By Betty Tran, MD, MS, Assistant Professor of Medicine, Pulmonary and Critical Care Medicine, Rush University Medical Center, Chicago. Dr. Tran reports no financial relationships relevant to this field of study.
Synopsis: This study reports a correlation between the degree of abnormalities on high-resolution chest CT and both restrictive pulmonary dysfunction and poorer health-related quality of life among survivors of acute lung injury.
Source: Burnham EL, et al. Chest computed tomography features are associated with poorer quality of life in acute lung injury survivors. Crit Care Med 2013;41:445-456.
This collaborative study using data from a randomized controlled trial of acute lung injury (ALI) sought to determine whether pulmonary dysfunction contributed to poorer quality of life among survivors of ALI at 6 months and whether abnormalities on chest high-resolution CT (HRCT) were associated with and could predict its development.
The authors included 89 patients with ALI who had 180-day pulmonary function testing (PFT) and day 14 and/or day 180 chest HRCTs performed. They specifically excluded patients with a known history of underlying chronic obstructive pulmonary disease and interstitial lung disease. A radiologic score was developed to quantify the extent of a radiographic pattern (ground-glass opacification, intense parenchymal opacification, and reticulation) seen throughout the lungs. Higher chest HRCT scores indicated more radiographic involvement by a given pattern. Quality-of-life outcomes were measured at 180 days using the short form (SF)-36 and St. George’s respiratory questionnaires (SGRQ).
Of the 47 patients who had day 180 PFTs and chest HRCTs, overall HRCT scores were associated with decreased total lung capacity ([TLC] r = -0.60, P = 0.003). Higher day 180 HRCT scores were associated with poorer SF-36 physical function, role physical, and physical health subtotal scores (r = -0.4, P = 0.01 for all comparisons) and poorer SGRQ activity, impact, and total scores (r = 0.5-0.6, P < 0.05 for all comparisons). Both lower PFT parameters and higher HRCT scores at 180 days were associated with some pulmonary factors such as higher average plateau pressure exposure and a diagnosis of pneumonia as a risk factor for ALI. In multivariable models, forced vital capacity (FVC) was the only variable associated with poorer SF-36 physical health subtotal and SGRQ total scores; there was a trend of higher day 180 chest HRCT scores correlating with poorer SGRQ total scores, but this was not statistically significant.
Data from 43 patients who had chest HRCTs at day 14 revealed that higher HRCT scores were associated with lower TLC (r = -0.60, P = 0.0001), poorer SF-36 physical function, role physical, and physical health subtotal scores (r = -0.4 to -0.5, P < 0.05 for all comparisons), and poorer SGRQ activity, impacts, and total scores (r = 0.5-0.6, P < 0.05 for all comparisons). Higher day 14 HRCT scores were associated with fewer ventilator, ICU, and hospital-free days. In multivariable analyses, day 14 chest HRCT scores remained independently associated with lower SF-36 and poorer SGRQ scores measured at day 180.
The authors attempt to address whether the poorer quality of life and functional impairment seen in survivors of ALI can be attributable to pulmonary dysfunction rather than neuromuscular weakness, the latter of which has been and continues to be extensively studied. Results of the current study, however, are unable to make this distinction definitively. Only a modest number of ALI patients were included from the parent trial, and it is not surprising that the presence of day 180 HRCT abnormalities correlated with abnormal PFTs performed at the same time. However, the data examining the association between day 180 HRCT scores and poorer quality of life are limited by the fact that most chest HRCTs had normalized over the 6-month follow-up period, with wide variability in quality of life among those who had, on average, low HRCT scores. As a result, the regression lines used to model the association between day 180 chest HRCT scores and SF-36 and SGRQ scores appear to be overly influenced by a few data points, representing the very small number of patients who had more abnormal HRCTs 6 months after ALI diagnosis. Furthermore, the observation that day 180 FVC was the only variable significantly associated with poorer quality of life rather than HRCT scores in multivariable analyses suggests that nonpulmonary factors (e.g., neuromuscular weakness) may be playing a larger role.
Significant associations between day 14 chest HRCT scores with lung function and quality of life 6 months later were observed, although it is difficult to attribute these outcomes causatively to pulmonary dysfunction. It is conceivable that patients with more abnormal CTs 2 weeks into their ALI course were sicker (as evidenced by fewer ventilator, ICU, and hospital-free days in this group) and subsequently had longer rehabilitation times, higher rates of neuromuscular weakness, and poorer quality of life. The lack of formal nerve conduction/electromyographic testing for any of the patients was a significant limiting factor in eliminating neuromuscular dysfunction as a potential contributor to the observed associations. Overall, although this study was limited in its ability to delineate between pulmonary and neuromuscular etiologies for abnormal PFTs and poor quality of life among ALI survivors, the question is an important one to address as the answer could result in different therapeutic options that are offered.