Take Home Point: Early stylet removal is a technique that results in a greater success rate on lumbar punctures performed on infants

Note: This post is an update from 2014 – yes, I’ve been blogging that long

There are numerous techniques that we can use to improve our likelihood of success in performing a lumbar puncture. There is one that has a bit of nuance to it that I thought would be an excellent theme for a Why We Do What We Do post. So, without further ado, let’s talk about early stylet removal. Somehow it got the nickname “The Cincinnati Method” – but this was well before my time in the Queen City.

How does one actually perform it?

  1. Insert the spinal needle with the stylet in place
  2. Advance completely past the epidermis and dermis (<1cm in most children)
  3. Remove the stylet
  4. Advance forward until reflux of CSF noted
  5. Reinsert the stylet and withdraw the needle

Here is a video tutorial on lumbar puncture that I produced for the AAP’s PediaLink platform. Skip ahead to 4:27 wish if you want to go to the early stylet removal part.

So, why does this technique actually make a difference?

In short, you avoid overshooting the subarachnoid space and hitting the vascular plexus of the ventral epidural space. Interestingly, you can measure the depth to the subarachnoid space if you’re interested by using the following calculation which I promise to never, ever ask anyone to do on a shift:

MATH ALERT!!! Depth of LP = 0.77cm + (2:56 × BSA [in meters squared]) MATH ALERT!!!

I think this diagram is really the most helpful in showing why early stylet removal is beneficial.

As you can see in the diagram above, with the stylet still in place if you enter in the midline perpendicular to the CSF target you have the maximum space from which to get fluid. But, if your angle of entry is slightly off (only a few degrees will do it) you can see that the angle becomes more magnified. Using early stylet removal will allow you to see reflux of fluid into the spinal needle the instant you enter the space, thus giving you confirmation before you “back wall” the needle into a venous plexus.

Are there any risks?

Those of us who have been performing LPs for a loooong time may recall an epoch where butterfly needles were used to perform LPs. Those procedures left patients at risk for intraspinal epidermoid tumors – late appearing intraspinal masses after an unstyleted needle pushing epidermal cells into the intraspinal space. These can create a mass effect. See this case series from a while back for more information on how they presented. Fortunately, the use of styleted needles mitigated this risk. Theoretically the early stylet removal technique could cause the same risks if the stylet was removed before passing through the dermis – fortunately the best practice technique specifies that you should not remove the stylet until you have passed through the epidermis and dermis. There is no evidence – case series or otherwise –

What’s the evidence?

You wouldn’t want me to recommend something without supporting evidence would you? Well, in 2006 Baxter et al. published their findings of a prospective observational study in PEDIATRICS. They reviewed 428/594 (72%) infant LPs  – 377 of which were performed by trainees. Seventy-four percent (279/377) of the trainee LPs were successful. Amongst other factors local anesthesia was used for 280 (74%), and 225 (60%) were performed with early stylet removal. They found the following;

  • LPs were more likely to be successful in infants >12 weeks of age – OR=3.1 (95% CI 1.2-8.5)
  • Local anesthetic use showed increased odds of success OR=2.2 (95% CI 1.04-4.6)
  • In infants ≤12 weeks of age, early stylet removal improved success rates – OR=2.4 (95% CI 1.1-5.2)
  • Position (upright vs side-lying), drape use, and year of training were not significant predictors of success

So, as you can see – there is evidence and it stands firmly in the camp of those patients under the age of 12 weeks. However, that being said, I use this technique no matter the age of the patient. I do think that this is an example of where understanding a little bit more about why a certain technique is used will make a difference. 

References

Baxter et al. Local anesthetic and stylet styles: factors associated with resident lumbar puncture success. Pediatrics. 2006 Mar;117(3):876-81. PMID: 16510670.

Bonadio, Pediatric lumbar puncture and cerebrospinal fluid analysis. J Emerg Med. 2014 Jan;46(1):141-50. PMID: 24188604.

Ziv et al. Iatrogenic intraspinal epidermoid tumor: two cases and a review of the literature. Spine (Phila Pa 1976). 2004 Jan 1;29(1):E15-8. PMID: 14699293.