11/13/24, 7\:20 PM Guide | Lumbar puncture

Lumbar puncture

Table of contents

What is a lumbar puncture?

A lumbar puncture (LP), or “spinal tap”
, is an important and commonly used procedure carried out across a wide range of
specialities. It is, therefore, important to understand its indications, the steps involved and the potential complications.
It is also worth learning the layers the needle passes through during the procedure, as this is a common question in medical
exams (Figure 2). It should be noted that this guide is not intended to be used for performing this procedure on a patient.
Instead, it is aimed at informing medical students in preparation for exams.

Anatomy

A lumbar puncture is an invasive test designed to access the subarachnoid space in the lower spinal canal. The brain and
spinal cord are covered by three layers of meninges- the dura, arachnoid, and pia mater (Figure 1). The subarachnoid space lies
between the arachnoid and pia mater and contains a solution called cerebrospinal
that provides lubrication around the spinal cord, maintains intracranial pressure, acts as a mechanical shock absorber and
transports various metabolic products. The human body contains approximately 100-150ml of CSF. As you can see below, the
subarachnoid space lies close to the ventral and dorsal columns of the spinal cord, therefore anatomical spatial awareness is
crucial to performing a safe and accurate lumbar puncture.
Figure 1. Transverse section of the spinal cord showing the meningeal layers and CSF in the subarachnoid space.

Indications

A lumbar puncture may need to be performed for a variety of reasons, both diagnostic and therapeutic\: ²
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Cerebrospinal (i.e. meningitis, multiple sclerosis, subarachnoid haemorrhage)
Spinal epidural (i.e. during labour)
Spinal medications (i.e. analgesia, chemotherapy, antibiotics)
Fluid removal (i.e. to reduce intracranial pressure)

Contraindications

Performing a lumbar puncture in a patient with any of the following problems may be contraindicated and in rare
circumstances can lead to life-threatening complications. Therefore, a thorough review of the patient’s medical history and
presenting complaint should always be sought beforehand, and senior review or neurosurgical advice taken if there is any
doubt.
2,3
Suspicion of raised intracranial pressure
Anticoagulant therapy (i.e. Warfarin)
Thrombocytopenia or other clotting disorders
Suspicion of a spinal abscess
Risk of herniation (i.e. Arnold-Chiari malformation)
Acute spinal cord trauma
Congenital spinal abnormalities
In any of the above circumstances, imaging with CT or MRI should be undertaken before consideration of lumbar puncture.
3

Gather equipment

Gather the appropriate equipment to perform a lumbar puncture (these often come as a sterile lumbar puncture set in many
hospitals)\:
Lumbar puncture needle\: recent evidence supports the use of an atraumatic needle to reduce the risk of post-procedure
headaches. Needle size is based on experience and clinical judgement.
5
Sterile
Chlorhexidine cleaning solution (0.5 % in alcohol 70%) or alternatively iodine
Manometer\: to measure the opening pressure
Sample collection containers
Local anaesthetic (typically lidocaine 1%)
Syringe (5-10ml) and needles for local anaesthetic administration (usually need one for drawing up anaesthetic and one for
administration)
Dressing to apply after the lumbar puncture is complete
Pen for marking the planned insertion site

Introduction

Wash your hands and don PPE if appropriate.
Introduce yourself to the patient including your name and role.
Con
Explain what the procedure will involve using patient-friendly language\: " T o d a y I' v e b e e n a s k e d t o p e r f o r m a l u m b a r
p u n c t u r e , w h i c h i n v o l v e s i n s e r t i n g a
a n a e s t h e t i c , t o m a k e t h e p r o c e d u r e a s c o m f o r t a b l e a s p o s s i b l e . I t' s r e a l l y i m p o r t a n t t h a t w e c a r r y o u t t h i s t e s t b e c a u s e [ i n s e r t
r e a s o n t h e L P i s b e i n g p e r f o r m e d ] . T h e r e a r e s o m e c o m p l i c a t i o n s t h a t c a n b e a s s o c i a t e d w i t h p e r f o r m i n g a l u m b a r p u n c t u r e ,
s o m e o f t h e m o r e c o m m o n t h i n g s i n c l u d e a h e a d a c h e a n d s o m e b r u i s i n g o f t h e s k i n a f t e r t h e p r o c e d u r e . T h e r e a r e s o m e r a r e
b u t m u c h m o r e s e r i o u s c o m p l i c a t i o n s , w h i c h i n c l u d e d a m a g e t o n e r v e s r e s u l t i n g i n p a i n a n d w e a k n e s s i n t h e l e gs a n d a l s o
i n f e c t i o n .
"
Gain consent to perform a lumbar puncture.
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Ask the patient if they have any pain before continuing with the clinical procedure.

Identify the insertion site

Map out the insertion site on the patient\:
With the patient standing, mark out L4 by joining a line between the highest points of the iliac crests.
Palpate above for L3 and below for L5.
The insertion site can be marked out either between L3/4 or L4/5 depending on the patient's anatomical features.

Position the patient

Position the patient lying on their side in a fetal position\: ask the patient to
their chest.

Prepare the insertion site

Clean the insertion site and the surrounding area thoroughly using chlorhexidine solution and allow to dry.
Wash your hands and don sterile gloves.
Apply a sterile drape with an opening over the site of insertion.

Local anaesthetic

Draw up the local anaesthetic and then replace the drawing needle with a new one for the injection.
Inject local anaesthesia around the site and allow time for it to take e
It is important to warn the patient that this will sting initially but then should quickly go numb.

Perform the lumbar puncture

Advance the lumbar puncture needle through the insertion site slowly, tilted slightly cranially. The bevel of the needle
should face laterally as you insert it. If using an atraumatic needle, you
the longer atraumatic needle through this.
The needle passes through the following layers before it reaches the subarachnoid space\:
1. Skin
2. Subcutaneous fat
3. Supraspinous ligament
4. Interspinous ligament
5. Ligamentum
6. Dura mater
7. Subdural space
8. Arachnoid mater
As the needle passes through the three de
After the third ‘pop' (ligamentum
lumbar puncture needle. If there is no CSF
bevel of the needle to face cranially.
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Figure 2. Sagittal section of the lumbar spine showing the three spinal ligaments, which are passed through with the LP needle.

Measure the opening pressure

Once CSF is
and recording at what level the meniscus of the CSF settles at. Measurement of opening pressure does not need to be
performed routinely.

Collect a sample of CSF

CSF should be collected using an aseptic non-touch technique as it drips from the back of the lumbar puncture needle.
Removal of CSF can be diagnostic (e.g. suspected meningitis) or therapeutic (e.g. benign intracranial hypertension). You should
extract an appropriate volume based on your intentions (typically 8-15mL for diagnostic purposes), and place in the
appropriate laboratory containers.
For some conditions, such as subarachnoid haemorrhage, it is important to number the containers sequentially so you know
in which order the CSF samples were taken (this can allow you to di
haemorrhage).

Removal of the needle

Slowly remove the lumbar puncture needle and compress the site with some sterile gauze until you apply a dressing.
Immediately dispose of the lumbar puncture needle into a sharps bin.

To complete the procedure...

Dispose of the remaining clinical equipment into a clinical waste bin.
Wash your hands.
Explain to the patient that the procedure is now complete and advise them to lay
Dispose of PPE appropriately and wash your hands.
Ask the patient and nursing sta
Send the CSF samples to the laboratory for analysis.
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Interpretation of results

When a lumbar puncture is performed for diagnostic reasons, the results can be interpreted with a thorough analysis of the
CSF (Table 1). Some components of this analysis can be done at the bedside, while others require specialist review in the lab.
Component Where is this done? Interpretation
Opening
pressure
Bedside (attach a
manometer to the LP
needle after insertion)
Normal is 8-20cm CSF
7
Normal is clear
Cloudy/purulent suggests meningitis
Appearance Bedside
Blood-stained suggests a subarachnoid haemorrhage or a traumatic LP. A
SAH will typically result in multiple consistently bloody samples, whereas in
the case of a traumatic LP the amount of blood should reduce signi
in each subsequent sample.
Total protein Laboratory test Normal is 0.15-0.45 g/L
Glucose
Laboratory test-
(alongside blood glucose
concentration)
Normal is 40-60% of blood glucose
Gram stain and
culture
Laboratory test Performed if bacteria are suspected
High RBC is suggestive of a traumatic tap
High total WCC is suggestive of an infection
Microscopy for
cell counts
Laboratory test
High neutrophils suggest a bacterial meningitis
High lymphocytes suggest viral/TB/fungal meningitis
In patients presenting with clinical signs of meningitis (fever, neck sti
distinguish between- viral, bacterial, and tuberculous (Table 2). Viral meningitis is usually self-limiting, whereas bacterial
meningitis and tuberculous require prompt treatment with the appropriate antimicrobials. Therefore, if any form of meningitis is
suspected, microbiology results should not delay management, and patients should be started on immediate empirical
antibiotic therapy.
Viral Bacterial TB
Opening pressure Normal Raised Raised or Normal
Protein Raised or Normal Raised Raised
Glucose Normal Low Low
WCC Raised Raised Raised or Normal
Cells present Mainly lymphocytes Mainly neutrophils Lymphocytes

Complications

Headache
Infection
Bleeding
Cerebral herniation (i.e. Arnold-Chiari malformation)
Radiculopathy
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Back pain

References

1. Henry Gray. Gray's Anatomy. Thecal Sac. Available from\: [LINK].
2. Kimberly Johnson DS. Lumbar Puncture\: Technique, indications and complications in adults. UptoDate. 2018 [cited 2018 Jun 11].
Available from\: [LINK].
3. Engelborghs S, Niemantsverdriet E, Struyfs H, Blennow K, Brouns R, Comabella M, et al. Consensus guidelines for lumbar
puncture in patients with neurological diseases. Alzheimer’s Dementia Diagnosis, Assess Dis Monit. 2017;8\:111–26.
4. Rochwerg Bram, Almenawer Saleh A, Siemieniuk Reed A C, Vandvik Per Olav, Agoritsas Thomas LL et al. Atraumatic (pencil-
point) versus conventional needles for lumbar puncture\: a clinical practice guideline. BMJ. 2018;361.
5. Abe KK, Yamamoto LG, Itoman EM, Nakasone TAF, Kanayama SK. Lumbar puncture needle length determination. Am J Emerg
Med. 2005;23(6)\:742–6.
6. Henry Gray. Gray's Anatomy. Supraspinatus ligament. Available from\: [LINK].
7. Paul Hamilton IB. Neurological Investigations. In\: Kerr E, editor. Data Interpretation for Medical Students. 2nd ed. Lancaster\:
Carnegie Book Production; 2012. p. 223–7.

Reviewer

Mr George Spink (FRCS SN)
Consultant Neurosurgeon
Source\: geekymedics.com
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