What is a Wada test?

A Wada test is a procedure that your doctor may perform before you have surgery for epilepsy or a brain tumor. The procedure answers two questions about your brain:

• Which side of the brain controls your language functions or the right side?
• How important are each of your brain's sides regarding memory functions?

The Wada test enables your neurosurgeon (brain surgeon) to determine whether you may be vulnerable to changes in your speech or memory after surgery.

The procedure was first performed by Dr. Juhn Wada in 1949. Other names for the test are:

• Intracarotid amobarbital test.
• Intracarotid sodium amobarbital procedure.
• Sodium amytal test.
• Amytal study.
• Other tests your doctor may use before performing epilepsy surgery include:
• Functional magnetic resonance imaging scan (fMRI).
• Transcranial magnetic stimulation.
• Neuropsychiatric testing.

Which side of the brain controls language?

For most individuals, the left side of the brain controls speech. However, the Wada test is necessary because that isn't always true (especially with left-handed people).

Which side of the brain controls memory?

Both sides of your brain can function to control your memory. In general, the left side of the brain of left-hemisphere language-dominant people helps with verbal memory and the right side of the brain with visual memory. The Wada test helps your healthcare provider determine which side has better memory function.

Who can be tested?

Both children and adults can undergo the Wada test. However, your child must be old and mentally mature enough to talk and understand to participate in the test. A toddler would not understand the words flashed to him during the test.

Who conducts the Wada test?

A team of experts will conduct this test-

• An epileptologist is a neurologist who specializes in epilepsy.
• An interventional neuroradiologist is an imaging doctor trained to perform catheterization procedures. During the Wada test, a radiologist inserts a catheter into both carotid arteries to administer anaesthetic medication.
• A neuropsychologist: Knowledge of how brain disorders affect your behaviour and cognition.

How to Prepare for a Wada Test?

You might be advised to hold some medications for up to two weeks from the test. Such medications include aspirin, NSAIDs, and blood thinners. However, you should take your prescribed drugs unless your doctor advises otherwise. You should also inform your doctor of some medications' allergies.

What happens before the Wada test in preparation?

You will be gowned when your procedure is going to start, and you will be readied for a shave of your groin as your provider will need access to a blood vessel in that area. Your provider will prepare you for an electroencephalogram by attaching glue electrodes to your scalp. The EEG will measure the activity of your brain during the test.

Your providers will inject you with some medication that will anesthetize your groin area's skin. Once that area is numb, they are going to put a needle into a blood vessel in your leg. Next, they will insert a long, thin tube called a catheter into the blood vessel. They will advance the catheter into an artery in your neck called the carotid artery. As this happens, you might feel a metallic taste and warmth in your mouth. It's going to feel some pressure, but it shouldn't hurt.

Before you have the Wada test, you will have an angiogram. An angiogram checks for abnormal blood flow within your brain and ensures there is nothing wrong with your brain before conducting the Wada test.

How is a Wada test performed?

Your interventional neuroradiologist will make half of your brain fall asleep by placing anesthetic medication in your catheter within the left or right carotid artery. If it enters your right carotid, then part of your brain simply cannot communicate with the other side of your body. This can make you see stars, feel that something is pushing on your eye, and warm your face. You'll lose the temporary ability to move the opposite side of your body. They will confirm to you that your brain is sleeping when they check the recordings from the EEG.

Once your providers are confident that one side of your brain is asleep, your epileptologist or neuropsychologist will ask you to try talking and show you cards with words and pictures. They will tell you to try remembering what you see. You may feel weak and have slurred normal speech. You may also fall asleep during the test.

In some situations, people are unable to speak at the test time. Under the following conditions, the test is not as helpful:

• When a child is under 10 years.
• If testing causes seizures during the process.
• If a patient's IQ is lower than 70.
• There will be doctors to help you if you are scared or worried.

The anesthesia will dissipate after a few minutes, and the resting half of your brain will be awake. The epileptologist or neuropsychologist will question what you recall. If you don't remember, they will present the cards individually and ask if you've ever seen them. That's okay, you don't have to remember what you saw on the cards.

After a while, your doctors will use the other side of your brain. They'll retract the catheter and advance it carefully into the second internal carotid artery. They'll repeat the angiogram. Once again, you'll see cards—different ones. When fully awake, you'll be questioned again what was on those cards.

Is the WADA test is given to an awake patient?

Yes, you will be awake for the procedure.

How long will the test last?

The duration of the Wada test differs from one medical center to another but usually takes around three to four hours. Generally, in most cases, each side of your brain will be tested during the test. You'll wait for a very small period until you feel you are recovered so that they can get on with the second side.

What happens after testing?

After the test, you will rest in the recovery unit. Periodically, your healthcare providers will monitor a pulse in your leg where the catheter was inserted. They will also monitor the dressings placed to cover the cut in your groin area and check if your sense of touch has returned to normal. They do all this to ensure you have normal circulation in your leg.

You can go home later in the day. You will likely be cautioned to avoid heavy exercise for 24 to 48 hours.

Is the Wada test invasive? Is it high-risk? Are there potential side effects?

The Wada test is very safe and low-risk. If you do experience some Wada test side effects, it'll probably be pain where the catheter was inserted (after the numbing medication has worn off). Rare complications include:

Because the Wada test is an invasive procedure, it carries a very low risk for bleeding and infection. If you have any of the following risk factors, that does increase your chance, but again, your chances are low. You are age 65 or older. You have atherosclerosis, or hardening of the arteries. You have had high cholesterol.

What do Wada test results mean?

The Wada test will help your treatment team determine which side of the brain is dominant for language, and which side is dominant for memory. They will compare this information with information from previous tests that indicate where seizures occur in your brain. Once all this information is compiled, your surgeon can see if any additional risks from brain surgery will impact your ability to function in terms of language and memory.

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