A lumbar puncture (LP) is a diagnostic procedure in which the lower part of the spine is pierced to get a sampling of cerebrospinal fluid (CSF). This could reveal disorders such as infection, inflammation or bleeding. The procedure for a lumbar puncture involves inserting a needle through the gap between two vertebrae so that it reaches the space around the spinal cord. Fluid samples are withdrawn through the needle and collected inside plastic tubes. A local anesthetic numbs the tissue around the needle entry point, and the whole procedure takes around 45 minutes.
The correct procedure for a lumbar puncture involves placing the patient in a position, either on the side or sitting, with the chin and thighs curled toward the chest. This curves the spine, opening up the spaces between the vertebrae and making it easier to insert a needle. After antiseptic has been applied and local anesthetic has been injected to numb the skin of the lower back, a needle is introduced between two of the large lumbar vertebrae. Normally, patients experience a feeling of pressure but the anesthetic should prevent any pain.
It is important that patients lie flat on their backs for several hours following the lumbar puncture procedure. This helps prevent headaches from occurring. It is also advisable to drink plenty of liquids.
Even when the correct procedure for a lumbar puncture is followed, complications occasionally occur. Fortunately, these are usually minor. Sometimes, there may be a small amount of bleeding from the puncture site. In some cases, the doctor may not feel confident that the needle can be inserted accurately and the procedure may have to be abandoned.
Lumbar puncture, which is commonly referred to as spinal tap, is most often used to diagnose problems such as meningitis. Meningitis is a condition in which the membranes enclosing the brain and spinal cord are inflamed, typically due to infection. Bacteria or viruses may be found in the sampled cerebrospinal fluid (CSF). Alternatively, medical analysis of CSF might reveal red blood cells, which could indicate a brain hemorrhage.
Occasionally, therapeutic lumbar puncture is performed to treat a condition called pseudotumor cerebri in which the intracranial pressure is too high. The intracranial pressure is the pressure inside the skull, and if it is raised, it can cause swelling of the optic nerve and blindness. In pseudotumor cerebri, it is sometimes possible to lower intracranial pressure by following the procedure for a lumbar puncture, drawing out some of the cerebrospinal fluid which surrounds the brain and spinal cord.
