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Pleurodesis aims to achieve a symphysis between parietal and visceral pleural surfaces, in order to prevent accumulation of fluid or air in the pleural space. Its major indications are malignant effusions and pneumothorax, and a reexpandable lung is essential for the success of the technique. Moreover, expectation of a reasonably long survival is important before attempting pleurodesis.A successful lung re-expansion is unlikely if the pleural pressure falls more than 20 cmH 2 O·L -1 of fluid removed, because there is a central bronchial obstruction or the lung is trapped by tumour and/or fibrin. Pleural fluid pH (<7.20) is a good indicator of the presence of trapped lung; moreover, a successful pleurodesis is less likely when pH is low, and this parameter is also a good predictor for survival of the patients.Among the many sclerosing agents that have been used for pleurodesis, talc has achieved the best results, with an average success rate of approximately 90%. The cellular and biochemical mechanisms involved in pleurodesis may be specific to the agent used, however, they may all follow a common final pathway leading to activation of the pleural coagulation cascade, the appearance of fibrin networks, and the proliferation of fibroblasts. The details of these mechanisms are still unclear and need to be further elaborated. Eur Respir J 1997; 10: 1648-1654 The aim of pleurodesis is to achieve a symphysis between visceral and parietal pleural layers, in order to prevent accumulation of either air or fluid in the pleural space. Its main indications are malignant pleural effusions and pneumothorax. The choice of the right technique, sclerosing agent to be applied, criteria for selection of patients and evaluation of results are important and controversial issues. Furthermore, there is little information about the mechanisms that lead to pleural symphysis or the factors that influence the outcome of pleurodesis. Pleurodesis in malignant effusionsRecurrent effusions of malignant origin are by far the most common indication for pleurodesis in clinical practice. This is because there is a lack of effective antitumoral treatment at later stages of the disease, and because palliative measures are necessary to improve symptoms related to the pleural effusion. Repeated thoracenteses are not usually suitable, since they may be troublesome to the patient and provoke important protein loss (about 40 g·L -1 of pleural fluid that is withdrawn), with infection of the pleural space as an added risk.

Pleurodesis aims to obliterate the pleural space by producing extensive adhesion of the visceral and parietal pleura, in order to control relapse of either pleural effusions (mostly malignant) or pneumothorax. A tight and complete apposition between the two pleural layers is a necessary condition to obtain a successful pleurodesis, but – besides this mechanical aspect – there are many biological mechanisms that appear to be common to most of the sclerosing agents currently used. Following intrapleural application of the sclerosing agent, diffuse inflammation, pleural coagulation-fibrinolysis imbalance (favoring the formation of fibrin adhesions), recruitment and subsequent proliferation of fibroblasts, and collagen production are findings in the pleural space. The pleural mesothelial lining is the primary target for the sclerosant and plays a pivotal role in the whole pleurodesis process, including the release of several mediators like interleukin-8, transforming growth factor-β and basic fibroblast growth factor. When the tumor burden is high, normal mesothelial cells are scarce, and consequently the response to the sclerosing agent is decreased, leading to failure of pleurodesis. Also, the type of tumor in the pleural cavity may also affect the outcome of pleurodesis (diffuse malignant mesothelioma and metastatic lung carcinomas have a poorer response). There is general agreement that talc obtains the best results, and there are also preliminary experimental studies suggesting that it can induce apoptosis in tumor cells and inhibit angiogenesis, thus contributing to a better control of the malignant pleural effusion. There is concern about complications (possibly associated with talc but other agents as well) related to systemic inflammation and possible activation of the coagulation cascade. In order to prevent extrapleural talc dissemination, large-particle talc is recommended. Although it could – to some degree – interfere with the mechanisms leading to pleurodesis and a carefully balanced clinical decision has therefore to be made, prophylactic treatment with subcutaneous heparin is recommended during hospitalization (immediately before and after the pleurodesis procedure).