It is a medical procedure in which a needle is inserted into the spinal canal, most often to collect cerebrospinal fluid (CSF) for diagnostic tests.
Lumbar puncture (LP) is also known as a spinal tap.
The main reason for a lumbar puncture is to help diagnose diseases of the central nervous system , including the brain and spine. Examples of these conditions include meningitis and subarachnoid hemorrhage .
It can also be used therapeutically in some conditions. Increased intracranial pressure (pressure in the skull) is a contraindication, due to the risk of brain matter being compressed and pushed into the spine.
It is carried out in the hospital by a doctor or specialized nurse. The procedure is generally performed under local anesthesia using sterile technique.
A hypodermic needle is used to access the subarachnoid space and the collected fluid. The fluid can be sent for biochemical, microbiological and cytological analysis.
The reason for a lumbar puncture may be to make a diagnosis or treat a disease. A lumbar puncture can be used to:
- Taking a sample of fluid from the spinal cord (cerebrospinal fluid) or measuring fluid pressure to help diagnose a condition.
- Inject medications, such as pain relievers, antibiotics, or chemotherapy.
- Remove some fluid to reduce pressure on the skull or spine.
The main diagnostic indications for lumbar puncture are for the collection of cerebrospinal fluid (CSF).
The most common target is suspicion of meningitis, as there is no other reliable tool with which to exclude meningitis, a life-threatening but highly treatable condition.
A lumbar puncture can also be used to detect if someone has ‘Trypanosoma brucei’ at ‘Stage 1’ or ‘Stage 2’. This is due to higher rates of meningitis than in older people.
Babies also do not reliably display the classic symptoms of meningeal irritation (meningism) such as a stiff neck and headache, as adults do.
Cerebrospinal fluid containing less than 10 red blood cells (RBC) / mm³ constitutes a “negative” tap in the context of treatment for subarachnoid hemorrhage, for example. Taps that are “positive” have a red blood cell count of 100 / mm³ or higher.
Serial lumbar punctures may be useful in the temporary treatment of idiopathic intracranial hypertension (IIH). This disease is characterized by increased pressure of cerebrospinal fluid that can cause headache and permanent loss of vision.
While the mainstays of treatment are medications, in some cases, multiple spinal tap can improve symptoms. It is not recommended as a basic treatment due to the discomfort and risk of the procedure, and the short duration of its effectiveness.
In addition, some people with normal pressure hydrocephalus (characterized by urinary incontinence, a modified ability to walk properly, and dementia) receive some relief from symptoms after removal of the cerebrospinal fluid.
What you can expect
Lumbar puncture is usually done in an outpatient center or hospital. Your doctor will discuss the potential risks and any discomfort you may feel during the procedure.
If a child has a lumbar puncture, a parent is generally allowed to stay in the room.
Before the procedure
Your doctor or nurse should explain what will happen and why you need a lumbar puncture. You may have a CT scan or MRI to make sure you need a lumbar puncture and it is safe to have one.
Tell the hospital if you are taking blood-thinning medication (such as blood thinners), such as warfarin. You can eat, drink and take medicine as usual and you will be asked to sign a consent form.
You are asked to change into a hospital gown before the procedure; you may also want to use the toilet. There are a few possible positions for this test. Typically, you lie on your side with your knees pulled up to your chest, or you sit and lean forward on a stable surface.
For an infant or toddler, someone will hold the child in position during the procedure.
During the procedure
In most cases, a lumbar puncture is performed as an emergency procedure to quickly diagnose meningitis. In some cases, it is done on an outpatient basis for other reasons.
Typically, you lie on a couch on your side with your knees against your chest. Sometimes it is done with you sitting and leaning forward on some pillows. The doctor will clean an area of your lower back with an antiseptic.
They will then inject some local anesthetic, in the lower back, into a small area of skin that is in a space between two lower spinal bones (vertebrae), to numb the puncture site before inserting the needle.
Local anesthesia burns / stings a bit at first when injected, but then leaves the skin numb. You will be awake during the procedure. Children can also be given medicine to help them relax and stay still.
The doctor then inserts a thin, hollow needle through the skin and tissues between two lower vertebrae (lumbar region), through the spinal membrane (dura), and into the spinal canal, into the space around the spinal cord. which is filled with cerebrospinal fluid.
Because the skin is numbed under local anesthesia, most people do not feel pain. You may feel pressure when you press the needle. However, some people have a sharp sensation in their back or leg when they push the needle.
Some fluid leaks through the needle and collects in a sterile pot. If you have possible meningitis, this fluid sample is sent to the laboratory to be examined under a microscope to look for germs (bacteria).
It is also “grown” to see if any bacteria grow and what type they are. The liquid can also be tested for protein, sugar, and other chemicals if necessary.
Sometimes the doctor will also measure the pressure of the fluid. This is done by connecting a special tube to the needle, which can measure the pressure of the fluid that comes out. The needle is generally in around 1-2 minutes.
If necessary, a drug or substance is injected. As soon as the required amount of fluid is collected, the needle is removed and the puncture site is placed in an adhesive plaster or covered with a bandage over the needle entry site.
The entire procedure generally takes between 30 and 45 minutes; Your doctor may suggest that you lie down after the procedure and you will need to stay in the hospital for at least another hour while the nurses monitor you.
You will be able to go home the same day if you are feeling well enough, but you will not be able to drive home.
Sometimes an ultrasound can be used as a guide during the procedure in infants and young children. Ultrasound can help prevent insertion of the needle too far.
After the procedure
You can return to work if your job does not require you to be physically active. Discuss your activities with your doctor if you have questions.
Take a pain reliever An over-the-counter pain reliever that contains acetaminophen can help reduce a headache or back pain.
The doctor or nurse who performs the lumbar puncture can often tell you some of the results right away and explain what they mean.
You may need to wait at least 48 hours for full results. Some lab test results are available within a couple of hours in an emergency.
The cerebrospinal fluid that is collected during a lumbar puncture contains protein and glucose and may also contain white blood cells. It will be examined for any disturbances in the normal flow of cerebrospinal fluid or damage to the blood- brain barrier .
The spinal fluid samples are sent to a laboratory for analysis. Laboratory technicians check several things when examining spinal fluid, including:
General appearance : spinal fluid is normally clear and colorless. If it is cloudy, yellow or pink in color, it could indicate abnormal bleeding. Spinal fluid that is green could indicate an infection or the presence of bilirubin.
Protein (total protein and the presence of certain proteins) : Elevated levels of total protein (more than 45 milligrams per deciliter (mg / dL)) may indicate an infection or other inflammatory condition. Specific lab values may vary from medical facility to medical facility.
White blood cells : Spinal fluid normally contains up to 5 mononuclear leukocytes (white blood cells) per microliter. An increase in the number may indicate an infection. Specific lab values may vary from medical facility to medical facility.
Sugar (glucose) : A low level of glucose in the spinal fluid can indicate infection or another condition.
Chemical tests : detect or measure chemicals in the cerebrospinal fluid, including levels of protein and glucose, which generally correlate with their concentration in the blood.
Infectious disease tests – Numerous tests can identify microorganisms if an infection is suspected.
Depending on the test results and the signs and symptoms the person experienced, a doctor may perform further tests. If analysis of the cerebrospinal fluid identifies any irregularities, a doctor will recommend additional tests to help make a diagnosis.
Are there any side effects or risks of a lumbar puncture?
A lumbar puncture is generally a safe procedure, and serious side effects are rare.
Some people develop a headache after the test. This usually occurs after a few hours, which can last up to a week, you will be given pain relievers in the hospital if you need them.
People have described the pain as a dull or throbbing ache in the front of the head, sometimes spreading to the neck and shoulders.
It is best to lie down for a few hours after the test, as this makes the headache less likely to develop.
Over-the-counter medications can help relieve pain, but if the pain is severe or accompanied by vomiting and illness, it is important to seek medical attention.
To reduce the risk of developing a post-lumbar puncture headache, a person will be asked to lie on their back silently and not lift their head for 1 to 2 hours after the procedure.
The lumbar puncture is done below the end of the spinal cord where there are small filaments of nerves. Sometimes the needle can come into contact with a small vein and cause a traumatic blow.
If this happens, a small amount of blood may leak into one or more of the samples, which can affect the results.
You may also develop lower back swelling and pain where the needle was inserted, while others may also feel pain in the back of the legs; this should get better on its own after a few days and is usually nothing to worry about.
Other problems are rare, for example infection or bleeding from the needle entry site. Any damage to the spinal cord or brain as a result of lumbar puncture is rare.
A person may also experience some bruising and swelling related to a small amount of fluid that leaks out and collects under the skin. This tends to go away without treatment.