The reason to perform a bubble study is to confirm the presence of shunting of blood from venous to arterial flow such as a Reverse VSD or a Reverse PDA. When severe right sided overload and eccentric hypertrophy is present in patients with exercise intolerance (cyanosis), the clinical sonographer may suspect a reverse VSD or reverse PDA owing to Eisenmenger’s physiology; reversal of flow owing to equalization for right sided compared to left sided pressures.
An IV catheter is placed in the cephalic vein. Take 20 cc saline or Hetastarch and draw a few cc of air into the syringe. Agitate the syringe and remove the free air. Dr. Peter Modler demonstrates the materials necessary on the attached PowerPoint “How To Make Bubbles.”
If reverse PDA is suspected then image the abdominal aorta as close to the body wall as possible. Then inject about 10 cc of the agitated saline into the cephalic vein. If a reverse PDA is present then the bubbles will be seen in the abdominal aorta. In a normal patient where a closed venous system is present, the bubbles would dissolve in the pulmonary capillary bed. In the case of reverse VSD, image the heart in 5-chamber right parasternal long axis and concentrate on the region of the interventricular septum where a relatively large defect will usually be present if the patient is starting to reverse the flow from a long standing VSD. If reversal of flow is present then the bubbles will enter the right atrium to right ventricle and cross into the left ventricle and aorta through the defect. The bubbles are then ejected into the aortic circulation without dissolution in the pulmonary circulation.
See this reverse VSD with bubble study performed by Dr. Doug Casey of Vancouver B.C. Canada. English Bay Ultrasound.