Thoracocentesis. Small Animal Diagnostic and Treatment Techniques

Although a needle and syringe can be used to perform thoracocentesis, a butterfly catheter attached via a 3-way stopcock to a syringe is preferred. When you are holding the plastic wings of the butterfly catheter, you can "feel" the tip of the needle as it touches structures in the chest. You lose this ability to "feel" that the needle is touching a structure in the chest if the needle is rigidly attached to a syringe. Once the needle is in the pleural space, let loose of the wings of the butterfly. If the animal struggles or the lungs move against the needle as they inflate during inspiration, it is less likely they will be lacerated if the needle isn't being held rigid in the pleural space.

Styleted Teflon catheters of similar conformation to the butterfly catheter can also be used (next page) The stylet is removed once the catheter is in the pleural space, then the syringe and 3-way stopcock are attached. The teflon catheter is less likely to lacerate a lung. The third opening in the 3-way stopcock is used to evacuate contents (air or fluid) from the pleural space. If removing fluid, attach an extension set to the unused opening of the stopcock. The other end of the extension set can be placed in a pan or bottle to collect the fluid from the pleural space.

The person inserting the needle should gently apply negative pressure to the syringe as the needle is advanced into the pleural space. This reduces the chance that the needle will pass through the fluid or air in the pleural space and lacerate lung. Notice the position of the pointer on the stopcock. The "closed" position is pointed to the unused opening. The syringe is in communication with the butterfly catheter. The intercostal vessels are located on the caudal margin of the rib. To avoid penetrating the intercostal vessels, place the needle on the surface of a rib then "walk" the needle off the cranial aspect of the rib.

In a small chested animals, the needle should be inserted at an oblique angle to the pleural space as opposed to straight into the pleural space to reduce the risk of lung lobe laceration. In moderate to large size animals the length of the needle on the butterfly catheter necessitates horizontal insertion to be able to penetrate into the pleural space through the intercostal musculature.