Recently McGowan Institute for Regenerative Medicine faculty member Derek Angus, MD, MD, MPH, FRCP, FCCM, FCCP, weighed in on two new studies that try to answer one of the most pressing questions in critical care medicine: How much pressure should be applied to keep open the partially collapsed lungs of people being treated for the deadly condition called acute respiratory distress syndrome?
Unfortunately, that question has not been definitively answered. To Dr. Angus, the answer from the studies published in the Journal of the American Medical Association is that higher positive end-expiratory pressure (PEEP) is better, but the exact amount of pressure must be adapted to each person.
“The results should have some impact on medical practice, pushing intensive care units toward use of higher PEEP levels, based on a patient's needs,” said Dr. Angus.
The new studies were aimed at settling a debate about how much PEEP should be applied at the end of each breath, enough to prevent lung collapse, but not so much as to damage lung tissue. The two research teams involved in the studies, from Canada and France, used different techniques to determine those needs. "The Canadian study titrated PEEP based on the reading of how oxygenated the lung tissue was," explained Angus. "The French relied on more sophisticated measures. One was slightly simpler than the other, but both were trying to convert a set of principles into a recipe to titrate PEEP, so you end with a different measure for each person."
Neither formula had a major effect on the death rate. In the French study of 767 people treated for acute respiratory distress syndrome (ARDS), the hospital mortality was 39 percent among those who got conventional treatment using relatively low PEEP, and 35.4 percent among those who got higher PEEP based on individual calculations. The comparable figures for the 983 people treated for ARDS in the Canadian study was 40.4 percent for those getting conventional treatment, and 36.4 percent for receiving higher PEEP based on individual characteristics.
"While neither study changed overall mortality much, both made moves in the right direction," Angus said. "There was a trend toward lower mortality in both studies [with higher PEEP]. In both studies, there was clearly improved oxygenation. And both reduced the need to use rescue therapies, last-ditch attempts to use experimental, sometimes crazy, things to keep patients alive."
ARDS develops in people who suffer major injuries or who are critically ill with diseases such as pneumonia or bacterial infections. Fluid builds up in the lungs until breathing becomes more and more difficult. In treatment, air is forced into the lungs. A marked feature of the two studies was a continuation of the trend to change the pattern of forced breathing, with the number of breaths per minute doubled, and the tidal volume, the amount of air forced into the lung with each breath, halved.
Dr. Angus is also an Associate Professor of Medicine, an Associate Professor in Health Policy and Management, a Professor with Tenure in Critical Care Medicine, and also Vice Chair for Research in the Department of Critical Care Medicine all at the University of Pittsburgh.
Illustration: McGowan Institute for Regenerative Medicine.
Washington Post (02/12/08)
US News & World Report (02/12/08)
Dental Plans (02/12/08)
CBS News/Canada (02/12/08)
Health Central (02/12/08)
Editorial, Angus (JAMA. 2008; 299(6):693-695)
Abstract, Mercat (JAMA. 2008; 299(6):607)
Abstract, Meade (JAMA. 2008; 299(6):607)