What is a Lumbar Puncture?
Lumbar puncture (LP, sometimes referred to as a spinal tap), is a medical procedure that involves collecting a sample of cerebrospinal fluid (CSF). CSF is a substance that surrounds the spinal cord and is present in the brain in compartments (ventricles). The purpose of CSF is to cushion the brain from vibration, as well as provides nutrition and immune functions in the central nervous system [1]. CSF can be tested for signs of medical conditions and infections.
Why is a Lumbar Puncture Performed?
A lumbar puncture is performed to obtain CSF, which contains a large portfolio of diagnostic markers. A lumbar puncture is used as a diagnostic test, and CSF is analysed in the laboratory. Multiple laboratory evaluations are performed, which are similar to those used to analyse blood, including:
- complete cell count,
- glucose and protein levels,
- presence of bacteria,
- presence of antibodies,
- presence of protein markers for various diseases [2].
In addition, CSF is a vital source of biomarkers and molecules of interest in research of diseases of the nervous system, including Alzheimer's or Parkinson's [3, 4].
How is a Lumbar Puncture Performed?
A lumbar puncture involves placing a needle into the spinal column and allow for CSF to drip out. The patient is usually positioned lying on their side or sitting up. The procedure involves:
- sterilising the area,
- applying a local anaesthetic to numb the area,
- inserting a spinal needle between two vertebrae in the lower back (lumbar spine region),
- advancing the needle through the dura (protective layer surrounding the spinal canal) into the subarachnoid space where the CSF circulates,
- allowing the CSF to drip out into the collection container [3].
Risks of Lumbar Puncture
A lumbar puncture is considered a very safe procedure, however, it does carry some risks (as is the case with every medical procedure). Some of the potential risks include:
- bleeding from the puncture site into the CSF,
- allergic reaction to the anesthetic,
- infection at the puncture site.
Some people may experience a headache after the procedure; this is fairly common, however usually goes away within 24 hours [5, 6, 7].
In very rare cases, serious complications can occur, including:
- damage to the spinal nerves,
- persistent leaking of the CSF at the puncture site,
- and brain herniation if a brain mass is present [8].
A lumbar puncture is particularly dangerous for people with clotting problems such as a low platelet count or those on blood thinners, as they have a heightened risk of bleeding [5, 6] and therefore LP should be very carefully considered.
What is an Epidural?
An epidural is an anaesthetic procedure used to numb the lower body. It is commonly used during labor and delivery. The procedure involves administering anesthetic medication into the epidural space of the spine [9].
Epidurals are one of the most commonly-used modalities of pain management anesthesia. Many women choose to have an epidural for a more comfortable birthing experience. In some cases, an epidural may be a medical necessity, such as with a cesarean delivery (C-section) [9].
How is an Epidural Performed?
The procedure involves placing a catheter into the surrounding the spinal cord without perforating the dura. The patient is usually seated, leaning forward for the procedure. This involves:
- sterilising the area,
- applying a local anaesthetic to numb the area,
- inserting a needle between two vertebrae in the lower back (lumbar spine region) into the epidural space,
- advancing a catheter (a small-diameter, flexible tube) through the needle and removing the needle,
- delivering the medication through the catheter [9].
The procedure takes about 10 minutes, and the effects of the epidural can be felt within an additional 10-15 minutes [9].
Risks of an Epidural
Epidurals are safe and common procedures, however, they do carry potential risks. These can include:
- back pain and soreness,
- bleeding from the puncture site,
- fever,
- breathing difficulties,
- drop in blood pressure [9].
However, these side effects are generally rare. In some very rare cases (between 1 in 4000 and 1 in 200,000 cases), the procedure can result in nerve damage [2]. Other potential complications when epidural is used in childbirth include increased risk of tearing during vaginal delivery, and difficulty in pushing which can increase the chance of needing interventions such as forceps-assisted delivery or a switch to a C-section [5].
What are the differences between a lumbar puncture and an epidural?
A lumbar puncture and an epidural are two different medical procedures that involve inserting a needle into the spinal area. There are, however, major differences between the procedures.
- Purpose - LP is a diagnostic procedure (aiming to obtain a sample), whereas an epidural aims to deliver drugs.
- Location - In a LP, the needle is advanced through the dura to reach the cerebrospinal fluid. Epidural does not penetrate the dura.