One-Year Outcomes in Survivors of Acute Respiratory Distress Syndrome
Abstract & Commentary
Synopsis: In this prospective, longitudinal study of 195 patients, it was found that patients who survived acute respiratory distress syndrome (ARDS) have persistent functional limitation 1 year post-ICU discharge secondary to extrapulmonary limitation.
Source: Herridge M, et al. N Engl J Med. 2003;348:683-692.
Until recently, survival-to-hospital discharge was the primary outcome for critical care studies, but recently clinicians have become increasingly aware of the importance of measuring the quality of life in survivors of critical care illnesses. As survival rates improve among patients with acute respiratory distress syndrome (ARDS), there is a growing need to understand the long-term effects of this condition and its treatment. In the past, few studies have prospectively evaluated ARDS patients postdischarge in terms of their physiological, functional, and quality-of-life outcomes.
This was a prospective, longitudinal study in Canada evaluating 195 patients postdischarge from the hospital who had been diagnosed and treated for ARDS. The goal of this study was to characterize long-term pulmonary and extrapulmonary function in a prospectively identified cohort of patients with ARDS.
The inclusion criteria were age older than 16 years, PaO2:FiO2 ratio less than 200, PEEP of 5 cm H2O, chest roentgenograms (CXR) consistent with ARDS, and an identifiable risk factor for ARDS. The exclusion criteria were immobility prior to admission, pulmonary resection, or a previously documented neurological/psychiatric disease.
The severity of illness was determined using the APACHE II scores, the multiple organ dysfunction score (MODS), and the modified lung injury score. Outpatient follow-up was done at 3, 6, and 12 months postdischarge from the ICU.
The primary outcome measure of the study was the distance walked in 6 minutes 3, 6, and 12 months after discharge from ICU, and secondary outcome measures were evaluation of pulmonary function tests (PFTs) and quality of life. The rate of follow-up at 12 months was 86%.
The 1-year mortality rate of those patients who survived to hospital discharge was 11%. On discharge from the ICU, these patients were noted to have severe weight loss, mean of 18% of their baseline weight.
At 3 months, PFTs were consistent with a mild restrictive pattern and with a mild-moderate gas exchange abnormality as determined by DLCO. At 6 months, the spirometric and median lung volume measures had returned to within normal values. The DLCO, although improved by 9 percentage points over 1 year, was still mildly reduced. The 6-minute walk distance also improved over 1 year, but was still lower than predicted, with 6% of patients remaining hypoxic during the test (SaO2 < 88%). However, no patients required home oxygen at 1 year. A year postdischarge from the ICU, 49% of the patients were working and quality of life, as measured by the SF-36 score, improved as well.
Chest radiographs were normal in 80% of the patients at 1 year.
The results of univariate analysis demonstrated that a low Lung Injury Score (< 3) (P = 0.009), the use of systemic steroids in the ICU, the presence of illness acquired in the ICU, and the rate of resolution of MODS and Lung Injury were the most important determinants of the 6-minute walk score at 1 year. In the multivariate analysis, the most important determinants of 6-minute walk at 1 year were the slopes of the Lung Injury Score and MODS, the APACHE II on admission in ICU, and the presence of any illness acquired in the ICU. The only factor associated with a longer distance walked in 6 minutes at 1 year was rapid resolution of lung injury.
Comment by David Ost, MD, and Andreas Kyprianou, MD
Previous authors have retrospectively evaluated morbidity of ARDS survivors with PFTs1 and quality-of-life measures2 and most have found persistent morbidity on follow-up. This was the first prospective study to assess ARDS survivors and the long-term physiologic, functional, and quality-of-life outcomes. The conclusion of this study is that patients who survive ARDS have persistent functional limitation 1 year postdischarge from the hospital, primarily attributable to extrapulmonary disease, and to a much lesser extent due to intrinsic pulmonary morbidity as demonstrated by PFTs. Muscle fatigue and weakness was reported among the survivors of ARDS, as well as a 20% weight loss, so the possibility of an association between these may exist. In view of the above, critical-illness polyneuropathy or myopathy may also be an important contributing factor in determining the amount of functional recovery.
Dr. Kyprianou is Resident, New York Hospital Medical Center of Queens/Cornell Medical Program, New York, NY.
1 Ghio AJ, Jensen RL, et al. Am Rev Respir Dis. 1989; 139:1158-1162.
2 Angus DC, Clermont G, et al. Am J Respir Crit Care Med. 2001;163:818-829.