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Lying Face Down May Help Critical Care Patients: Prone Position Improves Oxygenation

(DES PLAINES, Ill., December 1, 2003) - Critical care patients with acute lung injury or acute respiratory distress syndrome (ALI/ARDS) who responded to lying face down with improved respiratory gas exchange have increased survival rates, according to an article in the December issue of Critical Care Medicine .

"This research underlines the importance of considering carbon dioxide clearance together with oxygenation. PaCO2 clearance is usually neglected or under-considered. However, carbon dioxide changes, more so than oxygen changes, relate to the anatomical status of the lung," said lead author Luciano Gattinoni, MD, FRCP, professor at the Istituto di Anestesia e Rianimazione, Universita' degli Studi di Milano in Italy.

PaCO2 , the carbon dioxide portion of the blood-gas equation, is an indicator of the blood level of carbon dioxide, which is the metabolic waste exhaled by the lungs. Many lung diseases prevent the lungs from physiologically clearing carbon dioxide thus causing gas retention and a rise in PaCO2 levels. A PaCO2 decrease indicates that lung conditions have improved allowing a better carbon dioxide clearance.

The researchers studied 225 ICU patients with acute lung injury or acute respiratory distress syndrome to evaluate the association between improved respiratory gas exchange in the prone position and patient outcome. The patients meeting ALI/ARDS criteria were positioned on their stomachs (proning) six hours a day for 10 days.

The researchers found that patients who responded positively to proning with reduced PaCO2 had an increased 28-day survival rate. The patients who responded to proning with decreased PaCO2 levels had a mortality rate of 35.1 percent and those who did not respond to proning had a mortality rate of 52.2 percent. The researchers believe that improved respiratory efficiency is an important marker for surviving acute respiratory failure.

"The different responses of PaCO2 to the prone position likely reveals underlying pathology," said Dr. Gattinoni. "When PaCO2 decreases in the prone position, the prevalent underlying pathology is lung collapse - like a wet sponge, the lung collapses under its own weight. When

PaCO2 increases, the prevalent phenomenon is likely pulmonary consolidation with lung blood flow redistribution."

Increases in PaCO2 over time are associated with worse outcomes in patients with lasting acute respiratory distress syndrome. In late acute respiratory distress syndrome, PaCO2 increases reflect major structural changes in the lungs, including some associated with pneumonia.

Before starting the study, the researchers evaluated computed tomography (CT) scans which showed that ALI/ARDS patients had lung collapse in gravity-dependent areas. The researchers placed their patients in the prone position to facilitate oxygenation. "Although some anecdotal reports found similar results, the combination of CT scan and prone position opened the way for widespread use of this technique in the ICU," stated Dr. Gattinoni.

Dr. Gattinoni suggests that practitioners who have only limited ICU tools or are working under suboptimal conditions place hypoxic patients in the prone position.

The prone position is widely used in the treatment of severe ALI/ARDS without scientific verification of improved survival. Severe hypoxemia, or insufficient blood oxygenation, is the main indication for the prone position, which is associated with a significant and lasting improvement in oxygenation in 60 percent to 80 percent of patients. Previously, researchers did not know if gas exchange improvements in the prone position were associated with better outcomes.

"This study highlights the immense pathophysiologic importance of carbon dioxide elimination during ventilation, and it provides the clinician with additional prognostic information. It is useful clinically for the intensivist to know that if a patient has a good carbon dioxide response to prone ventilation, they have an improved survival," said Joseph E. Parrillo, MD, editor-in-chief of Critical Care Medicine .

Critical Care Medicine is the official journal of the Society of Critical Care Medicine. It is the premier peer-reviewed, scientific publication in critical care medicine. Each issue presents critical care practitioners with clinical breakthroughs that lead to better patient care, the latest news on promising research, and advances in equipment and techniques.

Editor's note: This study was conducted independently of, but partially funded by, Hill-rom Italy, which supported investigators' meetings and secretarial activities of the coordinating center.

For more information, contact Thomas Joseph, MPS, CAE at (847) 827-7282 or tjoseph@sccm.org.

The Society of Critical Care Medicine is the leading professional organization dedicated to ensuring excellence and consistency in the practice of critical care medicine. With over 11,000 members worldwide, the Society is the only professional organization devoted exclusively to the advancement of multidisciplinary, multiprofessional intensive care through excellence in patient care, professional education, public education, research and advocacy. Members of the Society include intensivists, critical care nurses, critical care pharmacists, clinical pharmacologists, respiratory care practitioners and other professionals with an interest in critical care, which may include physician assistants, social workers, dieticians, and members of the clergy.

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