"Stick a needle in it"—How to perform a thoracocentesis

"Stick a needle in it"—How to perform a thoracocentesis

Quick thinking and teamwork resulted in a successful thoracocentesis any may have saved this cat's life.

A 10-year-old cat named Kylie is having trouble breathing. A technician brings the cat back, and her initial assessment reveals shallow, rapid breathing and cyanotic mucous membranes. The team begins to administer 100 percent oxygen through a face mask, and Kylie's mucous membranes become slightly pink. Another technician auscultates the thoracic cavity and hears decreased ventral lung sounds. Dorsally, the lungs are clear. The veterinarian then arrives to examine Kylie. He confirms the technician's auscultation assessment and requests that the team obtain radiographs of the thoracic cavity.

Don't ignore clinical signs

Removing fluid from the thoracic cavity of a patient with chylothorax. (Photo courtesy of Kerr and Gottlieb)
Diagnostic work ups are important to determine why a patient is having difficulty breathing. Unfortunately, the stress of radiography can sometimes cause a dyspneic patient to go into respiratory arrest. Patients experiencing respiratory distress have optimal lung expansion in a sternal position. When they are restrained for radiographs, the stress can cause an increased respiratory rate, which, in turn, can create an arrest situation. In Kylie's case, the decreased ventral lung sounds may indicate that she has fluid buildup in the pleural space. If the lung sounds were dorsally decreased, a pneumothorax may be a concern. Gravity causes air to rise and fluid to fall, so it is important to assess all four quadrants of the chest cavity bilaterally when auscultating a patient in a sternal position.1 Fluid can restrict the lungs from expanding, limiting the amount of oxygen that can be inhaled for gas exchange. This dynamic could explain the rapid, shallow breathing pattern observed when Kylie first arrived.

About 20 percent of room air is oxygen, so by delivering 100 percent oxygen to Kylie, we are increasing the oxygen concentration to her lungs. This increased oxygen concentration may give her some temporary relief, but to help her breathe effectively, the fluid needs to be removed from the space between the pleura of the lungs and the pleura of the thoracic wall. Taking this information into account, the technicians request that the veterinarian "stick a needle in it"—perform a thoracocentesis—before they obtain radiographs.

Performing a thoracocentesis

Veterinarians perform thoracocentesis to remove fluid or air for diagnostic analysis and therapeutic intervention. Removing the fluid or air allows for better functional lung expansion. During a thoracocentesis, the team must work together to decrease the patient's stress. Placing a cat in a sternal or standing position is the most opportune for acquiring the fluid or air, but the patient's comfort is the priority. Administer oxygen through a mask; however, if this stresses the patient, remove the mask and simply hold the oxygen flow tube near its airway. Ideally, the midsection area (seventh to ninth intercostal space) on both sides of the chest should be clipped and aseptically scrubbed. However, if the patient is in severe respiratory distress, you can avoid this step. If the patient is stable, administer a small amount of lidocaine (1 to 2 mg/kg) subcutaneously to desensitize the site. A technician can perform this step by using a 1-ml syringe and 25-ga needle. While the lidocaine is taking effect, a team member can make sure the thoracocentesis kit is ready. The kit should include the items listed in "Assembling a Thoracocentesis Kit."

To begin a thoracocentesis, the stopcock should be turned in the off position to the patient. The veterinarian inserts the needle or catheter near the cranial portion of the rib because the arterial blood supply and nerves are located at the caudal side. If fluid is thought to be in the thoracic cavity, then the veterinarian should aim the needle or catheter ventrally and insert it lower on the chest in the eighth intercostal space. If air is thought to be in the thoracic cavity, then the veterinarian should aim the needle or catheter dorsally and insert it higher in the eighth intercostal space. The needle or catheter is advanced at a 45-degree angle into the pleural space, and a pop is usually felt. If using a catheter, remove the stylet before attaching the extension set. At this point, the stopcock is turned off to room air and open to the patient. The veterinarian can now apply slight negative pressure to the syringe attached to the butterfly or extension set. When the syringe is filled, the stopcock is turned off to the patient. Note the amount of fluid or air in the syringe and then empty the contents. If fluid is aspirated, save a sample in a sterile nonseparator red top tube and a purple top tube containing EDTA. These samples can be analyzed after the procedure.

If the veterinarian continues to feel resistance instead of a pop, he or she redirects the needle. If no fluid or air is obtained again with applied negative pressure, then the needle is removed, and this procedure can be repeated on the other side, if needed.2 If a large amount of air or fluid is present or a patient requires multiple centesis procedures, placing a chest tube may be warranted.

Once the fluid or air is removed from the pleural space, the lungs will have less resistance to expansion, ventilation will improve, and oxygen intake will increase. The patient will not have to exert as much effort to breathe, and stress levels will decrease.

In Kylie's case, a milky liquid is aspirated, and a chylothorax is suspected. Chyle is the type of fluid that accumulates to form a chylothorax. When centrifuged, the liquid will not separate, and cytologic examination will reveal small lymphocytes and some neutrophils. In addition, if the patient has a true chylothorax, then when the fluid's triglyceride and cholesterol concentrations are measured, the cholesterol concentration will be lower than the cholesterol concentration of the patient's serum.