The Wada test, officially know as the intracarotid sodium amobarbital test, looks at memory and language functions by putting one cerebral hemisphere to sleep with a short-acting anesthetic called amobarbital, and studying what functions are still working in the other hemisphere.
The test begins with an angiogram, a test that examines the flow of a dye through the blood vessels. A thin plastic tube (catheter) is introduced through an artery in the inner portion of the upper thigh. A local anesthetic is given to numb the area, and a needle is then inserted into the artery. The tube is threaded through the needle, and the needle is removed. There is some mild discomfort during the local anesthesia, but the rest of the test is painless. The tube is guided up to the carotid artery in the neck. A small amount of contrast dye is injected through the tube into the artery, and x-rays are taken to study the flow of blood in the brain. Some warmth or flashing lights may be experienced with the injection of the dye. Next, the radiologist injects the amobarbital, which quite literally puts almost half of the cerebral hemisphere to sleep for several minutes.
Immediately after the amobarbital injection, tests are given to see how well language and memory are working with half of the brain sleeping. This provides information on the functions of the cerebral hemisphere that is sleeping and the hemisphere that is awake. The same procedure is usually repeated on the opposite side after a delay to ensure that the patient’s level of alertness has returned to normal. Most centers wait 30 to 60 minutes, and some wait a day
Like any other test involving a cerebral angiogram, this test has the possibility of causing a stroke, but the risk is extremely low. The risk is greatest, but still quite low, in older people with atherosclerosis (a disease in which arteries are partially or completely clogged).