Let's talk about infant LP stylet practices for insertion & removal. As an intern, I memorized these techniques, but didn't understand why.

I hope this #tweetorial helps explain the WHY and improves your procedural acumen! #PEM #PEMTwitter

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Img: NEJM

It's important to understand the anatomy of an LP needle/stylet. An LP needle is hollow with an inner stylet. Why the stylet? Why not just use a hollow needle to access the subarachnoid space?

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Img: JAMA

Standard LP needles are "cutting" (dissect soft tissue). A hollow needle without a stylet traps skin cells & pushes them into the subarachnoid space, causing a clogged needle, or in the long term, an epidermoid tumor. Adding a stylet prevents this.

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Img: @DFTBubbles

BUT, with a stylet, you can't see CSF return. In infants, it's easy to backwall into the surrounding venous plexus ("traumatic tap"). In early stylet removal (insert needle/stylet through dermis only, then remove stylet), you see CSF as soon as you're in.

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Img: @PEMTweets

So you're in the space () and have collected your CSF. It's important to replace the stylet before you remove the needle. Why?

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Img: EM News

The short term reason to replace the stylet is that it decreases post-LP headache (in babies: fussiness). It's theorized that nerves are sucked into the needle then drawn through the dura as you remove the needle, resulting in prolonged CSF leakage.
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Img: Google

The long term reason is that dragging nerve fibers to outside the subarachnoid space can result in entrapped lumbar/sacral nerves and pseudomeningocele.

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Img: MSK Key

In summary:
*Using stylets to go through skin prevents epidermoid tumors & clogged needles
*Early stylet removal once through the skin minimizes "traumatic taps"
*Stylet replacement before needle removal decreases post LP headache & nerve entrapment

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#FOAMed summaries w/references:
https://pemcincinnati.com/blog/why-we-do-what-we-do-early-stylet-removal-for-lumbar-puncture-in-infants/
https://rebelem.com/post-lumbar-puncture-headaches/
https://pedemmorsels.com/spinal-needle-stylet/

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