I talk to so many vets who are hesitant to perform thoracocentesis, even though thoracocentesis is less technically challenging than collecting blood from a vein. With thoracocentesis you are usually targeting a large volume of air or fluid, as opposed to a tiny vessel. The procedure is generally safe, even when you get a negative tap. Thoracocentesis is a life-saving procedure, and many patients that need this procedure will die without it.

I’m going to walk you through a simple approach to thoracocentesis.

In this video, we will demonstrate how to do thoracocentesis in a dog.

Video coming soon!

Diagnosing Pleural Space Disease and Indications for Thoracocentesis:

Pleural space disease should be considered in any patient with rapid, shallow, laboured breathing and muffled/dull lung sounds. Pleural space disease encompasses the accumulation of air, fluid or tissue between the lungs and the chest wall, compressing the lungs so that they cannot inflate.

Pneumothorax is the accumulation of air within the chest cavity, between the lungs and chest wall. This is a relatively common finding in trauma patients. Traumatic pneumothorax can result from a penetrating wound through the chest wall (enabling outside air to rush into the chest cavity, causing the negative pressure within the chest cavity to be lost) or from internal leakage of air from the injured lungs or airways (this is called tension pneumothorax). In fact, tension pneumothorax is said to be the most common preventable cause of death in trauma patients.  Spontaneous pneumothorax can happen in the absence of trauma, and is usually caused be the rupture of a bulla (cavitated structure resembling a bubble) within the lungs.

Pleural effusion is the accumulation of fluid within the chest cavity, between the lungs and chest wall. This fluid can be blood (hemothorax), pus/inflammatory fluid (pyothorax), a clear-ish fluid called transudate (usually heart failure or cancer related), neoplastic effusion, or chylous effusion.

Other types of pleural space disease you man encounter include diaphragmatic hernia and neoplasia.


On physical examination, you will likely notice rapid, shallow, labored breathing with muffled or very decreased lung sounds. Other physical exam findings and history can also provide clues.

For me, ultrasound is by far the easiest way to diagnose pleural effusion. It’s quick, easy, minimally invasive, and is a very sensitive diagnostic test. A focused ultrasound of the thoracic cavity (as well as the abdominal cavity and pericardial space) to check for any significant effusion can usually be performed in less than 5 minutes, without shaving any fur (use alcohol), and with the patient resting comfortably in sternal recumbency. Focused ultrasound has become a standard part of the emergency exam, particularly in trauma (link to video on how to perform a focused ultrasound for cavitary effusion). The classic ultrasound finding in pneumothorax is the loss of the thoracic glide sign (a thin, hyperechoic line that you can see gliding where the pleural surface of the lungs glides against the pleural surface of the chest wall). 

You don’t need a top of the line $30,000 ultrasound machine for most emergency procedures. If you don’t have an ultrasound machine, you can usually find  a used  laptop-sized unit from a radiology technician. These units are priceless for helping to identify fluid in the body cavities and for ultrasound-guided centesis.

Although the diagnosis of pleural effusion or pneumothorax is more challenging without ultrasound, you should not let this stop you from performing thoracocentesis. Thoracic radiographs are diagnostic but STOP– please don’t rush your dyspneic patient to x-ray. In the highly compromised patient, the degree of stress, restraint or sedation that is typically required for x-ray may result in sudden decompensation or death. Personally, I feel that it is much safer to perform a quick, blind diagnostic thoracocentesis than to restrain a dyspneic patient for x-ray.

Indications for thoracocentesis and considerations:

Thoracocentesis is indicated as an emergency treatment for pneumothorax and pleural effusion resulting in dyspnea. It usually takes a lot of air or fluid (> 20 ml/kg) to cause clinical signs of dyspnea.

Thoracocentesis is generally considered a safe procedure, but it is not completely without risk, and everyone, including the owner, should be made aware that a severely compromised patient can decompensate during the procedure, and that complications such as laceration of underlying structures (lungs, blood vessels, tumors, etc.) is uncommon but can occur. Depending on the underlying cause, the air or fluid can re-accumulate and may need to be drained again; if frequent drainage is needed, then a chest tube may need to be placed. Dyspneic patients can decompensate during the procedure, in fact, they can decompensate at any minute

Before you start:

Prepare the Patient:

First, you need to prepare your patient. Bearing in mind that you want to always minimize stress as much as possible in the dyspneic patient, as a routine initial approach to emergency patients you should aim to provide supplemental oxygen, obtain venous access, and monitoring equipment (EKG, blood pressure and SPO2).

If you have a couple moments to spare, it is helpful collect some baseline blood samples and run a couple quick, easy point of care tests. In most cases, there is a quick and easy way to collect baseline blood samples during IV catheter placement, which we demo in another video (click here).

It is nice to run a couple quick, easy point of care tests. Minimally, I always like to run a baseline PCV/TP, lactate (“how sick are you?”) and blood glucose on emergency patients, because it usually takes less than 2 minutes to prepare these samples, and there is usually enough blood in the IV catheter stylet to get these tests started.

If you have that ability to run a very quick STAT emergency panel (with electrolytes, BUN/creatinine), great. Checking blood clotting times (PT/PTT or ACT) is an excellent idea if clinical signs of anemia are present(pale mucous membranes, tachycardia, weak pulses). But in the highly compromised patient, do not delay pericardiocentesis excessively, as you may risk allowing your patient to decompensate.

It is desirable for patients to be comfortable and free from anxiety and pain at all times. Analgesia (fentanyl: 2-6 mcg/kg IV followed by CRI 2-6 mcg/kg/h) Administering gentle sedation can be very helpful. Stress, anxiety and fear can increase oxygen demands, and make things harder for everybody. For gentle sedation, I like to titrate butorphanol (0.1-0.2 mg/kg IV; skip the butorphanol if you gave another opiod for pain) and midazolam (0.05-0.2 mg/kg IV).

Prepare the owner:

Before the procedure, I also like to prepare the owner. I explain that there is usually negative pressure in the chest cavity, which holds the lungs against the chest wall like a vacuum. When air or fluid accumulates between the lungs and chest wall, this causes the lungs to collapse or deflate. If the patient is experiencing very laboured breathing, this is considered a life-threatening emergency. To alleviate this pressure and improve circulation, we need to drain the air or fluid by inserting a needle into the chest cavity.

If pleural effusion has been identified, I prepare the owners that there are many potential causes for the fluid. Once the fluid (or “pleural effusion”)  has been drained, further testing is still needed in order to understand the underlying cause of the fluid. This can be extensive diagnostic testing, which may include comprehensive lab work, cellular analysis of the fluid, echocardiogram (ultrasound of the heart, preferably by a board-certified cardiologist or other highly experienced radiology professional,), advanced imaging of the chest and abdomen (x-rays, abdominal ultrasound), and further testing.

I inform the owners that the procedure is generally safe but not completely without risk. Rare complications can include laceration of the lungs or another structure (tumor, etc.), which could result in hemorrhage. Depending on the underlying cause, the air or fluid can reaccumulate and may need to be drained again or frequent drainage is needed, then a chest tube may need to be placed. Dyspneic patients can decompensate during the procedure, in fact, they can decompensate at any minute. I do tell the owners that if their pet is struggling to breathe, I feel that performing a diagnostic thoracocentesis is safer than restraining their pet for x-rays.

I also prepare the owners prior to the procedure (especially if they are going to be present), that it is possible to get a negative tap (meaning there is probably another cause of the dyspnea), and that it is relatively common to get a little bit of blood in the syringe (up to a couple ml) regardless of the cause.


Before you start: Prepare the patient

Step Helpful Tips
Administer supplemental oxygen


Consider spending $5 on pediatric nasal cannulae. They can be easily secured, are generally well-tolerated, and free up your staff from holding flow-by or a mask up to the patient’s face.
Place an IV catheter
Apply monitoring equipment (EKG, minimally;  blood pressure, SPO2 ideally)

Collect baseline blood samples if you have a couple minutes to spare.


Administer analgesia if the patient is a trauma patient and is in pain. Fentanyl 2-5 mcg/kg IV (may repeat q 20-30 minutes as needed) followed by CRI: 1-5 mcg/kg/h IV


hydromorphone: 0.05 mg/kg IV


Administer gentle sedation if the patient is very anxious or distressed. If patient did not receive opioid above then:

titrate butorphanol (0.1-0.2 mg/kg IV)


midazolam (0.05-0.2 mg/kg IV) –best when used in combination with an opioid


Collect baseline blood samples -lavender top tube [EDTA]

-serum separator tube

-green top tube [sodium heparin]-if required by your in-house analyzers

-necessary samples  (usually a blue top [sodium citrate]) for assessing coagulation times.


Check point of care tests (and STAT emergency panel if there is time) PCV/TP, BG, Lactate

(iSTAT, electrolytes, BUN/CRE)


How to Perform Pericardiocentesis : Step by Step

Prepare your supplies:

Start by getting all of your supplies out and ready to go. Remember to label any syringes containing drugs and medications.

-Clippers and surgical scrub
-Lidocaine for local anesthetic usually 1-2 mL depending on patient size; I prefer a 25 ga needle to minimize discomfort
-A marker or sharpie
-Sterile gloves (for you) and regular/nitrile gloves (for your assistant) Some people do this without sterile gloves. Personally, I don’t.
– 20-20 Ga hypodermic needle attached to a regular IV extension set (~30 cm)


-23-21 Ga Buttery fly catheter

I prefer this setup for medium to large dogs



And this setup for small dogs and cats

-A three-way stopcock or one-way valve
-60- ml syringe (or smaller if the patient is tiny)
– If pleural effusion is present] sample tubes labeled “effusion” for fluid analysis/cytology (lavender/ EDTA tube) and culture.
-[If pleural effusion is present] bowl or other container for collecting the effusion



Attach the extension set to the three-way stopcock and syringe, and ensure that all of the connections are very secure. Make sure that your assistant knows how to operate the three-way stopcock.

Select Site, Clip Fur, and Infuse Local Anesthetic

Start by selecting your optimal centesis site; this is most easily accomplished using ultrasound. You can also use your stethoscope.

Thoracocentesis is usually performed at approximately the 8th intercostal space (7-9th). I usually start at the caudalmost rib (13th) and count backwards until I reach the 8th intercostal space. Another shortcut to finding the 8th intercostal space is to imagine a ribbon around the chest cavity at the level of the xyphoid process (the last sternebra), and trace this line until you reach the lateral thorax.

If you are alleviating a pleural effusion, the needle is introduced in the ventral 1/3 (gravity-dependent) of the lung field. For pneumothorax, the needle is introduced in the dorsal 1/3 of the lung field.

Generously clip the selected site (from approximately the 3rd rib to the 11th rib). You may need to do the opposite side

I like to circle my optimal centesis site (identified by ultrasound) with a sharpie, and then infiltrate local anesthetic into that area, making sure that I go deep enough into the intercostal musculature to minimize discomfort as I pass the needle through the chest wall.

Your assistant can then aseptically scrub the site while you put your sterile gloves on.

Introducing the Needle:

At the selected intercostal space, remember that you will want to advance your needle along the cranial aspect of the caudal rib to avoid the vessels and nerves that run along the caudal aspect of the ribs. You can begin to slowly advance the needle through the skin, and then continue creeping along the cranial aspect of the rib. If you feel a gentle scratch on the rib, that can help you gauge your depth as you are advancing the needle into the chest cavity.

It is generally recommended to direct the needle so that the bevel of the needle is parallel to the lung. I hold the needle lightly between my fingers to minimize the risk of lacerating lung.

Your assistant can begin to aspirate the fluid or air by drawing back on the syringe.  Your assistant should communicate with you, indicating when fluid or air is flowing into the syringe, or when they are getting negative pressure.

If you get negative pressure and feel the lungs lightly scratch against the needle, that usually means your are getting a negative tap, and you can back out. It is not wrong to try a different site (move 1 rib in either direction; slightly ventral or caudal; try the opposite side.

If you are draining an effusion, prepare your samples for fluid analysis, and then continue draining the effusion.

When you are done, remove the needle. Continue to monitor the patient for dyspnea (as well as other changes in vital parameters), and check the site intermittently with ultrasound for recurrence.

In the absence of complicating factors, you should see a dramatic and immediate improvement. Your goal is to attain normal respiratory rate, heart rate, normal blood pressure, normal oxygenation and normal lactate levels.

Analyze the fluid:

Quantify the volume you retrieved and record it in the patient’s chart.

Check the PCV/TS of the fluid, to determine whether it is a hemorrhagic or mixed hemorrhagic effusion.

If the PCV of the fluid is less than 10-15%, it would be worth while to prepare a cyto-prep of the fluid, and evaluate this under the microscope. To prepare a cyto-prep, spin sample of the effusion, draw off the supernatant, and prepare the white buffy coat onto a slide. You can also do this using standard hematocrit tubes, and using a needle to extract the buffy coat (this is usually where bacteria, white blood cells, and other type of cancer cells will be located.)

Aftercare and managing complications:

Ongoing hemorrhage:

If a hemorrhagic effusion was drained from the chest cavity, but notice that it is filling up again quickly, to me this indicates ongoing hemorrhage.

Start by checking blood clotting times. If these are significantly prolonged, fresh frozen plasma will likely be needed to restore clotting factors. Many patients with significant ongoing hemorrhage will develop a consumptive coagulopathy, where clotting factors are consumed so that the blood can no longer clot effectively. With active hemorrhage and prolonged clotting times, the bleeding will probably not stop until the coagulopathy has been addressed.

Accumulating blood in the thoracic cavity resulting from ongoing hemorrhage can be collected and administered back to the patient using a technique called autotransfusion (click here to learn how to perform autotransfusion).

Recurrence of pneumothorax:

If a large volume of air is retrieved from the chest cavity, and it appears to be reaccumulating quickly, you may need to place a chest tube. (Post and video on chest tube placement coming soon) Chest tube placement is pretty similar to thoracocentesis. (Video coming soon)

Laceration or puncture of the lung resulting in pneumothorax is uncommon. If this happens and the degree of pneumothorax is clinically significant, you can alleviate the pneumothorax by performing thoracocentesis.