title: Occult pneumothoraces in acute trauma patients.
abstract: BACKGROUND
  Many traumatic pneumothoraces (PTX) are not seen on initial chest radiograph (CR) (occult PTX) but are detected only on computed tomography (CT). Although CR remains the first tool for detecting PTX, most trauma patients with significant thoracoabdominal injuries will receive both CT and CR. The primary objective of this study was to retrospectively determine the effectiveness of CR for detecting PTX in trauma patients. Our hypotheses were that CR is a sensitive indicator of PTX on CT, that chest pain and shortness of breath are good predictors of PTX on CR, and that we could determine other predictors of PTX on CR.
  
  
  METHODS
  All trauma patients presenting to our Level I trauma center with a CT-diagnosed PTX over a 2-year period who had both a CR and a chest CT were included. The CT reading was considered the gold standard for PTX diagnosis. Electronic medical records were searched using key words for diagnoses, symptoms, demographics, and radiologic results. We recorded the official radiologist readings for both CR and CT (positive or negative) and the size of the PTX on CT (large, moderate, small, or tiny). The outcome variable was dichotomized based on presence or absence of PTX detected on CR. Descriptive statistics and χ(2) tests were used for univariate analysis. A regression analysis was performed to determine characteristics predictive of a PTX on CR, and 1 variable was added to the model for every 10 positive CRs. With equal-size groups, this study has the power of 80% to detect a 10% absolute difference in single predictors of PTX on CR with 45 subjects in each group.
  
  
  RESULTS
  There were 134 CT-documented PTXs included in the study. Mean age was 42, and 74% were men. For 66 (49%) patients, PTX was detected on CR (sensitivity = 50%). The CR detected 30% of small PTX, 35% of moderate PTX, and 33% of large PTX. Comparing patients with and without PTX on CR, there were no significant differences in shortness of breath or chest pain. There no relationships between PTX detected on CR and age, gender, penetrating versus blunt injury, bilaterality of the PTX, or presence of lung contusion or hemothorax on CT. After adjusting for all significant variables, predictor of a PTX detected on CR was air in the tissue on CR (adjusted odds ratio [OR] = 3.8) and PTX size (compared to a tiny PTX, adjusted OR = 2.0 for a small PTX, 7.5 for a moderate PTX, and 51 for a large PTX). Chest tubes were used in 89% of patients with PTX on CR and 44% of patients with PTX only on CT (difference 45%; 95% confidence interval 30, 58).
  
  
  CONCLUSIONS
  Factors associated with PTX on CR included air in the soft tissue on CR and size of the PTX. Even when PTX is not apparent on CR, 44% of these PTXs received placement of a chest tube.
authors: University of New Mexico, Department of Emergency Medicine, Albuquerque, New Mexico.
authors: Amy A
authors: AA
authors: Ernst
authors: William A
authors: WA
authors: McIntyre
authors: Steven J
authors: SJ
authors: Weiss
authors: Chad
authors: C
authors: Berryman