Pleural effusion refers to the effusion of fluid into the pleural space. The pleural space normally contains approximately 5 to 20 ml of fluid. The pH, glucose and electrolytes of the fluid are equilibrated with plasma, but the fluid is relatively protein-free. The fluid is the result of the hydrostatic-oncotic pressure of the capillaries of the parietal pleura. About 80-90% of the fluid is reabsorbed by the pulmonary venous capillaries of the visceral pleura, and the remaining 10-20% is reabsorbed by the pleural lymphatic system. The turnover of fluid in the pleural space is normally quite rapid--roughly 35 to 75% per hour, so that 5 to 10 liters of fluid move through the pleural space each day.
A disruption in the balance between the movement of fluid into the pleural space and the movement of fluid out of the pleural space may produce excessive fluid accumulation in the pleural space. Such disruptions may include, for example, (1) increased capillary permeability resulting from inflammatory processes such as pneumonia, (2) increased hydrostatic pressure as in congestive heart failure, (3) increased negative intrapleural pressure as seen in atelectasis, (4) decreased oncotic pressure as occurs in the nephrotic syndrome with hypoalbuminemia, and (5) increased oncotic pressure of pleural fluid as occurs in the inflammation of pleural tumor growth or infection. Pleural effusion is particularly common in patients with disseminated breast cancer, lung cancer or lymphatic cancer and patients with congestive heart failure, but also occurs in patients with nearly all other forms of malignancy.
The clinical manifestations of pleural effusion include dyspnea, cough and chest pain which diminish the patient's quality of life. Although pleural effusion typically occurs toward the end of terminal malignancies such as breast cancer, it occurs earlier in other diseases. Therefore relieving the clinical manifestations of pleural effusion is of a real and extended advantage to the patient. For example, non-breast cancer patients with pleural effusion have been known to survive for years. See "Pleural Effusion in Cancer Patients", Izbicki, et al., Cancer October 1975, p. 1511.
There are a number of treatments for pleural effusion. If the patient is asymptomatic and the effusion is known to be malignant or paramalignant, treatment may not be required. Such patients may develop progressive pleural effusions that eventually do produce symptoms requiring treatment, but some will reach a stage where the effusions and reabsorption reach an equilibrium that is still asymptomatic and does not necessitate treatment.
Pleurectomy and pleural abrasion is generally effective in obliterating the pleural space and, thus, controlling the malignant pleural effusion. This procedure is done in many patients who undergo thoracotomy for an undiagnosed pleural effusion and are found to have malignancy, since this would prevent the subsequent development of a symptomatic pleural effusion. However, pleurectomy is a major surgical procedure associated with substantial morbidity and some mortality. Therefore, this procedure is usually reserved for patients with an expected survival of at least several months, who are in relative good condition, who have a trapped lung, or who have failed a sclerosing agent procedure.
In general, systemic chemotherapy is disappointing for the control of malignant pleural effusions. However, patients with lymphoma, breast cancer, or small cell carcinoma of the lung may obtain an excellent response to chemotherapy.
Another approach to removing fluid from the pleural space is to surgically implant a chest tube. Such tubes are commonly quite rigid and fairly large in diameter and are implanted by making a surgical incision and spreading apart adjacent ribs to fit the tube into place. Such procedures are painful to the patient, both initially when the chest tube is inserted and during the time it remains within the pleural space.
Thoracentesis is a common approach to removing pleural fluid, in which a needled catheter is introduced into the pleural space through an incision in the chest cavity and fluid is positively drawn out through the catheter using a syringe or a vacuum source. The procedure may also include aspiration utilizing a separate syringe. There are a number of difficulties in thoracentesis, including the risk of puncturing a lung with the catheter tip or with the needle used to introduce the catheter, the risk of collapsing a lung by relieving the negative pressure in the pleural space, the possibility of aggravating the pleural effusion by stimulating fluid production in the introduction of the catheter, and the risk of infection. One of the primary difficulties with ordinary thoracentesis procedures is that fluid reaccumulates in the pleural space relatively quickly after the procedure is performed, and so it is necessary to perform the procedure repeatedly--as often as every few days. In fact, some studies found that the fluid re-accumulates in one to three days in most cases and re-accumulates within a month in 97% of the cases studied. See "Diagnosis and Treatment of Malignant Pleural Effusion", F. J. Hausheer, J. W. Yarbro, Seminars in Oncology, March 1985, p. 54; "Malignant Effusion", Anderson, et al., Cancer, April 1974, p. 916. Of course, each time the procedure is repeated the risks identified above are heightened. Moreover, the comfort to the patient resulting from the procedure begins to be offset by the discomfort of the procedure itself.
There is therefore a need for a treatment method for removing pleural effusion which does not require repeated invasion of the pleural space in a manner which produces repeated patient discomfort, infection risks, risks of accidental trauma to the lungs, and the potential for stimulating fluid production. Ideally, such a method and apparatus would employ instruments that are relatively simple in design and manufacture and would be within the capabilities of ordinary physicians to use, and would involve at least the possibility of reducing future pleural effusion.