Trapped lung results from a remote inflammatory process leading to development of a fibrous pleural membrane on the visceral pleura which prevents normal lung expansion. Pleural fluid persistence is due to hydrostatic equilibrium in the presence of an irreducible pleural space. Diagnosis of trapped lung implies chronicity and the absence of active inflammation or bronchial obstruction. Pleural fluid analysis, manometry, and radiographic data of 10 patients with trapped lung are presented.
Manometry was performed on 202 consecutive patients referred for therapeutic thoracentesis at the Medical University of South Carolina between 10/2001 and 3/2005. Mean pleural liquid pressure (Ppl) was obtained initially and at aliquots of 50-250cc. In the absence of malignancy or active pleural inflammation, air is introduced to allow for safe removal of all pleural fluid and to evaluate visceral pleura thickness by CT.
Abbreviations: C= cirrhosis, L=lymphocyte, Mac= macrophages, NC= nucleated cells, CS=Cardiac Surgery,Plp= pleural liquid pressure, U=Uremia, R=Radiation, *=lab error, ** PLel= pleural space elastance (pressure change)/(volume removed); cmH2O/L.
Prevalence of trapped lung was 10/202 (5%). Cardiac surgery was the most common cause partially due to its frequency. All cases had evidence of visceral pleural restriction with PLel≥16 cmH2O and visceral pleural thickening by air-contrast CT. Pleural fluid protein values greater than 4 mg/dl were seen in two cases suggesting abnormal protein transport. Cell counts were low with lymphocyte predominance in most. Together with a low LDH, these findings indicate minimal or absent pleural inflammation. The present series documents a benign and chronic clinical and pathophysiological syndrome distinct from the more common active malignant or infectious pleural processes complicated by lung entrapment.
The diagnosis of trapped lung requires documentation of visceral pleural restriction by pleural manometry or CT combined with the history of a remote inflammatory insult. Pleural fluid analysis typically reveals a transudate with a paucity of nucleated cells, although the protein level at times may be slightly above the cut-points due to abnormal protein transport.
John Huggins, None.
Pleural Fluid Characteristics of Trapped LungCase12345678910DiagnosisCSUCSCSUCSCUCSRpH7.447.427.267.337.38*7.397.467.407.33Total protein (g/dl)22.214.171.124.64.12.02.02.03.22.8LDH9911410015317013210715557118NC214192183714831523553821352213Differential64% Mac94% L96% L39% L67% L63% L70% L74% Mac76% L69% LInitial Plp(cmH2O)-2.7-8.0-34.0+6.6-1.0+3.0+4+2.2+4.5-1.2PLel ** (cmH2O/L)241498619304222171689