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How to perform a thoracocentesis | VETgirl Veterinary CE Podcasts

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In this VETgirl podcast, we discuss how to perform a thoracocentesis in the dyspneic dog or cat. If you don’t commonly perform a thoracocentesis, you may not feel comfortable. However, keep in mind that thoracocentesis is easy to perform and is generally safe.

A thoracocentesis is often life-saving, and should be performed immediately in any dyspneic patient that is suspected of having pleural space disease secondary to pneumothorax or pleural effusion. Base this on your auscultation and physical examination findings; the presence of muffled heart sounds or dull lung sounds increases suspicion of pleural space disease, and that’s the location where you want to perform the thoracocentesis.

In fact, when I’m presented a dyspneic cat, I prefer to do a benign, diagnostic thoracocentesis to radiographs (which can be ultimately very stressful, resulting in acute respiratory arrest in severe cases). That’s how benign and safe a diagnostic and therapeutic thoracocentesis can be!
Contraindications for thoracocentesis are rare, but include any disease that can’t be treated by thoracocentesis; in other words, diaphragmatic hernia (with no secondary effusion), pleural masses, pneumomediastinum,1 and diseases where the lungs may be friable and more at risk for an iatrogenic pneumothorax (e.g., asthma, disseminated fungal pulmonary infection, etc.).

The good thing about performing a thoracocentesis is that it also doesn’t require very much in terms of equipment:

• Your stethoscope
• Clippers
• Surgical scrub solution
• Alcohol in a spray bottle
• A butterfly needle or appropriately sized hypodermic needle (ranging from 16 to 21 gauge)
• A three-way stopcock (ideally)
• Sterile gloves (ideally)
• Extension set
• A 10- to 60-cc syringe, depending on the anticipated amount of air or effusion
• Appropriate sterile collection tubes (for sample collection for cytology and/or culture purposes)
• Oxygen flow by
• An ultrasound (bonus, but not imperative!)
• Two other people: one to help restrain the patient, and the other to aspirate and collect the fluid (or air)

When performing a thoracocentesis, select the position that is most comfortable for the patient that causes the least amount of dyspnea: sternal, standing, or in lateral. Provide flow-by oxygen to help stabilize the patient. Next, shave a wide region and aseptically prepare it. I like to clip the area and spray alcohol on immediately. This allows me to use my ultrasound for a rapid focused assessment of sonography in trauma (FAST) ultrasound, and allows me to rapidly identify a fluid pocket for thoracocentesis. The alcohol also helps remove the initial greasy layer of oil directly on the skin.
ThoracVG414

A thoracocentesis should be performed cranial to the rib, as the blood vessels and nerves lie caudal to the rib (“hiding” behind the rib). Thoracocentesis should be performed at the 7th to 9th intercostal space (ICS) to avoid the heart (3-5th ICS) or liver (caudal to the 9th ICS). My short cut technique? Rather than counting rib spaces in critically ill, fragile dyspneic patients, I draw an imaginary line from the end to the xiphoid up along the lateral body wall. This is approximately the 8th ICS, and thoracocentesis can be performed in this area. If pleural effusion is present, the needle should be directed ventrally on the bottom 1/3 of the chest cavity; if abnormal air is present within the pleural space, the dorsal 1/3 of the chest cavity should be used for thoracocentesis.
The use of a 3-way stopcock, extension tubing, an appropriately sized needle or catheter, and syringe should be used to collect air or fluid. In cats, I prefer to use a 1” butterfly 21-gauge needle; however, the needle size may not be large enough in grossly obese patients. In dogs, I generally use a 18 to 21 gauge, 1-1.5′ needle.

The needle should be advanced into the pleural space. Once the needle is in place, gentle aspiration should be applied to the syringe. If a scraping sensation is detected (e.g., scratching the lung surface) or if hemorrhage is present, the needle should be slowly backed out 1-3 millimeters. Ideally, the needle should not be completely removed out of the pleural space, due to the pain upon repeated entry. If the thoracocentesis is negative, the needle can be re-directed at different angles until air or fluid is obtained.

Complications from thoracocentesis are generally rare. Remember that there typically has to be a significant amount of effusion or air to result in clinical signs of tachypnea (e.g., gross estimates of approximately 20-60 ml/kg within the chest cavity). Due to all this abnormal fluid or air, your needle is well removed from the surface of the lung, making risks of pneumothorax or laceration rare. While risks of hematomas, pneumothorax, arterial laceration, hypotension, reexpansion pulmonary edema or vagal reactions can occur with thoracocentesis, they are rare. Keep in mind that the demise of dyspneic patients is often due to not preforming a thoracocentesis as compared to performing an unnecessary one.1

Need more? Check out our VETgirl video of how to perform a thoracocentesis here.

References:
1. Sigrist NE. Thoracocentesis. In Small Animal Critical Care Medicine, Eds. Silverstein DC, Hopper K. Elsevier-Saunders 2009. St. Louis. pp. 131-133.

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