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Medical Meeting Reports

American College of Surgery Clinical Congress

October 10-15, 1999


font=>By Karen Sandrick

Joseph Zwischenberger, MD, of the University of Texas Medical Branch, Galveston, asserted that, in the next five years, one of the current experimental forms of extracorporeal oxygen support will emerge as an essential part of the treatment for adult respiratory distress syndrome (ARDS). A promising candidate is percutaneous arterioventricular carbon dioxide removal.

Gas Exchange vs. Carbon Dioxide Removal

The discovery that the survival of adults in respiratory failure could improve by percutaneously removing carbon dioxide -- rather than by completely exchanging oxygen and carbon dioxide -- has led to a smorgasbord of extracorporeal oxygenation options that do not require 24-hour-a-day bedside support. Dr. Zwischenberger is developing one of them -- arterioventricular carbon dioxide removal. This procedure uses a simple arteriovenous shunt and a gas exchange membrane that has a large enough surface area to allow almost complete removal of carbon dioxide. Unlike extracorporeal membrane oxygenation (ECMO), it does not require continuous monitoring or maintenance by skilled personnel.

Beginning Clinical Trials

Dr. Zwischenberger recently completed a preliminary trial of the technique in five adult patients with unresponsive ARDS and carbon dioxide retention who were not eligible for or had not responded to other experimental therapies. He inserted a femoral-femoral arteriovenous shunt with a 10-12 F arterial cannula and a 15 F percutaneous venous cannula, used a commercially available low-resistance oxygenator, and administered systemic heparin at a rate of 250-300 seconds at the bedside. All five patients completed a 72-hour trial on this form of extracorporeal oxygen support, three improved enough to be discharged promptly from the hospital, and all had only minor complications. On the basis of this investigation, Dr. Zwischenberger has designed several prospective randomized controlled unblinded multicenter outcomes studies, and he is in the process of accruing patients with ARDS for these trials.

Results of Carbon Dioxide Removal in Animals

Dr. Zwischenberger reported on the use of arterioventricular carbon dioxide removal in 16 large animals that were subjected to smoke inhalation injury. In combination with low-frequency mechanical ventilation, the arterioventricular carbon dioxide removal technique significantly reduced minute ventilation, tidal volume, and peak airway pressures. It maintained the hemodynamic status of the animals and improved arterial oxygenation. While only three of eight control animals survived, all eight animals receiving arterioventricular carbon dioxide removal survived.

Other Experimental Techniques

Dr. Zwischenberger pointed out that researchers are studying other investigational approaches to ARDS that involve the use of partial liquid ventilation, nitric oxide, and high-frequency mechanical ventilation. Critical care surgeons will have to wait for the results of outcomes studies to learn which of these strategies prove to be effective for ARDS. Until then, Dr. Zwischenberger advised treating adults in severe respiratory failure on the basis of sound critical care principles, including mechanical ventilation, fluid restriction, and adequate utrition with a positive nitrogen balance. He emphasized the importance of finding and treating the source of the infection that is causing ARDS and instituting advanced respiratory support procedures, including diuresis and pressure- and volume-limited ventilation. He could not advocate, however, use of ECMO, common carotid carbon dioxide removal, or intravencaval gas exchange for adults with ARDS because of less-than-stellar results in evidence-based outcomes analyses worldwide.

Ortho Biotech

Funded through an unrestricted educational grant by Ortho Biotech.

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