Lumbar puncture 1

Important  - Good patient positioning and an experienced assistant are the most important factors for success.   

What is a lumbar puncture ?

A lumbar puncture is an invasive diagnostic test, involving the extraction of cerebrospinal fluid (CSF) for examination, and the measurement of pressure of the fluid.

The CSF is used to diagnose or rule out conditions such as meningitis, encephalitis, neoplasms of the brain or spinal cord, degenerative brain diseases, demyelinating disorders (e.g. MS) and autoimmune diseases of the central nervous system.

In anaesthesia, spinal anaesthetics are given by injecting local anaesthetics +/- opiates.    


- fever with no obvious clinical focus in an infant or toddler
- fever with headache and / or meningism
- fever and prolonged seizures
- possible subarachnoid haemorrhage     


- focal neurological signs
- GCS less than 9
- infants who are not responsive.    

Equipment you need

- An experienced assistant
- sterile dressing tray
- sterile drapes
- skin antiseptic - eg betadine,chlorhexidine
- gauze squares
- sterile CSF collecting tubes x3 : labelled 1- 3
- CSF manometer : older children
-local anaesthetic : 1% lignocaine + 1:100,000 adrenaline 5ml
- 5ml syringe and 25G needle for infiltration of local anaesthetic
- dressing for puncture site e.g. transparent film    

lp kit

Spinal needles - types

There is a choice between the traditional bevel point (Quincke needle) and a pencil point (Sprotte), shown here.

The pencil point needles seem to cause slightly less post-dural puncture headaches.    
Link Randomised controlled trial of different spinal needles (for spinal anaesthesia) 

lp need 

Spinal needles - sizes

The size (diameter) of the needle varies from 29G (the smallest) to 18G.
The risk of post LP headache seems to be related to the size of the needle, so smaller needles are better.
Thinner (25G or less) needles more difficult to use, as they also need a guide needle through which they are inserted. This is because they are so flexible they are difficult to push through the skin layers without bending.
The most commonly used size for diagnostic punctures is 22G.


30 mm for neonates and infants (although in neonates a normal 22G needle is often used)
50 mm for 4 - 10 yo
60 mm for older children
70-90 mm for adults

obese patients may require specially long needles

lp spinal

Quiz question 1


Which of the following is NOT an indication for a lumbar puncture ?

1) fever without a focus in child.

2) prolonged seizure with no precipitent.

3) to measure CSF pressure.

4) closed head injury

5) severe headache


Show answer


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