Respiratory Dialysis Device Safely Removed CO₂ in Ovine Study

PHILADELPHIA—A lung replacement device that oxygenates blood and removes CO₂ was safely tested over a seven-day period in sheep. “Target CO₂ removal was achieved,” while daily blood work values were not significantly affected; no adverse effects were found, reported Andriy I. Batchinsky, MD, at the American College of Chest Physicians 2008 Annual International Scientific Assembly. A device of this type potentially could replace currently available mechanical ventilators and thus eliminate the risks associated with their use, Dr. Batchinsky suggested.

The company who manufactures the device hopes to conduct a 20-patient feasibility study this year, followed by a 200-patient randomized controlled trial, said Nicholas J. Kuhn, President and Chief Operating Officer of ALung Technologies, Inc, in Pittsburgh. The Hemolung will be tested in patients with active respiratory failure due to exacerbation of COPD for whom noninvasive ventilation (ie, supplemental oxygen by face mask) was inadequate.

A PROMISING FUTURE

The Hemolung is a small, cylindrical, veno-venous extracorporeal CO₂ removal device, said Dr. Batchinsky, a research scientist at the US Army Institute of Surgical Research, Fort Sam Houston, Texas. “It provides roughly 30% to 40% CO₂ removal at blood flows in the range of 400 to 500 mL/min,” which, in this ovine study, translated into a CO₂ removal of 66 mL/min. The Hemolung requires a prime volume of 300 mL and minimal heparinization.

The military is investigating the artificial lung with the goal of delivering new critical care technology to the battlefield, Dr. Batchinsky indicated. “The Hemolung may be beneficial during the transport of combat casualties with acute lung injury back from the front lines to the Continental US. It is a ‘set it and forget it’–type device that is easy to use and operate.” Additional potential applications include use as a bridge prior to lung transplantation and as an intermittent therapy for ARDS and COPD.

Another extracorporeal respiratory dialysis device on the horizon is the BioLung (MC3, Ann Arbor, Michigan).

SHEEP SAFETY STUDY

As reported at the meeting, Dr. Batchinsky and colleagues—led by Meir Rosenberg, MSc, and Scott Morley, BSc, of ALung Technologies—conducted a safety study in seven awake sheep. The Hemolung was connected to a 15 French dual lumen catheter, which was inserted into the jugular vein. The proximal set of openings of the catheter was positioned in the superior vena cava and was used to channel venous blood to the Hemolung through a set of plastic tubing.

“Arterialized” blood was returned to the animal via the distal tip of the catheter, located in the superior vena cava just above the right atrium, Dr. Batchinsky explained. The catheter position was confirmed by fluoroscopy. In humans, there is the potential to achieve higher blood flows and gas exchange by using the femoral vein and 18 French catheters, he noted.

The animals were anticoagulated with heparin to maintain an activated clotting time of about 150 seconds. Blood flows through the cannulae were maintained at 350 to 450 mL/min—similar to flow rates used in hemodialysis. The Hemolung provided “fairly steady” CO₂ removal, at a mean 66 mL/min, Dr. Batchinsky reported.

Hematologic effects were minimal and included a small increase in fibrinogen, an increase in white blood cell count, and a transient decrease in platelet count, with initial counts dropping to 241,000/uL by 72 hours but recovering to baseline on day 4 and remaining stable thereafter. This effect was probably due to circuit deposition of platelets, Dr. Batchinsky said. Hematocrit was stable over the study duration, and normothermia was maintained.

Other health effects included the need for anticoagulation. There was no requirement for blood products, and necropsy showed no signs of thromboembolism or organ damage.

In two animals, hemolysis was attributed to device failure due to malfunction of seals and bearings.

“However, these defective devices were replaced, the urine cleared up, and the study was successfully completed,” said Dr. Batchinsky. The manufacturer has since changed the design of the device to prevent failure.

—Elizabeth G. Douglas

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