Lumbar puncture

A lumbar puncture, also referred to as a
‘spinal tap’, is a commonly performed procedure carried out by all kinds of
doctors. It involves inserting a small needle into an area that surrounds the
spinal cord named the ‘sub-arachnoid space’ . Contained within this area is
something called ‘cerebrospinal fluid’ or CSF. CSF acts as a surrounding
cushion, helping to protect the spine and brain (the nervous system) from
injury as well as nourishing the cells that make up your nervous system.
Additionally, CSF can provide doctors with information regarding the health of
these structures. CSF is collected from the lower part of the back, named the
‘lumbar region’ . This is the safest place for CSF to be taken, hence the name
‘lumbar’ puncture. 

why do we do them?

Lumbar punctures are used for a variety of reasons. The first use involves helping doctors to diagnose patients with conditions or injuries of the nervous system. This includes:

– Infections such as meningitis and encephalitis

– Bleeds around the brain (what doctors may refer to as ‘subarachnoid haemorrhage’)

– Cancers of the nervous system and conditions such as multiple sclerosis. 

Lumbar punctures can also be used to measure the pressure of the CSF. If the pressure is too high, like in hydrocephalus, the lumbar puncture itself can alleviate some of this pressure so that the brain and spinal cord can function normally. 

Lastly, lumbar punctures can be used to administer important medicines and dyes into the CSF. Examples include antibiotics, pain relief, cancer drugs, dyes to help with imaging of the nervous system and finally anaesthesia so that the lower body is numb during an operation. Anaesthetists will often perform this and it is called an epidural. The technique is slightly different.

Lets take a look at the procedure

Before the lumbar puncture, you might be required to sign a consent form once you have been given information about the procedure, why it is being done and the potential risks. 

During the procedure you will be asked to lie on the side of your body with your knees tucked up to your chest.

This position helps to spread out the bones of the spine so that the needle can be inserted more easily to where it needs to get to. The chosen area will then be cleaned and some local anaesthetic inserted so that you do not feel the puncture. Once the lower part of your back is numb, the needle will be inserted through the skin and eventually into the space around the spinal cord.

Even though you won’t feel pain, it can still be uncomfortable and you will feel pushing and pulling.

Once it is in place, pressure can be measured, fluid for sampling can be obtained, and any medicines or dyes can be inserted. The whole process is expected to last approximately 45 minutes and is described by patients as somewhat uncomfortable. The medical team performing your procedure are aware of this and will aim to make you as comfortable as possible.

After the process is complete and the needle removed, a plaster will be placed over the site. You will be advised to lie flat for approximately an hour as the lumbar puncture can temporarily alter the pressures around the nervous system resulting in headaches. Headaches after a lumbar puncture are common and should ease after a couple of days. Staying hydrated and taking pain killers can also help with this.

Are there any risks involved with having a lumbar puncture?

Common side effects are expected after such procedures. These include headaches and some backache over the site. Serious complications are rare and if these were to occur, would normally happen during the procedure itself. An example may be inserting the needle at the incorrect angle, which can irritate local spinal nerves and cause some shooting leg/ back pain. If this were to occur, the doctor performing the procedure will immediately change the needle position.

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