Agitated Saline-Bubble Injection

November 05, 2004

Preparation:
Two 10ml syringes are prepared, each with 9 ml saline along with 1 ml air. A 20-gauge iv cannula with a plastic tube extension to a 3-way stopcock, is placed in one antecubital vein. One port of the stopcock opens the needle lumen to the atmosphere to make blood apparent when the vein is entered. A small amount of blood is drawn into one saline syringe via the 3-way stopcock. (The blood aids suspension of air into smaller bubbles.) The tourniquet is removed, the needle cleared of blood with a small amount of saline, and the needle is stabilized with paper tape across the butterfly.
 

A suspension of microbubbles is produced by back and forth exchanges of the saline-blood mixture via the 3-way stopcock with another syringe containing 1 ml of air. Two injections of the bubble contrast are made, the 1^st one with normal respiration and a 2^nd with the respiratory strain.

Doppler ultrasound probe

Have it placed on the internal carotid. First recording at time of agitated saline injection and second recording with agitated saline injection combined with Valsalva. If there is a shunt,  then  a shower can be seen. This is the poor man’s version of  TCD (Transcranial Doppler) and a cheap but inadequate substitute for TOE(transesophageal echocardiogram) looking for significant right to left cardiac shunts.

Power M mode TCD (Transcranial Doppler)

If  your department is lucky enough to have  funding for transcranial Doppler:

Below is seen the results of a positive bubble test in a patient with a 12mm diameter PFO:

TCD during agitated saline injection

TCD during saline injection with Valsalva

The grading scale for bilateral monitoring is as follows:

For unilateral TCD monitoring, the scale is reduced to the following: 1-5, 6-15, 16-50, 51-150, and >150. These conductance scales allow for quantification of the capability of the shunt to conduct embolic material directly from the venous to the cerebral circulations.