were older and had worse predictive mortality scores than survivors. We found that death in patients supported with VV ECMO in our study most often occurs prior to decannulation and lung recovery. This study demonstrated that the most common cause of death in patients supported with VV ECMO was removal of LST due MSOF. Acute hemorrhage (systemic or intracranial) was not found to be a common cause of death in our patient population.

What Is Different in Acute Hematologic Malignancy-Associated ARDS? An Overview of the Literature

Background and Objectives: Acute hematologic malignancies are a group of heterogeneous blood diseases with a high mortality rate, mostly due to acute respiratory failure (ARF). Acute respiratory distress syndrome (ARDS) is one form of ARF which represents a challenging clinical condition. The paper aims to review current knowledge regarding the variable pathogenic mechanisms, as well as therapeutic options for ARDS in acute hematologic malignancy patients. Data collection: We provide an overview of ARDS in patients with acute hematologic malignancy, from an etiologic perspective. We searched databases such as PubMed or Google Scholar, including articles published until June 2022, using the following keywords: ARDS in hematologic malignancy, pneumonia in hematologic malignancy, drug-induced ARDS, leukostasis, pulmonary leukemic infiltration, pulmonary lysis syndrome, engraftment syndrome, diffuse alveolar hemorrhage, TRALI in hematologic malignancy, hematopoietic stem cell transplant ARDS, radiation pneumonitis. We included relevant research articles, case reports, and reviews published in the last 18 years. Results: The main causes of ARDS in acute hematologic malignancy are: pneumonia-associated ARDS, leukostasis, leukemic infiltration of the lung, pulmonary lysis syndrome, drug-induced ARDS, radiotherapy-induced ARDS, diffuse alveolar hemorrhage, peri-engraftment respiratory distress syndrome, hematopoietic stem cell transplantation-related ARDS, transfusion-related acute lung injury. Conclusions: The short-term prognosis of ARDS in acute hematologic malignancy relies on prompt diagnosis and treatment. Due to its etiological heterogeneity, precision-based strategies should be used to improve overall survival. Future studies should focus on identifying the relevance of such etiologic-based diagnostic strategies in ARDS secondary to acute hematologic malignancy.

A Comparison of Anticoagulation Strategies in Veno-venous Extracorporeal Membrane Oxygenation

Bleeding remains a major source of morbidity associated with veno-venous extracorporeal membrane oxygenation (VV-ECMO). Moreover, there remains significant controversy, and a paucity of data regarding the ideal anticoagulation strategy for VV-ECMO patients. All patients undergoing isolated, peripheral VV-ECMO between January 2009 and December 2014 at our institution were retrospectively reviewed. Patients (n = 123) were stratified into one of three sequential eras of anticoagulation strategies: activated clotting time (ACT: 160-180 seconds, n = 53), high-partial thromboplastin time (H-PTT: 60-80 seconds, n = 25), and low-PTT (L-PTT: 45-55 seconds, n = 25) with high-flow (>4 L/min). Pre-ECMO APACHE II scores, SOFA scores, and Murray scores were not significantly different between the groups. Patients in the L-PTT group required less red blood cell units on ECMO than the ACT or H-PTT group (2.1 vs. 1.3 vs. 0.9; p < 0.001) and patients in the H-PTT and L-PTT group required less fresh frozen plasma than the ACT group (0.33 vs. 0 vs. 0; p = 0.006). Overall, major bleeding events were significantly lower in the L-PTT group than in the ACT and H-PTT groups. There was no difference in thrombotic events. In this single-institution experience, a L-PTT, high-flow strategy on VV-ECMO was associated with fewer bleeding and no difference in thrombotic events than an ACT or H-PTT strategy.

Mechanical Power during Veno-Venous Extracorporeal Membrane Oxygenation Initiation: A Pilot-Study

Mechanical power (MP) represents a useful parameter to describe and quantify the forces applied to the lungs during mechanical ventilation (MV). In this multi-center, prospective, observational study, we analyzed MP variations following MV adjustments after veno-venous extra-corporeal membrane oxygenation (VV ECMO) initiation. We also investigated whether the MV parameters (including MP) in the early phases of VV ECMO run may be related to the intensive care unit (ICU) mortality. Thirty-five patients with severe acute respiratory distress syndrome were prospectively enrolled and analyzed. After VV ECMO initiation, we observed a significant decrease in median MP (32.4 vs. 8.2 J/min, p < 0.001), plateau pressure (27 vs. 21 cmH₂O, p = 0.012), driving pressure (11 vs. 8 cmH₂O, p = 0.014), respiratory rate (RR, 22 vs. 14 breaths/min, p < 0.001), and tidal volume adjusted to patient ideal body weight (V_T/IBW, 5.5 vs. 4.0 mL/kg, p = 0.001) values. During the early phase of ECMO run, RR (17 vs. 13 breaths/min, p = 0.003) was significantly higher, while positive end-expiratory pressure (10 vs. 14 cmH₂O, p = 0.048) and V_T/IBW (3.0 vs. 4.0 mL/kg, p = 0.028) were lower in ICU non-survivors, when compared to the survivors. The observed decrease in MP after ECMO initiation did not influence ICU outcome. Waiting for large studies assessing the role of these parameters in VV ECMO patients, RR and MP monitoring should not be underrated during ECMO.

Extracorporeal Life Support: The Next Step in Moderate to Severe ARDS-A Review and Meta-Analysis of the Literature

Despite the use of lung protective ventilation (LPV) strategies, a severe form of acute respiratory distress syndrome (ARDS) is unfortunately associated with high mortality rates, which sometimes exceed 60%. Recently, major technical improvements have been applied in extracorporeal life support (ECLS) systems, but as these techniques are costly and associated with very serious adverse events, high-quality evidence is needed before these techniques can become the “cornerstone” in the management of moderate to severe ARDS. Unfortunately, evaluation of previous randomized controlled and observational trials revealed major methodological issues. In this review, we focused on the most important clinical trials aiming at a final conclusion about the effectiveness of ECLS in moderate to severe ARDS patients. Totally, 20 published clinical studies were included in this review. Most studies have important limitations with regard to quality and design. In the 20 included studies (2,956 patients), 1,185 patients received ECLS. Of them, 976 patients received extracorporeal membrane oxygenation (ECMO) and 209 patients received extracorporeal carbon dioxide removal (ECCO₂R). According to our results, ECLS use was not associated with a benefit in mortality rate in patients with ARDS. However, when restricted to higher quality studies, ECMO was associated with a significant benefit in mortality rate. Furthermore, in patients with H1N1, a potential benefit of ECLS in mortality rate was apparent. Until more high-quality data are derived, ECLS should be an option as a salvage therapy in severe hypoxemic ARDS patients.

Ventilator-induced lung injury during controlled ventilation in patients with acute respiratory distress syndrome: less is probably better

INTRODUCTION

Mechanical ventilation is required to support respiratory function in the acute respiratory distress syndrome (ARDS), but it may promote lung damage, a phenomenon known as ventilator-induced lung injury (VILI). Areas covered: Several mechanisms of VILI have been described, such as: inspiratory and/or expiratory stress inducing overdistension (volutrauma); interfaces between collapsed or edema-filled alveoli with surrounding open alveoli, acting as stress raisers; alveoli that repetitively open and close during tidal breathing (atelectrauma); and peripheral airway dynamics. In this review, we discuss: the definition and classification of ARDS; ventilatory parameters that act as VILI determinants (tidal volume, respiratory rate, positive end-expiratory pressure, peak, plateau, driving and transpulmonary pressures, energy, mechanical power, and intensity); and the roles of prone positioning and muscle paralysis. We seek to provide an up-to-date overview of the evidence in the field from a clinical perspective. Expert commentary: To prevent VILI, mechanical ventilation strategies should minimize inspiratory/expiratory stress, dynamic/static strain, energy, mechanical power, and intensity, as well as mitigate the hemodynamic consequences of positive-pressure ventilation. In patients with moderate to severe ARDS, prone positioning can reduce lung damage and improve survival. Overall, volutrauma seems to be more harmful than atelectrauma. Extracorporeal support should be considered in selected cases.