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. 2015 Sep;79(3):417-24.
doi: 10.1097/TA.0000000000000760.

Misclassification of acute respiratory distress syndrome after traumatic injury: The cost of less rigorous approaches

Carolyn M Hendrickson  1 , Sarah Dobbins, Brittney J Redick, Molly D Greenberg, Carolyn S Calfee, Mitchell Jay Cohen
Affiliations

Misclassification of acute respiratory distress syndrome after traumatic injury: The cost of less rigorous approaches

Carolyn M Hendrickson et al. J Trauma Acute Care Surg. 2015 Sep.

Abstract

Background: Adherence to rigorous research protocols for identifying adult respiratory distress syndrome (ARDS) after trauma is variable. To examine how misclassification of ARDS may bias observational studies in trauma populations, we evaluated the agreement of two methods for adjudicating ARDS after trauma: the current gold standard, direct review of chest radiographs and review of dictated radiology reports, a commonly used alternative.

Methods: This nested cohort study included 123 mechanically ventilated patients between 2005 and 2008, with at least one PaO2/FIO2 less than 300 within the first 8 days of admission. Two blinded physician investigators adjudicated ARDS by two methods. The investigators directly reviewed all chest radiographs to evaluate for bilateral infiltrates. Several months later, blinded to their previous assessments, they adjudicated ARDS using a standardized rubric to classify radiology reports. A κ statistics was calculated. Regression analyses quantified the association between established risk factors as well as important clinical outcomes and ARDS determined by the aforementioned methods as well as hypoxemia as a surrogate marker.

Results: The κ was 0.47 for the observed agreement between ARDS adjudicated by direct review of chest radiographs and ARDS adjudicated by review of radiology reports. Both the magnitude and direction of bias on the estimates of association between ARDS and established risk factors as well as clinical outcomes varied by method of adjudication.

Conclusion: Classification of ARDS by review of dictated radiology reports had only moderate agreement with the current gold standard, ARDS adjudicated by direct review of chest radiographs. While the misclassification of ARDS had varied effects on the estimates of associations with established risk factors, it tended to weaken the association of ARDS with important clinical outcomes. A standardized approach to ARDS adjudication after trauma by direct review of chest radiographs will minimize misclassification bias in future observational studies.

Level of evidence: Diagnostic study, level II.

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Conflict of interest statement

Conflicts of Interest: The authors have no relevant conflicts of interest to disclose.

Figures

Figure 1
Figure 1. Agreement of two adjudication methods for ARDS after traumatic injury
Raw data is shown to demonstrate the agreement of two adjudication methods of ARDS after traumatic injury in intubated, hypoxemic patients (1A). From the raw data Kappa statistics can be calculated under a variety of schemata to handle the equivocal subjects (1B). In the weighted Kappa (†) calculation, equivocal subjects were assigned 0.5 agreement with either positive or negative findings by alternative method. The two adjudication methods show only moderate agreement under all classification schemata.
Figure 2
Figure 2. Association of ARDS and Clinical Outcomes in Linear Regression Models
Graphical presentation of findings from linear regression models showing the point estimates and 95%CI of the β coefficients on the ARDS predictor variable for various clinical outcomes. All analyses excluded patients who died. Each style of marker represents a different method for adjudicating ARDS in hypoxemic trauma patients: direct review of chest radiographs, systematic evaluation of dictated reports of chest radiographs, and use of hypoxemia alone without consideration of chest radiograph findings. Multivariate models are adjusted for and injury severity score (ISS). The findings for the outcome Ventilator-Free Days were similar to ventilator days (Table 4B) but are not graphed here in order to streamline the visual presentation by limiting the range of values on the y-axis.
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