And after the above excerpt, I’ve posted links with excerpts to three resources on how to perform an agitated saline injection (bubble test) to determine if hypoxia in a patient with pulmonary embolus is due to right-to-left shunt caused by the pulmonary embolus or to another cause.
Here is the excerpt of the above:
PE with refractory hypoxemia
differential diagnosis: causes of hypoxemia refractory to ~100% FiO2
- Refractory hypoxemia always reflects some sort of shunt. The differential diagnosis here is pretty short.
- (1) Right-to-left shunting of blood through a patent foramen ovale (PFO) or atrial septal defect.
- PE causes an elevation of right-sided pressures.
- This causes right-to-left shunting of deoxygenated blood.
- (2) Another co-existent pulmonary process (e.g. pneumonia, mucus plugging, or pneumothorax).
- Cardiopulmonary ultrasound with bedside bubble study* to evaluate for shunting.
- Injection of agitated saline while imaging the heart is the test of choice to evaluate for right-to-left shunting.
- Additional chest imaging (especially if the bubble study is negative) – such as chest X-ray and possibly CT chest.*Here are resources on how to perform an agitated saline injection (bubble test).
Here are the links and excerpts on the resources on how to perform and interpret the agitated saline injection (echo bubble study):
An Echo Bubble Study is an injection of saline after agitation with air to create micro-bubbles that are ultrasound reflective into a vein in order to reach and opacify the right heart chambers, the coronary sinus in cases of persistent left superior vena cava (PLSVC), or the pericardium during pericardiocentesis.
7 INDICATIONS FOR AN ECHO BUBBLE STUDY
1- Detection of shunts (PFO, ASD, pulmonary)
In general; the appearance of micro-bubbles on the left side of the heart after their appearance in the right heart chambers is considered positive shunt study.
Most commonly, apical four-chamber view is used, also parasternal short-axis view at the level of the atrial septum (aortic valve level) or a subcostal four-chamber view may be used.
See the article for details on the findings in ASD/PFO, and Pulmonary Arteriovenous Malformations (PAVM’s),
2- Detection of persistent left superior vena cava.
In case of dilated coronary sinus and doubtful persistent left superior vena cava; the cannula must be inserted in the left arm, and the agitated saline should be injected through the left arm.
The test is positive for LSVC if the agitated saline appears in the coronary sinus before appearance in the right side of the heart.
Imaging is better through the parasternal long axis view. M-mode can be employed for better temporal resolution, with the beam centered on CS and RVOT.
Experienced operators use angulated A4C with posterior tilt showing CS opening into RA. As more complex anatomic variants exist, 2nd injection into right arm is suggested.
3- Intensifying TR signal when you have difficult estimating RV systolic pressure
In case that the TR signal by CW is suboptimal and pulmonary artery systolic pressure is important for clinical decision making; injecting agitating saline and obtaining CW of TR make the signal more visible and measurable but CW gain should be decreased as agitated saline make cause some noise. In this case gelofusine will cause a lot of background noise and should be better be avoided.
4- Delineating right heart borders and masses (including RV wall thickness).
Sometimes in suboptimal views; the RV borders are not clear, or you may have doubt about a mass or trabeculations within the RV cavity. Injecting agitated saline may help delineating RV borders for accurate measurements as it goes within the myocardial recesses and separate the dense compacted myocardium from the cavity. This also helps to delineate RV free wall.
5- Improving imaging of the pulmonary trunk and arteries, especially when looking for thrombi, which will appear as contrast filling defects.
For proper determination of pulmonary artery size & sub/supravalvular area; agitated saline may help if the image is suboptimal. Thrombi and masses can appear as filling defects.
6- During echo-guided pericardiocentesis.
During pericardiocentesis; agitated saline could be used during the procedure to differentiate if puncture is within the pericardium or in one the cardiac chambers (mostly RV) by noticing the microbubbles either in the pericardium or within a chamber.
7- For central venous line control after insertion.
Contrast should appear immediately in RA after forceful push through one of the central line ports, if not appearing at all this means arterial cannulation, if appearing late – this means coiling of the catheter. When using a central venous line port and forceful saline push some agitation takes place even without air, so you can skip the step with 0.5 – 1 ml of air.
Review the post for detailed instructions on how to perform the agitated saline injection (echo bubble study).
Agitated Saline (Bubble Test) YouTube video. Published on May 19, 2015. 3:44.