Patients will be asked to either sit up or lie down on their sides with the back parallel to the bed and the chin tucked under and the legs curled in the fetal position. The healthcare provider will use the bony protrusions of the hip to determine the most appropriate location to remove fluid. This is usually known as the lower lumbar region.
A germ cleaning solution will be used to clean off the area. A sterile sheet will be draped over the body. In infants and small children, a numbing cream will be placed on the skin local about 1 hour before the procedure. In adults, numbing medicine will be injected under the skin.
A thin 20-gauge needle will then be inserted into the interspace between the vertebra. Depending on how much subcutaneous tissue there is, this may require shallow or deeper penetration of the needle. There may be an audible "pop" when the needle penetrates the dura (membrane that surrounds the spinal cord and encases the fluid).
At that point there will be fluid flowing out of the needle and this will be collected in plastic containers. Under normal circumstances, the opening pressure will be measured with a manometer and spinal fluid will be collected and sent for evaluation under the microscope.
Under experienced hands there should not be any pain. There may be a feeling of pressure when the needle is inserted but with appropriate anesthetic, this should not hurt. Occasionally, some people may feel numbness shooting down the leg. This may be due to irritation of a nerve root.
The needle is withdrawn, the sensation subsides and is not permanent. Following the procedure, the patient is advised to remain lying down for a short time to prevent low-pressure headaches. The entire procedure takes approximately 20 minutes.
