Chest
Volume 131, Issue 1, January 2007, Pages 206-213
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Original Research
Characteristics of Trapped Lung: Pleural Fluid Analysis, Manometry, and Air-Contrast Chest CT

https://doi.org/10.1378/chest.06-0430Get rights and content

Abstract

Study objectives:To review the pleural fluid characteristics, pleural manometry, and radiographic data of patients who received a diagnosis of trapped lung in our pleural diseases service.

Design:Retrospective case series.

Methods:The procedure records of 247 consecutive patients who underwent pleural manometry at the Medical University of South Carolina between October 2002 and November 2005 were reviewed. Eleven patients in whom a diagnostic pneumothorax was introduced were identified. Manometry data, radiographic findings, pleural fluid analysis, final clinical diagnosis, and information regarding the initial pleural insult were retrieved from the medical record.

Results:All 11 patients had a clinical diagnosis of trapped lung. The causes of trapped lung were attributed to coronary artery bypass graft surgery, uremia, thoracic radiation, pericardiotomy, spontaneous bacterial pleuritis and repeated thoracentesis, and complicated parapneumonic effusion. Mean pleural fluid pH was 7.30, pleural fluid lactate dehydrogenase (LDH) was 124 IU/L, and pleural fluid total protein was 2.9 g/dL. Pleural fluid was paucicellular with mononuclear cell predominance. Pleural space elastance was increased in all cases and ranged from 19 to 149 cm H2O/L of pleural fluid removed. All demonstrated abnormal visceral pleural thickness on air-contrast chest CT.

Conclusions:Trapped lung is a clinical entity characterized by the presence of a restrictive visceral pleural peel that was first described in 1967. The pleural fluid is paucicellular, LDH is low, and protein may be in the exudative range. The elevated total pleural fluid protein may be related to factors other than active pleural inflammation or malignancy and does not exclude the diagnosis.

Section snippets

Materials and Methods

We performed a retrospective review of 247 consecutive patients referred for therapeutic thoracentesis in our database at the Medical University of South Carolina between October 2002 and November 2005. We identified 11 patients in whom a diagnostic pneumothorax was performed in accordance with the clinical protocol that we established in 2001.

The clinical protocol we use routinely during pleural manometry requires a diagnostic pneumothorax to be performed when all of the following criteria are

Results

Eleven patients with a clinical diagnosis of trapped lung were identified in this series. The causes of trapped lung were attributed to coronary artery bypass graft surgery (CABG) in four patients, uremia in three patients, thoracic radiation in one patient, spontaneous bacterial pleuritis and multiple thoracenteses in one patient, pericardiotomy in one patient, and complicated parapneumonic effusion in one patient. Mean pleural fluid pH was 7.37 (range, 7.26 to 7.46). Mean pleural fluid

Background

At our pleural disease service, we are frequently asked to evaluate patients with chronic, persistent pleural effusions that have defied diagnosis and have undergone multiple thoracenteses. In our database, there were patients in whom a diagnostic pneumothorax was induced that provided a confident clinical diagnosis of trapped lung. The detection of a trapped lung was a direct consequence of the clinical protocol we introduced in 2001 that was designed for the evaluation of pleural effusion.

Conclusions

Trapped lung represents the end stage of dysfunctional healing of pleural injury that begins as a form of lung entrapment that results in the formation of a visceral pleural peel and a persistent pleural effusion. Trapped lung should be included in the differential diagnosis of patients with a remote pleural injury and in whom a chronic, radiographically stable pleural effusion without obvious cause is encountered. A high index of suspicion must be maintained in order to avoid repeated

References (13)

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None of the authors have any conflicts of interest to disclose.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (http://www.chestjournal.org/misc/reprints.shtml).

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