Lumbar Puncture Part 2: Pearls, Pitfalls, and Troubleshooting

a monthly blog series on procedures

Take your LP skills to Eleven: this is spinal tap!

Last week we discussed the basics of the adult LP. This week we will guide you through some difficult scenarios and their solutions.


troubleshootingYour patient is nervous and squirmy

  • Consider having an assistant hold and position the patient.
  • Steady the shaft of the needle with your non-dominant hand.
  • Talk to the patient. Here are some examples of what you can say prior to the procedure:
    • “I will numb up your back, and that should be the only part that hurts.”
    • “Most of the procedure is just setting up my materials.”
  • During the procedure, the patient cannot see you, which can be anxiety provoking. Describe each step of the procedure in a calm manner. And try to avoid THIS.
  • If necessary, administer an anxiolytic such as a benzodiazepine.

troubleshootingYour patient is very sensitive to pain

  • First, lidocaine!
    • Did you inject enough volume into the deeper structures of the back? As Dr. Whit Fisher mentioned in the comments of the previous post, make sure you gather extra lidocaine (only 5ml in the LP tray). In a sterile fashion, draw up an extra 5-10 ml with the help of an assistant.
    • Note: if trying a new interspace, make sure this area is also anesthetized.
  • Patient still in pain? Consider administration of an analgesic such as an opioid.


pitfall-sign The vertebral column is easily visualized. You decide to start the procedure without palpating their back

WAIT! Like every procedure, success is all about preparation. Place the patient in the lateral recumbent position without the sterile drape, and palpate their posterior-superior iliac crests. Get to know their lower back. Use a marking pen to approximate your entry point.

pitfall-sign You injected an enormous wheal of anesthetic and now your landmarks are obscured

Only inject about 1 ml! Be frugal with the wheal.

pearl12 You are waiting to “feel a pop” as you pass the ligamentum flavum

You will often, but not always, feel this legendary “pop” just prior to entering the correct space for CSF flow. DO NOT depend on it. You may actually feel a series of pops instead since several spinal ligaments are encountered prior to entering the subarachnoid space (see below).


From Roberts & Hedges’ Clinical Procedures in Emergency Medicine, 6th ed, 2013


troubleshootingYour patient is elderly, and you are hitting bone with only 25% of your needle inserted

  • In most patients, you will need to insert the needle 50-75% of its length prior to obtaining CSF flow. In the above scenario, you may be hitting a calcified supraspinal ligament.
  • Try the lateral approach to bypass this calcification (see picture below).



From Roberts & Hedges’ Clinical Procedures in Emergency Medicine, 6th ed, 2013

pearl12Your patient is obese

  • You will likely need to hub the 3.5-inch needle, or use the 6-inch “harpoon” needle.
  • Try the upright sitting position.

troubleshootingYour patient had prior lumbar fusion surgery, or has severe curvature of their spine

  • Consider a fluoroscopy-guided LP, or an ultrasound-guided LP.

pearl12Ultrasound-guided LP

A meta-analysis demonstrated that ultrasound-guided LPs reduce the frequency of failed attempts (1). If you anticipate great difficulty, it may be worth taking a peak with the ultrasound.


troubleshootingYou cannot obtain CSF fluid

Return to the basics!

  • Poor patient positioning
    • Are they in the fetal position (back fully flexed, spine parallel to bed)?
      • Note: Do not force the patient to flex their neck. Focus on the rest of their back.
    • Ask for assistance to help hold the patient in the correct position.
    • Try the upright sitting position to visualize the midline better. Hip flexion is key with this position. You can also place their feet on a stool.
  • Poor needle positioning
    • Is the needle parallel to the bed, aiming toward the umbilicus and midline?
    • Ask the patient if the needle feels off midline. They are usually the best judge.
    • Try rotating the needle 90 degrees.
    • Are you hitting bone? This is likely the spinous process of the lower vertebra. Try to pull the needle back an inch, and then redirect the tip of the needle toward the umbilicus. Still hitting bone? Pull back again, and direct it slightly more cephalad.
  • If all else fails, try a different interspace with a new needle.

pitfall-signYour patient’s CSF is red or red-tinged

You may have gone too far lateral or too deep, and hit a venous plexus, causing a traumatic tap. Or it is SAH. Or even meningitis. Send the fluid to the lab.

Signs of a traumatic tap (234):

  • Absence of xanthochromia (shows up within 12 hours and persists 2-4 weeks)
  • RBC count < 2000
  • RBC count that diminishes from tube 1 to 4. This is not fully reliable unless it is completely clear by the 4th tube, but classically, the RBC count decreases by 30%

Examining the 4th tube as a separate entity can also help rule out SAH

  • <100 RBC: almost certainly traumatic
  • <500 RBC: probably traumatic
  • >10K RBC: likely SAH.

Lastly, for the diagnosis of meningitis, check out this CSF analysis table from Lifeinthefastlane.

Please share any of your own pearls, pitfalls, and troubleshooting for the LP in the comments section!

Textbook References

Euerle, B. Spinal Puncture and Cerebrospinal Fluid Examination. Chapter 60, 1218-1242.e3. In: Roberts J, et al. Roberts & Hedges’ Clinical Procedures in Emergency Medicine. 6th Saunders; 2013.

Article References

  1. Shaikh F, Brzezinski J, Alexander S, Arzola C, Carvalho JC, et al. Ultrasound imaging for lumbar punctures and epidural catheterisations: systematic review and meta-analysis. BMJ. 2013 Mar 26;346:f1720. PubMed PMID: 23532866.
  2. Perry JJ, Alyahya B, Sivilotti ML, Bullard MJ, Émond M, et al. Differentiation between traumatic tap and aneurysmal subarachnoid hemorrhage: prospective cohort study. BMJ. 2015 Feb 18;350:h568. PubMed PMID: 25694274; PubMed Central PMCID: PMC4353280.
  3. Heasley DC, Mohamed MA, Yousem DM. Clearing of red blood cells in lumbar puncture does not rule out ruptured aneurysm in patients with suspected subarachnoid hemorrhage but negative head CT findings. AJNR Am J Neuroradiol. 2005 Apr;26(4):820-4. PubMed PMID: 15814927.
  4. Czuczman AD, Thomas LE, Boulanger AB, Peak DA, Senecal EL, et al. Interpreting red blood cells in lumbar puncture: distinguishing true subarachnoid hemorrhage from traumatic tap. Acad Emerg Med. 2013 Mar;20(3):247-56. PubMed PMID: 23517256.

Image References

Figure 1 medical imagesRobgorsimd.comANWresidency

Jonathan Ameli MD

19 thoughts on “Lumbar Puncture Part 2: Pearls, Pitfalls, and Troubleshooting

  1. Another part of prepping the patient is to describe the procedure carefully. I have found most people cringe at the term “spinal tap”, and I use lumbar puncture instead and explain that we are taking a small amount of fluid from a little pool at the bottom of the vertebrae. People are also afraid that you are jabbing a needle in to their spinal column, and are worried about their nerves. So, I say, “we will be going below the level of your spinal column and the risk of damaging your nerves is very low.”

    A caveat about injecting a large amount of lidocaine – make sure you know where it is going. We had an obese patient require LP via Interv Radiology where she was still difficult to get and they injected more and more lidocaine. She came back to the ED, with LP unsuccessful, but with a nice epidural block and unable to feel or move her legs from the knees down for about 2 hours!

  2. I learned something! I’ve never actually asked the patient if it feels like I’m in the midline. I’ve felt and looked twice and marched my fingers up and down spinous processes–but never thought to ask. **Facepalm!** Nice tip!

  3. Another tip for the “pain sensitive” patient (including every pediatric patient): Use a topical anesthetic in addition to subcutaneous lidocaine. Most pediatric emergency departments use lidocaine 4% cream (LMX, fondly referred to as “L-max”) for LPs as well as venipunctures. (Not sure if this is even available in adult EDs…. which is why I will bring my own should I ever need an LP!) Super easy to use:

    1. Place a glob of LMX cream on the patient’s skin at the desired space (I usually try to cover L3-L4 and L4-L5 just in case.)

    2. Cover with an occlusive dressing, like a Tegaderm, to ensure adequate coverage of the site and to prevent it from getting all over the place (including into the patient’s mouth… Think: child’s hand → mouth)

    3. Wait 30 minutes prior to procedure for maximal effect. (There is really no added benefit with longer application times. Anesthetic duration is about 60 minutes once removed.)

    4. Perform further anesthesia and LP on happy patient!

    • Thanks Robyn. I also learned (from you!) to use sucrose for infants. And an extremely important part of the pediatric LP is having an experienced HOLDER. Thanks for the comment!

  4. Pingback: Lumbar Puncture Part 1: The Basics | Brown Emergency Medicine

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