Circuit oxygenator contributes to extracorporeal membrane oxygenation-induced hemolysis

Characterizing the Racial Discrepancy in Hypoxemia Detection in Venovenous Extracorporeal Membrane Oxygenation: An Extracorporeal Life Support Organization Registry Analysis

PURPOSE

Skin pigmentation influences peripheral oxygen saturation (SpO2) compared to arterial saturation of oxygen (SaO2). Occult hypoxemia (SaO2 ≤ 88% with SpO2 ≥ 92%) is associated with increased in-hospital mortality in venovenous-extracorporeal membrane oxygenation (VV-ECMO) patients. We hypothesized VV-ECMO cannulation, in addition to race/ethnicity, accentuates the SpO2-SaO2 discrepancy due to significant hemolysis.

METHODS

Adults (≥ 18 years) supported with VV-ECMO with concurrently measured SpO2 and SaO2 measurements from over 500 centers in the Extracorporeal Life Support Organization Registry (1/2018-5/2023) were included. Multivariable logistic regressions were performed to examine whether race/ethnicity was associated with occult hypoxemia in pre-ECMO and on-ECMO SpO2-SaO2 calculations.

RESULTS

Of 13,171 VV-ECMO patients, there were 7772 (59%) White, 2114 (16%) Hispanic, 1777 (14%) Black, and 1508 (11%) Asian patients. The frequency of on-ECMO occult hypoxemia was 2.0% (N = 233). Occult hypoxemia was more common in Black and Hispanic patients versus White patients (3.1% versus 1.7%, P < 0.001 and 2.5% versus 1.7%, P = 0.025, respectively). In multivariable logistic regression, Black patients were at higher risk of pre-ECMO occult hypoxemia versus White patients (adjusted odds ratio [aOR] = 1.55, 95% confidence interval [CI] = 1.18-2.02, P = 0.001). For on-ECMO occult hypoxemia, Black patients (aOR = 1.79, 95% CI = 1.16-2.75, P = 0.008) and Hispanic patients (aOR = 1.71, 95% CI = 1.15-2.55, P = 0.008) had higher risk versus White patients. Higher pump flow rates (aOR = 1.29, 95% CI = 1.08-1.55, P = 0.005) and on-ECMO 24-h lactate (aOR = 1.06, 95% CI = 1.03-1.10, P < 0.001) significantly increased the risk of on-ECMO occult hypoxemia.

CONCLUSION

SaO2 should be carefully monitored if using SpO2 during ECMO support for Black and Hispanic patients especially for those with high pump flow and lactate values at risk for occult hypoxemia.

Empirical and Computational Evaluation of Hemolysis in a Microfluidic Extracorporeal Membrane Oxygenator Prototype

Microfluidic devices promise to overcome the limitations of conventional hemodialysis and oxygenation technologies by incorporating novel membranes with ultra-high permeability into portable devices with low blood volume. However, the characteristically small dimensions of these devices contribute to both non-physiologic shear that could damage blood components and laminar flow that inhibits transport. While many studies have been performed to empirically and computationally study hemolysis in medical devices, such as valves and blood pumps, little is known about blood damage in microfluidic devices. In this study, four variants of a representative microfluidic membrane-based oxygenator and two controls (positive and negative) are introduced, and computational models are used to predict hemolysis. The simulations were performed in ANSYS Fluent for nine shear stress-based parameter sets for the power law hemolysis model. We found that three of the nine tested parameters overpredict (5 to 10×) hemolysis compared to empirical experiments. However, three parameter sets demonstrated higher predictive accuracy for hemolysis values in devices characterized by low shear conditions, while another three parameter sets exhibited better performance for devices operating under higher shear conditions. Empirical testing of the devices in a recirculating loop revealed levels of hemolysis significantly lower (<2 ppm) than the hemolysis ranges observed in conventional oxygenators (>10 ppm). Evaluating the model's ability to predict hemolysis across diverse shearing conditions, both through empirical experiments and computational validation, will provide valuable insights for future micro ECMO device development by directly relating geometric and shear stress with hemolysis levels. We propose that, with an informed selection of hemolysis parameters based on the shear ranges of the test device, computational modeling can complement empirical testing in the development of novel high-flow blood-contacting microfluidic devices, allowing for a more efficient iterative design process. Furthermore, the low device-induced hemolysis measured in our study at physiologically relevant flow rates is promising for the future development of microfluidic oxygenators and dialyzers.

COVID-19 Drug Treatments Are Prone to Sequestration in Extracorporeal Membrane Oxygenation Circuits: An Ex Vivo Extracorporeal Membrane Oxygenation Study

Drug treatments for coronavirus disease 2019 (COVID-19) dramatically improve patient outcomes, and although extracorporeal membrane oxygenation (ECMO) has significant use in these patients, it is unknown whether ECMO affects drug dosing. We used an ex vivo adult ECMO model to measure ECMO circuit effects on concentrations of specific COVID-19 drug treatments. Three identical ECMO circuits used in adult patients were set up. Circuits were primed with fresh human blood (temperature and pH maintained within normal limits). Three polystyrene jars with 75 ml fresh human blood were used as controls. Remdesivir, GS-441524, nafamostat, and tocilizumab were injected in the circuit and control jars at therapeutic concentrations. Samples were taken from circuit and control jars at predefined time points over 6 h and drug concentrations were measured using validated assays. Relative to baseline, mean (± standard deviation [SD]) study drug recoveries in both controls and circuits at 6 h were significantly lower for remdesivir (32.2% [±2.7] and 12.4% [±2.1], p < 0.001), nafamostat (21.4% [±5.0] and 0.0% [±0.0], p = 0.018). Reduced concentrations of COVID-19 drug treatments in ECMO circuits is a clinical concern. Remdesivir and nafamostat may need dose adjustments. Clinical pharmacokinetic studies are suggested to guide optimized COVID-19 drug treatment dosing during ECMO.

A pilot study to evaluate clinical factors associated with iron and ferritin elevations during pediatric extracorporeal membrane oxygenation

Introduction: Elevations in serum ferritin and serum iron occur during pediatric extracorporeal membrane oxygenation (ECMO). Previous reports attribute the elevation to frequent red blood cell transfusions and/or hemolysis. Chronic transfusion can cause iron deposition in tissues leading to multisystem organ dysfunction. This study aims identify clinical factors associated with elevated ferritin and iron in pediatric ECMO patients, along with post-decannulation magnetic resonance imaging (MRI) assessment of iron deposition in liver and brain.Methods: Prospective, pilot study, using descriptive statistics to investigate potential associations between patient characteristics, serum ferritin and iron levels, and post-decannulation hepatic and basal ganglia iron deposition.Results: In this study, nine patients (100%) had elevated serum ferritin levels during ECMO. High ferritin levels were more common with veno-arterial than with veno-venous cannulation (p = 0.026) and were also associated with high plasma free hemoglobin levels (p < 0.001). Five patients presented with elevated serum iron levels. High serum iron levels were associated with higher daily (p = 0.016) and cumulative transfusion volumes (p = 0.013) as well ECMO duration beyond 7 days. MRI scans were performed on three patients with no evidence of abnormal iron deposition detected in the liver or brain.Conclusions: This pilot study shows that during pediatric ECMO, elevations in serum ferritin and serum iron occur and those elevations may be related to the cannulation modality, ECMO duration, amount of hemolysis, and volume of red blood cell transfusions. Further investigation is warranted to fully understand the implications of elevated serum iron and ferritin in pediatric ECMO.

Fluid Flow Analysis of Neonatal Dual-Lumen Cannulas for Venovenous Extracorporeal Membrane Oxygenation

Hemolysis persists as a common and serious problem for neonatal patients on extracorporeal membrane oxygenation (ECMO). Since the cannula within the ECMO circuit is associated with hemolysis-inducing shear stresses, real-world internal fluid flow measurements are urgently needed to understand the mechanism and confirm computational estimates. This study appears to be the first experimental study of fluid flow inside commercial ECMO dual-lumen cannulas (DLCs) and first particle image velocimetry (PIV) visualization inside a complicated medical device. The internal geometries of four different opaque neonatal DLCs, both atrial and bicaval positioning geometries each sized 13 Fr and 16 Fr, were replicated by three-dimensional printing clear lumen scaled-up models, which were integrated in a circuit with appropriate ECMO flow parameters. PIV was then used to visualize two-dimensional fluid flow in a single cross section within the models. An empirical model accounting for shear stress and exposure time was used to compare the maximum expected level of hemolysis through each model. The maximum measured peak shear stress recorded was 16±2 Pa in the top arterial bicaval 13 Fr model. The atrial and 16 Fr cannula models never produced greater single-pass peak shear stress or hemolysis than the bicaval and 13 Fr models, respectively, and no difference was found in hemolysis at two different flow rates. After 5 days of flow, small DLC-induced hemolysis values for a single pass through each cannula were modeled to linearly accumulate and caused the most severe hemolysis in the bicaval 13 Fr DLC. Engineering and clinical solutions to improve cannula safety are proposed.

Meropenem extraction by ex vivo extracorporeal life support circuits

BACKGROUND

Meropenem is a broad-spectrum carbapenem-type antibiotic commonly used to treat critically ill patients infected with extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae. As many of these patients require extracorporeal membrane oxygenation (ECMO) and/or continuous renal replacement therapy (CRRT), it is important to understand how these extracorporeal life support circuits impact meropenem pharmacokinetics. Based on the physicochemical properties of meropenem, it is expected that ECMO circuits will minimally extract meropenem, while CRRT circuits will rapidly clear meropenem. The present study seeks to determine the extraction of meropenem from ex vivo ECMO and CRRT circuits and elucidate the contribution of different ECMO circuit components to extraction.

METHODS

Standard doses of meropenem were administered to three different configurations (n = 3 per configuration) of blood-primed ex vivo ECMO circuits and serial sampling was conducted over 24 h. Similarly, standard doses of meropenem were administered to CRRT circuits (n = 4) and serial sampling was conducted over 4 h. Meropenem was administered to separate tubes primed with circuit blood to serve as controls to account for drug degradation. Meropenem concentrations were quantified, and percent recovery was calculated for each sample.

RESULTS

Meropenem was cleared at a similar rate in ECMO circuits of different configurations (n = 3) and controls (n = 6), with mean (standard deviation) recovery at 24 h of 15.6% (12.9) in Complete circuits, 37.9% (8.3) in Oxygenator circuits, 47.1% (8.2) in Pump circuits, and 20.6% (20.6) in controls. In CRRT circuits (n = 4) meropenem was cleared rapidly compared with controls (n = 6) with a mean recovery at 2 h of 2.36% (1.44) in circuits and 93.0% (7.1) in controls.

CONCLUSION

Meropenem is rapidly cleared by hemodiafiltration during CRRT. There is minimal adsorption of meropenem to ECMO circuit components; however, meropenem undergoes significant degradation and/or plasma metabolism at physiological conditions. These ex vivo findings will advise pharmacists and physicians on the appropriate dosing of meropenem.

Interaction of ceftazidime and clindamycin with extracorporeal life support

BACKGROUND

Ceftazidime and clindamycin are commonly prescribed to critically ill patients who require extracorporeal life support such as ECMO and CRRT. The effect of ECMO and CRRT on the disposition of ceftazidime and clindamycin is currently unknown.

METHODS

Ceftazidime and clindamycin extraction were studied with ex vivo ECMO and CRRT circuits primed with human blood. The percent recovery of these drugs over time was calculated to determine the degree of interaction between these drugs and circuit components.

RESULTS

Neither ceftazidime nor clindamycin exhibited measurable interactions with the ECMO circuit. In contrast, CRRT cleared 100% of ceftazidime from the experimental circuit within the first 2 h. Clearance of clindamycin from the CRRT circuit was slower, with about 20% removed after 6 h.

CONCLUSION

Clindamycin and ceftazidime dosing adjustments are likely required in patients who are supported with CRRT, and future studies to quantify these adjustments should consider the pathophysiology of the patient in combination with the clearance due to CRRT. Dosing adjustments to account for adsorption to ECMO circuit components are likely unnecessary and should focus instead on the pathophysiology of the patient and changes in volume of distribution. These results will help improve the safety and efficacy of ceftazidime and clindamycin in patients requiring ECMO and CRRT.

Characterizing the Racial Discrepancy in Hypoxemia Detection in VV-ECMO: An ELSO Registry Analysis

Importance

Skin pigmentation influences peripheral oxygen saturation (SpO2) measured by pulse oximetry compared to the arterial saturation of oxygen (SaO2) measured via arterial blood gas analysis. However, data on SpO2-SaO2 discrepancy are limited in venovenous-extracorporeal membrane oxygenation (VV-ECMO) patients.

Objective

To determine whether there is racial/ethnical discrepancy between SpO2 and SaO2 in patients receiving VV-ECMO. We hypothesized VV-ECMO cannulation, in addition to race/ethnicity, accentuates the SpO2-SaO2 discrepancy due to significant hemolysis.

Design

Retrospective cohort study of the Extracorporeal Life Support Organization Registry from 1/2018-5/2023.

Setting

International, multicenter registry study including over 500 ECMO centers.

Participants

Adults (≥ 18 years) supported with VV-ECMO with concurrently measured SpO2 and SaO2 measurements.

Exposure

Race/ethnicity and ECMO cannulation.

Main outcomes and measures

Occult hypoxemia (SaO2 ≤ 88% with SpO2 ≥ 92%) was our primary outcome. Multivariable logistic regressions were performed to examine whether race/ethnicity was associated with occult hypoxemia in pre-ECMO and on-ECMO SpO2-SaO2 calculations. Covariates included age, sex, temporary mechanical circulatory support, pre-vasopressors, and pre-inotropes for pre-ECMO analysis, plus single-lumen versus double-lumen cannulation, hemolysis, hyperbilirubinemia, ECMO pump flow rate, and on-ECMO 24h lactate for on-ECMO analysis.

Results

Of 13,171 VV-ECMO patients (median age = 48.6 years, 66% male), there were 7,772 (59%) White, 2,114 (16%) Hispanic, 1,777 (14%) Black, and 1,508 (11%) Asian patients. The frequency of on-ECMO occult hypoxemia was 2.0% (N = 233). Occult hypoxemia was more common in Black and Hispanic versus White patients (3.1% versus 1.7%, P < 0.001 and 2.5% versus 1.7%, P = 0.025, respectively).In multivariable logistic regression, Black patients were at higher risk of pre-ECMO occult hypoxemia versus White patients (adjusted odds ratio [aOR] = 1.55, 95% confidence interval [CI] = 1.18-2.02, P = 0.001). For on-ECMO occult hypoxemia, Black patients (aOR = 1.79, 95%CI = 1.16-2.75, P = 0.008) and Hispanic patients (aOR = 1.71, 95%CI = 1.15-2.55, P = 0.008) had higher risk versus White patients. Furthermore, higher pump flow rate (aOR = 1.29, 95%CI = 1.08-1.55, P = 0.005) and higher on-ECMO 24h lactate (aOR = 1.06, 95%CI = 1.03-1.10, P < 0.001) significantly increased the risk of on-ECMO occult hypoxemia.

Conclusions and Relevance

Hispanic and Black VV-ECMO patients experienced occult hypoxemia more than White patients. SaO2 should be carefully monitored during ECMO support for Black and Hispanic patients especially for those with high pump flow and lactate values at risk for occult hypoxemia.

Smaller Return Cannula in Venoarterial Extracorporeal Membrane Oxygenation Does Not Increase Hemolysis: A Single-Center, Cohort Study

The aim of this study was to explore the association between arterial return cannula diameter and hemolysis during peripheral VA ECMO. We identified 158 adult patients who received peripheral VA ECMO at our institution from the national ECMO database (EXCEL) between January 2019 and July 2021. We classified patients into a small cannula group (15 Fr diameter, n = 45) and a large cannula group (≥17 Fr diameter, n = 113), comparing incidences of clinical hemolysis and plasma free hemoglobin ( pf Hb). Moderate hemolysis is defined as having pf Hb 0.05-0.10 g/L and severe hemolysis as having pf Hb >0.10 g/L sustained for at least two consecutive readings or leading to a circuit change. There were no significant differences in rates of moderate hemolysis between small and large cannula groups (1 vs . 6; p = 0.39) and severe hemolysis (0 vs . 3; p = 0.27), nor was the pf Hb level significantly different at 4 hours (0.086 ± 0.096 vs . 0.112 ± 0.145 g/L; p = 0.58) and at 24 hours (0.042 ± 0.033 vs . 0.051 ± 0.069 g/L; p = 0.99). There were no increased rates of hemolysis when comparing small versus large arterial return cannula diameter in peripheral VA ECMO.

Extracorporeal membrane oxygenation and acute kidney injury: a single-center retrospective cohort

To assess the relationship between acute kidney injury (AKI) with outcomes among patients requiring extracorporeal membrane oxygenation (ECMO). This is a single-center, retrospective cohort study of adult patients admitted to intensive care units (ICU) at a tertiary referral hospital requiring ECMO from July 1, 2015, to August 30, 2019. We assessed the temporal relationship of AKI and renal replacement therapy with ECMO type (VV vs. VA). The primary outcome was in-hospital mortality rates. We used Kruskal-Wallis or chi-square tests for pairwise comparisons, cause-specific Cox proportional hazards models were utilized for the association between AKI prevalence and in-hospital mortality, and a time-dependent Cox model was used to describe the association between AKI incidence and mortality. After the screening, 190 patients met eligibility criteria [133 (70%) AKI, 81 (43%) required RRT]. The median age was 61 years, and 61% were males. Among AKI patients, 48 (36%) and 85 (64%) patients developed AKI before and after ECMO, respectively. The SOFA Day 1, baseline creatinine, respiratory rate (RR), use of vasopressin, vancomycin, proton pump inhibitor, antibiotics, duration of mechanical ventilation and ECMO, and ICU length of stay were higher in AKI patients compared with those without AKI (P < 0.01). While ICU and in-hospital mortality rates were 46% and 50%, respectively, there were no differences based on the AKI status. The type and characteristics of ECMO support were not associated with AKI risk. Among AKI patients, 77 (58%) were oliguric, and 46 (60%) of them received diuretics. Urine output in the diuretic group was only higher on the first day than in those who did not receive diuretics (P = 0.03). Among ECMO patients, AKI was not associated with increased mortality but was associated with prolonged duration of mechanical ventilation and ICU length of stay.

U-Shaped Association Between Carboxyhemoglobin and Mortality in Patients With Acute Respiratory Distress Syndrome on Venovenous Extracorporeal Membrane Oxygenation

Background

Carbon monoxide (CO) is an endogenous signaling molecule that activates cytoprotective programs implicated in the resolution of acute respiratory distress syndrome (ARDS) and survival of critical illness. Because CO levels can be measured in blood as carboxyhemoglobin, we hypothesized that carboxyhemoglobin percent (COHb%) may associate with mortality.

OBJECTIVES

To examine the relationship between COHb% and outcomes in patients with ARDS requiring venovenous extracorporeal membrane oxygenation (ECMO), a condition where elevated COHb% is commonly observed.

DESIGN

Retrospective cohort study.

SETTING

Academic medical center ICU.

PATIENTS

Patients were included that had ARDS on venovenous ECMO.

MEASUREMENTS AND MAIN RESULTS

We examined the association between COHb% and mortality using a Cox proportional hazards model. Secondary outcomes including ECMO duration, ventilator weaning, and hospital and ICU length of stay were examined using both subdistribution and causal-specific hazard models for competing risks. We identified 109 consecutive patients for analysis. Mortality significantly decreased per 1 U increase in COHb% below 3.25% (hazard ratio [HR], 0.35; 95% CI, 0.15-0.80; p = 0.013) and increased per 1 U increase above 3.25% (HR, 4.7; 95% CI, 1.5-14.7; p = 0.007) reflecting a nonlinear association (p = 0.006). Each unit increase in COHb% was associated with reduced likelihood of liberation from ECMO and mechanical ventilation, and increased time to hospital and ICU discharge (all p < 0.05). COHb% was significantly associated with hemolysis but not with initiation of hemodialysis or blood transfusions.

CONCLUSIONS

In patients with ARDS on venovenous ECMO, COHb% is a novel biomarker for mortality exhibiting a U-shaped pattern. Our findings suggest that too little CO (perhaps due to impaired host signaling) or excess CO (perhaps due to hemolysis) is associated with higher mortality. Patients with low COHb% may exhibit the most benefit from future therapies targeting anti-oxidant and anti-inflammatory pathways such as low-dose inhaled CO gas.

A retrospective analysis of the hemolysis occurrence during extracorporeal membrane oxygenation in a single center

INTRODUCTION

Extracorporeal membrane oxygenation (ECMO)-associated hemolysis still represents a serious complication. The present study aimed to investigate those predictive factors, such as flow rates, the use of anticoagulants, and circuit connected dialysis, that might play a pivotal role in hemolysis in adult patients.

METHODS

This is a retrospective single-center case series of 35 consecutive adult patients undergoing veno-venous ECMO support at our center between April 2014 and February 2020. Daily plasma-free hemoglobin (pfHb) and haptoglobin (Hpt) levels were chosen as hemolysis markers and they were analyzed along with patients' characteristics, daily laboratory findings, and corresponding ECMO system variables, as well as continuous renal replacement therapy (CRRT) when administered, looking for factors influencing their trends over time.

RESULTS

Among the many settings related to the ECMO support, the presence of CRRT connected to the ECMO circuit has been found associated with both higher daily pfHb levels and lower Hpt levels. After correction for potential confounders, hemolysis was ascribable to circuit-related variables, in particular the membrane oxygenation dead space was associated with an Hpt reduction (B = -215.307, p = 0.004). Moreover, a reduction of ECMO blood flow by 1 L/min has been associated with a daily Hpt consumption of 93.371 mg/dL (p = 0.001).

CONCLUSIONS

Technical-induced hemolysis during ECMO should be monitored not only when suspected but also during quotidian management and check-ups. While considering the clinical complexity of patients on ECMO support, clinicians should not only be aware of and anticipate possible circuitry malfunctions or inadequate flow settings, but they should also take into account the effects of an ECMO circuit-connected CRRT, as an equally important key factor triggering hemolysis.

Extended Cellular Deposits on Gas Exchange Capillaries are Not an Indicator of Clot Formation: Analysis of Different Membrane Oxygenators

Antithrombogenic coatings of artificial surfaces within extracorporeal membrane oxygenation (ECMO) circuits improved its bio- and hemocompatibility. However, there is still a risk of thrombus formation in particular within the membrane oxygenator (MO). Since inflammatory cells are essential components within clots, the aim was to identify the extent of cellular accumulations on gas exchange capillaries from different ECMO systems. Thirty-four MOs (PLS, n = 27, Getinge; Hilite 7000 LT, n = 7, Fresenius Medical Care, Germany) were collected from adult patients. The extent of cellular deposits on gas exchange capillaries was classified using nuclear 4',6-diamidino-2-phenylindole staining and fluorescence microscopy. All Hilite oxygenators exhibited small cellular deposits. In contrast, the cellular distribution was heterogeneous on capillaries from PLS oxygenators: small deposits (34%), clusters (44%) and membrane-spanning cell structures (pseudomembranes) (22%). Overall, the median fluorescence intensity was significantly higher in the PLS group. Nevertheless, within 3 days before MO removal, there was no alteration in critical parameters (d-dimer and fibrinogen levels, platelet counts, and pressure drop across the MO). In conclusion, despite the histological differences on the gas capillaries from different types of oxygenators, there was no further evidence of increased inflammation and coagulation parameters that indicate clot formation within oxygenators.

Mechanical Assist Device-Assisted Percutaneous Coronary Intervention: The Use of Impella Versus Extracorporeal Membrane Oxygenation as an Emerging Frontier in Revascularization in Cardiogenic Shock

The extracorporeal membrane oxygenation (ECMO) procedure aids in the provision of prolonged cardiopulmonary support, whereas the Impella device (Abiomed, Danvers, MA) is a ventricular assist device that maintains circulation by pumping blood into the aorta from the left ventricle. Blood is circulated in parallel with the heart by Impella. It draws blood straight into the aorta from the left ventricle, hence preserving the physiological flow. ECMO bypasses the left atrium and the left ventricle, and the end consequence is a non-physiological flow. In this article, we conducted a detailed analysis of various publications in the literature and examined various modalities pertaining to the use of ECMO and Impella for cardiogenic shocks, such as efficacy, clinical outcomes, cost-effectiveness, device-related complications, and limitations. The Impella completely unloads the left ventricle, thereby significantly reducing the effort of the heart. Comparatively, ECMO only stabilizes a patient with cardiogenic shock for a short stretch of time and does not lessen the efforts of the left ventricle ("unload" it). In the acute setting, both devices reduced left ventricular end-diastolic pressure and provided adequate hemodynamic support. By comparing patients on Impella to those receiving ECMO, it was found that patients on Impella were associated with better clinical results, quicker recovery, limited complications, and reduced healthcare costs; however, there is a lack of conclusive studies performed demonstrating the reduction in long-term mortality rates. Considering the effectiveness of given modalities and taking into account the various studies described in the literature, Impella has reported better clinical outcomes although more clinical trials are needed for establishing the effectiveness of these interventional approaches in revascularization in cardiogenic shock.

Fatigue of red blood cells under periodic squeezes in ECMO

Hemolysis usually happens instantly when red blood cells (RBCs) rupture under a high shear stress. However, it is also found to happen gradually in the extracorporeal membrane oxygenation (ECMO) under low but periodic squeezes. In particular, the gradual hemolysis is accompanied by a progressive change in morphology of RBCs. In this work, the gradual hemolysis is studied in a microfluidic device with arrays of narrow gaps the same as the constructions in ECMO. RBCs are seen to deform periodically when they flow through the narrow gaps, which causes the release of adenosine-triphosphate (ATP) from RBCs. The reduced ATP level in the cells leads to the fatigue of RBCs with the progressive changes in morphology and the gradual loss of deformability. An empirical model for the fatigue of RBCs is established under the periodic squeezes with controlled deformation, and it reveals a different way of the hemolysis that is dominated by the squeeze frequency. This finding brings a new insight into the mechanism of hemolysis, and it helps to improve the design of circulatory support devices.

Coagulation and hemolysis complications in neonatal ECLS: Role of devices

Neonatal extracorporeal life support (ECLS) has enjoyed a long history of successful patient support for both cardiac and respiratory failure. The small size of this patient population has provided many technical challenges from cannulation to pumps and oxygenators. This is further complicated by the relatively meager commercial options for equipment owing to the relatively low utilization of neonatal ECLS compared to adults, which has exploded following the H1N1 epidemic and the availability of the polymethylpentene oxygenator. This paper focuses on the impact of equipment choices on thrombosis and hemolysis in neonatal ECLS and the underlying mechanisms behind them. Based upon the available evidence, it is clear neonatal ECLS requires careful attention to the selection and operation of all parts of the ECLS system. Practitioners should also be aware of the factors that increase blood cell fragility, which can impact decisions around equipment and subsequent operation.

Hemocompatibility challenge of membrane oxygenator for artificial lung technology

The artificial lung (AL) technology is one of the membrane-based artificial organs that partly augments lung functions, i.e. blood oxygenation and CO₂ removal. It is generally employed as an extracorporeal membrane oxygenation (ECMO) device to treat acute and chronic lung-failure patients, and the recent outbreak of the COVID-19 pandemic has re-emphasized the importance of this technology. The principal component in AL is the polymeric membrane oxygenator that facilitates the O₂/CO₂ exchange with the blood. Despite the considerable improvement in anti-thrombogenic biomaterials in other applications (e.g., stents), AL research has not advanced at the same rate. This is partly because AL research requires interdisciplinary knowledge in biomaterials and membrane technology. Some of the promising biomaterials with reasonable hemocompatibility - such as emerging fluoropolymers of extremely low surface energy - must first be fabricated into membranes to exhibit effective gas exchange performance. As AL membranes must also demonstrate high hemocompatibility in tandem, it is essential to test the membranes using in-vitro hemocompatibility experiments before in-vivo test. Hence, it is vital to have a reliable in-vitro experimental protocol that can be reasonably correlated with the in-vivo results. However, current in-vitro AL studies are unsystematic to allow a consistent comparison with in-vivo results. More specifically, current literature on AL biomaterial in-vitro hemocompatibility data are not quantitatively comparable due to the use of unstandardized and unreliable protocols. Such a wide gap has been the main bottleneck in the improvement of AL research, preventing promising biomaterials from reaching clinical trials. This review summarizes the current state-of-the-art and status of AL technology from membrane researcher perspectives. Particularly, most of the reported in-vitro experiments to assess AL membrane hemocompatibility are compiled and critically compared to suggest the most reliable method suitable for AL biomaterial research. Also, a brief review of current approaches to improve AL hemocompatibility is summarized. STATEMENT OF SIGNIFICANCE: The importance of Artificial Lung (AL) technology has been re-emphasized in the time of the COVID-19 pandemic. The utmost bottleneck in the current AL technology is the poor hemocompatibility of the polymer membrane used for O₂/CO₂ gas exchange, limiting its use in the long-term. Unfortunately, most of the in-vitro AL experiments are unsystematic, irreproducible, and unreliable. There are no standardized in-vitro hemocompatibility characterization protocols for quantitative comparison between AL biomaterials. In this review, we tackled this bottleneck by compiling the scattered in-vitro data and suggesting the most suitable experimental protocol to obtain reliable and comparable hemocompatibility results. To the best of our knowledge, this is the first review paper focusing on the hemocompatibility challenge of AL technology.

Remdesivir and GS-441524 Extraction by Ex Vivo Extracorporeal Life Support Circuits

Patients with severe, COVID-related multi-organ failure often require extracorporeal life support (ECLS) such as extracorporeal membrane oxygenation (ECMO) or continuous renal replacement therapy (CRRT). An ECLS can alter drug exposure via multiple mechanisms. Remdesivir (RDV) and its active metabolite GS-441524 are likely to interact with ECLS circuits, resulting in lower than expected exposures. We evaluated circuit-drug interactions in closed loop, ex vivo ECMO and CRRT circuits. We found that mean (standard deviation) recovery of RDV at 6 hours after dosing was low in both the ECMO (33.3% [2.0]) and CRRT (3.5% [0.4]) circuits. This drug loss appears to be due primarily to drug adsorption by the circuit materials and potentially due to metabolism in the blood. GS-441524 recovery at 6 hours was high in the ECMO circuit 75.8% (16.5); however, was not detectable at 6 hours in the CRRT circuit. Loss in the CRRT circuit appears to be due primarily to efficient hemodiafiltration. The extent of loss for both molecules, especially in CRRT, suggests that in patients supported with ECMO and CRRT, RDV dosing adjustments are needed.

Risk factors for hemolysis with centrifugal pumps in pediatric extracorporeal membrane oxygenation: Is pump replacement an answer?

INTRODUCTION

Hemolysis during pediatric extracorporeal membrane oxygenation (ECMO) is associated with increased risk for renal failure and mortality.

OBJECTIVES

We aim to describe risk factors for hemolysis in pediatric ECMO supported by centrifugal pumps.

METHODS

We conducted an analysis of retrospective data collected at an academic children's hospital from January 2017 to December 2019.

MEASUREMENTS AND RESULTS

Plasma-free hemoglobin (PFH) levels were measured daily, and hemolysis was defined as PFH>50 mg/dL. Of 46 ECMO runs over 528 ECMO days, hemolysis occurred in 23 (58%) patients over a total of 40 (8%) ECMO days. In multivariable logistic regression models, VA-ECMO (aOR=4.69, 95% CI: 1.01-21.83) and higher hemoglobin (aOR = 1.38, 95% CI: 1.06-1.81) were independently associated with hemolysis. There were also non-significant trends toward increased risk for hemolysis with higher rotational pump speed (aOR=2.39, 95% CI: 0.75-7.65), higher packed red blood cell transfusions (aOR=1.15, 95% CI: 0.99-1.34), and higher cryoprecipitate transfusions (aOR=2.01, 95% CI: 0.83-4.86). Isolated pump exchanges that were performed in 12 patients with hemolysis led to significant decreases in PFH levels within 24 h (89 vs 11 mg/dL, p<0.01).

CONCLUSIONS

Hemolysis is common in pediatric ECMO using centrifugal pumps. Avoidance of high pump speeds and conservative administration of blood products may help to mitigate the risk for hemolysis. Furthermore, pump exchange may be an effective first-line treatment for hemolysis.

Inflammation and Oxidative Stress in the Context of Extracorporeal Cardiac and Pulmonary Support

Extracorporeal circulation (ECC) systems, including cardiopulmonary bypass, and extracorporeal membrane oxygenation have been an irreplaceable part of the cardiothoracic surgeries, and treatment of critically ill patients with respiratory and/or cardiac failure for more than half a century. During the recent decades, the concept of extracorporeal circulation has been extended to isolated machine perfusion of the donor organ including thoracic organs (ex-situ organ perfusion, ESOP) as a method for dynamic, semi-physiologic preservation, and potential improvement of the donor organs. The extracorporeal life support systems (ECLS) have been lifesaving and facilitating complex cardiothoracic surgeries, and the ESOP technology has the potential to increase the number of the transplantable donor organs, and to improve the outcomes of transplantation. However, these artificial circulation systems in general have been associated with activation of the inflammatory and oxidative stress responses in patients and/or in the exposed tissues and organs. The activation of these responses can negatively affect patient outcomes in ECLS, and may as well jeopardize the reliability of the organ viability assessment, and the outcomes of thoracic organ preservation and transplantation in ESOP. Both ECLS and ESOP consist of artificial circuit materials and components, which play a key role in the induction of these responses. However, while ECLS can lead to systemic inflammatory and oxidative stress responses negatively affecting various organs/systems of the body, in ESOP, the absence of the organs that play an important role in oxidant scavenging/antioxidative replenishment of the body, such as liver, may make the perfused organ more susceptible to inflammation and oxidative stress during extracorporeal circulation. In the present manuscript, we will review the activation of the inflammatory and oxidative stress responses during ECLP and ESOP, mechanisms involved, clinical implications, and the interventions for attenuating these responses in ECC.

Overview of Veno-Arterial Extracorporeal Membrane Oxygenation (VA-ECMO) Support for the Management of Cardiogenic Shock

Cardiogenic shock accounts for ~100,000 annual hospital admissions in the United States. Despite improvements in medical management strategies, in-hospital mortality remains unacceptably high. Multiple mechanical circulatory support devices have been developed with the aim to provide hemodynamic support and to improve outcomes in this population. Veno-arterial extracorporeal membrane oxygenation (VA-ECMO) is the most advanced temporary life support system that is unique in that it provides immediate and complete hemodynamic support as well as concomitant gas exchange. In this review, we discuss the fundamental concepts and hemodynamic aspects of VA-ECMO support in patients with cardiogenic shock of various etiologies. In addition, we review the common indications, contraindications and complications associated with VA-ECMO use.

Extracorporeal Membrane Oxygenation-Induced Hemolysis: An In Vitro Study to Appraise Causative Factors

In vitro hemolysis testing is commonly used to determine hemocompatibility of ExtraCorporeal Membrane Oxygenation (ECMO). However, poor reproducibility remains a challenging problem, due to several unidentified influencing factors. The present study investigated potential factors, such as flow rates, the use of anticoagulants, and gender of blood donors, which could play a role in hemolysis. Fresh human whole blood was anticoagulated with either citrate (n = 6) or heparin (n = 12; 6 female and 6 male blood donors). Blood was then circulated for 360 min at 4 L/min or 1.5 L/min. Regardless of flow rate conditions, hemolysis remained unchanged over time in citrated blood, but significantly increased after 240 min circulation in heparinized blood (p ≤ 0.01). The ratio of the normalized index of hemolysis (NIH) of heparinized blood to citrated blood was 11.7-fold higher at 4 L/min and 16.5–fold higher at 1.5 L/min. The difference in hemolysis between 1.5 L/min and 4 L/min concurred with findings of previous literature. In addition, the ratio of NIH of male heparinized blood to female was 1.7-fold higher at 4 L/min and 2.2-fold higher at 1.5 L/min. Our preliminary results suggested that the choice of anticoagulant and blood donor gender could be critical factors in hemolysis studies, and should be taken into account to improve testing reliability during ECMO.

Amiodarone Extraction by the Extracorporeal Membrane Oxygenation Circuit

Amiodarone is an anti-arrhythmic agent that is frequently used to treat tachycardias in critically ill adults and children. Because of physicochemical properties of amiodarone, extracorporeal membrane oxygenation (ECMO) circuits are expected to extract amiodarone from circulation, increasing the risk of therapeutic failure. The present study seeks to determine amiodarone extraction by the ECMO circuit. Amiodarone was administered to three ex vivo circuit configurations (n = 3 per configuration) to determine the effect of each circuit component on drug extraction. The circuits were primed with human blood; standard amiodarone doses were administered; and serial samples were collected over 24 hours. Additional circuits were primed with crystalloid fluid to analyze the effect of blood on extraction and to investigate circuit saturation by drug. The crystalloid circuits were dosed multiple times over 72 hours, including a massive dose at 48 hours. For both setups, the flow was set to 1 L/min. Drug was added to separate tubes containing the prime solution to serve as controls. Drug concentrations were quantified with a validated assay, and drug recovery was calculated for each sample. Mean recovery for the circuits and controls were compared to correct for drug degradation over time. Amiodarone was heavily extracted by all ECMO circuit configurations. Eight hours after dosing, mean recovery in the blood prime circuits was 13.5-22.1%. In the crystalloid prime circuits, drug recovery decreased even more rapidly, with a mean recovery of 22.0% at 30 minutes. Similarly, drug recovery decreased more quickly in the crystalloid prime controls than in the blood prime controls. Saturation was not achieved in the crystalloid prime circuits, as final amiodarone concentrations were at the lower limit of quantification. The results suggest that amiodarone is rapidly extracted by the ECMO circuit and that saturation is not achieved by standard doses. In vivo circuit extraction may cause decreased drug exposure.

Anticoagulation in ECMO patients: an overview

Extracorporeal membrane oxygenation (ECMO) is a form of cardiorespiratory support, and is being increasingly used to support refractory heart and respiratory failure. It involves draining blood from the vascular system, which is then circulated outside the body by a mechanical pump and then later reinfused back into the circulation. The blood that is circulated outside the body comes in contact with a large surface area of non-endothelial biosurface. This exposure leads to a pro-thrombotic state, and hence anticoagulation is required. Unfractionated heparin is the most commonly used anticoagulation in most ECMO centers, but it does require close monitoring. Despite the advances made, hemostasis remains a challenge for physicians who manage patients on ECMO.

Parallel veno-venous and veno-arterial extracorporeal membrane circuits for coexisting refractory hypoxemia and cardiovascular failure: a case report

Background

The complexity of extracorporeal membrane oxygenation (ECMO) techniques continues to evolve. Different cannulation methods and configurations have been proposed as a response to a challenging cardiovascular and pulmonary physiology of the patients. The use of parallel ECMO circuits represents a unique and novel approach for patients with refractory respiratory failure and cardiovascular collapse with very large body surface areas.

Case presentation

We present the case of a 25-year-old morbidly obese male patient admitted for severe acute respiratory distress syndrome (ARDS) and refractory hypoxemia, requiring institution of double cannulation for veno-venous ECMO. Since his hypoxemia persisted, likely due to insufficient flows given his large body surface area, an additional drainage venous cannula was implemented to provide higher flows, temporarily addressing his oxygenation status. Unfortunately, the patient developed concomitant cardiogenic shock refractory to inotropic support and extracorporeal fluid removal, further worsening his oxygenation status, thus the decision was to institute four-cannulation/parallel-circuits veno-venous and veno-arterial ECMO, successfully controlling both refractory hypoxemia and cardiogenic shock.

Conclusions

Our case illustrates a novel and complex approach for combined severe ARDS and cardiovascular collapse through the use of parallel veno-venous and veno-arterial ECMO circuits, and exemplifies the expansion of ECMO techniques and its life-saving capabilities when conservative approaches are futile.

Acute Kidney Injury, Fluid Overload, and Renal Replacement Therapy Differ by Underlying Diagnosis in Neonatal Extracorporeal Support and Impact Mortality Disparately

INTRODUCTION

We aimed to characterize acute kidney injury (AKI), fluid overload (FO), and renal replacement therapy (RRT) utilization by diagnostic categories and examine associations between these complications and mortality by category.

METHODS

To test our hypotheses, we conducted a retrospective multicenter, cohort study including 446 neonates (categories: 209 with cardiac disease, 114 with congenital diaphragmatic hernia [CDH], 123 with respiratory disease) requiring extracorporeal membrane oxygenation (ECMO) between January 1, 2007, and December 31, 2011.

RESULTS

AKI, FO, and RRT each varied by diagnostic category. AKI and RRT receipt were most common in those neonates with cardiac disease. Subjects with CDH had highest peak %FO (51% vs. 28% cardiac vs. 32% respiratory; p < 0.01). Hospital survival was 55% and varied by diagnostic category (45% cardiac vs. 48% CDH vs. 79% respiratory; p < 0.001). A significant interaction suggested risk of mortality differed by diagnostic category in the presence or absence of AKI. In its absence, diagnosis of CDH (vs. respiratory disease) (OR 3.04, 95% CL 1.14-8.11) independently predicted mortality. In all categories, peak %FO (OR 1.20, 95% CL 1.11-1.30) and RRT receipt (OR 2.12, 95% CL 1.20-3.73) were independently associated with mortality.

DISCUSSION/CONCLUSIONS

Physiologically distinct ECMO diagnoses warrant individualized treatment strategies given variable incidence and effects of AKI, FO, and RRT by category on mortality.

The Prolonged Use of VV ECMO Support in COVID-19: A Case Report

COVID-19 has resulted in unprecedented global health and economic challenges. The reported mortality in patients with COVID-19 requiring mechanical ventilation is high. VV ECMO may serve as a lifesaving rescue therapy for a minority of patients with COVID-19; however, its impact on overall survival of these patients is unknown. To date, few reports describe successful discharge from ECMO in COVID-19 after a prolonged ECMO run. The only Australian case of a COVID-19 patient, supported by prolonged VV ECMO in conjunction with prone ventilation, complicated by significant airway bleeding, and successfully decannulated after forty-two days, is described. VV ECMO is a resource-intense form of respiratory support. Providing complex therapies such as VV ECMO during a pandemic has its unique challenges. This case report provides a unique insight into the potential clinical sequelae of COVID-19, supported in an intensive care environment which was not resource-limited at the time, and adds to the evolving experience of prolonged VV ECMO support for ARDS with a goal to lung recovery.

Semiquantification of Systemic Venous Admixture During Venovenous Extracorporeal Oxygenation Via Bicaval Double-Lumen Cannula in Critically Ill Patients

Venovenous extracorporeal membrane oxygenation (VV-ECMO) is increasingly utilized in acute reversible cases of severe respiratory failure and as a bridge to lung transplantation. Venovenous extracorporeal membrane oxygenation using a bicaval double-lumen cannula (BCDLC) has several advantages over the traditional ECMO configuration; however, it also presents with several unique challenges. The assessment and quantification of venous admixture is difficult due to the specific position of BCDLC within the circulatory system. We describe the nature of the double-lumen bicaval venovenous ECMO cannula and relevant specific issues associated with monitoring complex details of oxygenation within different parts of circulation, including existing barriers for quantification of recirculation and venous admix. New conceptual approach to the quantification of venous admix is described. Right side echocardiographic contrast, when sequentially injected in separate superior vena cava (SVC) and inferior vena cava (IVC) venous basins, bypasses drainage ports of the catheter in double-lumen bicaval VV-ECMO configuration together with deoxygenated returning from the periphery venous blood. It was easily detectable entering right heart chambers by two- and three-dimensional echocardiography. Amount of bubbles from the agitated fluid contrast within right atrium indicates relative amount of venous admixture in relation to the returning from the oxygenator blood which is bubble free.

Biomarkers of Inflammation and Lung Recovery in Extracorporeal Membrane Oxygenation Patients With Persistent Pulmonary Hypertension of the Newborn: A Feasibility Study

OBJECTIVES

Extracorporeal membrane oxygenation is a treatment for Persistent Pulmonary Hypertension of the Newborn with high mortality.

HYPOTHESIS

the extracorporeal membrane oxygenation circuit results in inflammatory responses that mitigate against successful weaning.

DESIGN

Single-center prospective observational feasibility study.

SETTING

PICU.

PATIENTS

Twenty-four neonates requiring extracorporeal membrane oxygenation support for Persistent Pulmonary Hypertension of the Newborn.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The reference outcome was death or more than 7 days of extracorporeal membrane oxygenation support. Other outcomes included serial measures of plasma-free hemoglobin and markers of its metabolism, leucocyte, platelet and endothelial activation, and biomarkers of inflammation. Of 24 participants recruited between February 2016 and June 2017, 10 died or required prolonged extracorporeal membrane oxygenation support. These patients were sicker at baseline with higher levels of plasma-free hemoglobin within 12 hours of cannulation (geometric mean ratio, 1.92; 95% CIs, 1.00-3.67; p = 0.050) but not thereafter, versus those requiring less than 7 days extracorporeal membrane oxygenation. Serum haptoglobin concentrations were significantly elevated in both groups. Patients who died or required prolonged extracorporeal membrane oxygenation support demonstrated elevated levels of platelet-leucocyte aggregation, but decreased concentrations of mediators of the inflammatory response: interleukin-8, C-reactive protein, and tumor necrosis factor α.

CONCLUSIONS

Clinical status at baseline and not levels of plasma-free hemoglobin or the systemic inflammatory response may determine the requirement for prolonged extracorporeal membrane oxygenation support in neonates.

Incidence and Impact of Acute Kidney Injury in Patients Receiving Extracorporeal Membrane Oxygenation: A Meta-Analysis

BACKGROUND

Although acute kidney injury (AKI) is a frequent complication in patients receiving extracorporeal membrane oxygenation (ECMO), the incidence and impact of AKI on mortality among patients on ECMO remain unclear. We conducted this systematic review to summarize the incidence and impact of AKI on mortality risk among adult patients on ECMO.

METHODS

A literature search was performed using EMBASE, Ovid MEDLINE, and Cochrane Databases from inception until March 2019 to identify studies assessing the incidence of AKI (using a standard AKI definition), severe AKI requiring renal replacement therapy (RRT), and the impact of AKI among adult patients on ECMO. Effect estimates from the individual studies were obtained and combined utilizing random-effects, generic inverse variance method of DerSimonian-Laird. The protocol for this systematic review is registered with PROSPERO (no. CRD42018103527).

RESULTS

41 cohort studies with a total of 10,282 adult patients receiving ECMO were enrolled. Overall, the pooled estimated incidence of AKI and severe AKI requiring RRT were 62.8% (95%CI: 52.1%-72.4%) and 44.9% (95%CI: 40.8%-49.0%), respectively. Meta-regression showed that the year of study did not significantly affect the incidence of AKI (p = 0.67) or AKI requiring RRT (p = 0.83). The pooled odds ratio (OR) of hospital mortality among patients receiving ECMO with AKI on RRT was 3.73 (95% CI, 2.87-4.85). When the analysis was limited to studies with confounder-adjusted analysis, increased hospital mortality remained significant among patients receiving ECMO with AKI requiring RRT with pooled OR of 3.32 (95% CI, 2.21-4.99). There was no publication bias as evaluated by the funnel plot and Egger's regression asymmetry test with p = 0.62 and p = 0.17 for the incidence of AKI and severe AKI requiring RRT, respectively.

CONCLUSION

Among patients receiving ECMO, the incidence rates of AKI and severe AKI requiring RRT are high, which has not changed over time. Patients who develop AKI requiring RRT while on ECMO carry 3.7-fold higher hospital mortality.

Hemoadsorption in isolated conjugated hyperbilirubinemia after extracorporeal membrane oxygenation support. Cholestasis of sepsis: A case report and review of the literature on differential causes of jaundice in ICU patient

Hyperbilirubinemia occurs in up to 40% of critically ill. In ICU, hyperbilirubinemia is an independent factor that influences patients’ morbidity and mortality. Jaundice can reflect the course of disease or be caused by treatment (e.g. extracorporeal membrane oxygenation (ECMO)), thus can be difficult to differentiate. Sepsis was also associated with development of jaundice secondary to intrahepatic cholestasis. Prolonged cholestasis should be addressed to avoid liver damage. The patient with diagnosis of septic shock and severe acute respiratory distress syndrome was retrieved to our hospital for ECMO. Three days after initiation of ECMO, the patient developed jaundice, with increase of bilirubin, Gamma-glutamyltransferase and Alkaline phosphatase, without elevation of alanine aminotransferase and INR. Although ECMO was stopped, bilirubin serum levels were increasing, reaching the peak of 18.41 mg/dL of total and 15.67 mg/dL of direct bilirubin. Abdominal computed tomography showed homogeneous liver and non-dilated bile ducts. Viral hepatitis was excluded. CIOMS/RUCAM score was 0. Sepsis-related cholestasis was diagnosed. Despite cessation of sedation, the patient remained unconscious. Hemoadsorption therapy was initiated due to prolonged high levels of conjugated bilirubin. After 48 h of CytoSorb treatment, total bilirubin level was decreased to 2.4 mg/dL, the patient regained spontaneous eyes opening and could be transferred to regional hospital. Hyperbilirubinemia did not return in 3 months. Sepsis-related cholestasis is a diagnosis of exclusion that should be considered in case of jaundice in critically ill patients. In our patient, CytoSorb was a useful therapeutic option in prolonged cholestasis. Adsorption therapy was able to facilitate long-term regain of balance between inflammatory process, cytokine production and bilirubin turnover in the liver.

Oxidative Stress and Neonatal Respiratory Extracorporeal Membrane Oxygenation

Oxidative stress is a frequent condition in critically ill patients, especially if exposed to extracorporeal circulation, and it is associated with worse outcomes and increased mortality. The inflammation triggered by the contact of blood with a non-endogenous surface, the use of high volumes of packed red blood cells and platelets transfusion, the risk of hyperoxia and the impairment of antioxidation systems contribute to the increase of reactive oxygen species and the imbalance of the redox system. This is responsible for the increased production of superoxide anion, hydrogen peroxide, hydroxyl radicals, and peroxynitrite resulting in increased lipid peroxidation, protein oxidation, and DNA damage. The understanding of the pathophysiologic mechanisms leading to redox imbalance would pave the way for the future development of preventive approaches. This review provides an overview of the clinical impact of the oxidative stress during neonatal extracorporeal support and concludes with a brief perspective on the current antioxidant strategies, with the aim to focus on the potential oxidative stress-mediated cell damage that has been implicated in both short and long-term outcomes.

Impact of Hemolysis on Acute Kidney Injury and Mortality in Children Supported with Cardiac Extracorporeal Membrane Oxygenation

Intravascular hemolysis with elevated plasma-free hemoglobin (PFH) complicates extracorporeal membrane oxygenation (ECMO). In 50 consecutive pediatric cardiac patients requiring ECMO, we sought to describe the relationship between PFH and clinical outcomes; primary outcomes were acute kidney injury (AKI) and prolonged (>14 days) renal replacement therapy (RRT). Median age was 35 days, median weight 3.9 kg, and median ECMO duration 4.2 days. Seventy-eight percent (39/50) weaned off ECMO; survival to discharge was 50% (25/50). Seventy percent (35/50) had AKI on ECMO. Seventy-seven percent (30/39) required RRT post-ECMO; median duration was 5.2 days (0, 14.2). Prolonged RRT was associated with higher daily PFH (67.5 mg/dL [54.1, 102.5] vs. 46.7 mg/dL [40, 72.6], p = .025) and higher peak PFH (120 mg/dL [90, 200] vs. 60 mg/dL [40, 135], p = .016). After adjusting for ECMO duration and oliguria/elevated creatinine on ECMO day 0, peak PFH >90 mg/dL was associated with prolonged RRT (operating room [OR] = 18, confidence interval [CI] 1.9-167.8). Patients who died had higher daily PFH (65 mg/dL [51.6, 111.7] vs. 42.5 mg/dL [37.5, 60], p = .0040). Adjusting for ECMO duration and blood product administration, daily PFH >53 mg/dL was associated with mortality (OR 4.8, CI 1.01-23.3). Elevated PFH during pediatric cardiac ECMO is associated with prolonged RRT and non-survival to discharge. Initiatives to decrease PFH burden may improve clinical outcomes.

An Analysis of Risk Factors for Hemolysis in Children on Extracorporeal Membrane Oxygenation

OBJECTIVES

Hemolysis is a known complication of pediatric extracorporeal membrane oxygenation associated with renal failure and mortality. We sought to identify predictors of hemolysis in pediatric extracorporeal membrane oxygenation patients and determine its influence on outcomes.

DESIGN

Retrospective, single-center study.

SETTING

Urban, quaternary care center pediatric and neonatal ICU.

PATIENTS

Ninety-six patients requiring extracorporeal membrane oxygenation.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Daily measurements of plasma-free hemoglobin were obtained while patients were on extracorporeal membrane oxygenation. Patients with a prior extracorporeal membrane oxygenation run, on extracorporeal membrane oxygenation for less than 24 hours, or without complete medical records were excluded from the study. Ninety-six patients met inclusion criteria, of which, 25 patients (26%) had plasma-free hemoglobin greater than 30 mg/dL. Of those patients, 15 of 25(60%) had plasma-free hemoglobin greater than 50 mg/dL, and 21 of 25(84%) occurred during the first 7 days on extracorporeal membrane oxygenation. Compared with patients without hemolysis, those with hemolysis were younger (0.2 mo [0.06-3.2 mo] vs 8.2 mo [0.6-86 mo]; p < 0.001), had a higher pericannulation international normalized ratio (3.9 [3.5-5.5] vs 2.6 [1.8-3.7]; p = 0.003), lower pericannulation platelet count (33 × 10/μL [22-42 × 10/μL] vs 61 × 10/μL [38-86 × 10/μL]; p < 0.001), and had a less negative inlet pressure (-3.5 mm Hg [-14 to 11.5 mm Hg] vs -19 mm Hg [-47 to 0 mm Hg]; p = 0.01). A greater proportion of patients with hemolysis had a heparin assay less than 0.2 mg/dL (50% vs 17%; p = 0.001) and had fluid removal via slow continuous ultrafiltration (32% vs 6%; p < 0.001). Patients with hemolysis had increased risk of in-hospital mortality (odds ratio 10.0; 95% CI 3.4-32; p < 0.001). On multivariable analysis, continuous ultrafiltration (odds ratio, 8.0; 95% CI, 1.9-42; p = 0.007) and pericannulation international normalized ratio greater than 3.5 (odds ratio, 7.2; 95% CI, 2.3-26; p = 0.001) were significantly associated with hemolysis.

CONCLUSIONS

Hemolysis is a common complication of pediatric extracorporeal membrane oxygenation. We found that patients with hemolysis (plasma-free hemoglobin > 30 mg/dL) had a 10-fold increase in in-hospital mortality. In our study cohort, hemolysis was associated with continuous ultrafiltration use, but not continuous renal replacement therapy. Additionally, our results suggest that the degree of coagulopathy (international normalized ratio > 3.5) at the time of cannulation influences hemolysis. Additional prospective studies are necessary to define further strategies to prevent hemolysis and improve outcomes in pediatric extracorporeal membrane oxygenation patients.

von Willebrand Factor, Free Hemoglobin and Thrombosis in ECMO

Though extracorporeal membrane oxygenation (ECMO) provides life-saving support, this intervention exposes patients to certain risks. Circulating free hemoglobin (fHb) resulting from mechanically induced hemolysis and insufficient haptoglobin/hemopexin may promote thrombosis within the ECMO circuit. Thrombi in the circuit can result in thromboembolic complications in these patients. Prevention of thrombus formation and propagation in the ECMO circuit may improve clinical outcome. fHb released during hemolysis has been shown to have multiple adverse effects, including thrombosis, but the mechanism by which fHb contributes to thrombosis in an ECMO circuit remains elusive. It is well established that (1) high shear stress generated in the circuit may cause hemolysis, and (2) plasma fibrinogen is adsorbed onto the inner tubing of the ECMO circuit over time. Plasma von Willebrand factor (pVWF) mediates platelet deposition at sites of vascular injury under high shear stress by sensing alterations in the hemodynamic environment. This biophysical property of pVWF that enables hemostasis may also contribute to the pathogenesis of ECMO-induced thrombosis. pVWF contains binding sites for both adsorbed fibrin(ogen) and fHb. High concentrations of fHb increase pVWF-mediated platelet adhesion and thrombus formation on a surface-adsorbed fibrin(ogen) under high shear stress. The molecular mechanism(s) by which fHb drives the conformation of pVWF into a prothrombotic state is currently unknown. Reduction of thrombotic risks during ECMO intervention warrants further investigations into the interaction between pVWF and fHb.

Plasma Free Hemoglobin Generation Using the EOS PMP™ Oxygenator and the CentriMag® Blood Pump

Hemolysis is a known consequence of extracorporeal membrane oxygenation (ECMO) resulting from shear force within the different components of the extracorporeal circuit. The primary aim of this study was to evaluate the EOS PMP^™ oxygenator for generation of plasma free hemoglobin (PfHg) over 24 hours at nominal operating range flow rates. The EOS ECMO^™ (LivaNova, Inc.; formerly Sorin, Arvada, CO) is equipped with a plasma tight polymethylpentene (PMP) hollow fiber oxygenator. We hypothesized that PfHg generation would be elevated in circuits with higher flow rates, because of the significant pressure drop across the oxygenator according to manufacturer provided flow charts. Generated PfHg concentrations were compared with PfHg concentrations from blood not exposed to an ECMO circuit. The secondary aim was to evaluate circuit flow-rate-induced changes in platelet count and platelet function over 24 hours. Circuits contained a CentriMag^® (St. Jude Medical, St. Paul, MN) blood pump and an EOS ECMO PMP^™ oxygenator. Circuits in triplicate were run continuously for 24 hours at three flow rates [1, 3, and 5 liters per minute {LPM}]. PfHg was analyzed at baseline, 6, 12, 18, and 24 hours. Platelet count and function were measured at baseline and 24 hours. Concentrations of PfHg at baseline for circuits operating at 1, 3, and 5 LPM were 24.4 ± 4.0, 38.4 ± 28.6, and 26.7 ± 6.9 mg/dL, respectively. PfHg concentrations after 24 hours were statistically compared for the three flow rates using analysis of variance; PfHg concentrations at 1 LPM (181.4 ± 29.1 mg/dL), 3 LPM (145.9 ± 8.7 mg/dL), and 5 LPM (100.1 ± 111.3 mg/dL) circuits. The F-test was not statistically significant (p = .632), indicating that PfHg generation at 24 hours was similar among the three flow rates. Excessive hemolysis using PfHg levels in the EOS PMP^™ membrane oxygenator was not observed.

Impact of an inline extracorporeal membrane oxygenation hemofilter system in neonatal acute kidney injury

Extracorporeal membrane oxygenation (ECMO) is considered a recognized lifesaving support for patients with cardiorespiratory failure. Acute kidney injury (AKI) and fluid overload are significant morbidity factors resulting in serious complications. The inline hemofilter system (IHS) and the continuous renal replacement therapy (CRRT) machine are different methods of renal replacement therapy for patients with ECMO. IHS is the alternate, safe dialysis modality of choice because it is user-friendly, inexpensive, and efficiently removes fluid overload and renal diffusive clearance. We report on a 20-day-old male neonate with multiple congenital cardiac defects who needed venoarterial ECMO and had AKI necessitating renal replacement therapy using IHS. The patient had stable electrolyte parameters, good ultrafiltration, and efficient diffusive clearance. He was decannulated from ECMO therapy after 9 days without any related complications. Therefore, neonatal IHS is a safe and efficient alternative approach to AKI.

Incidence, Risk Factors, and Outcomes of Hyperbilirubinemia in Adult Cardiac Patients Supported by Veno-Arterial ECMO

The aims of this study were to evaluate the incidence, risk factors, and outcomes of hyperbilirubinemia in cardiac patients with veno-arterial (VA) ECMO. Data on 89 adult patients with cardiac diseases who received VA ECMO implantation in our hospital were retrospectively reviewed. All patients were divided into the following three groups: 24 in normal group (N, total bilirubin [TBIL] ≤3 mg/dL), 30 in high bilirubin group (HB, 6 mg/dL ≥ TBIL > 3 mg/dL), and 35 in severe high bilirubin group (SHB, TBIL > 6 mg/dL). lg(variables + 1) was performed for nonnormally distributed variables. The incidence of hyperbilirubinemia (>3 mg/dL) was 73%. In a multiple linear regression analysis, lg(peak TBIL + 1) was significantly associated with lg(peak AST + 1) (b-coefficient 0.188, P = 0.001), lg(peak pFHb + 1) (b-coefficient 0.201, P = 0.003), and basic TBIL (b-coefficient 0.006, P = 0.009). Repeated measurement analysis of variance revealed that the main effect for three groups in pFHb and lg(AST + 1) was significant at first 3 days during ECMO. The patients in SHB had low platelets during ECMO and low in-hospital survival rate. Hyperbilirubinemia remains common in patients with VA ECMO and is associated with low platelets and high in-hospital mortality. Hemolysis and liver dysfunction during ECMO and basic high bilirubin levels are risk factors of hyperbilirubinemia.

Impact of membrane lung surface area and blood flow on extracorporeal CO2 removal during severe respiratory acidosis

BACKGROUND

Veno-venous extracorporeal CO₂ removal (vv-ECCO₂R) is increasingly being used in the setting of acute respiratory failure. Blood flow rates through the device range from 200 ml/min to more than 1500 ml/min, and the membrane surface areas range from 0.35 to 1.3 m². The present study in an animal model with similar CO₂ production as an adult patient was aimed at determining the optimal membrane lung surface area and technical requirements for successful vv-ECCO₂R.

METHODS

Four different membrane lungs, with varying lung surface areas of 0.4, 0.8, 1.0, and 1.3m² were used to perform vv-ECCO₂R in seven anesthetized, mechanically ventilated, pigs with experimentally induced severe respiratory acidosis (pH 7.0-7.1) using a 20Fr double-lumen catheter with a sweep gas flow rate of 8 L/min. During each experiment, the blood flow was increased stepwise from 250 to 1000 ml/min.

RESULTS

Amelioration of severe respiratory acidosis was only feasible when blood flow rates from 750 to 1000 ml/min were used with a membrane lung surface area of at least 0.8 m². Maximal CO₂ elimination was 150.8 ml/min, with pH increasing from 7.01 to 7.30 (blood flow 1000 ml/min; membrane lung 1.3 m²). The membrane lung with a surface of 0.4 m² allowed a maximum CO₂ elimination rate of 71.7 mL/min, which did not result in the normalization of pH, even with a blood flow rate of 1000 ml/min. Also of note, an increase of the surface area above 1.0 m² did not result in substantially higher CO₂ elimination rates. The pressure drop across the oxygenator was considerably lower (<10 mmHg) in the largest membrane lung, whereas the smallest revealed a pressure drop of more than 50 mmHg with 1000 ml blood flow/min.

CONCLUSIONS

In this porcine model, vv-ECCO₂R was most effective when using blood flow rates ranging between 750 and 1000 ml/min, with a membrane lung surface of at least 0.8 m². In contrast, low blood flow rates (250-500 ml/min) were not sufficient to completely correct severe respiratory acidosis, irrespective of the surface area of the membrane lung being used. The converse was also true, low surface membrane lungs (0.4 m²) were not capable of completely correcting severe respiratory acidosis across the range of blood flows used in this study.

Pediatric Extracorporeal Membrane Oxygenation

Extracorporeal life support is a modified form of cardiopulmonary bypass. Experience in extracorporeal membrane oxygenation (ECMO) has come largely from the neonatal population. Most centers have transitioned the ECMO pumps from roller pumps to centrifugal technology. Modes of support include venovenous for respiratory support and venoarterial for cardiac support. "Awake" ECMO is the trend with extubation and tracheostomy on the rise. Fluid overload is common and managed with diuretics or hemofiltration. Nutrition is important and provided enterally or via total parenteral nutrition. Overall survival for pediatric cardiac and respiratory ECMO has remained at approximately 50% to 60%.

The Complex Relationship of Extracorporeal Membrane Oxygenation and Acute Kidney Injury: Causation or Association?

Extracorporeal membrane oxygenation (ECMO) is a modified cardiopulmonary bypass (CPB) circuit capable of providing prolonged cardiorespiratory support. Recent advancement in ECMO technology has resulted in increased utilisation and clinical application. It can be used as a bridge-to-recovery, bridge-to-bridge, bridge-to-transplant, or bridge-to-decision. ECMO can restitute physiology in critically ill patients, which may minimise the risk of progressive multiorgan dysfunction. Alternatively, iatrogenic complications of ECMO clearly contribute to worse outcomes. These factors affect the risk : benefit ratio of ECMO which ultimately influence commencement/timing of ECMO. The complex interplay of pre-ECMO, ECMO, and post-ECMO pathophysiological processes are responsible for the substantial increased incidence of ECMO-associated acute kidney injury (EAKI). The development of EAKI significantly contributes to morbidity and mortality; however, there is a lack of evidence defining a potential benefit or causative link between ECMO and AKI. This area warrants investigation as further research will delineate the mechanisms involved and subsequent strategies to minimise the risk of EAKI. This review summarizes the current literature of ECMO and AKI, considers the possible benefits and risks of ECMO on renal function, outlines the related pathophysiology, highlights relevant investigative tools, and ultimately suggests an approach for future research into this under investigated area of critical care.

Comparison of a New Miniaturized Extracorporeal Membrane Oxygenation System With Integrated Rotary Blood Pump to a Standard System in a Porcine Model of Acute Lung Injury

Extracorporeal membrane oxygenation (ECMO) is used for severe acute respiratory distress syndrome. However, available ECMO systems are large and not well designed for fast delivery, emergency implantation, and interhospital transfer. Therefore, a new miniaturized oxygenator with integrated rotary blood pump (ILIAS) was developed and compared with a standard ECMO system in a large animal model. Acute lung injury was induced with repeated pulmonary saline lavage in 14 pigs until PaO2 /FiO2 -ratio was <100 mm Hg with a positive-end-expiratory-pressure of 5 mbar. Pigs were assigned to the following three groups: group 1 (n = 4): control group with conventional ventilation; group 2 (n = 5): standard vv-ECMO; group 3 (n = 5): vv-ILIAS. Gas exchange, hemodynamics, hemolysis, and coagulation activation were examined over a period of 8 h. No device failed during the observation period. PaCO2 decreased from 59.40 ± 4.14 mm Hg to 48.62 ± 4.50 mm Hg after 1 h in the ILIAS group compared with an improvement of PaCO2 from 48.86 ± 7.45 to 40.10 ± 6.02 in the conventional ECMO group (P = not significant [n.s.]). ARDS-induced respiratory acidosis was controlled promptly with a pH of 7.2 ± 0.1 at baseline increasing to 7.4 ± 0.1 in both study groups after 60 min of ECMO support. Mean carbon dioxide transfer was comparable between the conventional ECMO and ILIAS (211.36 ± 78.39 mL/min vs. 219.99 ± 76.72 mL/min, P = n.s.). PaO2 /FiO2 increased from 118.4 ± 15.5 mm Hg to 179.1 ± 72.4 mm Hg in the ILIAS group compared with an improvement of oxygenation from 107.1 ± 24.9 mm Hg to 179.0 ± 45.7 mm Hg in the standard ECMO group (P = n.s.). Mean oxygen transfer was calculated with 136.09 ± 30.25 mL/min for the ILIAS and 129.05 ± 36.28 mL/min for the standard ECMO. Hemodynamic instability or significant activation of the plasmatic coagulation was not observed. However, hemolysis was significantly higher in the ILIAS group compared with the conventional ECMO. As the ILIAS prototype provided excellent gas exchange with hemodynamic stability comparable with a standard ECMO system, we believe this study serves as a proof of concept. Further development and design modifications (optimized rotation speed and surface coating of rotor) are already done and another experiment is projected to reduce hemolysis and platelet consumption for clinical application.

Technical-Induced Hemolysis in Patients with Respiratory Failure Supported with Veno-Venous ECMO - Prevalence and Risk Factors

The aim of the study was to explore the prevalence and risk factors for technical-induced hemolysis in adults supported with veno-venous extracorporeal membrane oxygenation (vvECMO) and to analyze the effect of hemolytic episodes on outcome. This was a retrospective, single-center study that included 318 adult patients (Regensburg ECMO Registry, 2009–2014) with acute respiratory failure treated with different modern miniaturized ECMO systems. Free plasma hemoglobin (fHb) was used as indicator for hemolysis. Throughout a cumulative support duration of 4,142 days on ECMO only 1.7% of the fHb levels were above a critical value of 500 mg/l. A grave rise in fHb indicated pumphead thrombosis (n = 8), while acute oxygenator thrombosis (n = 15) did not affect fHb. Replacement of the pumphead normalized fHb within two days. Neither pump or cannula type nor duration on the first system was associated with hemolysis. Multiple trauma, need for kidney replacement therapy, increased daily red blood cell transfusion requirements, and high blood flow (3.0–4.5 L/min) through small-sized cannulas significantly resulted in augmented blood cell trauma. Survivors were characterized by lower peak levels of fHb [90 (60, 142) mg/l] in comparison to non-survivors [148 (91, 256) mg/l, p≤0.001]. In conclusion, marked hemolysis is not common in vvECMO with modern devices. Clinically obvious hemolysis often is caused by pumphead thrombosis. High flow velocity through small cannulas may also cause technical-induced hemolysis. In patients who developed lung failure due to trauma, fHb was elevated independantly of ECMO. In our cohort, the occurance of hemolysis was associated with increased mortality.