Ultrasound for Lumbar Puncture: how to maximize first-pass success in patients with large body habitus

Author: Stephen Alerhand MD (@SAlerhand, Emergency Medicine, Icahn School of Medicine at Mount Sinai) // Edited by Alex Koyfman, MD (@EMHighAK)


On a regular overnight shift in a busy urban hospital, you bring your patient over to what amounts to a private room amidst the jungle of hospital stretchers. You need to prepare the patient for a lumbar puncture to further assess for subarachnoid hemorrhage following a negative CT. You (the resident) have performed about 10-20 LPs with varying success and comfort. In this case, the patient’s large body habitus and anxiety about having a needle inserted into his back forebode a tricky experience.

The ED is extremely busy, and the last thing you want is to look stupid and need to pull the attending over for assistance because you failed to get the LP right. You bring your supplies into the room, set up the patient’s position, and then your mind drifts off…

(…cue Wayne’s World 2 drift-off into dreamland…)
Wayne's World

Oh no… you didn’t get the LP. You retracted the needle and re-inserted several times, thought you felt that distinctive ‘pop’ once or twice, but at no point did CSF come out. Now the patient is angry, more anxious, and keeps asking if you are finished sticking a needle in his back. Eyes facing downward, chin to the floor, you slowly walk over to your attending. “Done with the LP?” he asks. But the look of failure in your eyes is a dead giveaway, and he can barely hide his annoyance. You melt in shame, just a  little.. And then…

(…cue Wayne’s World 2 drift-off back from dreamland…)

You shake your head and snap back to reality, finding your mind reverted to just at the point before getting sterile. You recall last week’s ultrasound lecture about performing an LP with US-guided assistance for localization of needle insertion, as well as angle and depth of penetration. The patient is now ready and willing, the anxious and pissed-off version of him a mere imaginary figment in your daydream. It’s time to go. You grab the literature in one hand and ultrasound in the other.



Nomura, Jason T. et al. A randomized controlled trial of ultrasound-assisted lumbar puncture. Journal of Ultrasound. Oct 1 2007, 1341-1348.

Question: Does US increase success rate and ease of performing LP in obese patients?
Type of study: Randomized, prospective, double-blind
Treatment groups: Undergo LP using palpation landmarks (PL) or US landmarks
Results: 6 of 22 failed with PLs, 1 of 24 failed with US. In 12 obese patients, 4 of 7 failed with PL’s, 0 of 5 failed with US.
Conclusions: The use of ultrasound for LP significantly reduced the number of failures in all patients and improved the ease of the procedure in obese patients.

LP 1

LP 2

LP 3

Ferre, Robinson M. Sweeney, Timothy W. Emergency physicians can easily obtain ultrasound images of anatomical landmarks relevant to lumbar puncture. Am Jour EM. March 2007. 291-296.

Question: Can ED physicians obtain ultrasound images useful for lumbar puncture?
Methods: Two physicians sought to identify relevant anatomy for LP.
Results: Soft tissue and anatomical structures identified in all subjects (n=76). Mean BMI was 31.4. Images obtained in less than 1 minute in 87.9% of scans and within 5 minutes in 100%.

LP 4

LP 5

Strony R. Ultrasound-assisted lumbar puncture in obese patients. Crit Care Clin. 2010 Oct;26(4):661-664.LP 6

LP 7

Ferre, RM. Sweeney, TW. Strout, TD. Ultrasound identification of landmarks preceding lumbar puncture: a pilot study. Emerg Med J. 2009 Apr;26(4):276-277.

Question: What is utility of bedside US in adults undergoing LP?
Method: US used as primary means to determine site of skin puncture, angle of needle advancement, and depth needed to access subarachnoid space.
Results: CSF obtained from 36 of 39 patients in first interspinous space attempted.

LP 8


What can ultrasound accomplish?

–Locate the best site for needle insertion
–Show the appropriate angle of insertion
–Measure the distance to reach the subarachnoid space

How to use the ultrasound for lumbar puncture

(Dawson, Matt. Mallin, Mike. Introduction to Bedside Ultrasound. Volumes 1&2)
Curvilinear probe for obese patients (lower frequency, improved penetration)
Linear array probe for thin and pediatric patients

1. Palpate both superior iliac spines. Draw imaginary line to connect them.
2. Identify L3-4 or L4-5 space.
3. Place probe in short axis. Paraspinal muscles will appear as circular bundles on either side of spinous process (hyperechoic crescent with posterior shadow).

4. Identify spinous process.
5. Mark skin above and below probe to indicate midline.
6. Identify spinous processes above and below the proposed puncture site.
7. Rotate probe to long axis.
8. Center the interspinous process. Mark it.
9. Intersection of lines (sagittal and transverse) is site of needle entry

.LP 12

10. Align proposed needle insertion with the visualized interspinous space.


11. Measure depth required to penetrate subarachnoid space.LP 8

Further Reading

  1. Mofidi, M. et al. Ultrasound guided lumbar puncture in emergency department: time saving and less complications. J Res Med Sci. 2013 Apr; 18(4)303-7.
  2. Peterson, MA. et al. Ultrasoudnd for routine lumbar puncture. Acad Emerg Med. 2014 Feb; 21(2):130-6. (negative study)

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