Lumbar puncture: how is this technique done and what are the risks

Lumbar puncture is a procedure that usually aims to collect a sample of cerebrospinal fluid that bathes the brain and spinal cord, by inserting a needle between two lumbar vertebrae until reaching the subarachnoid space, which is a space between layers that line the spinal cord, where the fluid passes.

This technique is used to identify neurological changes, which can be infections, such as meningitis or encephalitis, as well as diseases such as multiple sclerosis or subarachnoid hemorrhage for example. In addition, it can also be used to insert drugs into the cerebrospinal fluid, such as chemotherapy or antibiotics.

What is it for

Lumbar puncture has several indications, which include:

• Laboratory analysis of cerebrospinal fluid, to identify and evaluate diseases; Measurement of cerebrospinal fluid pressure; Spinal decompression; Injection of medications such as antibiotics and chemotherapeutic agents; Staging or treatment of leukemias and lymphomas; Injection of contrast or radioactive substances to perform radiographs.

Laboratory analysis is intended to detect the existence of changes in the central nervous system, such as bacterial, viral or fungal infections such as meningitis, encephalitis or syphilis, for example, to identify bleeding, cancer or the diagnosis of certain inflammatory or degenerative conditions of the nervous system, such as multiple sclerosis, Alzheimer's disease or Guillain-Barré syndrome.

How the puncture is done

Before the procedure, no special preparation is required, unless there is a clotting problem or the use of some medication that interferes with the technique, such as anticoagulants.

The person can be placed in one of the two positions, or lying on the side with the knees and the head close to the chest, called the fetal position, or sitting with the head and spine flexed forward and with the arms crossed.

Then, the doctor applies an antiseptic solution to the lumbar region and looks for the space between the L3 and L4 or L4 and L5 vertebrae, being able to inject an anesthetic medication in this location. Then a fine needle is inserted slowly and between the vertebrae, until it reaches the subarachnoid space, from where the liquid will drain and drip through the needle, being collected in a sterile test tube.

Finally, the needle is removed and a dressing is applied to the bite. This procedure usually lasts a few minutes, however the doctor may not be able to obtain the cerebrospinal fluid sample right when inserting the needle, and it may be necessary to deviate the direction of the needle or make the sting in another region again.

Possible side effects

This procedure is generally safe, with low chances of presenting complications or risks for the person. The most common adverse effect that can occur after a lumbar puncture is temporary headache due to a decrease in cerebrospinal fluid in the adjacent tissues, and nausea and vomiting can also be avoided if the person lies down for a while after the exam.

There may also be pain and discomfort in the lower back that can be alleviated with painkillers prescribed by the doctor, and although it is rare, infection or bleeding may also occur.

Contraindications for lumbar puncture

Lumbar puncture is contraindicated in the presence of intracranial hypertension, such as that caused by a brain mass, due to the risk of displacement of the brain and herniation. It should also not be done on people who have a skin infection to be punctured or who have a brain abscess.

In addition, the doctor should always be informed about the medication they are taking, especially if the person is taking anticoagulants such as warfarin or clopidogrel, due to the risk of bleeding.

Results

The cerebrospinal fluid samples are sent to the laboratory for analysis of various parameters such as appearance, which is usually transparent and colorless. If it is yellowish or pink or has a cloudy appearance, it may indicate infection, as well as the presence of microorganisms such as bacteria, viruses or fungi.

In addition, total proteins and quantity of white blood cells are also evaluated, which, if elevated, may indicate infection or some inflammatory condition, glucose, which, if low, may be a sign of infection or other diseases, as well as the presence of abnormal cells may indicate certain types of cancer.