Wada Test

If phase 1 testing indicates that surgery may help you, the team will use the Wada test (developed by neurologist Juhn Wada in the 1940s) to evaluate whether you are a good candidate for surgery. This test is also used in preparation for surgery.

The test is the only known way to examine how a specific side of the brain works. It does this by:

  • Determining the memory and language functions in each side of your brain
  • Mapping how each side of your brain works
  • Tracing the arteries that supply blood to each side of your brain

The Wada test involves injecting a short-acting sedative through a catheter in the carotid artery. This puts one half of the brain "to sleep" for up to five minutes while the other side of the brain continues to function as usual. This allows the neurologist and neuropsychologist to test each side of the brain separately for speech and memory.

How do I prepare for the test?

A radiologist (an X-ray doctor) and neurologist will discuss the procedure with you, and you will be asked to sign a consent form.

Before the Wada test, you will have an angiogram, which takes X-ray pictures of the arteries that supply blood to your brain.

For both the angiogram and the Wada test, the radiologist will insert a thin tube called a catheter and then guide the catheter to the area to be studied.

  1. The radiologist will insert the catheter into your skin, usually in the groin area, and will also start an IV (intravenous) line in your arm.
  2. You may have small adhesive discs applied to your chest to monitor your heart, and Velcro strips placed across your head to prevent movement during the X-rays.
  3. The radiologist will make a tiny cut into your skin and insert a special needle into a blood vessel. Some patients report mild discomfort when the needle is inserted, but most patients do not feel the catheter's movement through the blood vessel.
  4. Some dye will be given through the catheter so that the blood vessels will show up on the X-rays. The radiologist will guide the catheter towards the carotid artery using an image on a television screen. When the dye enters the bloodstream, most patients experience a feeling of heat, pressure, and sometimes pain. You may have a metallic taste in your mouth, which will subside after the procedure.
  5. After the X-ray, and with the catheter still in place in the carotid artery, the neurologist and several neuropsychologists will enter the room.
  6. The radiologist will administer sodium amytal through the catheter. Sodium amytal is a short-acting sedative that, when injected, will put one half of the brain "to sleep" for up to five minutes while the other side continues to function as usual. This allows the doctor and neuropsychologist to test each side of the brain separately for speech and memory. You will not be able to move one side of your body, and may or may not be able to speak immediately after the injection. You may feel very happy or elated, or you may be tearful; everyone responds differently. The weakness and inability to speak will subside in several minutes. The amytal usually wears off completely in 5 to 10 minutes.

What will happen during the test?

  1. During the first several minutes, the neurologist will ask you to follow some simple commands, such as pointing to a particular picture. The neuropsychologist will then ask you to identify some pictures, words, objects, and designs.
  2. Ten minutes after the injection, you will be asked to remember the items that you were shown earlier.
  3. The radiologist will then move the catheter into the opposite carotid artery. This will not require another incision; the same catheter will simply be guided to the next area. After the catheter is in place, the dye will once again be injected to check the circulation to that side of the brain.
  4. Half an hour after the first injection, you will be given another amytal injection. Again, you will be weak on one side of your body and may or may not be able to speak for several minutes. The neuropsychologist will again show you some objects, words, and designs. Ten minutes later, you will be asked to remember what you were shown.
  5. After the testing is complete, the radiologist will remove the catheter and apply pressure to that spot to prevent bleeding. A clamp on the stretcher may be used to keep a constant pressure on that spot until you are taken to your hospital room.

What happens after the test?

  • Because of amytal's sedative effect, you must go to the Angio Recovery Room for about four hours of observation.
  • The dye, which is colorless and odorless, will pass through your urine. You will be asked to drink extra liquids. Drinking fluids will help to flush it through your kidneys.
  • You may eat whenever you like.
  • You will be asked to keep your leg straight and remain flat in bed for several hours.
  • A nurse will check the catheter spot and your vital signs frequently for several hours.
  • You may notice some bruising, swelling, and soreness in the area where the catheter was inserted. This should completely subside within a week or two.
  • Your neurologist will discuss the results of the test with you after you are settled in your room.
  • On the day after the test, you will usually have a quick visual field test in Ophthalmology to check your ability to see up, down, and to the side.

What are the risks?

While risks are rare, your team is fully prepared to help you in any situation that might occur, such as:

  • Sensitivity to contrast dye: Reactions may include nausea, hives, and itching. Patients rarely experience difficulty breathing. Let the physician know if you are allergic to any dyes or have asthma.
  • Bleeding: Insertion of the catheter requires the puncture of a blood vessel. If blood should leak around the catheter into the tissue, a hematoma (a swollen area filled with blood) may result. It will become black and blue but will get better in time as the blood is absorbed by the body.
  • Sensitivity to sodium amytal: Sodium amytal is a strong sedative. In rare cases, it can cause difficulty breathing or low blood pressure.
  • Blood clot: In rare cases, a clot can form in the leg or brain, which may cause a stroke. This happens in only about one in a thousand cases.