Incidence of Acute Lung Injury Higher Than Previously Thought

There may be a lot more cases of acute lung injury in the United States than previous estimates suggested—perhaps 2.5 to five times as much.

An estimated 190,600 cases of acute lung injury occur each year that result in 3.6 million hospital stays and 74,500 deaths, Gordon D. Rubenfeld, M.D., and colleagues of the University of Washington here reported in the Oct. 20 issue of the New England Journal of Medicine.

The yearly mortality rate of 24% to 60%, depending on age, is on par with that of breast cancer or HIV infection, they asserted. Their study was the first large prospective investigation of the incidence and mortality associated with acute lung injury in the U.S.

The researchers analyzed data for 1,113 patients, 15 years or older, admitted to hospitals in the King County (Seattle) area between April 1999 and July 2000 who met the consensus criteria for acute lung injury.

These criteria include the presence of acute hypoxemia with a ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen of 300 mm Hg or less, bilateral infiltrates seen on a frontal chest radiograph that are consistent with pulmonary edema, and/or no clinical evidence of left atrial hypertension or a pulmonary artery wedge pressure of 18 mm Hg or less.

Although criteria for identifying acute lung injury were developed by the American-European Consensus Conference on Acute Respiratory Distress Syndrome (ARDS) in 1994, controversy still surrounds their validity. In addition, variations in clinician knowledge, practice, and interpretation of chest films make acute lung injury difficult to identify.

Acute lung injury and ARDS occur primarily in elderly patients hospitalized in intensive care units for severe infection, most often pneumonia. Sepsis, from a pulmonary or non-pulmonary source, is the most common risk factor.

Average follow up in the study was one year. Key findings included:

The age-adjusted incidence of acute lung injury was 86.2 per 100,000 person-years.
The in-hospital mortality rate for acute lung injury was 38.5%. (95% confidence interval=34.9-42.2).
The incidence of acute lung injury increased with age. For patients 15 to 19 years old, the incidence was 16 per 100,000 person-years. For patients 75 to 84 years old, the incidence was 306 per 100,000 person-years. (P<.001 for trend.)
Mortality also increased with age. For patients 15 to 19 years old, the mortality rate was 24%. For patients 85 or older, the mortality rate was 60% (P<.001 for trend).

“On the basis of our results, acute lung injury and ARDS occur with a higher incidence than previously reported and therefore have a substantial impact on public health in the United States,” the study authors concluded. “Data from population-based epidemiologic studies of critical illnesses are essential for understanding the mechanism, trends, and burden of these diseases.”

More practical screening approaches for acute lung injury must be developed and implemented in the care of critically ill patients said Margaret S. Herridge, M.D., M.P.H., of the University of Toronto, and Derek C. Angus, M.D., M.P.H., of the University of Pittsburgh, in an editorial.

“In the meantime, all clinicians caring for critically ill patients at the bedside must remain vigilant about identifying patients with these syndromes,” they advised.

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