▶ PFO DIANOSIS USING PMD DOPPLER WITH BUBBLE CONTRAST
-----------John White, BS, VT Spencer Vascular, Seattle WA

▶ PROCEDURE

- The following components are required for the Right-to-Left cardiac/pulmonary shunt test.

- Materials :

  • Spencer Technologies PMD-100M
  • Headframe with bilateral ball probes and cables.
  • 2Mhz Spencer Technologies handheld probd.
  • 18-21G¾X12" Vacutainer (Blood Collection Set) with tubing.
  • (3) 10ml syringes (Luer-lok system)
  • 3way large bore stopcocks
  • (2) 21G (syringe draw) needles
  • (3) 10ml single-dose 0.9% NaCl (normal saline)
  • (Several) Sterile cotton balls
  • Tourniquet
  • (Several) Gauze (4X4 or 2X2)
  • (Roll) Paper tape
  • (18X24) Sterile drape
  • (18X24) Plastic tray
  • Rubber gloves
  • Valsalvometer (gauge in mmHg up to 100)
  • Disposable mouthpiece (for Valsalvometer gauge)

▶ Setting Up

Start the PMD Doppler setup by probing the temporal windows, bilaterally with the 2Mhz handheld probe for the middle cerebral arteries. The patient can either be sitting up or supine during MCA insonation. This will guide you for placing/securing the ball probes in the patient and secure snuggly yet comfortable for the patient. Place the right and left specific ball probes into the knob locking mechanism and tighten down when desired signal is reached. Plug bilateral cables into the ball probes and advance to monitoring. Guide the patient to a supine position on a bed or gurney. Allow 30 minutes of uninterrupted spontaneous cerebral micro-embolus monitoring before starting intravenous line.

During 30 minute monitoring, you can have the patient practice a Valsalva strain by having the patient blow on the Valsalvometer to 40 mmHg and holding it for 10 seconds.
Notice the MCA velocities drop during this test. Also prepare the materials needed for starting an IV line and contrast injection syringes.

 

▶ To Set Up a Sterile Field Tray :

Use latex or nitril gloves when preparing materials for sterile field. Open a sterile (18X24) drape and place on tray of similar size. This will be the sterile field in which you are going to place the syringes, needles, Vacutainer set, 3way stopcock and cotton balls.

Open three syringes, Vacutainer, 3way stopcock and 21G needle in individually and let items freefall to the sterile tray lining. Salvage packaging of Vacutainer and stopcock for which you will be using to hold loaded (drawn) syringes and stopcock Place the 21G needle on the syringe, remove cap and draw 9cc of NaC1 (normal saline). Repeat this for multiple contrast injections. Place loaded syringe(s) into open stopcock packaging for which this remains sterile.

 

▶ Preparing Arm :

Often the antecubital fossa is chosen because there is a large antecubital vein easily accessible there. For agitated contrast injections generally 21-gauge is a good compromise, which is a sufficient caliber for fast injections but still small enough to be easy to insert.

Patient is supine. Apply a tourniquet high on the upper arm. It should be tight so that it visibly indents the skin but without causing patient discomfort. Have the patient squeeze their hand to make a fist several times in order to maximize venous engorgement. Now start the search for a suitable distended subcutaneous vein. If you cannot see any veins popping up from the distention caused by the tourniquet, you can sometimes feel them by palpating the arm.
Once a suitable vein is found, then it is necessary to clean and disinfect this area by swiping several times in a circular outward motion with alcohol wipes or alcohol saturated cotton balls.

 

▶ Puncture Vein :

Use one hand to apply counter tension against the skin. This hand will be pulling the skin distally towards the wrist in the opposite direction the needle will be advancing. Connent the Butterfly set tubing (12 inches long) to the 3way stopcock and turn the long arm 90-degree to the tubing (this allows flashback of blood into the tube). Hold butterfly set at a 45-degree angle and use a quick, jab motion to minimize patient discomfort. Then advance the butterfly needle well into the vein and look for the dark red flashback of blood in the tubing to the stopcock. Turn the stopcock back to the off position of the tubing (back 90-degrees). Release the tourniquet. Secure the butterfly set with tape over the actual skin puncture site using a strip of tape and then the butterfly portion to prevent accidental removal. You can test the IV by injecting saline. Thers should be no resistance of stinging complaint by the patient.

 

▶ Preparing for Injection :

Attach one 9cc loaded saline syringe and one empty syrings with 1cc of air drawn to the Luer-lock ends of the 3way stopcock. With the saline syrings, open the stopcock to that syringe and flush blood column from tubing with a little saline and then draw back a small amount of the patient's blood. Then close the stopcock once again. Start agitating (1ml air/9ml saline exchange) by alternating the contents of the syringe back and fourth ten times while hearing a swooshing sound of the mixture. The contrast injection is now ready.

 

▶ Injection :

---* Make sure the PMD-100M is recording during injections!

1st Injection : Open the stopcock to the tube (patient). While holding the syringe outlet in the up position with the foam surfaced, begin injection as a bolus (<3 seconds). Confirm intravenous injection by positive findings on the PMD screen. If negative, ask patient of a stinging sensation around the puncture site and then monitor ipsilateral subclavian vein with a separate Doppler probe during injection to confirm bubbles in the vein.

2nd Injection : Repeat injection with a Valsalva strain. Contrast agent will be injected five seconds before the start of a Valsalva strain. The patient should start the Valsalva strain on examiner's command. For Valsalva strain. The patient should start the Valsalva strain on examiner's command. For Valsalva strain, have the patient blow/push on the mouthpiece of the Valsalvometer and bring the needle up to 40mmHg and maintain constant for ten seconds (a dramatic decrease in MCA velocities insures and optimal Valsalva strain). Count off the seconds for the patient and instruct them to release when appropriate. A hyperemic MCA velocity response is normal.

PMD Real-time results :

Positive for Right-to-Left cardiac/pulmonary shunt = several microembolic signals appear on the PMD screen.
Negative for a Right-to-Left cardiac/pulmonary shunt = zero microembolic signals appear.