A lumbar puncture may be done in your doctor's office, in an emergency room, or at your bedside in the hospital. It may also be done in the radiology department if fluoroscopy is used.

You will lie on a bed on your side with your knees drawn up toward your chest. Or you may sit on the edge of a chair or bed and lean forward over a table with your head and chest bent toward your knees. These positions help widen the spaces between the bones of the lower spine so that the needle can be inserted more easily. If fluoroscopy is used, you will lie on your stomach so the fluoroscopy machine can take pictures of your spine during the procedure. See a picture of a lumbar puncture .

Your doctor marks your lower back (lumbar area) with a pen where the puncture will occur. The area is cleaned with a special soap and draped with sterile towels. A numbing medicine (local anesthetic) is put in the skin.

Then a long, thin needle is put in the spinal canal. When the needle is in place, the solid central core of the needle (stylet) is removed. If the needle is in the right spot in the spinal canal, a small amount of cerebrospinal fluid (CSF) will drip from the end of the needle. If not, the stylet will be put back in and the needle will be moved in a little farther or at a different angle to get to the fluid. Your doctor may need to move to another area of your spine if it is hard to get to the spinal fluid.

When the needle is in the spinal canal, a device called a manometer is hooked to the needle to measure the pressure of the CSF. You may be asked to straighten your legs while you are lying down. Your doctor takes the pressure reading, called the opening pressure, and checks whether the fluid is clear, cloudy, or bloody. Several small samples of fluid are collected and sent to the lab for study.

A final pressure reading, called the closing pressure, may be taken after the fluid samples are done. The needle is taken out and the puncture site is cleaned and bandaged.

The doctor also may look into your eyes using a special lighted scope (ophthalmoscope) to see if the pressure is high.

The entire procedure takes about 30 minutes.

To lower your chance of getting a headache following a lumbar puncture, you may be told to lie flat in bed or with your head slightly raised for 1 to 4 hours. Since your brain makes new CSF all the time and replaces it 2 to 3 times a day, the small amount of fluid that is removed will be quickly replaced. You may be told to drink extra fluids after the procedure to help prevent or to reduce the severity of a headache.