#444: What Is a Bubble Study?

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Have you ever heard about a nurse purposefully injecting bubbles into a patient’s vein as part of a diagnostic test? It’s called an agitated saline study and it’s one of the key ways we identify serious cardiac abnormalities in patients. 

Bubble study overview

An agitated saline study (also known as a “bubble study”) is a technique utilized to detect abnormal intracardiac or intrapulmonary shunts. It involves agitating saline with air to create micro-bubbles that can be visualized during an echocardiogram and provide information about blood flow through the heart.

Indications for a bubble study

Bubble studies are indicated when the patient has a suspected cardiac or pulmonary abnormality that causes a right-to-left (RTL) shunt. When a patient has a RTL shunt, blood moves from the right side of the heart to the left side without first flowing through pulmonary circulation. When this occurs, un-oxygenated blood enters the left side of the heart and is pumped into systemic circulation. This can occur due to a PFO (patent foramen ovale), ASD (atrial septal defect) and pulmonary AVMs.

Since a RTL shunt can lead to significantly low oxygen saturation levels, a bubble study may also be conducted for a patient with unexplained episodes of hypoxemia.

Another common reason for a bubble study is in a patient who has had a stroke or TIAs of unknown origin. If the patient does not have known risk factors such as hypertension or atrial fibrillation, a bubble study may be conducted to determine if a PFO is the cause.

Bubble studies may also be utilized in critically ill patients to aid in pericardiocentesis (to ensure the needle is in the pericardium and not in the chamber of the heart), and to verify position of central venous catheters.

To review, some indications for a bubble study include: 

• Confirming presence of PFO, ASD, or pulmonary AVM (PFO is the most common cause of a RTL shunt)
• Evaluating a patient with unexplained hypoxemia
• Determining if a PFO is the cause for an unexplained stroke or TIAs
• Confirming needle position in pericardiocentesis
• Verifying position of central venous catheters

How does a bubble study work?

Bubble studies are conducted during an echocardiogram, which is a test that utilizes sound waves to create images of the heart. There are two types of echocardiogram – transesophageal (TEE) and transthoracic (TTE). Because a TEE requires sedation in order to place the transducer in the esophagus, the most common type utilized is the TTE. A transthoracic echocardiogram is a non-invasive procedure which simply involves placing the transducer against the chest wall.

Once the agitated saline is injected into the vasculature, the micro-bubbles are visible on the monitor and the sonographer is able to map the flow of blood through the heart. In a patient with no abnormalities, the lungs absorb the micro-bubbles so they do not reach the left side of the heart. However, in a patient with a RTL shunt, some of the microbubbles bypass pulmonary circulation and appear in the left chambers.

Step-by-step for assisting with a bubble study

In critical care areas, bubble studies may be performed at the bedside with the RN assisting the sonographer. 

Step 1: Gather supplies. You will need a 3-way stopcock, one 10 ml syringe of 0.9% NaCl, one empty 10 ml syringe, and extension tubing (not necessary, but recommended). Since you may need to perform the agitation and injection more than once, be sure to bring extra syringes to the bedside.

Step 2: Ensure the patient has adequate IV access. Note that 20 gauge and higher is easier to utilize and is less likely to lead to vein rupture during the forceful push of agitated saline. The antecubital vein is the optimal location, though a central line may also be utilized for this test. 

Step 3: Remove 1 to 2 ml of saline from the pre-filled syringe. This gives room in the syringe for a small amount of air which will be agitated into bubbles. Remove all air from this syringe.

Step 4: Flush the 3-way stopcock and extension tubing (if using) with 0.9% NaCl.

Step 5: Attach the stopcock directly to the IV catheter or through the extension tubing. Using extension tubing makes manipulating the syringes and stopcock a bit easier.

Step 6: Draw 0.5 to 1 ml of air into the empty syringe and attach it to one side of the stopcock. Attach the filled syringe to the other side of the stopcock. 

Step 7: Turn the stopcock OFF to the empty syringe and withdraw 0.5 to 1 ml of blood into your saline-filled syringe as this enhances contrast appearance. In some cases, a contrast material may be utilized. If that is the case, then adding blood to the syringe is not necessary.

Step 8: Turn the stopcock OFF to the patient. Begin agitating the saline by moving it forcefully from one syringe to the other.

Step 9: When instructed by the sonographer, open the stopcock to the patient (turn it OFF to the empty syringe) and forcefully inject the agitated saline into the vein. 

Step 10: In some cases, the patient may need to perform a Valsalva maneuver if the first injection is inconclusive. In this case, repeat the steps and inject during the Valsalva maneuver, which helps increase RTL shunt visibility.

What is a “positive” result?

A positive bubble study means that bubbles were seen in the left side of the heart, which is an abnormal finding. If the bubbles appear within 3 to 4 cardiac cycles, this generally suggests an intracardiac shunt such as a PFO or ASD. If the bubbles appear after 5 or more cardiac cycles, this suggests the patient has a pulmonary AVM and the shunt is in the lungs.

Is a bubble study safe?

Bubble studies are generally considered safe procedures with no significant risks or side effects. However, research conducted by the American Heart Association indicates that TIAs and small strokes have occurred in patients with RTL shunts undergoing bubble studies. It’s important to note that the study does state that inadequate agitation and improper injection technique may be contributing factors. In addition, bubbles studies are considered contraindicated in patients with known right to left shunting due to heightened risk for air embolism.

Tips for conducting a bubble study safely:

• Ensure the saline is adequately agitated and no large bubbles are present.
• Inject with the syringe in a vertical position so larger bubbles rise to the top and can be withheld. Using extension tubing makes this easier than connecting the stopcock directly to the IV cannula.

Want more cardiac topics? Explore here!

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References:

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Bernard, S., Churchill, T. W., Namasivayam, M., & Bertrand, P. B. (2021). Agitated Saline Contrast Echocardiography in the Identification of Intra- and Extracardiac Shunts: Connecting the Dots. Journal of the American Society of Echocardiography, 34(1), 1–12. https://doi.org/10.1016/j.echo.2020.09.013

Bhatt, D. (2022, October 1). What is a bubble study? – Harvard Health. https://www.health.harvard.edu/heart-health/what-is-a-bubble-study

Blanco, P., & Bello, G. (2019). Agitated saline echo testing: Two useful indications in critical care patients. Medicina Intensiva (English Edition), 43(2), 124–125. https://doi.org/10.1016/j.medine.2018.09.010

Buckland, J. (2023a, September 11). 7 Indications for an Echo Bubble Study. Cardioserv. https://www.cardioserv.net/indications-echo-bubble-study/

Buckland, J. (2023b, September 25). 9 Steps to Perform an Echo Bubble Study. Cardioserv. https://www.cardioserv.net/9-steps-to-perform-an-echo-bubble-study/

Cleveland Clinic. (2025, July 15). What Is a Transesophageal Echocardiogram (TEE)? Cleveland Clinic. https://my.clevelandclinic.org/health/diagnostics/4992-echocardiogram-transesophageal-tee

Li, F., Shen, Q., Deng, X., Yan, M., Zheng, X., & Zhang, G. (2023). Agitated saline with 10% blood increases number and stability of microbubbles in detection right-to-left shunt by contrast-enhanced transcranial Doppler: an in vitro and in vivo observational study. Journal of Thoracic Disease, 15(4), 1970–1977. https://doi.org/10.21037/jtd-23-284

Maggiore, P., Bellinge, J., Chieng, D., & et al. (2019). Ischaemic Stroke and the Echocardiographic “Bubble Study”: Are We Screening the Right Patients? – PubMed. Heart Lung Circ., 28(8), 1183–1189. https://pubmed.ncbi.nlm.nih.gov/30131285/

Mayerhofer, E., Kanz, D., Guschlbauer, B., Anderson, C. D., Asmussen, A., Grundmann, S., Strecker, C., & Harloff, A. (2022). Bubble Test and Carotid Ultrasound to Guide Indication of Transesophageal Echocardiography in Young Patients With Stroke. Frontiers in Neurology, 13, 836609. https://doi.org/10.3389/fneur.2022.836609

National Neuroscience Institute. (2021, July). Transcranial Doppler (TCD) Bubble Study. National Neuroscience Institute. https://www.nni.com.sg/our-specialties/neurodiagnostic-laboratory/tcd-bubble

NeuraSignal. (n.d.). Importance of a Bubble Study | NeuraSignal Academy. NeuraSignal. https://neurasignal.com/academy/importance-of-a-bubble-study/

Tsivgoulis, G., Heliopoulos, I., & Stamboulis, E. (2010). Safety of TCD “Bubble Study.” Stroke, 41(4), e195–e195. https://doi.org/10.1161/STROKEAHA.109.562793

Last Updated on October 23, 2025 by Maureen Osuna, MSN, RN