TORONTO (FRONTLINE MEDICAL NEWS) – The incidence of acute respiratory distress syndrome (ARDS) is on the decline, according to a retrospective, population-based cohort study conducted at the Mayo Clinic in Rochester, Minn.

“This is very promising data in combating this syndrome,” reported Augustin Joseph of the Mayo Clinic, and “it suggests that ARDS may in part be a completely preventable disease.”

This study was inspired by a previous effort by Guangxi Li et al. who conducted a population-based cohort study on trends in ARDS using data from the Olmsted County (Minn.) Epidemiology Project from 2001 to 2008. ( Am J Respir Crit Care Med. 2011;183:59-66 ). At that time, a steady and significant decline in ARDS incidence was noted, attributable to a reduced incidence of hospital-acquired ARDS. “We attributed this to improvements in hospital practices and management of ARDS and all the research that’s been done over the past 2 decades,” Mr. Joseph said at the CHEST annual meeting.

To see if ARDS incidence has continued to decline, Mr. Joseph’s group studied all patients admitted during 2009-2014 to the Mayo Clinic’s ICU, the only facility in the county that cares for ARDS patients. From 82,388 ICU admissions, they identified 505 patients with ARDS according to the Berlin definition of ARDS developed in 2012.

The number of annual cases dropped from 108 in 2009 to 59 in 2014, and the incidence steadily declined from 74.5 cases per 100,000 in 2009 to 39.3 per 100,000 in 2014.

Median age was 67 years in 2009 and 62 years in 2014. Hospital mortality ranged from 15% to 26% during the study period, while hospital length of stay ranged from 8 to 15 days, with no clear decline in either.

“For hospital and ICU mortality and hospital and ICU length of stay, we did not see much difference [from 2009 to 2014], so the overall picture between the Guangxi Li study and mine was that we did not see much of a difference in the patients who had ARDS, but [in terms of] preventing ARDS, the incidence has continued to decline,” Mr. Joseph reported.

While the earlier study used the American-European Consensus Conference (AECC) definition of ARDS, Mr. Joseph and his colleagues diagnosed ARDS according to the Berlin definition. One of the major changes seen in the new Berlin rules is that acute lung injury no longer exists and patients with a P/F ratio (PaO2/FiO2 ratio, or the ratio of arterial oxygen partial pressure to fractional inspired oxygen) between 200 and 300 are now considered to have “mild ARDS,” Mr. Joseph explained. With the AECC definition, a P/F ratio in this range was classified as acute lung injury and only one less than 200 was considered ARDS.

The researchers are now trying to parse out how changing ARDS diagnosis and management at their institution might be contributing to declining incidence, said Mr. Joseph.