Removing extra CO2 in COPD patients

First 24-Hour-Long Intensive Care Unit Testing of a Clinical-Scale Microfluidic Oxygenator in Swine: A Safety and Feasibility Study

Microfluidic membrane oxygenators are designed to mimic branching vasculature of the native lung during extracorporeal lung support. To date, scaling of such devices to achieve clinically relevant blood flow and lung support has been a limitation. We evaluated a novel multilayer microfluidic blood oxygenator (BLOx) capable of supporting 750-800 ml/min blood flow versus a standard hollow fiber membrane oxygenator (HFMO) in vivo during veno-venous extracorporeal life support for 24 hours in anesthetized, mechanically ventilated uninjured swine (n = 3/group). The objective was to assess feasibility, safety, and biocompatibility. Circuits remained patent and operated with stable pressures throughout 24 hours. No group differences in vital signs or evidence of end-organ damage occurred. No change in plasma free hemoglobin and von Willebrand factor multimer size distribution were observed. Platelet count decreased in BLOx at 6 hours (37% dec, P = 0.03), but not in HFMO; however, thrombin generation potential was elevated in HFMO (596 ± 81 nM·min) versus BLOx (323 ± 39 nM·min) at 24 hours ( P = 0.04). Other coagulation and inflammatory mediator results were unremarkable. BLOx required higher mechanical ventilator settings and showed lower gas transfer efficiency versus HFMO, but the stable device performance indicates that this technology is ready for further performance scaling and testing in lung injury models and during longer use conditions.

A Portable Servoregulation Controller to Automate CO2 Removal in Artificial Lungs

Artificial lung (AL) systems provide respiratory support to patients with severe lung disease, but none can adapt to the changing respiratory needs of the patients. Precisely, none can automatically adjust carbon dioxide (CO2) removal from the blood in response to changes in patient activity or disease status. Because of this, all current systems limit patient comfort, activity level, and rehabilitation. A portable servoregulation controller that automatically modulates CO2 removal in ALs to meet the real-time metabolic demands of the patient is described. The controller is based on a proportional-integral-derivative (PID) based closed-loop feedback control system that modulates sweep gas (air) flow through the AL to maintain a target exhaust gas CO2 partial pressure (target EGCO2 or tEGCO2). The presented work advances previous research by (1) using gas-side sensing that avoids complications and clotting associated with blood-based sensors, (2) incorporating all components into a portable, battery-powered package, and (3) integrating smart moisture removal from the AL to enable long term operation. The performance of the controller was tested in vitro for ∼12 h with anti-coagulated bovine blood and 5 days with distilled water. In tests with blood, the sweep gas flow was automatically adjusted by the controller rapidly (<2 min) meeting the specified tEGCO2 level when confronted with changes in inlet blood partial pressure of CO2 (pCO2) levels at various AL blood flows. Overall, the CO2 removal from the AL showed a strong correlation with blood flow rate and blood pCO2 levels. The controller successfully operated continuously for 5 days when tested with water. This study demonstrates an important step toward ambulatory AL systems that automatically modulate CO2 removal as required by lung disease patients, thereby allowing for physiotherapy, comfort, and activity.

Toward a Servoregulation Controller to Automate CO2 Removal in Wearable Artificial Lungs

A laptop-driven, benchtop control system that automatically adjusts carbon dioxide (CO2) removal in artificial lungs (ALs) is described. The proportional-integral-derivative (PID) feedback controller modulates pump-driven air sweep gas flow through an AL to achieve a desired exhaust gas CO2 partial pressure (EGCO2). When EGCO2 increases, the servoregulator automatically and rapidly increases sweep flow to remove more CO2. If EGCO2 decreases, the sweep flow decreases to reduce CO2 removal. System operation was tested for 6 hours in vitro using bovine blood and in vivo in three proof-of-concept sheep experiments. In all studies, the controller automatically adjusted the sweep gas flow to rapidly (<1 minute) meet the specified EGCO2 level when challenged with changes in inlet blood or target EGCO2 levels. CO2 removal increased or decreased as a function of arterial pCO2 (PaCO2). Such a system may serve as a controller in wearable AL systems that allow for large changes in patient activity or disease status.

Design and construction of three-dimensional physiologically-based vascular branching networks for respiratory assist devices

Microfluidic lab-on-a-chip devices are changing the way that in vitro diagnostics and drug development are conducted, based on the increased precision, miniaturization and efficiency of these systems relative to prior methods. However, the full potential of microfluidics as a platform for therapeutic medical devices such as extracorporeal organ support has not been realized, in part due to limitations in the ability to scale current designs and fabrication techniques toward clinically relevant rates of blood flow. Here we report on a method for designing and fabricating microfluidic devices supporting blood flow rates per layer greater than 10 mL min^-1 for respiratory support applications, leveraging advances in precision machining to generate fully three-dimensional physiologically-based branching microchannel networks. The ability of precision machining to create molds with rounded features and smoothly varying channel widths and depths distinguishes the geometry of the microchannel networks described here from all previous reports of microfluidic respiratory assist devices, regarding the ability to mimic vascular blood flow patterns. These devices have been assembled and tested in the laboratory using whole bovine or porcine blood, and in a porcine model to demonstrate efficient gas transfer, blood flow and pressure stability over periods of several hours. This new approach to fabricating and scaling microfluidic devices has the potential to address wide applications in critical care for end-stage organ failure and acute illnesses stemming from respiratory viral infections, traumatic injuries and sepsis.

Toward Development of a Higher Flow Rate Hemocompatible Biomimetic Microfluidic Blood Oxygenator

The recent emergence of microfluidic extracorporeal lung support technologies presents an opportunity to achieve high gas transfer efficiency and improved hemocompatibility relative to the current standard of care in extracorporeal membrane oxygenation (ECMO). However, a critical challenge in the field is the ability to scale these devices to clinically relevant blood flow rates, in part because the typically very low blood flow in a single layer of a microfluidic oxygenator device requires stacking of a logistically challenging number of layers. We have developed biomimetic microfluidic oxygenators for the past decade and report here on the development of a high-flow (30 mL/min) single-layer prototype, scalable to larger structures via stacking and assembly with blood distribution manifolds. Microfluidic oxygenators were designed with biomimetic in-layer blood distribution manifolds and arrays of parallel transfer channels, and were fabricated using high precision machined durable metal master molds and microreplication with silicone films, resulting in large area gas transfer devices. Oxygen transfer was evaluated by flowing 100% O2 at 100 mL/min and blood at 0-30 mL/min while monitoring increases in O2 partial pressures in the blood. This design resulted in an oxygen saturation increase from 65% to 95% at 20 mL/min and operation up to 30 mL/min in multiple devices, the highest value yet recorded in a single layer microfluidic device. In addition to evaluation of the device for blood oxygenation, a 6-h in vitro hemocompatibility test was conducted on devices (n = 5) at a 25 mL/min blood flow rate with heparinized swine donor blood against control circuits (n = 3). Initial hemocompatibility results indicate that this technology has the potential to benefit future applications in extracorporeal lung support technologies for acute lung injury.

The use of extracorporeal CO2 removal in acute respiratory failure

Background

Chronic obstructive pulmonary disease (COPD) exacerbation and protective mechanical ventilation of acute respiratory distress syndrome (ARDS) patients induce hypercapnic respiratory acidosis.

Main text

Extracorporeal carbon dioxide removal (ECCO₂R) aims to eliminate blood CO₂ to fight against the adverse effects of hypercapnia and related acidosis. Hypercapnia has deleterious extrapulmonary consequences, particularly for the brain. In addition, in the lung, hypercapnia leads to: lower pH, pulmonary vasoconstriction, increases in right ventricular afterload, acute cor pulmonale. Moreover, hypercapnic acidosis may further damage the lungs by increasing both nitric oxide production and inflammation and altering alveolar epithelial cells. During an exacerbation of COPD, relieving the native lungs of at least a portion of the CO₂ could potentially reduce the patient's respiratory work, Instead of mechanically increasing alveolar ventilation with MV in an already hyperinflated lung to increase CO₂ removal, the use of ECCO₂R may allow a decrease in respiratory volume and respiratory rate, resulting in improvement of lung mechanic. Thus, the use of ECCO₂R may prevent noninvasive ventilation failure and allow intubated patients to be weaned off mechanical ventilation. In ARDS patients, ECCO₂R may be used to promote an ultraprotective ventilation in allowing to lower tidal volume, plateau (Pplat) and driving pressures, parameters that have identified as a major risk factors for mortality. However, although ECCO₂R appears to be effective in improving gas exchange and possibly in reducing the rate of endotracheal intubation and allowing more protective ventilation, its use may have pulmonary and hemodynamic consequences and may be associated with complications.

Conclusion

In selected patients, ECCO₂R may be a promising adjunctive therapeutic strategy for the management of patients with severe COPD exacerbation and for the establishment of protective or ultraprotective ventilation in patients with ARDS without prognosis-threatening hypoxemia.

Effect of Hematocrit on the CO2 Removal Rate of Artificial Lungs

Extracorporeal CO2 removal (ECCO2R) can permit lung protective or noninvasive ventilation strategies in patients with chronic obstructive pulmonary disease (COPD) and acute respiratory distress syndrome (ARDS). With evidence supporting ECCO2R growing, investigating factors which affect CO2 removal is necessary. Multiple factors are known to affect the CO2 removal rate (vCO2) which can complicate the interpretation of changes in vCO2; however, the effect of hematocrit on the vCO2 of artificial lungs has not been investigated. This in vitro study evaluates the relationship between hematocrit level and vCO2 within an ECCO2R device. In vitro gas transfer was measured in bovine blood in accordance with the ISO 7199 standard. Plasma and saline were used to hemodilute the blood to hematocrits between 33% and 8%. The vCO2 significantly decreased as the blood was hemodiluted with saline and plasma by 42% and 32%, respectively, between a hematocrit of 33% and 8%. The hemodilution method did not significantly affect the vCO2. In conclusion, the hematocrit level significantly affects vCO2 and should be taken into account when interpreting changes in the vCO2 of an ECCO2R device.

Very low blood flow carbon dioxide removal system is not effective in a chronic obstructive pulmonary disease exacerbation setting

Extracorporeal carbon dioxide removal (ECCO₂ R) is a low blood flow veno-venous extracorporeal membrane oxygenation technique that provides artificial blood CO₂ removal. Recently, a new ECCO₂ R system (PrismaLung), providing very low blood flow has been commercialized. The aim of this study is to report its use in severe chronic obstructive pulmonary disease (COPD) patients needing an ECCO₂ R therapy. Six severe COPD patients with acute exacerbation leading to refractory hypercapnic respiratory acidosis were treated with ECCO₂ R therapy. Two different systems were used: a PrismaLung system and a conventional ECCO₂ R device. The maximum blood flow provided by PrismaLung was significantly lower than that with the conventional ECCO₂ R system. In three patients initially treated with PrismaLung, there were no improvements in pH, PaCO₂ , or RR. Thus, the therapy was switched to a conventional ECCO₂ R system in these three patients, and three others were treated from the outset by the conventional ECCO₂ R system, providing significant improvement in pH, PaCO₂ , and RR. The present retrospective study describes the first use of PrismaLung in severe COPD patients with acute exacerbation. When compared with a higher blood flow ECCO₂ R system, our results show that this novel, very low-flow device is not able to remove sufficient CO₂ , normalize pH or decrease respiratory rate.

The use of extracorporeal carbon dioxide removal in acute chronic obstructive pulmonary disease exacerbation: a narrative review

Chronic obstructive pulmonary disease (COPD) exacerbation induces hypercapnic respiratory acidosis. Extracorporeal carbon dioxide removal (ECCO2R) aims to eliminate blood carbon dioxide (CO2) in order to reduce adverse effects from hypercapnia and the related acidosis. Hypercapnia has deleterious extra-pulmonary consequences in increasing intracranial pressure and inducing and/or worsening right heart failure. During COPD exacerbation, the use of ECCO2R may improve the efficacy of non-invasive ventilation (NIV) in terms of CO2 removal, decrease respiratory rate and reduce dynamic hyperinflation and intrinsic positive end expiratory pressure, which all contribute to increasing dead space. Moreover, ECCO2R may prevent NIV failure while facilitating the weaning of intubated patients from mechanical ventilation. In this review of the literature, the authors will present the current knowledge on the pathophysiology related to COPD, the principles of the ECCO2R technique and its role in acute and severe decompensation of COPD. However, despite technical advances, there are only case series in the literature and few prospective studies to clearly establish the role of ECCO2R in acute and severe COPD decompensation.

Dual Carbon Dioxide Capture to Achieve Highly Efficient Ultra-Low Blood Flow Extracorporeal Carbon Dioxide Removal

Extracorporeal CO₂ removal is a highly promising support therapy for patients with hypercapnic respiratory failure but whose clinical implementation and patient benefit is hampered by high cost and highly specialized expertise required for safe use. Current approaches target removal of the gaseous CO₂ dissolved in blood which limits their ease of clinical use as high blood flow rates are required to achieve physiologically significant CO₂ clearance. Here, a novel hybrid approach in which a zero-bicarbonate dialysis is used to target removal of bicarbonate ion coupled to a gas exchange device to clear dissolved CO₂, achieves highly efficiently total CO₂ capture while maintaining systemic acid-base balance. In a porcine model of acute hypercapnic respiratory failure, a CO₂-reduction of 61.4 ± 14.4 mL/min was achieved at a blood flow rate of 248 mL/min using pediatric-scale priming volumes. The dialyzer accounted for 81% of total CO₂ capture with an efficiency of 33% with a minimal pH change across the entire circuit. This study demonstrates the feasibility of a novel hybrid CO₂ capture approach capable of achieving physiologically significant CO₂ removal at ultralow blood flow rates with low priming volumes while leveraging widely available dialysis platforms to enable clinical adoption.

Control of respiratory drive by extracorporeal CO2 removal in acute exacerbation of COPD breathing on non-invasive NAVA

Background

Veno-venous extracorporeal CO₂ removal (vv-ECCO₂R) and non-invasive neurally adjusted ventilator assist (NIV-NAVA) are two promising techniques which may prevent complications related to prolonged invasive mechanical ventilation in patients with acute exacerbation of COPD.

Methods

A physiological study of the electrical activity of the diaphragm (Edi) response was conducted with varying degrees of extracorporeal CO₂ removal to control the respiratory drive in patients with severe acute exacerbation of COPD breathing on NIV-NAVA.

Results

Twenty COPD patients (SAPS II 37 ± 5.6, age 57 ± 9 years) treated with vv-ECCO₂R and supported by NIV-NAVA were studied during stepwise weaning of vv-ECCO₂R. Based on dyspnea, tolerance, and blood gases, weaning from vv-ECCO₂R was successful in 12 and failed in eight patients. Respiratory drive (measured via the Edi) increased to 19 ± 10 μV vs. 56 ± 20 μV in the successful and unsuccessful weaning groups, respectively, resulting in all patients keeping their CO₂ and pH values stable. Edi was the best predictor for vv-ECCO₂R weaning failure (ROC analysis AUC 0.95), whereas respiratory rate, rapid shallow breathing index, and tidal volume had lower predictive values. Eventually, 19 patients were discharged home, while one patient died. Mortality at 90 days and 180 days was 15 and 25%, respectively.

Conclusions

This study demonstrates for the first time the usefulness of the Edi signal to monitor and guide patients with severe acute exacerbation of COPD on vv-ECCO₂R and NIV-NAVA. The Edi during vv-ECCO₂R weaning was found to be the best predictor of tolerance to removing vv-ECCO₂R.

Electronic supplementary material

The online version of this article (10.1186/s13054-019-2404-y) contains supplementary material, which is available to authorized users.

Development of zwitterionic sulfobetaine block copolymer conjugation strategies for reduced platelet deposition in respiratory assist devices

Respiratory assist devices, that utilize ∼2 m2 of hollow fiber membranes (HFMs) to achieve desired gas transfer rates, have been limited in their adoption due to such blood biocompatibility limitations. This study reports two techniques for the functionalization and subsequent conjugation of zwitterionic sulfobetaine (SB) block copolymers to polymethylpentene (PMP) HFM surfaces with the intention of reducing thrombus formation in respiratory assist devices. Amine or hydroxyl functionalization of PMP HFMs (PMP-A or PMP-H) was accomplished using plasma-enhanced chemical vapor deposition. The generated functional groups were conjugated to low molecular weight SB block copolymers with N-hydroxysuccinimide ester or siloxane groups (SBNHS or SBNHSi) that were synthesized using reversible addition fragmentation chain transfer polymerization. The modified HFMs (PMP-A-SBNHS or PMP-H-SBNHSi) showed 80-95% reduction in platelet deposition from whole ovine blood, stability under the fluid shear of anticipated operating conditions, and uninhibited gas exchange performance relative to non-modified HFMs (PMP-C). Additionally, the functionalization and SBNHSi conjugation technique was shown to reduce platelet deposition on polycarbonate and poly(vinyl chloride), two other materials commonly found in extracorporeal circuits. The observed thromboresistance and stability of the SB modified surfaces, without degradation of HFM gas transfer performance, indicate that this approach is promising for longer term pre-clinical testing in respiratory assist devices and may ultimately allow for the reduction of anticoagulation levels in patients being supported for extended periods. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2681-2692, 2018.

Bench Validation of a Compact Low-Flow CO2 Removal Device

Background

There is increasing evidence demonstrating the value of partial extracorporeal CO₂ removal (ECCO₂R) for the treatment of hypercapnia in patients with acute exacerbations of chronic obstructive pulmonary disease and acute respiratory distress syndrome. Mechanical ventilation has traditionally been used to treat hypercapnia in these patients, however, it has been well-established that aggressive ventilator settings can lead to ventilator-induced lung injury. ECCO₂R removes CO₂ independently of the lungs and has been used to permit lung protective ventilation to prevent ventilator-induced lung injury, prevent intubation, and aid in ventilator weaning. The Low-Flow Pittsburgh Ambulatory Lung (LF-PAL) is a low-flow ECCO₂R device that integrates the fiber bundle (0.65 m²) and centrifugal pump into a compact unit to permit patient ambulation.

Methods

A blood analog was used to evaluate the performance of the pump at various impeller rotation rates. In vitro CO₂ removal tested under normocapnic conditions and 6-h hemolysis testing were completed using bovine blood. Computational fluid dynamics and a mass-transfer model were also used to evaluate the performance of the LF-PAL.

Results

The integrated pump was able to generate flows up to 700 mL/min against the Hemolung 15.5 Fr dual lumen catheter. The maximum vCO₂ of 105 mL/min was achieved at a blood flow rate of 700 mL/min. The therapeutic index of hemolysis was 0.080 g/(100 min). The normalized index of hemolysis was 0.158 g/(100 L).

Conclusions

The LF-PAL met pumping, CO₂ removal, and hemolysis design targets and has the potential to enable ambulation while on ECCO₂R.

Extracorporeal carbon dioxide removal in acute exacerbations of chronic obstructive pulmonary disease

Extracorporeal carbon dioxide removal (ECCO2R) has been proposed as an adjunctive intervention to avoid worsening respiratory acidosis, thereby preventing or shortening the duration of invasive mechanical ventilation (IMV) in patients with exacerbation of chronic obstructive pulmonary disease (COPD). This review will present a comprehensive summary of the pathophysiological rationale and clinical evidence of ECCO2R in patients suffering from severe COPD exacerbations.

Principi e indicazioni dell’assistenza circolatoria e respiratoria extracorporea in chirurgia toracica

In origine, l’extracorporeal membrane oxygenation (ECMO) era una tecnica di assistenza respiratoria che utilizzava uno scambiatore gassoso a membrana. Per estensione, l’ECMO è diventata una tecnica respiratoria e cardiopolmonare utilizzata in caso di deficit respiratorio e/o cardiaco nell’attesa della restaurazione della funzione deficitaria o di un eventuale trapianto. Il supporto emodinamico può essere parziale o totale. Gli accessi vascolari possono essere periferici o centrali. Questo tipo di assistenza utilizza il concetto di circolazione extracorporea (CEC) sanguigna che in epoca moderna si è estesa con l’utilizzo di polmoni artificiali a membrana. Il circuito di base è semplice e comprende una pompa, un ossigenatore (che permette al sangue di caricarsi di O₂ e di eliminare CO₂) e delle vie d’accesso (una di drenaggio e una di reinfusione). La sua attuazione è facile, veloce e può essere avviata al letto del malato. Il miglioramento delle attrezzature, una migliore conoscenza delle tecniche e delle indicazioni, e le politiche di salute pubblica hanno reso popolare questa tecnica. Alcuni centri di chirurgia toracica la utilizzano di routine come assistenza alla realizzazione di un intervento terapeutico (soprattutto trapianto) assieme a team di rianimazione per il trattamento della sindrome da distress respiratorio acuto. Nel quadro della malattia polmonare dell’adulto, l’idea principale è quella di sviluppare il concetto di strategia minimalista con l’uso di una CEC adiuvante parziale – più che sostitutiva totale – che permetterebbe il recupero metabolico ad integrum del paziente. Nei prossimi anni, i progressi della tecnologia e dell’ingegneria così come le conoscenze approfondite permetteranno il miglioramento della prognosi dei pazienti colpiti da deficit respiratorio sotto assistenza meccanica.

An extracorporeal carbon dioxide removal (ECCO2R) device operating at hemodialysis blood flow rates

Background

Extracorporeal carbon dioxide removal (ECCO₂R) systems have gained clinical appeal as supplemental therapy in the treatment of acute and chronic respiratory injuries with low tidal volume or non-invasive ventilation. We have developed an ultra-low-flow ECCO₂R device (ULFED) capable of operating at blood flows comparable to renal hemodialysis (250 mL/min). Comparable operating conditions allow use of minimally invasive dialysis cannulation strategies with potential for direct integration to existing dialysis circuitry.

Methods

A carbon dioxide (CO₂) removal device was fabricated with rotating impellers inside an annular hollow fiber membrane bundle to disrupt blood flow patterns and enhance gas exchange. In vitro gas exchange and hemolysis testing was conducted at hemodialysis blood flows (250 mL/min).

Results

In vitro carbon dioxide removal rates up to 75 mL/min were achieved in blood at normocapnia (pCO₂ = 45 mmHg). In vitro hemolysis (including cannula and blood pump) was comparable to a Medtronic Minimax oxygenator control loop using a time-of-therapy normalized index of hemolysis (0.19 ± 0.04 g/100 min versus 0.12 ± 0.01 g/100 min, p = 0.169).

Conclusions

In vitro performance suggests a new ultra-low-flow extracorporeal CO₂ removal device could be utilized for safe and effective CO₂ removal at hemodialysis flow rates using simplified and minimally invasive connection strategies.

[Extracorporeal lung support]

Systems for extracorporeal lung support have recently undergone significant technological improvements leading to more effective and safe treatment. Despite limited scientific evidence these systems are increasingly used in the intensive care unit for treatment of different types of acute respiratory failure. In general two types of systems can be differentiated: devices for extracorporeal carbon dioxide removal (ECCO₂R) for ventilatory insufficiency and devices for extracorporeal membrane oxygenation (ECMO) for severe hypoxemic failure. Despite of all technological developments extracorporeal lung support remains an invasive and a potentially dangerous form of treatment with bleeding and vascular injury being the two main complications. For this reason indications and contraindications should always be critically considered and extracorporeal lung support should only be carried out in centers with appropriate experience and expertise.

[Extracorporeal life support in thoracic surgery: What are the indications and the pertinence?]

INTRODUCTION

In thoracic surgery, extracorporeal life support (ECLS) technologies are used in cases of severe and refractory respiratory failure or as intraoperative cardiorespiratory support. The objectives of this review are to describe the rationale of ECLS techniques, to review the pulmonary diseases potentially treated by ECLS, and finally to demonstrate the efficacy of ECLS, using recently published data from the literature, in order to practice evidence based medicine.

STATE OF THE ART

ECLS technologies should only be undertaken in expert centers. ECLS allows a protective ventilatory strategy in severe ARDS. In the field of lung transplantation, ECLS may be used successfully as a bridge to transplantation, as intraoperative cardiorespiratory support or as a bridge to recovery in cases of severe primary graft dysfunction. In general thoracic surgery, ECLS technology seems to be safe and efficient as intraoperative respiratory support for tracheobronchial surgery or for severe respiratory insufficiency, without significant increase in perioperative risk.

PERSPECTIVE

The indications for ECLS are going to increase. Future improvements both in scientific knowledge and bioengineering will improve the prognosis of patients treated with ECLS for respiratory failure. Multicenter randomized controlled trials will refine the indications for ECLS and improve the global care strategies for these patients.

CONCLUSION

ECLS is an efficient therapeutic strategy that will improve the prognosis of patients suffering from, or exposed to, the risks of severe respiratory failure.

Principi e indicazioni dell’assistenza circolatoria e respiratoria extracorporea in chirurgia toracica

In origine, l’extracorporeal membrane oxygenation (ECMO) era una tecnica di assistenza respiratoria che utilizzava uno scambiatore gassoso a membrana. Per estensione, l’ECMO è diventata una tecnica respiratoria e cardiopolmonare utilizzata in caso di deficit respiratorio e/o cardiaco nell’attesa della restaurazione della funzione deficitaria o di un eventuale trapianto. Il supporto emodinamico può essere parziale o totale. Gli accessi vascolari possono essere periferici o centrali. Questo tipo di assistenza utilizza il concetto di circolazione extracorporea (CEC) sanguigna che in epoca moderna si è estesa con l’utilizzo di polmoni artificiali a membrana. Il circuito di base è semplice e comprende una pompa, un ossigenatore (che permette al sangue di caricarsi di O₂ e di eliminare CO₂) e delle vie d’accesso (una di drenaggio e una di reinfusione). La sua attuazione è facile, veloce e può essere avviata al letto del malato. Il miglioramento delle attrezzature, una migliore conoscenza delle tecniche e delle indicazioni, e le politiche di salute pubblica hanno reso popolare questa tecnica. Alcuni centri di chirurgia toracica la utilizzano di routine come assistenza alla realizzazione di un intervento terapeutico (soprattutto trapianto) assieme a team di rianimazione per il trattamento della sindrome da distress respiratorio acuto. Nel quadro della malattia polmonare dell’adulto, l’idea principale è quella di sviluppare il concetto di strategia minimalista con l’uso di una CEC adiuvante parziale – più che sostitutiva totale – che permetterebbe il recupero metabolico ad integrum del paziente. Nei prossimi anni, i progressi della tecnologia e dell’ingegneria così come le conoscenze approfondite permetteranno il miglioramento della prognosi dei pazienti colpiti da deficit respiratorio sotto assistenza meccanica.

Adult venovenous extracorporeal membrane oxygenation for severe respiratory failure: Current status and future perspectives

Extracorporeal membrane oxygenation (ECMO) for severe acute respiratory failure was proposed more than 40 years ago. Despite the publication of the ARDSNet study and adoption of lung protective ventilation, the mortality for acute respiratory failure due to acute respiratory distress syndrome has continued to remain high. This technology has evolved over the past couple of decades and has been noted to be safe and successful, especially during the worldwide H1N1 influenza pandemic with good survival rates. The primary indications for ECMO in acute respiratory failure include severe refractory hypoxemic and hypercarbic respiratory failure in spite of maximum lung protective ventilatory support. Various triage criteria have been described and published. Contraindications exist when application of ECMO may be futile or technically impossible. Knowledge and appreciation of the circuit, cannulae, and the physiology of gas exchange with ECMO are necessary to ensure lung rest, efficiency of oxygenation, and ventilation as well as troubleshooting problems. Anticoagulation is a major concern with ECMO, and the evidence is evolving with respect to diagnostic testing and use of anticoagulants. Clinical management of the patient includes comprehensive critical care addressing sedation and neurologic issues, ensuring lung recruitment, diuresis, early enteral nutrition, treatment and surveillance of infections, and multisystem organ support. Newer technology that delinks oxygenation and ventilation by extracorporeal carbon dioxide removal may lead to ultra-lung protective ventilation, avoidance of endotracheal intubation in some situations, and ambulatory therapies as a bridge to lung transplantation. Risks, complications, and long-term outcomes and resources need to be considered and weighed in before widespread application. Ethical challenges are a reality and a multidisciplinary approach that should be adopted for every case in consideration.

Extracorporeal Support for Chronic Obstructive Pulmonary Disease: A Bright Future

In the past the only option for the treatment of respiratory failure due to acute exacerbation of chronic obstructive pulmonary disease (aeCOPD) was invasive mechanical ventilation. In recent decades, the potential for extracorporeal carbon dioxide (CO₂) removal has been realized. We review the various types of extracorporeal CO₂ removal, outline the optimal use of these therapies for aeCOPD, and make suggestions for future controlled trials. We also describe the advantages and requirements for an ideal long-term ambulatory CO₂ removal system for palliation of COPD.

Vascular access for extracorporeal life support: tips and tricks

In thoracic surgery, extracorporeal life support (ECLS) techniques are performed to (I) provide a short to mid term extracorporeal mechanical support; (II) realize the gas exchanges; and (III)-depending the configuration of the circuit-substitute the failed heart function. The objective of this review is to describe the rational of the different ECLS techniques used in thoracic surgery and lung transplantation (LTx) with a specific attention to the vascular access. Venovenous extracorporeal membrane oxygenation (VV ECMO) is the most common ECLS technique used in thoracic surgery and represents the best strategy to support the lung function. VV ECMO needs peripheral vascular access. The selection between his double-site or single-site configuration should be decided according the level of O2 requirements, the nosological context, and the interest to perform an ECLS ambulatory strategy. Venoarterial (VA) ECMO uses peripheral and/or central cannulation sites. Central VA ECMO is mainly used in LTx instead a conventional cardiopulmonary bypass (CPB) to decrease the risk of hemorrhagic issues and the rate of primary graft dysfunction (PGD). Peripheral VA ECMO is traditionally realized in a femoro-femoral configuration. Femoro-femoral VA ECMO allows a cardiocirculatory support but does not provide an appropriate oxygenation of the brain and the heart. The isolated hypercapnic failure is currently supported by extracorporeal CO2 removal (ECCO2R) devices inserted in jugular or subclavian veins. The interest of the Novalung (Novalung GmbH, Hechingen, Germany) persists due to his central configuration indicated to bridge to LTx patients suffering from pulmonary hypertension. The increasing panel of ECLS technologies available in thoracic surgery is the results of a century of clinical practices, engineering progress, and improvements of physiological knowledges. The selection of the ECLS technique-and therefore the vascular access to implant the device-for a given nosological context trends to be defined according an evidence-based medicine.

Extracorporeal carbon dioxide removal (ECCO2R) in respiratory deficiency and current investigations on its improvement: a review

The implementation of extracorporeal carbon dioxide removal (ECCO₂R) as one of the extracorporeal life support system is getting more attention today. Thus, the objectives of this paper are to study the clinical practice of commercial ECCO₂R system, current trend of its development and also the perspective on future improvement that can be done to the existing ECCO₂R system. The strength of this article lies in its review scope, which focuses on the commercial ECCO₂R therapy in the market based on membrane lung and current investigation to improve the efficiency of the ECCO₂R system, in terms of surface modification by carbonic anhydrase (CA) immobilization technique and respiratory electrodialysis (R-ED). Our methodology approach involves the identification of relevant published literature from PubMed and Web of Sciences search engine using the terms Extracorporeal Carbon Dioxide Removal (ECCO₂R), Extracorporeal life support, by combining terms between ECCO₂R and CA and also ECCO₂R with R-ED. This identification only limits articles in English language. Overall, several commercial ECCO₂R systems are known and proven safe to be used in patients in terms of efficiency, safety and risk of complication. In addition, CA-modified hollow fiber for membrane lung and R-ED are proven to have good potential to be applied in conventional ECCO₂R design. The detailed technique and current progress on CA immobilization and R-ED development were also reviewed in this article.

Acidic sweep gas with carbonic anhydrase coated hollow fiber membranes synergistically accelerates CO2 removal from blood

The use of extracorporeal carbon dioxide removal (ECCO2R) is well established as a therapy for patients suffering from acute respiratory failure. Development of next generation low blood flow (<500 mL/min) ECCO2R devices necessitates more efficient gas exchange devices. Since over 90% of blood CO2 is transported as bicarbonate (HCO3(-)), we previously reported development of a carbonic anhydrase (CA) immobilized bioactive hollow fiber membrane (HFM) which significantly accelerates CO2 removal from blood in model gas exchange devices by converting bicarbonate to CO2 directly at the HFM surface. This present study tested the hypothesis that dilute sulfur dioxide (SO2) in oxygen sweep gas could further increase CO2 removal by creating an acidic microenvironment within the diffusional boundary layer adjacent to the HFM surface, facilitating dehydration of bicarbonate to CO2. CA was covalently immobilized onto poly (methyl pentene) (PMP) HFMs through glutaraldehyde activated chitosan spacers, potted in model gas exchange devices (0.0151 m(2)) and tested for CO2 removal rate with oxygen (O2) sweep gas and a 2.2% SO2 in oxygen sweep gas mixture. Using pure O2 sweep gas, CA-PMP increased CO2 removal by 31% (258 mL/min/m(2)) compared to PMP (197 mL/min/m(2)) (P<0.05). Using 2.2% SO2 acidic sweep gas increased PMP CO2 removal by 17% (230 mL/min/m(2)) compared to pure oxygen sweep gas control (P<0.05); device outlet blood pH was 7.38 units. When employing both CA-PMP and 2.2% SO2 sweep gas, CO2 removal increased by 109% (411 mL/min/m(2)) (P<0.05); device outlet blood pH was 7.35 units. Dilute acidic sweep gas increases CO2 removal, and when used in combination with bioactive CA-HFMs has a synergistic effect to more than double CO2 removal while maintaining physiologic pH. Through these technologies the next generation of intravascular and paracorporeal respiratory assist devices can remove more CO2 with smaller blood contacting surface areas.

STATEMENT OF SIGNIFICANCE

A clinical need exists for more efficient respiratory assist devices which utilize low blood flow rates (<500 mL/min) to regulate blood CO2 in patients suffering from acute lung failure. Literature has demonstrated approaches to chemically increase hollow fiber membrane (HFM) CO2 removal efficiency by shifting equilibrium from bicarbonate to gaseous CO2, through either a bioactive carbonic anhydrase enzyme coating or bulk blood acidification with lactic acid. In this study we demonstrate a novel approach to local blood acidification using an acidified sweep gas in combination with a bioactive coating to more than double CO2 removal efficiency of HFM devices. To our knowledge, this is the first report assessing an acidic sweep gas to increase CO2 removal from blood using HFM devices.

Gas Transfer in Cellularized Collagen-Membrane Gas Exchange Devices

Chronic lower respiratory disease is highly prevalent in the United States, and there remains a need for alternatives to lung transplant for patients who progress to end-stage lung disease. Portable or implantable gas oxygenators based on microfluidic technologies can address this need, provided they operate both efficiently and biocompatibly. Incorporating biomimetic materials into such devices can help replicate native gas exchange function and additionally support cellular components. In this work, we have developed microfluidic devices that enable blood gas exchange across ultra-thin collagen membranes (as thin as 2 μm). Endothelial, stromal, and parenchymal cells readily adhere to these membranes, and long-term culture with cellular components results in remodeling, reflected by reduced membrane thickness. Functionally, acellular collagen-membrane lung devices can mediate effective gas exchange up to ∼288 mL/min/m(2) of oxygen and ∼685 mL/min/m(2) of carbon dioxide, approaching the gas exchange efficiency noted in the native lung. Testing several configurations of lung devices to explore various physical parameters of the device design, we concluded that thinner membranes and longer gas exchange distances result in improved hemoglobin saturation and increases in pO2. However, in the design space tested, these effects are relatively small compared to the improvement in overall oxygen and carbon dioxide transfer by increasing the blood flow rate. Finally, devices cultured with endothelial and parenchymal cells achieved similar gas exchange rates compared with acellular devices. Biomimetic blood oxygenator design opens the possibility of creating portable or implantable microfluidic devices that achieve efficient gas transfer while also maintaining physiologic conditions.

Applying a low-flow CO2 removal device in severe acute hypercapnic respiratory failure

A novel and portable extracorporeal CO2-removal device was evaluated to provide additional gas transfer, auxiliary to standard therapy in severe acute hypercapnic respiratory failure. A dual-lumen catheter was inserted percutaneously in five subjects (mean age 55 ± 0.4 years) and, subsequently, connected to the CO2-removal device. The median duration on support was 45 hours (interquartile range 26-156), with a blood flow rate of approximately 500 mL/min. The mean PaCO2 decreased from 95.8 ± 21.9 mmHg to 63.9 ± 19.6 mmHg with the pH improving from 7.11 ± 0.1 to 7.26 ± 0.1 in the initial 4 hours of support. Three subjects were directly weaned from the CO2-removal device and mechanical ventilation, one subject was converted to ECMO and one subject died following withdrawal of support. No systemic bleeding or device complications were observed. Low-flow CO2 removal adjuvant to standard therapy was effective in steadily removing CO2, limiting the progression of acidosis in subjects with severe acute hypercapnic respiratory failure.

Extracorporeal Co2 removal in hypercapnic patients at risk of noninvasive ventilation failure: a matched cohort study with historical control

OBJECTIVES

To assess efficacy and safety of noninvasive ventilation-plus-extracorporeal Co2 removal in comparison to noninvasive ventilation-only to prevent endotracheal intubation patients with acute hypercapnic respiratory failure at risk of failing noninvasive ventilation.

DESIGN

Matched cohort study with historical control.

SETTING

Two academic Italian ICUs.

PATIENTS

Patients treated with noninvasive ventilation for acute hypercapnic respiratory failure due to exacerbation of chronic obstructive pulmonary disease (May 2011 to November 2013).

INTERVENTIONS

Extracorporeal CO2 removal was added to noninvasive ventilation when noninvasive ventilation was at risk of failure (arterial pH ≤ 7.30 with arterial PCO2 > 20% of baseline, and respiratory rate ≥ 30 breaths/min or use of accessory muscles/paradoxical abdominal movements). The noninvasive ventilation-only group was created applying the genetic matching technique (GenMatch) on a dataset including patients enrolled in two previous studies. Exclusion criteria for both groups were mean arterial pressure less than 60 mm Hg, contraindications to anticoagulation, body weight greater than 120 kg, contraindication to continuation of active treatment, and failure to obtain consent.

MEASUREMENTS AND MAIN RESULTS

Primary endpoint was the cumulative prevalence of endotracheal intubation. Twenty-five patients were included in the noninvasive ventilation-plus-extracorporeal CO2 removal group. The GenMatch identified 21 patients for the noninvasive ventilation-only group. Risk of being intubated was three times higher in patients treated with noninvasive ventilation-only than in patients treated with noninvasive ventilation-plus-extracorporeal CO2 removal (hazard ratio, 0.27; 95% CI, 0.07-0.98; p = 0.047). Intubation rate in noninvasive ventilation-plus-extracorporeal CO2 removal was 12% (95% CI, 2.5-31.2) and in noninvasive ventilation-only was 33% (95% CI, 14.6-57.0), but the difference was not statistically different (p = 0.1495). Thirteen patients (52%) experienced adverse events related to extracorporeal CO2 removal. Bleeding episodes were observed in three patients, and one patient experienced vein perforation. Malfunctioning of the system caused all other adverse events.

CONCLUSIONS

These data provide the rationale for future randomized clinical trials that are required to validate extracorporeal CO2 removal in patients with hypercapnic respiratory failure and respiratory acidosis nonresponsive to noninvasive ventilation.

Management of severe hypercapnia post cardiac arrest with extracorporeal carbon dioxide removal

Normocapnia is recommended in intensive care management of patients after out-of-hospital cardiac arrest. While normocapnia is usually achievable, it may be therapeutically challenging, particularly in patients with airflow obstruction. Conventional mechanical ventilation may not be adequate to provide optimal ventilation in such patients. One of the recent advances in critical care management of hypercapnia is the advent of newer, low-flow extracorporeal carbon dioxide clearance devices. These are simpler and less invasive than conventional extracorporeal devices. We report the first case of using a novel, extracorporeal carbon dioxide removal device in Australia on a patient with out-of-hospital cardiac arrest where mechanical ventilation failed to achieve normocapnia.