Percutaneous extracorporeal arteriovenous CO2 removal for severe respiratory failure

In Vivo Testing of an Ambient Air Based, Portable, and Automated CO 2 Removal Controller for Artificial Lungs

Portable artificial lung (AL) systems are under development, but there are few technologies available that adjust the carbon dioxide (CO 2 ) removal in response to changes in patient metabolic needs. Our work describes the second generation of a CO 2 -based portable servoregulation system that automatically adjusts CO 2 removal in ALs. Four adult sheep (68 ± 14.3 kg) were used to test the servoregulator. The servoregulator controlled air sweep flow through the lung to meet a target exhaust gas CO 2 (tEGCO 2 ) level in normocapnic and hypercapnic (arterial partial pressure of CO 2 [PaCO 2 ] >60 mm Hg) conditions at varying flow rates (0.5-1.5 L/min) and at tEGCO 2 levels of 10, 20, and 40 mm Hg. In hypercapnic sheep, average post-AL blood partial pressure of CO 2 (pCO 2 ) values were 22.4 ± 3.6 mm Hg for tEGCO 2 of 10 mm Hg, 28.0 ± 4.1 mm Hg for tEGCO 2 of 20 mm Hg and 40.6 ± 4.8 mm Hg for tEGCO 2 of 40 mm Hg. The controller successfully and automatically adjusted the sweep gas flow to rapidly (<10 minutes) meet the tEGCO 2 level when challenged with changes in inlet blood flow or target EGCO 2 levels for all animals. These in vivo data demonstrate an important step toward portable ALs that can automatically modulate CO 2 removal and allow for substantial changes in patient activity or disease status in ambulatory applications.

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.

Current concepts in the pathophysiology and treatment of inhalation injury

The opinions or assertions contained herein are the private views of the author, and are not to be construed as official or as reflecting the official views of the Department of the Army or Department of Defense. Smoke inhalation injury occurs in about 10% of patients admitted to burn centres, and increases the mortality of burn patients by up to 20% over predictions based on age and burn size alone. The primary lesion in smoke inhalation injury is localized to the small airways, with alveolar injury and pulmonary oedema exercising a less prominent role during the initial phases. Injury incites a cascade of events that include ventilation-perfusion mismatch, secondary lung injury, systemic inflammation, impaired immune function, and pneumonia. The most important recent developments in the treatment of inhalation injury have included improved methods of pulmonary care targeted at the pathophysiology of the injury, such as high-frequency percussive ventilation and gentle mechanical ventilation.

Large Animal Model of Pumpless Arteriovenous Extracorporeal CO₂ Removal Using Room Air via Subclavian Vessels

End-stage lung disease (ESLD) causes progressive hypercapnia and dyspnea and impacts quality of life. Many extracorporeal support (ECS) configurations for CO2 removal resolve symptoms but limit ambulation. An ovine model of pumpless ECS using subclavian vessels was developed to allow for ambulatory support. Vascular grafts were anastomosed to the left subclavian vessels in four healthy sheep. A low-resistance membrane oxygenator was attached in an arteriovenous (AV) configuration. Device function was evaluated in each animal while awake and spontaneously breathing and while mechanically ventilated with hypercapnia induced. Sweep gas (FiO2 = 0.21) to the device was increased from 0 to 15 L/min, and arterial and postdevice blood gases, as well as postdevice air, were sampled. Hemodynamics remained stable with average AV shunt flows of 1.34 ± 0.14 L/min. In awake animals, CO2 removal was 3.4 ± 1.0 ml/kg/min at maximum sweep gas flow. Respiratory rate decreased from 60 ± 25 at baseline to 30 ± 11 breaths per minute. In animals with induced hypercapnia, PaCO2 increased to 73.9 ± 15.1. At maximum sweep gas flow, CO2 removal was 3.4 ± 0.4 ml/kg/min and PaCO2 decreased to 49.1 ± 6.7 mm Hg. Subclavian AV access is effective in lowering PaCO2 and respiratory rate and is potentially an effective ambulatory destination therapy for ESLD patients.

Seventy-two hour gas exchange performance and hemodynamic properties of NOVALUNG®iLA as a gas exchanger for arteriovenous carbon dioxide removal

Objective: Acute respiratory failure is complicated by acidosis and altered end-organ perfusion. NOVA-LUNG®iLA is an interventional lung assist (ILA) device for arteriovenous carbon dioxide removal (AVCO2R). The present study was conducted to evaluate the device for short-term CO2 removal performance and hemodynamic response.

Methods: Six adult sheep received cannulation of the jugular vein and carotid artery. The ILA-AVCO2R circuit was placed on the sheep for 72 hours. Hemodynamics and PaCO2 were measured; CO2 removal was calculated while varying sweep gas flow rates (Qg), device blood flow rates (Qb), and PaCO2.

Results: Hemo-dynamic variables remained normal throughout the 72 hour study. CO2 removal increased with increases in Qgor Qb. Mean CO2 removal was 119.3 ml/min for Qb 1L/min, Qg 5 L/min, and PaCO2 40 - 50 mmHg.PaCO2 was directly proportional to CO2 clearance (R-0.72, p B/0.001).

Conclusion: NOVALUNG®iLA can provide near total CO2 removal with Qb 1 - 2 L/min,Qg 5 L/min, and minimal flow resistance (3.889/0.82 mmHg/L/min). PaCO2 correlates with CO2 removal and is dependent on Qb and Qg.

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.

Current Applications for the Use of Extracorporeal Carbon Dioxide Removal in Critically Ill Patients

Mechanical ventilation in patients with respiratory failure has been associated with secondary lung injury, termed ventilator-induced lung injury. Extracorporeal venovenous carbon dioxide removal (ECCO₂R) appears to be a feasible means to facilitate more protective mechanical ventilation or potentially avoid mechanical ventilation in select patient groups. With this expanding role of ECCO₂R, we aim to describe the technology and the main indications of ECCO₂R.

The promise of microfluidic artificial lungs

Microfluidic or microchannel artificial lungs promise to enable a new class of truly portable, therapeutic artificial lungs through feature sizes and blood channel designs that closely mimic those found in their natural counterpart. These new artificial lungs could potentially: 1) have surface areas and priming volumes that are a fraction of current technologies thereby decreasing device size and reducing the foreign body response; 2) contain blood flow networks in which cells and platelets experience pressures, shear stresses, and branching angles that copy those in the human lung thereby improving biocompatibility; 3) operate efficiently with room air, eliminating the need for gas cylinders and complications associated with hyperoxemia; 4) exhibit biomimetic hydraulic resistances, enabling operation with natural pressures and eliminating the need for blood pumps; and, 5) provide increased gas exchange capacity enabling respiratory support for active patients. This manuscript reviews recent research efforts in microfluidic artificial lungs targeted at achieving the advantages above, investigates the ultimate performance and scaling limits of these devices using a proven mathematical model, and discusses the future challenges that must be overcome in order for microfluidic artificial lungs to be applied in the clinic. If all of these promising advantages are realized and the remaining challenges are met, microfluidic artificial lungs could revolutionize the field of pulmonary rehabilitation.

Fabrication and in vivo thrombogenicity testing of nitric oxide generating artificial lungs

Hollow fiber artificial lungs are increasingly being used for long-term applications. However, clot formation limits their use to 1-2 weeks. This study investigated the effect of nitric oxide generating (NOgen) hollow fibers on artificial lung thrombogenicity. Silicone hollow fibers were fabricated to incorporate 50 nm copper particles as a catalyst for NO generation from the blood. Fibers with and without (control) these particles were incorporated into artificial lungs with a 0.1 m(2) surface area and inserted in circuits coated tip-to-tip with the NOgen material. Circuits (N = 5/each) were attached to rabbits in a pumpless, arterio-venous configuration and run for 4 h at an activated clotting time of 350-400 s. Three control circuits clotted completely, while none of the NOgen circuits failed. Accordingly, blood flows were significantly higher in the NOgen group (95.9 ± 11.7, p < 0.01) compared to the controls (35.2 ± 19.7; mL/min), and resistance was significantly higher in the control group after 4 h (15.38 ± 9.65, p < 0.001) than in NOgen (0.09 ± 0.03; mmHg/mL/min). On the other hand, platelet counts and plasma fibrinogen concentration expressed as percent of baseline in control group (63.7 ± 5.7%, 77.2 ± 5.6%; p < 0.05) were greater than those in the NOgen group (60.4 ± 5.1%, 63.2 ± 3.7%). Plasma copper levels in the NOgen group were 2.8 times baseline at 4 h (132.8 ± 4.5 μg/dL) and unchanged in the controls. This study demonstrates that NO generating gas exchange fibers could be a potentially effective way to control coagulation inside artificial lungs.

Extracorporeal membrane oxygenation as a bridge to lung transplantation and recovery

OBJECTIVE

Respiratory failure develops in many patients on lung transplant waiting lists before a suitable donor organ becomes available. Extracorporeal membrane oxygenation may be used to bridge such patients to recovery or lung transplantation.

METHODS

This is a review of a single-institution's experience with placing patients on extracorporeal membrane oxygenation with the intention of bridging them to lung transplantation. End points included successful bridging, duration of extracorporeal membrane oxygenation support, extubation, weaning from extracorporeal membrane oxygenation, overall survival, and extracorporeal membrane oxygenation-related complications. During an approximate 5-year period, acute respiratory failure developed in 18 patients (median age, 34 years) on the institution's lung transplant waiting list (8 hypoxemic, 9 hypercarbic, and 1 combined) who were placed on extracorporeal membrane oxygenation (13 venovenous and 5 venoarterial).

RESULTS

All patients achieved appropriate extracorporeal membrane oxygenation blood flow rates (median, 4.05 L/min) and good gas exchange (median, on extracorporeal membrane oxygenation partial pressure of arterial carbon dioxide 43 mm Hg and partial pressure of arterial oxygen 196 mm Hg). Thirteen patients (72%) were successfully bridged: 10 to transplant and 3 returned to baseline function. Eleven patients (61%) survived beyond 3 months, including the 10 (56%) who underwent transplantation and are still alive. The median duration of extracorporeal membrane oxygenation support for patients who underwent transplantation was 6 days (3.5-31 days) versus 13.5 days (11-19 days) for those who did not undergo transplantation (P = .45). Six patients (33%) were extubated on extracorporeal membrane oxygenation, 4 of whom underwent transplantation. Four patients (22%) who were too unstable for conventional interhospital transfer were transported on extracorporeal membrane oxygenation to Columbia University Medical Center. This subgroup had a 75% bridge to transplant or recovery rate and 100% survival in transplanted patients.

CONCLUSIONS

Extracorporeal membrane oxygenation is a safe and effective means of bridging well-selected patients with refractory respiratory failure to lung transplantation or return to their baseline condition.

Extracorporeal CO(2) removal in ARDS

Acute respiratory distress syndrome remains one of the most clinically vexing problems in critical care. As technology continues to evolve, it is likely that extracorporeal CO(2) removal devices will become smaller, more efficient, and safer. As the risk of extracorporeal support decreases, devices' role in acute respiratory distress syndrome patients remains to be defined. This article discusses the functional properties and management techniques of CO(2) removal and intracorporeal membrane oxygenation and provides a glimpse into the future of long-term gas-exchange devices.

Computational model-based design of a wearable artificial pump-lung for cardiopulmonary/respiratory support

Mechanical ventilation and extracorporeal membrane oxygenation are the only immediate options available for patients with respiratory failure. However, these options present significant shortcomings. To address this unmet need for respiratory support, innovative respiratory assist devices are being developed. In this study, we present the computational model-based design, and analysis of functional characteristics and hemocompatibility performance, of an innovative wearable artificial pump-lung (APL) for ambulatory respiratory support. Computer-aided design and computational fluid dynamics (CFD)-based modeling were utilized to generate the geometrical model and to acquire the fluid flow field, gas transfer, and blood damage potential. With the knowledge of flow field, gas transfer, and blood damage potential through the whole device, design parameters were adjusted to achieve the desired specifications based on the concept of virtual prototyping using the computational modeling in conjunction with consideration of the constraints on fabrication processes and materials. Based on the results of the CFD design and analysis, the physical model of the wearable APL was fabricated. Computationally predicted hydrodynamic pumping function, gas transfer, and blood damage potential were compared with experimental data from in vitro evaluation of the wearable APL. The hydrodynamic performance, oxygen transfer, and blood damage potential predicted with computational modeling, along with the in vitro experimental data, indicated that this APL meets the design specifications for respiratory support with excellent biocompatibility at the targeted operating condition.

Carbon dioxide dialysis will save the lung

Mechanical ventilation and ventilator-associated lung injury could be avoided by decreasing the ventilatory needs of the patient by extracorporeal carbon dioxide removal. The reasons for the increased ventilatory needs of the patients with acute respiratory distress syndrome are outlined, as well as some of the mechanisms of continuing damage. Extracorporeal gas exchange has been used mainly as a rescue procedure for severely hypoxic patients. Although this indication remains valid, we propose that extracorporeal carbon dioxide removal could control the ventilatory needs of the patient and allow the maintenance of spontaneous breathing while avoiding intubation and decreasing the concurrent sedation needs. A scenario is depicted whereby an efficient carbon dioxide removal device can maintain blood gas homeostasis of the patient with invasiveness comparable to hemodialysis. High carbon dioxide removal efficiency may be achieved by combinations of hemofiltration and metabolizable acid loads.

Clinical pathological characteristics and management of acute respiratory distress syndrome resulting from influenza A (H1N1) virus

Young adults, especially pregnant woman and patients with pre-existing medical conditions, appear to be at risk for the development of severe acute respiratory distress syndrome (ARDS) from influenza A (H1N1) infection, leading to critical hypoxemia. This may require high ventilator settings, the use of nonconventional modes, and extracorporeal membrane oxygenation in some cases. This severe ARDS may be related to prolonged and virulent viral infection, inducing ongoing aberrant immune responses and leading to extensive lung damage. Duration of antiviral therapy, the timing of steroid introduction, and moving away from standard ventilation techniques in ARDS may be key points in disease management.

Arteriovenous CO2 removal improves survival compared to high frequency percussive and low tidal volume ventilation in a smoke/burn sheep acute respiratory distress syndrome model

OBJECTIVES AND SUMMARY BACKGROUND: Low tidal volume ventilation (LTV) has improved survival with acute respiratory distress syndrome (ARDS) by reducing lung stretch associated with volutrauma and barotrauma. Additional strategies to reduce lung stretch include arteriovenous carbon dioxide removal (AVCO2R), and high frequency percussive ventilation (HFPV). We performed a prospective, randomized study comparing these techniques in our clinically relevant LD100 sheep model of ARDS to compare survival, pathology, and inflammation between the 3 ventilator methods.

METHODS

Adult sheep (n = 61) received smoke inhalation (48 breaths) and a 40% third-degree burn. After ARDS developed (Pao2/FiO2 <200), animals were randomized. In experiment 1, animals were killed at 48 hours after randomization. Hemodynamics, pulmonary function, injury scores, myeloperoxidase (MPO) in lung tissues and neutrophils, IL-8 in lung tissues, and apoptosis were evaluated. In experiment 2, the end point was survival to 72 hours after onset of ARDS or end-of-life criteria with extension of the same studies performed in experiment 1.

RESULTS

There were no differences in hemodynamics, but minute ventilation was lower in the AVCO2R group and Paco2 for the HFPV and AVCO2R animals remained lower than LTV. Airway obstruction and injury scores were not different among the 3 ventilation strategies. In experiment 1, lung tissue MPO and IL-8 were not different among the ventilation strategies. However, in experiment 2, lung tissue MPO was significantly lower for AVCO2R-treated animals (AVCO2R < HFPV < LTV). TUNEL staining showed little DNA breakage in neutrophils from experiment 1, but significantly increased breakage in all 3 ventilator strategies in experiment 2. In contrast, AVCO2R tissue neutrophils showed significant apoptosis at 72 hours post-ARDS criteria as measured by nuclear condensation (P < 0.001). Survival 72 hours post-ARDS criteria was highest for AVCO2R (71%) compared with HFPV (55%) and LTV (33%) (AVCO2R vs. LTV, P = 0.05).

CONCLUSIONS

Significantly more animals survived AVCO2R than LTV. In experiment 2, Lung MPO was significantly lower for AVCO2R, compared with LTV (P < 0.05). This finding taken together with the TUNEL and neutrophil apoptosis results, suggested that disposition of neutrophils 72 hours post-ARDS criteria was different among the ventilatory strategies with neutrophils from AVCO2R-treated animals removed chiefly through apoptosis, but in the cases of HFPV and LTV, dying by necrosis in lung tissue.

Clinical experience with the iLA Membrane Ventilator pumpless extracorporeal lung-assist device

Extracorporeal gas exchange by extracorporeal membrane oxygenation has been established clinically in patients with acute lung failure. The interventional lung-assist (iLA) Membrane Ventilator device (Novalung) is a sophisticated representative of a new generation of pumpless extracorporeal lung-assist devices that are driven by the patient's cardiac output and therefore, do not require extracorporeal pump assistance. The system is characterized by a new membrane gas exchange system with optimized blood flow that is integrated in an arteriovenous bypass established by vascular cannulation. This particular pumpless extracorporeal lung-assist device was applied in 1800 patients for artificial lung assistance with easy use and low cost. This article reviews the present state of clinical Novalung device implementation focusing on encountered limitations and conceivable future developments in the field.

Combination of Arteriovenous Extracorporeal Lung Assist and High-Frequency Oscillatory Ventilation in a Porcine Model of Lavage-Induced Acute Lung Injury: A Randomized Controlled Trial

BACKGROUND

To compare the combined effects of arteriovenous extracorporeal lung assist (AV-ECLA) and high-frequency oscillatory ventilation (HFOV) on pulmonary gas exchange, hemodynamics, and respiratory parameters in a lavage-induced porcine lung injury model.

METHODS

A prospective, randomized animal study. Saline lung lavage was performed in 33 healthy female pigs, weighing 52 +/- 4.1 kg (mean +/- SD), until the Pao2 decreased to 53 +/- 8 mm Hg. After a stabilization period of 60 minutes, the animals were randomly assigned to four groups: group 1, pressure-controlled ventilation (PCV) with a tidal volume of 6 mL/kg; group 2, PCV with a tidal volume of 6 mL/kg and AV-ECLA; group 3, HFOV; group 4, HFOV and AV-ECLA. In groups 2 and 4, the femoral artery and vein were cannulated and a low-resistance membrane lung was interposed. After isolated evaluation of AV-ECLA, the mean airway pressure was increased by 3 cm H2O from 16 to 34 cm H2O every 20 minutes, accompanied by blood gas analyses and measurements of respiratory and hemodynamic variables.

RESULTS

Only in AV-ECLA-treated animals was normocapnia achieved. No significant increase of Pao2 attributable to AV-ECLA alone was detected. Mean airway pressure augmentation resulted in a significant increase in Pao2 in all groups. Peak inspiratory pressure was significantly lower in HFOV-treated animals.

CONCLUSIONS

The combination of AV-ECLA and HFOV resulted in normocapnia and comparable Pao2, although a smaller ventilator pressure amplitude was applied. Long-term animal studies are needed to assess whether this approach results in further lung protection.

Experimental safety and efficacy evaluation of an extracorporeal pumpless artificial lung in providing respiratory support through the axillary vessels

OBJECTIVE

We sought to investigate the safety and feasibility of implanting the pumpless interventional lung assist device (Novalung; Novalung GmbH, Hechingen, Germany) to the axillary vessels either by means of direct cannulation or end-to-side graft interposition and the capability of either type of vascular access to provide respiratory support during apneic ventilation in adult pigs.

METHODS

Ten pigs were ventilated for 4 hours (respiratory rate, 20-25 breaths/min; tidal volume, 10-12 mL/kg; fraction of inspired oxygen, 1.0; positive end-expiratory pressure, 5 cm H2O). Thereafter, the interventional lung assist device was surgically connected to the right axillary artery and vein by using direct cannulation (n = 5) or end-to-side ringed polytetrafluoroethylene graft interposition (n = 5), and ventilatory settings were reduced to achieve near apneic ventilation (respiratory rate, 4 breaths/min; tidal volume, 1-2 mL/kg; fraction of inspired oxygen, 1.0; positive end-expiratory pressure, 20 cm H2O). Hemodynamic and intrathoracic volumes and lung cytokine levels were measured.

RESULTS

Blood flow through the interventional lung assist device was 1.7 +/- 0.4 L/min or 30% +/- 14% of the cardiac output, and the mean pressure gradient across the interventional lung assist device was 10 +/- 2 mm Hg. The interventional lung assist device allowed an O2 transfer of 225.7 +/- 70 mL/min and a CO2 removal of 261.7 +/- 28.5 mL/min. Although the amount of blood flow perfusing the interventional lung assist device was significantly higher (P < .01) with direct cannulation (2.1 +/- 0.3 L/min) compared with that seen in graft interposition (1.3 +/- 0.3 L/min), the latter allowed similar respiratory support with reduced hemodynamic instability.

CONCLUSIONS

The axillary vessels are a safe and attractive cannulation site for pumpless partial respiratory support. Compared with direct cannulation, graft interposition was equally able to support the interventional lung assist device-driven gas exchange requirements during apneic ventilation with better hemodynamic stability.

Artificial lung: progress and prototypes

Lung disease is the fourth leading cause of death (one in seven deaths) in the USA. Acute respiratory distress syndrome (ARDS) affects approximately 150,000 patients a year in the USA, and an estimated 16 million Americans are afflicted with chronic lung disease, accounting for 100,000 deaths per year. Medical management is the standard of care for initial therapy, but is limited by the progression of disease. Chronic mechanical ventilation is readily available, but is cumbersome, expensive and often requires tracheotomy with loss of upper airway defense mechanisms and normal speech. Lung transplantation is an option for less than 1100 patients per year since demand has steadily outgrown supply. For the last 15 years, the authors' group has studied ARDS in order to develop viable alternative treatments. Both extracorporeal gas exchange techniques, including extracorporeal membrane oxygenation, extracorporeal and arteriovenous CO(2) removal, and intravenous oxygenation, aim to allow for a less injurious ventilatory strategy during lung recovery while maintaining near-normal arterial blood gases, but precludes ambulation. The paracorporeal artificial lung (PAL), however, redefines the treatment of both acute and chronic respiratory failure with the goal of ambulatory total respiratory support. PAL prototypes tested on both normal sheep and the absolute lethal dose smoke/burn-induced ARDS sheep model have demonstrated initial success in achieving total gas exchange. Still, clinical trials cannot begin until bio- and hemodynamic compatibility challenges are reconciled. The PAL initial design goals are for a short-term (weeks) bridge to recovery or transplant, but eventually, for long-term support (months).

An Update on Interventional Lung Assist Devices and Their Role in Acute Respiratory Distress Syndrome

In recent years, pumpless arteriovenous systems for extracorporeal gas exchange have become a new therapeutic option for the treatment of patients suffering from acute respiratory failure. Experiences with the pumpless extracorporeal membrane lung in animal experiments and in patients with adult respiratory distress syndrome published in the current literature are reviewed. In addition this article presents a case of varicella pneumonia with persistent hypoxemia and hypercapnia under mechanical ventilation that showed a significant improvement with treatment with a pumpless extracorporeal lung assist using an arteriovenous shunt for eight days. The patient made a complete recovery. This is the first report of a patient with a life-threatening varicella pneumonia successfully treated with pumpless extracorporeal lung assist device. This review provides an update on interventional lung assist devices and a critical discussion of their advantages and limitations.

Bridge to lung transplantation with the novel pumpless interventional lung assist device NovaLung

BACKGROUND

Worsening of lung failure in patients awaiting a lung transplantation might lead to ventilation-refractory hypercapnia and respiratory acidosis. Most transplant centers consider pretransplantation extracorporeal membrane oxygenation as a contraindication for lung transplantation because of the poor outcome. We have, for the first time, applied the novel pumpless interventional lung assist NovaLung for bridge to lung transplantation in patients with severe ventilation-refractory hypercapnia. We report on our initial experience.

METHODS

Between March 2003 and March 2005, 176 lung transplantations were performed, of which 60% were high-urgency lung transplantations. Twelve of the high-urgency recipients had severe ventilation-refractory hypercapnia and respiratory acidosis. These patients were connected to the novel pumpless interventional lung assist NovaLung for bridge to lung transplantation.

RESULTS

The length of interventional lung assist NovaLung support was 15 +/- 8 days (4-32 days). PaO2, pH, and PaCO2 levels in arterial blood prior to interventional lung assist NovaLung implantation were 71 +/- 27 mm Hg, 7.121 +/- 0.1, and 128 +/- 42 mm Hg, respectively. Six hours after interventional lung assist NovaLung implantation, PaO2, pH, and PaCO2 levels had changed to 83 +/- 17 mm Hg (ns), 7.344 +/- 0.1 (P < .05), and 52 +/- 5 mm Hg (P < .05), respectively. Four patients died of multiorgan failure, 2 patients before and 2 after lung transplantation. Thus, 10 out of 12 patients were successfully bridged to lung transplantation, and 8 are still alive (1-year survival, 80%).

CONCLUSIONS

This report suggests that interventional lung assist NovaLung implantation is an effective bridge to lung transplantation strategy in patients with ventilation-refractory hypercapnia.

Evaluation of a pumping assist lung that uses a rotating fiber bundle

A paracorporeal respiratory assist lung (PRAL) is being developed for supplemental gas exchange to allow the native lungs of acute lung failure patients to heal. The device consists of a rotating annular microporous hollow fiber membrane bundle. The rotation augments the gas exchange efficiency of the device at constant flow-rate thereby uncoupling gas exchange and flow rate. The rotating fibers also enable the PRAL to pump the blood without the need for an additional pump or arterial cannulation. Blood flow rates will be between 500 and 750 ml/min with CO(2) removal rates of 100-130 ml/min. A prototype was manufactured with an overall surface area of 0.25 m. When rotated at 1500 rpm, CO(2) removal increased by 133% and O(2) transfer increased by 157% during an in vitro bovine blood study. The pumping of the rotating fiber bundle was assessed in a glycerol/water solution. At 1500 rpm, the PRAL generated 750 ml/min against 52 mm Hg pressure. Hemolysis of the device was assessed using in vitro bovine blood from a slaughterhouse. Plasma free hemoglobin levels were similar regardless of whether the rotating fibers were present in the PRAL, indicating that a rotating fiber bundle can be used to increase gas exchange without causing blood trauma.

Adjuncts to Mechanical Ventilation in ARDS

Since its first description, acute respiratory distress syndrome has been characterized by abnormal physiologic and gas exchange properties of the lungs. Many adjunctive therapies have been developed to reduce the stresses of mechanical ventilation on already damaged lungs. We examined the mechanism of action and the latest clinical trial information of several adjunctive therapies including prone positioning, nitric oxide, extracorporeal membrane oxygenation, arterial venous carbon dioxide removal, and liquid ventilation. While all of these therapies have demonstrated short-term improvements in arterial blood gases and in the limitation of lung injury, none have shown an evidence-based survival benefit.

Development of Ambulatory Arterio-Venous Carbon Dioxide Removal (AVCO2R): The Downsized Gas Exchanger Prototype for Ambulation Removes Enough CO2 with Low Blood Resistance

We are developing an ultra compact gas exchanger to allow ambulation during arterial-venous CO2 removal (AVCO2R). The ambulatory AVCO2R gas exchanger (135 ml prime volume and 1.3 M2 gas exchange surface area) is made of polymethylpentene hollow fibers. The gas exchanger was attached to sheep carotid artery (12F) and jugular vein (14F) by percutaneous cannulae for 6 hours (n = 5). Device CO2 removal was measured and calculated at a constant blood flow rate of 1 L/min coupled with varying sweep gas from 1 to 15 L/min, and at constant sweep gas flow of 2 L/min coupled with varying blood flow from 0.5 to 1.25 L/min to determine capacity of CO2 removal at Pa CO2 = 40-50 mm Hg. Blood gases, CO2 removal and hemodynamics were recorded at 0, 3, and 6 hours. CO2 removal increased with sweep gas flow rate and with increase of device blood flow. Hemodynamics remained unchanged throughout study. Gas exchanger resistance remained stable at 2.3 +/- 0.53 mm Hg/L/min. CO2 removal with 1 L/min blood flow and 2 L/min sweep gas was 110 +/- 12 then stabilized at 85 +/- 14 mL/min to 6 hours. The compact ambulatory AVCO2R gas exchanger achieves stable, near total CO2 removal for at least 6 hours with a simple arteriovenous shunt.

Acute Respiratory Distress Syndrome

Acute lung injury is a syndrome diagnosed clinically and is one of the most common causes of respiratory failure seen in the intensive care unit. A consensus definition of this and its more severe form, acute respiratory distress syndrome (ARDS), has allowed for better consistency in determining the epidemiology and facilitates consistent clinical trial design to better find therapies to treat or prevent it. Patients who present with ARDS usually show signs of tachpnea or dyspnea and have underlying conditions that promote inflammatory responses. The pathogenesis involves an inflammatory insult that eventually destroys the pulmonary capillary vasculature as well as alveoli. Pathophysiologically, the patient with ARDS may progress through as many as 3 phases: exudative, proliferative, and fibrotic. Treatment options can be either nonpharmacologic or pharmacologic and are limited. Ventilator strategies such as low-tidal-volume ventilation have improved outcomes in these patients, while corticosteroid use is not as established to provide morbidity or mortality benefit. Other therapies have been investigated with inconclusive or disappointing results for the treatment of this fatal syndrome.

Centromere DNA, proteins and kinetochore assembly in vertebrate cells

The centromere is a specialized region of the chromosome that is essential for faithful chromosome segregation during mitosis and meiosis in eukaryotic cells. It is the site at which the kinetochore, the functional nucleoprotein complex responsible for microtubule binding and chromosome movement, is assembled through complex molecular mechanisms. Herein, I review recent advances in our understanding of centromeric DNAs as sites for kinetochore assembly and the mechanisms underlying kinetochore assembly in vertebrate cells.

Successful Management of Adult Smoke Inhalation with Extracorporeal Membrane Oxygenation

Pulmonary complications remain one of the leading causes of mortality in patients with burns. We report two cases of adult patients with thermal and inhalation injuries who were placed on extracorporeal membrane oxygenation (ECMO) and survived. Patient 1 was a 42-year-old male who suffered 15% TBSA and a severe inhalation injury requiring intubation upon arrival to the emergency department. Patient 2 was a 24-year-old female in a house fire who received 20%TBSA and was noted to be in respiratory distress and intubated on the scene by the paramedic team. Three days after admission, patient 1 developed severe respiratory failure. He decompensated, despite maximum conventional management, and was placed on ECMO. After 300 hours of ECMO, his pulmonary function had improved, and he was decannulated. Patient 2 also developed severe refractory respiratory failure and was placed on ECMO. She was decannulated 288 hours later. Both patients were discharged home shortly afterwards and have managed well. ECMO should be considered when patients are facing a respiratory death from inhalation injury on conventional mechanical ventilation.

New technologies for respiratory assist

"The artificial lung especially has lingered behind progress with artificial hearts and ventricular assist devices, not because the need for lungs has not been recognized, but because we have not had a full understanding of the engineering problems and the unique material requirements until recent years." Brack Hattler, MD PhD. The development from the first clinical use of haemodialysis over five decades ago to widespread chronic treatment took more than two decades. The histories of other artificial organ technologies, such as artificial hearts, follow similar long development paths. For five decades, due to a lack of technology, artificial lungs have been limited to use with a heart-lung machine for cardiopulmonary bypass (CPB) or extracorporeal membrane oxygenation (ECMO). The advent of pumpless biocompatible artificial lungs will open new treatment options for patients with acute or chronic lung failure.

Short term performance evaluation of a perfluorocopolymer coated gas exchanger for arteriovenous CO2 removal

A new perfluorocopolymer coating for micropore hollow fiber gas exchangers was developed to improve gas exchange, reduce plasma leakage, and reduce blood-surface interactions. The present authors evaluated gas exchanger performance using this new coating in a prospective, randomized, controlled, unblinded, large animal model of CO2 retention. Adult sheep (30-40 kg), under general anesthesia, underwent cannulation of the carotid artery (12 F) and jugular vein (14 F). The perfluorocopolymer coated (n = 5) and uncoated (n = 5) gas exchangers were attached to an arteriovenous CO2 removal (AVCO2R) circuit. Blood gases, CO2 removal, and hemodynamics were monitored throughout the 6 hour study. Average CO2 removal was 107.6 +/- 15.6 ml/min (coated) vs. 93.0 +/- 13.9 ml/min (uncoated; p < 0.01). PaCO2 and CO2 removal for both coated and uncoated did not deteriorate significantly over the study. Average AVCO2R blood flow was 1,130 +/- 25 ml/min (coated) versus 1,101 +/- 79 ml/min (uncoated; p = not significant). Likewise, cardiac output and AVCO2R blood flow did not change over the duration of the study. No significant differences in the pressure gradient or resistance between devices (coated, 6.89 +/- 1.14 mm Hg/L/min; uncoated, 6.42 +/- 0.23 mm Hg/L/min) was noted. The authors concluded that the new perfluorocopolymer coated gas exchanger improved CO2 removal without compromising hemodynamics in an acute performance evaluation.

Extracorporeal carbon dioxide removal to control arterial pH and PACO2 in a heart-beating donor with acute lung injury

BACKGROUND

Arteriovenous carbon dioxide (AVCO2R) removal is a technique of pumpless extracorporeal carbon dioxide removal. This system has been used successively to control pH and PaCO2 in patients with acute lung injury who could not be adequately ventilated. This report describes the use of this technology in an organ donor awaiting harvesting.

METHODS

AVCO2R was implanted using a hollow-fiber oxygenator attached to 12 F and 14 F vascular cannulas that were inserted into the femoral artery and vein, respectively. Oxygen was attached to the oxygenator to provide the sweep gas.

RESULTS

The PaCO2 and arterial pH promptly corrected after support was initiated (from 83-42 mm Hg and 7.18-7.38, respectively).

CONCLUSION

This case describes the successful use of pumpless arteriovenous extracorporeal removal of CO2 in a heart-beating donor awaiting organ harvest.

Toward Ambulatory Arteriovenous CO2 Removal: Initial Studies and Prototype Development

Extracorporeal arteriovenous carbon dioxide removal (AVCO2R) using percutaneous cannulae and a low resistance gas exchanger achieves near total CO2 removal, allowing lung rest and potentially improving survival. AVCO2R, redesigned to allow ambulation, has potential as treatment for severe chronic obstructive pulmonary disease or rehabilitation before lung transplant. The purposes of this study were to 1) determine the optimal ambulatory access for AVCO2 removal and 2) develop a prototype Ambulatory-AVCO2R gas exchanger. Initially, reinforced Gore-Tex 6 mm (two) and 8 mm (four) grafts were anastomosed to sheep carotid arteries and jugular veins as a loop in parallel to the cranial circulation to determine blood flow capabilities. Blood flow was 100-150 ml/min with a 14 gauge dialysis needle, and transected 6 mm Gore-Tex grafts achieved 500-900 ml blood flow, whereas transected 8 mm grafts achieved up to 2000 ml/min flow. The polytetrafluoroethylene (PTFE) loops were then connected to our newly developed ultra low resistance pumpless gas exchanger for ambulatory AVCO2R. The average pressure gradient across the prototype Ambulatory-AVCO2R gas exchangers (n = 5) was 2.8 +/- 0.8 mm Hg, and mean CO2 removal was 104.8 +/- 14.0 ml/min, with an average blood flow of 900 ml/min. We conclude that an 8 mm Gore-Tex reinforced graft arteriovenous loop supplies ample blood flow for our new ultra low resistance Ambulatory-AVCO2R to achieve near total CO2 removal.

Surgery for pulmonary metastases from colorectal cancer: the importance of prethoracotomy serum carcinoembryonic antigen as an indicator of prognosis

OBJECTIVE

Several investigators have analyzed prognostic factors of surgical treatment for pulmonary metastases from colorectal cancer, but the results remain inconclusive. This study was performed to determine the prognostic implications of the prethoracotomy serum level of carcinoembryonic antigen (CEA) in relation to the postthoracotomy recurrent pattern among patients with this disease.

METHODS

A retrospective analysis of prognostic factors was undertaken in 100 patients who had consecutively undergone initial surgical resection for pulmonary metastases of colorectal origin.

RESULTS

The overall 3- and 5-year survival rates were 62.2% and 49.4%, respectively. Univariate analysis revealed that the prethoracotomy serum CEA level and operative curability were strongly associated with prognosis, while in multivariate analysis, only the prethoracotomy serum CEA level was a significant prognostic indicator. Patients with a high level of prethoracotomy serum CEA more frequently exhibited recurrence in extrathoracic sites, especially in the brain.

CONCLUSION

Before thoracotomy for pulmonary metastases from colorectal cancer, the serum CEA level was the most useful prognostic factor. Patients with elevated serum CEA level should undergo a careful prethoracotomy systemic survey and postthoracotomy follow-up for extrathoracic metastases, in particular brain metastases, and an appropriate combined therapeutic modality should be considered.

Extracorporeal CO2 removal in a child with a single ventricle by the addition of an oxygenator to a dialysis circuit

OBJECTIVE

To optimize CO2 removal in a child with a single ventricle.

DESIGN

Case report.

SETTING

A ten-bed pediatric intensive care unit in a university-affiliated hospital.

PATIENT

A 6-yr-old boy with a single ventricle who underwent a Fontan procedure.

INTERVENTIONS

Addition of a membrane oxygenator to a venovenous hemodialysis circuit.

MEASUREMENTS

Patient respiratory variables were measured.

MAIN RESULTS

A clinically significant improvement in CO2 removal was achieved.

CONCLUSIONS

Addition of a membrane oxygenator to a dialysis circuit facilitates CO2 removal.

Artificial lungs: a new inspiration

An estimated 16 million Americans are afflicted with some degree of chronic obstructive pulmonary disease (COPD), accounting for 100,000 deaths per year. The only current treatment for chronic irreversible pulmonary failure is lung transplantation. Since the widespread success of single and double lung transplantation in the early 1990s, demand for donor lungs has steadily outgrown the supply. Unlike dialysis, which functions as a bridge to renal transplantation, or a ventricular assist device (VAD), which serves as a bridge to cardiac transplantation, no suitable bridge to lung transplantation exists. The current methods for supporting patients with lung disease, however, are not adequate or efficient enough to act as a bridge to transplantation. Although occasionally successful as a bridge to transplant, ECMO requires multiple transfusions and is complex, labor-intensive, time-limited, costly, non-ambulatory and prone to infection. Intravenacaval devices, such as the intravascular oxygenator (IVOX) and the intravenous membrane oxygenator (IMO), are surface area limited and currently provide inadequate gas exchange to function as a bridge-to-recovery or transplant. A successful artificial lung could realize a substantial clinical impact as a bridge to lung transplantation, a support device immediately post-lung transplant, and as rescue and/or supplement to mechanical ventilation during the treatment of severe respiratory failure.

Extracorporeal membrane oxygenation for severe respiratory failure

The use of extracorporeal technology to accomplish gas exchange with or without cardiac support is based on the premise that "lung rest" facilitates repair and avoids the baso- or volutrauma of mechanical ventilator management. Extracorporeal membrane oxygenation (ECMO), a modified form of cardiopulmonary bypass, has been shown to decrease mortality of neonatal, pediatric and adult respiratory failure and is capable of total gas exchange. In neonates, over 20,638 patients have been treated with an overall survival of 77% in a population thought to have 78% mortality.