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Christopher N. Schmickl, MD, MPH; Michelle Biehl, MD; Gregory A. Wilson, RRT; Ognjen Gajic, MD, FCCP
Author and Funding Information

From M.E.T.R.I.C. (Multidisciplinary Epidemiology and Translational Research in Intensive Care) (Drs Schmickl, Biehl, and Gajic and Mr Wilson), Division of Pulmonary and Critical Care Medicine, and the Department of Pulmonary and Critical Care Medicine (Drs Biehl and Gajic), Mayo Clinic, Rochester, MN; and the University Witten-Herdecke (Dr Schmickl), Witten, Germany.

CORRESPONDENCE TO: Christopher N. Schmickl, MD, MPH, Schnieglinger strasse 225, 90427 Nuremberg, Germany; e-mail: christopher.schmickl@mail.harvard.edu


CONFLICT OF INTEREST: None declared.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2015;148(6):e194-e195. doi:10.1378/chest.15-0037
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To the Editor:

We would like to thank Drs Ijaz and Adrish for their interest in our study1 and their insightful comments. We agree that lung-protective ventilation and severity of ARDS are important determinants of ARDS mortality. Unfortunately, we did not have these data available for inclusion into our analysis. However, the quoted (hospital) mortality rates of 27%, 32%, and 45% in mild, moderate, and severe ARDS, respectively, are based on a meta-analysis of very heterogeneous datasets partially predating the lung-protective ventilation era as well.2 Some 55% of the data were from randomized controlled trials enrolling patients from 1996 to 2005 with a mean age of 51 years and mortality of 30%, and 35% of the data were from population-based cohorts enrolling patients from 1999 to 2000 with a mean age of 61 years and mortality of 34% to 37%. In comparison, we enrolled patients on a population basis from 2006 to 2009, who were older (mean/median age, 68/72 years) and had a mortality of 43%.1

Randomized controlled trials generally report lower mortality rates than observational studies, which is likely owed to their inclusion and exclusion criteria optimizing internal validity but limiting external validity (“generalizability”).2,3 The slightly higher mortality compared with the previously mentioned population-based studies is somewhat surprising, given that the mean tidal volume (in milliliter per kilogram of predicted body weight) significantly decreased at our institution from 10.6 in 2001 to 6.8 in 2008,4 but this is likely explained by the age difference.3 Although there is little dispute that ARDS incidence is downtrending,4 two meta-analyses reached opposite conclusions about whether ARDS mortality in the past decades decreased or remained the same.3,5 Our results seem to support latter conclusions, but in any case we agree with Drs Ijaz and Adrish that ARDS remains a deadly disease with a very high mortality.

Regarding long-term mortality, there was an error in the Online First version of the article causing some confusion, for which we apologize, and we are grateful to Drs Ijaz and Adrish for pointing this out: Long-term mortality in the acute lung injury (ALI)/ALI + cardiogenic pulmonary edema (CPE) group was 60% (53 of 88) compared with 65% (92 of 141) in the CPE group (P = .44). [In Table 1, columns 2 and 3 were reversed on row “Long-term mortality” in the final version to correct for this error.] After adjusting for potential confounders, the hazard ratio for ALI vs CPE was 1.13 (95% CI, 0.79-1.62; P = .5). This difference is both statistically and—in our opinion—clinically nonsignificant.

References

Schmickl CN, Biehl M, Wilson GA, Gajic O. Comparison of hospital mortality and long-term survival in patients with acute lung injury/ARDS vs cardiogenic pulmonary edema. Chest. 2015;147(3):618-625. [CrossRef] [PubMed]
 
Ranieri VM, Rubenfeld GD, Thompson BT, et al; ARDS Definition Task Force. Acute respiratory distress syndrome: the Berlin Definition. JAMA. 2012;307(23):2526-2533. [PubMed]
 
Phua J, Badia JR, Adhikari NK, et al. Has mortality from acute respiratory distress syndrome decreased over time? A systematic review. Am J Respir Crit Care Med. 2009;179(3):220-227. [CrossRef] [PubMed]
 
Li G, Malinchoc M, Cartin-Ceba R, et al. Eight-year trend of acute respiratory distress syndrome: a population-based study in Olmsted County, Minnesota. Am J Respir Crit Care Med. 2011;183(1):59-66. [CrossRef] [PubMed]
 
Zambon M, Vincent JL. Mortality rates for patients with acute lung injury/ARDS have decreased over time. Chest. 2008;133(5):1120-1127. [CrossRef] [PubMed]
 

Figures

Tables

References

Schmickl CN, Biehl M, Wilson GA, Gajic O. Comparison of hospital mortality and long-term survival in patients with acute lung injury/ARDS vs cardiogenic pulmonary edema. Chest. 2015;147(3):618-625. [CrossRef] [PubMed]
 
Ranieri VM, Rubenfeld GD, Thompson BT, et al; ARDS Definition Task Force. Acute respiratory distress syndrome: the Berlin Definition. JAMA. 2012;307(23):2526-2533. [PubMed]
 
Phua J, Badia JR, Adhikari NK, et al. Has mortality from acute respiratory distress syndrome decreased over time? A systematic review. Am J Respir Crit Care Med. 2009;179(3):220-227. [CrossRef] [PubMed]
 
Li G, Malinchoc M, Cartin-Ceba R, et al. Eight-year trend of acute respiratory distress syndrome: a population-based study in Olmsted County, Minnesota. Am J Respir Crit Care Med. 2011;183(1):59-66. [CrossRef] [PubMed]
 
Zambon M, Vincent JL. Mortality rates for patients with acute lung injury/ARDS have decreased over time. Chest. 2008;133(5):1120-1127. [CrossRef] [PubMed]
 
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