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Pro tips for LPs in kids


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Though less commonly performed than it used to be, the lumbar puncture remains a key skill to master for anyone practising acute paediatrics. December’s Archives of Disease in Childhood Education and Practice contains an excellent paper entitled “How to use… lumbar puncture in children” (1), which flashes more pearls than a 4th of July garden party in the Hamptons. We share some of its wisdom below but highly recommend reading the paper to anyone who considers LP within their scope of practice.

How much is too much?

Adults have a CSF volume of about 150 mls and produce it at somewhere between 14-36 mls/hour. Neonates have about 50 mls of CSF, which they produce at a rate of 25 mls/day. Twenty drops of CSF equates to about 1 ml. How much CSF you need to take depends on what you want to do with it but 1.5 mls (or 30 drops) should be both safe and sufficient for your smallest patients.

It’s all about position

LP is commonly performed in the left lateral position in children. Hip flexion opens up the intervertebral spaces and makes the procedure easier. Neck flexion does nothing to help the procedure and will probably make it more uncomfortable for the child as well as making it harder for them to breathe. Supporting neonates in the sitting position with their hips flexed and their legs forward is associated with wider intervertebral spaces and less hypoxia than the left lateral position in this age group. Anecdotally I have recently changed my routine practice for neonatal LPs from left lateral to sitting and it also seems to be easier for holders with a wider range of experience to achieve an optimal position in relative comfort.

What am I aiming at?

The spinal cord in adults and older children ends around L1-L2, in neonates it extends down to L3. The sub-arachnoid space extends down to S2. L4-L5 is generally the best area to aim for (bearing in mind we are not always in the space we think we are) though L3-L4 is also OK. With the child in an appropriate position a line drawn between the most superior aspect of both Iliac crests (Tuffier’s line) crosses the midline over the body of L4 so the space just below this is ideal.

How deep do I need to go?

Medical folklore contains a few different answers to this question but the most scientific answer I have seen is following formula (2)

Depth (mm) = 0.4 x Weight (kg) + 20

So in a 10 kg child CSF should be found at a depth of 24 mm.

How can I make it more comfortable for the patient?

Use topical anaesthetic. EMLA has been shown to help in neonates(3). Post LP headache may be reduced by:

  • Using a smaller needle (25g in neonates, 22g in others)
  • Replacing stylet prior to needle withdrawal
  • Orientate the needle with the bevel parallel to the spine so it will separate the longitudinally running fibres of the Dura. (I think this feels natural in the left lateral position but requires more thought in the sitting position).

Have you thought about…

…CSF lactate? This is quite a good discriminator between viral and bacterial meningitis with levels over 3.5 suggestive of bacterial CNS infection. It’s not quite as accurate after antibiotic administration but may still be clinically useful.

…USS guidance? This is still waiting for a decisive trial in kids but small studies have shown it to be a promising option for further exploration.

Defence against the dark arts

Many a mythical formula has been conjured up to interpret a white cell count in the context of bloodstained CSF. The authors of this paper suggest you can get a feeling by comparing the ratio of white cells to red cells in the peripheral blood and basing your maths on this, but wisely acknowledge that accurate interpretation is difficult in this context. It’s also worth highlighting the well described trap that a normal CT does NOT exclude raised intracranial pressure.

Though LP is a procedure I perform fairly frequently this paper has shone a spotlight into several dusky areas of my knowledge and I hope it will suitably illuminate yours. Finally, if I am asked to supply a question for next year’s Christmas quiz it may well be “Where can you find Tuffier’s line?”.


  1. Schulga P, Grattan R, Napier C, et al. How to use… lumbar puncture in children. Arch Dis Child Educ Pract Ed 2015;100: 264–271.
  2. Bailie HC, Arthurs OJ, Murray MJ, et al. Weight-based determination of spinal canal depth for paediatric lumbar punctures. Arch Dis Child 2013;98:877–80.
  3. Kaur G, Gupta P, Kumar A. A randomized trial of eutectic mixture of local anesthetics during lumbar puncture in newborns. Arch Pediatr Adolesc Med 2003;157:1065–70.

About the authors

  • Ben Lawton is a paediatric emergency physician interested in education, retrieval medicine and simulation. Lives in Brisbane where he enjoys falling off his mountain bike and being outsmarted by his pre-teen children. @paedsem | + Ben Lawton | Ben's DFTB posts


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3 thoughts on “Pro tips for LPs in kids”

  1. Hi Ben,

    Great to read more about the procedures you do routinely. Keen to know more about this sitting position for Neonates. I agree neck position has nothing to do with positioning for the procedure. Similarly, if both the shoulder blades are in the same vertical line, the neck can be extended as per the comfort of child/Neonate. This is just my observation, would love to know what you think about it.

    Another observation with regards to adult size Teenagers, good to use stabilizers, it prolongs procedure time but improves adequate sampling.

    Any comments on post procedure care of Neonates?


  2. We received a comment on our Facebook page questioning the choice of needle size mentioned above given that in this person’s experience adult anaesthetists are using more 24-27g needles and they are therefore wondering whether we should be going smaller. This is a good question to which I don’t have a clear cut answer that I am completely comfortable with. Certainly smaller needles have been associated with reduced post LP headaches in adults (see ref 9 by Ahmed et al from the Schulga paper) but in what I think was a cleverly designed paediatric study (Crock C, Orsini F, Lee KJ, et al. Arch Dis Child 2014;99:203–207) the use of 22g vs 25g needles did not lead to a difference in post LP headaches and the use of 25g needles did lead to longer procedure times, the relevance of which will depend on the circumstances/sedation used. It is clearly reasonable to make a logical argument that bigger needles should lead to more CSF leak and consequently more post LP headache, and Dr Crock’s study did find that the functional impact on families of post LP headache was moderate to severe so reducing it is without doubt a noble aim. It is also possible there is a type 2 error in that single study, but the results would suggest using a 22g needle in bigger kids will give a shorter procedure with no increase in post LP headache. We would love to read your thoughts in the comments section on this page.



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