Trapped lung and refractory pleural effusion in a patient receiving peritoneal dialysis.

Dear Editor, Patients with chronic kidney disease often develop pleural effusion [1], although the latter can also develop in a variety of other conditions [2]. One of these is trapped lung, which may often go undetected. To our knowledge, no case of trapped lung in a patient undergoing regular peritoneal dialysis has been documented in detail hitherto. A 65-year-old male patient with renal failure had been receiving peritoneal dialysis for 6 years before presentation. Although his clinical course had been uneventful, chronic unilateral right pleural effusion had developed several months previously. Therefore, his dose of diuretics had been increased, and the dialysate converted to one with a high glucose concentration. However, the pleural fluid persisted. He was advised to switch to hemodialysis, but declined to do so, mostly because of difficulty with frequent hospital visits. As the pleural fluid was unresponsive to thoracentesis, we performed catheter insertion and drained the fluid sufficiently. During the entire period of drainage, there were no signs suggestive of pneumothorax such as air leakage. Chest computed tomography was performed and this allowed us to make a diagnosis of trapped lung (Figure 1). We suspected that air had entered the thoracic cavity via the catheter from outside as a result of negative pressure that had developed due to the trapped lung. Culture of the pleural fluid was negative for bacteria and mycobacteria, and no malignant cells were evident. The concentration of glucose in the pleural fluid was quite low relative to that of the dialysate, suggesting a lack of pleuroperitoneal communication. After removal of the catheter, the pleural effusion increased again to the previous level within a short period. We started the patient on hemodialysis, but despite intensified body fluid removal, the pleural effusion remained. As the patient complained of only mild exertional dyspnea, we decided that close observation alone would be appropriate. Trapped lung is a condition in which a fibrous layer of visceral pleura surrounds the lung and restricts its expansion [3], resulting in excessive negative intrapleural pressure, and constant formation of pleural fluid. This condition can be associated with several diseases, including pleural infections such as empyema or parapneumonic effusion, immunologic pleuritis, hemothorax, radiation pleuritis or uremia. The present patient's clinical course suggested that no causes other than renal failure had triggered the pleural thickening or the trapped lung. As a relationship between pleural fibrosis and renal failure has been described in the context of uremic pleuritis [4], it may be rational to consider that inadequate efficacy of dialysis might contribute to pleural thickening through sustained pleural inflammation. Therefore, we speculate that if hemodialysis had been started earlier in the present case, it may have prevented development of the trapped lung. However, regardless of the initial cause, persistent pleural fluid accumulation itself may lead to pleural thickening. Therefore, to avoid the development of trapped lung, it may be important to ensure that pleural effusion does not go untreated.