Agitated Saline-Bubble Injection
November 05, 2004
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 1st one with normal respiration and a 2nd 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 manís 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:
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.