Diagnosing Pleural Effusion
Diagnosis is usually accomplished with a simple chest x-ray, although further radiographic tests may be needed to confirm the presence of pleural fluid. Ultrasound and CT scan (computed tomography) of the chest are often used to confirm pleural effusion. A special chest x-ray technique, a lateral decubitus film, can confirm the presence of fluid and enable the physican to make an estimate of the amount. This x-ray technique is performed with the patient lying on his or her side, allowing the free-flowing fluid to shift in the chest. It can be seen pooling along the side wall of the chest and measuring the depth of the fluid gives an idea of how much fluid is present.
It is often necessary to obtain a fluid sample to determine the underlying cause of fluid accumulation. When the cause is obvious, such as severe congestive heart failure, and fluid has accumulated in both sides of the chest, a therapeutic trial directed at the underlying disease may resolve the underlying condition, and sampling is not necessary. Because the causes of pleural fluid range from benign to critical, samples of the fluid are usually taken. This is usually accomplished through a procedure called thoracentesis. It is also sometimes necessary to obtain a sample of cells (pleural biopsy) from the pleural membrane to determine the cause.
Thoracentesis is performed to obtain a sample of pleural fluid and to drain large amounts of fluid for therapeutic purposes. The patient usually sits at a table, leaning against it with his or her arms resting on the tabletop. The pleural fluid is located by ultrasound or through percussion. In percussion, the physician places one finger on the patient's back and taps against this finger with a finger from the other hand. Lungs that are filled with air sound hollow, while lungs surrounded by fluid sound dull.
The site and the surrounding area are sterilized with betadine. A small needle is inserted into the skin to administer lidocaine (an anesthetic). Once the skin is numb, the needle is advanced to infuse the underlying tissue with lidocaine. The needle is advanced further, infusing lidocaine all along the route, until the pleural space is entered. Entrance into the pleural space is accomplished when pleural fluid aspirates into the needle. Once the tissue from the skin to the outer (parietal) pleural membrane is numb, another slightly larger needle is inserted into the desensitized track to the pleural space. The larger needle efficiently drains the fluid.
A plastic catheter often covers this second needle, is passed partially into the pleural space, and the needle is withdrawn. This is much like the way an intravenous (IV) catheter is placed. Fluid can be drained by hooking the catheter to plastic tubing connected to a vacuum bottle that draws fluid out. The amount of fluid removed varies from 30 mL (about 2 tablespoons) to more than 1 liter. A chest x-ray is usually performed after the procedure to detect a possible pneumothorax.
Sometimes complications such as pneumothorax (air in the pleural space), bleeding, hypotension (drop in blood pressure), re-expansion pulmonary edema, and infection occurs during thoracentesis. Cough also may occur as the lung reexpands.
Pneumothorax usually happens when the needle punctures the lung or when air leaks into the space during thoracentesis. This can happen as the needle enters or as the lung reexpands while fluid is being drained. There are usually no symptoms, but the patient may experience significantly worsening breathlessness. A chest tube is inserted into the lung to reexpand it, and once the hole is sealed the tube is removed. Infection and significant bleeding are extremely rare.
Hypotension also is extremely rare. It occurs in a vasovagal (vascular-vagus nerve) reaction; to put it simply, nerve stimulation causes a reduction in blood pressure. When large amounts of fluid are withdrawn and a severely compressed lung reexpands, the lung can refill with fluid. This is called reexpansion pulmonary edema. It happens in patients who have a large amount of fluid drained, and it is uncommon. Infection is a risk in any invasive procedure.
Closed pleural biopsy
Sometimes a sample of the pleural membrane is needed to determine the underlying cause. A closed pleural biopsy is performed to obtain the sample in the same manner as a thoracentesis, except that a different needle is used. There are two different needles commonly used that share a similar characteristic. The pleural biopsy needle has a "hook" at the tip or a hole surrounded by very sharp cutting edges in the side of the needle.
The procedure is slightly more uncomfortable than thoracentesis, and general anesthetic is often given. After anesthetizing the skin and tissue to the pleural space, the needle is inserted along the track and into the pleural space. As the needle is retracted, the cutting edges hook the pleural membrane. Once the pleural membrane is hooked onto the cutting surface, the needle is manipulated to cut off a small piece of pleural membrane. The sample is retrieved either by removing the needle or by aspirating some fluid through the needle, which carries the biopsy specimen into a syringe. Typically, several pieces are sampled.
The risks in this procedure are essentially the same, but somewhat increased, as those in thoracentesis. There is greater risk for a pneumothorax and bleeding, and there is greater incidence of hypotension. Cutting the pleural membrane stimulates the nerves, which reflex and cause a transient reduction in blood pressure, called the vasovagal response. Premedicating the patient with atropine often can prevent the vasovagal response.
Closed pleural biopsy can only sample the outer pleural membrane, the parietal pleura. Also, the size of the sample is fairly small and the physician cannot see the pleural membrane.
In thoracoscopic biopsy the physician visualizes the pleural membranes and takes large samples of them. This is often performed with a system that allows smaller incisions and the aid of video cameras for better visualization. The procedure is performed under general anesthesia or intravenous sedation with local anesthetic. Small incisions are made in the skin; sometimes only one is required. A small thoracoscope is passed trough the incision to directly visualize the pleura. Biopsy forceps are passed through either a channel in the scope or through a separate incision in the skin to remove tissue samples.
Complications with this procedure include a small risk for bleeding and infection. Pneumothorax is uniformly present and requires a chest tube for a short time after the procedure. Small samples of lung tissue can be biopsied with this procedure as well.
Open pleural biopsy
Occasionally open pleural biopsy is performed under general anesthesia. A surgeon makes an incision on the patient's side and enters the pleural space. This allows maximum exploration of the pleural membranes, large sampling of the pleura, and, if needed, of the underlying lung.