Respiratory dialysis: a new therapy for chronic obstructive pulmonary disease

Introduction

Chronic obstructive pulmonary disease (COPD) is predicted to be the third leading cause of death in the United States by 2020. Approximately 125,000 people die yearly from acute exacerbations of the disease. Once intubation and mechanical ventilation become necessary, the death rate increases. To avoid the need for ventilator use we have developed a new device (the Hemolung), which is an integrated pump/oxygenator that functions at low blood flow rates (250–500 ml/min) equivalent to those used in renal dialysis. The small priming volume (190 ml), reduced membrane surface area (0.5 m²), and use of a percutaneously inserted dual lumen venous catheter (15 Fr) to provide blood inflow and outflow make the entire system suitable for repetitive use in patients with hypercapnic acute respiratory failure. We report here 7-day animal data stressing the hemocompatibility and gas exchange capabilities of the device.

Methods

The venous catheter was inserted into the right exterior jugular vein of four adult sheep and connected to the saline-primed Hemolung circuit. Hollow fiber membranes were coated with siloxane and heparin to prevent plasma wetting and to increase biocompatibility. Animals were minimally anticoagulated with heparin (ACT 150). Blood flow, CO₂ exchange, blood gases and key hematological parameters were measured over 7 days. Necropsy was performed on termination.

Results

Removal of CO₂ remained steady over 7 days, averaging 72 ± 12 ml/min at blood flows of 384 ± 18 ml/min. As the venous PCO₂ rose or fell, so did the level of CO₂ removal. No changes were necessary in the system and no plasma wetting was noted over the 7 days. Hematocrit remained stable and no blood products were required. Initial platelet counts dropped to 221,000 ± 58,000/μl by the second day, but recovered to baseline values on day 4 and remained stable. Necropsy showed no signs of thromboembolism or organ damage.

Conclusion

A simple alternative to mechanical ventilation for patients with COPD and hypercapnic respiratory failure has been successfully tested in animals. Human trials are planned for 2008 to determine what role 'respiratory dialysis' will have in this patient population.