Normal volume and cellular contents of pleural fluid.

Because of the technical difficulties in obtaining a-traumatical access to the normal pleural space, the exact volume and cellular content of normal pleural fluid in humans were still unknown until very recently, and animal-derived extrapolation data had to be used. After having developed a minimally invasive thoracoscopic technique for performing sympathectomy in patients suffering from essential hyperhidrosis, but with otherwise absence of thoracic disease, we have been able to achieve minimally traumatic access to normal pleural spaces. Using pleural lavage, a technique consisting of injection and immediate aspiration of 150 mL of prewarmed saline into the pleural space, we were able to determine the total and differential cell content of the few milliliters of original pleural fluid. The exact volume of this original pleural fluid could be measured using urea as an endogenous marker of dilution. Expressed per kilogram of body mass, total pleural fluid volume in healthy, non-smoking humans was 0.26+/-0.1 mL kg(-1). Total white blood cell count (after correction for dilution) was 1.716 x 10(3) cells mL(-1). Differential cell counts yielded median 75% (IR 16%) macrophages, 23% (IR 18%) lymphocytes, and marginally present mesothelial cells (1%, IR 2%), neutrophils (0%, IR 1%) and eosinophils (0%, IR 0%). There was no significant correlation between age and pleural lavage results in a study population aged 17 to 54 years old, which suggests that these results may be extrapolated to the situation in children and adolescents.