Volume and cellular content of normal pleural fluid in humans examined by pleural lavage

Currently, no reliable data are available on the volume or on the cellular content of pleural fluid in normal humans. In analogy with bronchoalveolar lavage (a technique enabling retrieval of small volumes of epithelial lining fluid from the lung), we developed a pleural lavage (PL) technique consisting of injection and retrieval of 150 ml of saline into the right pleural space, performed during a thoracoscopic sympathicolysis procedure in otherwise healthy subjects suffering from essential hyperhidrosis. With urea used as an endogenous marker of dilution, measured mean right-sided pleural fluid volume was 8.4 +/- 4.3 ml. In a subgroup of subjects, we confirmed that right- and left-sided pleural fluid volumes were similar. Expressed per kilogram of body mass, total pleural fluid volume in normal, nonsmoking humans is 0.26 +/- 0.1 ml/kg. Total cell count in the PL fluid of nonsmoking normal subjects yielded a median of 91 x 10(3) white blood cells (WBC) per milliliter of lavage fluid (interquartile range [IR] = 124 x 10(3) cells/ml). Taking into account a measured dilution factor of 18.86, the total WBC count in the original pleural fluid was 1,716 x 10(3) cells/ml. Differential cell counts yielded a predominance of macrophages (median: 75%; IR: 16%) and lymphocytes (median: 23%; IR: 18%). Mesothelial cells (median: 1%; IR: 2%), neutrophils (median: 0%; IR: 1%), and eosinophils (median: 0%; IR: 0%) were only marginally present. There were no significant differences between males and females or between right- and left-sided pleural fluid in total and differential cell counts. In contrast, in smokers a small but statistically significant increase in pleural fluid neutrophils (median: 1%; IR: 2%; p < 0.015) was observed. In conclusion, PL performed during thoracoscopy for sympathicolysis allowed for the first time determination of the volume and of the total and differential cell contents of the pleural fluid present in normal human pleura.