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

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

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.

Removing fluid from the thoracic cavity of a patient with chylothorax. (Photo courtesy of Kerr and Gottlieb)

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.

Diagnostic radiography

Performing diagnostic radiography after the thoracocentesis is more likely to yield a safer outcome and better radiographic results than before because the patient is more stable and the removal of the fluid may help to facilitate a clearer view of the underlying cause. Before moving the patient into the radiology room, a team member should take measurements and set up the radiography machine for the chest films. Make sure an oxygen source, an emergency endotracheal tube, and a laryngoscope are available. Ask the veterinarian if it is OK to acquire a dorsoventral view instead of a ventrodorsal view if the patient is uncomfortable lying on its back. Team members must be patient and keep calm during the radiographic examination so that the patient is relaxed.

Case outcome

In Kylie's case, radiography did not help diagnose the underlying cause of her chylothorax. The heart appeared normal, and no mediastinal mass was apparent. However, the analysis of the aspirated fluid did confirm a chylothorax.

A cat can develop a chylothorax because of heartworm disease, cardiomyopathy, mediastinal lymphoma, or trauma. Kylie's owners did not know of any traumatic event that could have caused the pleural effusion. Ultrasound capabilities were not available, so an in-depth examination of the thoracic cavity could not be performed. A feline heartworm test revealed negative results. The underlying cause could not be defined, so this patient was labeled as presumptively having an idiopathic chylothorax.3

Kylie was kept overnight for observation. The next day, she was comfortable, had no recurrence of dyspnea, and was discharged. Kylie's good outcome was a result of teamwork and quick thinking. If upon Kylie's arrival, the team had not worked together, the outcome could have been grave.

Kerr and Gottlieb are the founders of Four Paws Consulting in Cedar Grove, N.J., a veterinary consulting firm whose mission is to encourage excellence in technicians through continuing education.

REFERENCES

1. Silverstein DC, Hopper K. Small animal critical care medicine. St. Louis, Mo; Edinburgh: Saunders Elsevier, 2009;131.

2. Silverstein DC, Hopper K. Small animal critical care medicine. St. Louis, Mo; Edinburgh: Saunders Elsevier, 2009;132.

3. Kirby R. Self-assessment color review of small animal emergency & critical care medicine. Ames: Iowa State Press, 1998;50.

Assembling a thoracocentesis kit

A thoracocentesis must be facilitated quickly. During a crisis, you don't want to waste time gathering supplies. So having a thoracocentesis kit on hand is a must. Assemble it during a slow time in the clinic, and keep it in a crash cart until it's needed.

Kit for cats and small dogs

• Syringes (6 ml, 12 ml, 20 ml)

• Butterfly needles (various gauges)

• A three-way stopcock

• A collection bowl

• A nonseparator red top tube

• A purple top tube with EDTA

Kit for large dogs

• Large syringes (35 ml and 60 ml)

• An extension set

• Over-the-needle catheters (various sizes)

• A three-way stopcock

• A collection bowl

• A nonseparator red top tube

• A purple top tube with EDTA