WEDNESDAY, April 26, 2006 (HealthDay News) -- New research is answering a key question in the treatment of a dangerous lung condition called acute respiratory distress syndrome (ARDS): How much pressure should be applied to open a partially collapsed lung?
ARDS develops in people who suffer major injuries or are critically ill with diseases such as pneumonia or bacterial infections. Fluid builds up in the lungs until breathing becomes impossible. The death rate is close to 40 percent.
There is one at least partially effective treatment, positive end-expiratory pressure (PEEP), in which doctors force air into the lung to reverse the collapse. But PEEP remains something of a puzzle, because the response varies from patient to patient. A U.S. government-sponsored study two years ago found no difference in survival between patients given high or low levels of PEEP.
The reason for the puzzling result, according to an Italian team, is that the effect of PEEP varies according to the amount of "recruitable" (usable) lung tissue in different patients.
"In ARDS, the percentage of potentially recruitable lung is extremely variable and is strongly associated with the response to PEEP," noted a team led by Dr. Luciano Gattinoni of the Universita degli Studi di Milano, in Milan. The researchers published their findings in the April 27 issue of the New England Journal of Medicine.
"The question is whether opening the lung as much as possible helps," said Dr. Robert Hyzy, assistant professor of internal medicine at the University of Michigan, and an ARDS expert. "The issue of whether to open the lung in patients with lung injury is a controversial one."
The Italian researchers sought to settle the issue by using computed tomography to measure the amount of recruitable lung tissue in patients undergoing PEEP at different pressures. They found that many patients could not respond to an increase in PEEP pressure because they had very little recruitable tissue.
In those patients, the use of PEEP could cause damage by overexpanding the lungs, noted an accompanying editorial by Drs. Arthur S. Slutsky of the University of Toronto and Leonard D. Hudson of the University of Washington, in Seattle.
The Italian study "could possibly explain" the results of the U.S. trial, said Slutsky, who is professor of medicine, surgery and biomedical engineering at the University of Toronto.
The finding that PEEP did not improve survival in all patients "may be because higher levels of PEEP were used in all patients," he said. "It's possible that PEEP could have helped those patients who developed recruitment and made things worse for those who did not get any recruitment from the higher PEEP level."
The study "provides a potential solution to the problem of identifying which patients may benefit from PEEP," the editorial said. Doing computed tomography as pressure is increased "can be used to identify which collapsed units have a high potential for reopening," it said. "Hence, this approach could be used to identify which patients may benefit from higher levels of PEEP and which may potentially be harmed."
But there are questions to be answered, the editorial added. The PEEP pressure used in the Italian study might not be the best for monitoring patients; the researchers did not say how much recruitable tissue is needed for higher PEEP pressure to be used; and computed tomography is not practical in ordinary medical practice.
But the study does have a "major message," the editorial said: "Future studies investigating the optimal strategy for the setting of PEEP levels must take into account the degree to which the lungs can be recruited."
More information
For more on ARDS, head to the U.S. National Library of Medicine.
