Experts differ on what answers the research offers
TUESDAY, Feb. 12 (HealthDay News) -- Two new studies 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. Two experts have differing views on what the outcomes, which were not clear-cut, might mean. To one, the answer from the studies being published in the Feb. 13 issue of 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. Yet another contended there was no proof of the value of higher PEEP.
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. Derek C. Angus, chairman of the department of critical care medicine at the University of Pittsburgh, and author of an accompanying editorial.
The two research teams, 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."
Another expert was more cautious.
"I don't think the results of the Canadian study would be enough to change practice in a systematic way," said Dr. Leonard C. Hudson, head of the division of pulmonary and critical medicine at the University of Washington.
But the Canadian researchers begged to differ.
Their results do offer support for a change to higher PEEP levels, said Dr. Gordon H. Guyatt, a professor of medicine at McMaster University in Toronto and a member of the Canadian research team.
"It is not clear that higher PEEP is better, in terms of a lower mortality rate, but it is very likely that higher PEEP is at least as good," Guyatt said. "There is an established way of treatment using lower PEEP. We now have shown that using higher PEEP is at least as good, and perhaps better. Clinicians who prefer using a higher PEEP can now feel comfortable in doing so."
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.
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 basic point of the Canadian study to Hudson was tidal volume. "To me, what it says is that probably the most important thing about lung protection is making sure the tidal volume is low," he said. "That allows you to use as high a level of PEEP as you want."
Angus had a quite different view, saying that individually calculated higher PEEP levels were the decisive factors. "It's pretty hard to argue that we should continue to do what we have been doing," Angus said.
For more on ARDS, head to the U.S. National Library of Medicine.
SOURCES: Derek C. Angus, M.D., chairman, department of critical care medicine, University of Pittsburgh; Leonard C. Hudson, M.D., head, division of pulmonary and critical medicine, University of Washington, Seattle; Gordon H. Guyatt, M.D., professor, medicine, McMaster University, Toronto; Feb. 13, 2008, Journal of the American Medical Association
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