Its no secret that pediatric LPs can be daunting.  And for good reason! It turns out that only 45-63% of LPs are successful when performed by trainees (10).  How can we remedy this dismal success rate?  We know of multiple factors that can help to improve our success with LPs, including:

  • Use of a local anesthetic
  • A good holder
  • Early stylet removal (6)

But these tricks (while helpful), don’t seem to get to the real heart of the issue.  One could argue that the correct identification of landmarks is the most critical step of a successful LP.  In this Post, I would submit to you that the best way to overcome this barrier (and thus, increase your odds of a successful LP) is the use of a bedside ultrasound (i.e. ultrasound assisted LP – UALP).

What’s the evidence?

Infants < 6 months

The Effect of Bedside Ultrasonographic Skin Marking on Infant Lumbar Puncture Success: A Randomized Controlled Trial (1)

  • Population: infants < 6 months undergoing LP.   N= 128.
  • Intervention: used bedside ultrasonography to identify and mark the terminal end of the conus medullaris and the most appropriate intervertebral space
  • Control:  traditional LP (palpation of anatomic landmarks and subsequent “blind stick” of selected interspinous space)
  • Outcome: LP success rate (defined as return of CSF and RBC < 1000)
  •  Type of Study Design: Prospective, randomized, controlled trial.

Results

  • First attempt success rate for Ultrasound group was 58%, compared to 31% for control group (ARR 27%)
  • Success within 3 attempts for the ultrasound group was 75%, compared to 45% for the control group (ARR 31%)

Additional points

  • ultrasound assisted identification of the end of the conus medullaris is possible in infants <6 months due to decreased calcification of the spinous processes and is helpful because it “ensures the safety of repeated attempts in alternate interspaces”
  • It is difficult to know if these results are generalizable in low-resource settings
  • There are other important possibilities of bedside ultrasound use for LPs that were not addressed in this article (but might be helpful to you!) such as: interspinous space distance, needle entry angle, depth to spinal canal.

Infants < 2 months

Prospective Investigation of a Novel Ultrasound-assisted Lumbar Puncture Technique on Infants in the Pediatric Emergency Department (12)

  • Population: infants < 2 months undergoing LP. N= 43.
  • Intervention: used bedside ultrasonography (termed UALP or ultrasound assisted lumbar puncture in this paper) to identify/mark the terminal end of the conus medullaris, the most appropriate intervertebral space, and also to measure the “maximum safe depth” of needle.
  • Control: standard LP (palpation of anatomic landmarks without knowledge of ultrasound data)
  • Outcome: LP success rate (defined as return of CSF and RBC < 10,000). Note, this is a more lenient RBC count, potentially making “successful LP” rate higher in each group.
  • Type of Study Design: Prospective, randomized, controlled trial.

 Results

  • Success rate for Ultrasound group (UALP) was 95%, compared to 68%% for control group (NNT 3.7)

Obese patients and adults

A randomized controlled trial of ultrasound‐assisted lumbar puncture (5)

  • Population: patients >18 years old who needed an LP. N=80
  • Intervention: bedside ultrasound to identify correct insertion site
  • Control: traditional landmark identification via palpation
  • Outcome: various markers of LP success (time of procedure, pain score, number of attempts, number of traumatic attempts)
  • Results: the use of ultrasound assisted LP showed a decrease in the number of attempts, decrease the rate of traumatic taps, and decrease the procedure time. These results were even more pronounced in patients with BMI > 30.

For when you need a confidence-boost

 Ultrasound-assisted lumbar puncture in pediatric emergency medicine

  • Population: pediatric patients undergoing LP. N= 19
  • Intervention: bedside ultrasound to identify correct insertion site
  • Control: traditional landmark identification via palpation
  • Outcome: Confidence score using Wilcoxon Signed Rank test
  • Results: POCUS lead to significantly increased confidence score of providers doing the procedure (Wilcoxon Scores 4.79 vs 2.89 in control group, p< 0.001)(2)

Additional supportive evidence

  • Ultrasound has shown that the interspinous spaces appear to be greatest when the patient is in the seated position with hips flexed (3)
  • Interestingly, ultrasound has also demonstrated that the optimal angle in infants < 1 year if often approximately 50 degrees compared to the skin, compared to a sharper angle of approximately 60 degrees in older children. (4)

In what situations should we consider using an ultrasound for LP?

  • Obese patients in whom it is difficult to assess the landmarks. i.e. R/O idiopathic intracranial hypertension (formerly pseudo tumor cerebri)
  • Infants < 6 months, i.e. febrile neonate (where their interspinous processes are small and difficult to locate)
  • Or, anyone needing an LP really.

Performing the procedure itself

Equipment

  • Ultrasound machine with High frequency “small parts” probe (5-10 MHZ) on patients with a normal BMI and/or Low frequency “abdominal probe” (2-4 MHZ) on obese patients.
  • Gel (warmed if possible – the patient will thank you)
  • Marking pen (the marker in your LP kit works fine and won’t be easily rubbed off by the gel, but a permanent marker works too)

Steps

  • Position the patient (and don’t let them move if possible)
  • Estimate your landmarks by palpation first
  • Find the midline (transverse plane):
    • Rotate the transducer so that the probe marker (by convention) is pointing towards the practitioner’s left side
    • Move the probe from the patient’s side to side (in the transverse plane)
    • Look for a large hypoechoic (dark) dome. This is the shadow below the spinous process.
    • Center the transducer on that dome.  This is your midline.
    • At this point, you can clean skin with ETOH
    • Mark the skin in two places in the midline of your transducer
  • Find the best interspinous space (using the longitudinal/sagittal plane) – FIGURE 1
    • Staying midline, now rotate your probe marker so that is (by convention) pointing towards the patient’s head
    • Move the transducer up and down the spine (in the longitudinal plane)
    • Look for hyperechoic (lighter) crescents (they’ll look like fingernail tips) & hypoechoic (darker shadows) regions below: these are the tips of the spinous processes
    • Stop the transducer once the middle of your screen is between two spinous processes
    • At this point, you can clean skin with ETOH
    • Mark the skin in two places in the middle of your transducer

  • Extend markings so they intersect and make an X
  • To locate the conus (in a neonate < 6 months) FIGURE 2
    • Keep your transducer in the longitudinal plane
    • Move the probe up and down the spine
    • Look for the CONUS –  hypoechoic (dark), tapering structure
    • Note: distally you will see hyperechoic (white) strands of the cauda equina and anechoic (black) CSF.
    • Mark the distal end of the conus (so if you miss in your first LP attempt, you can feel safe going up by an intervertebral space safely)

Pearls

  • Limit patient movement after markings are placed
  • Don’t rush; allow for learning curve if you are new with the ultrasound machine
  • Be sure of your landmarks (don’t mistake the transverse process for the spinous process and don’t mistake the spinal cord for CSF)
  • Be careful about your sterile field (you could make your marks before getting sterile field prepared or do your ultrasound in a sterile manner with a probe cover)
  • Avoid too much gel as this can interfere with markings

In summary…

Point of care Ultrasound for your next LP is:

  • Safe
  • Easy to use
  • Time saving
  • Helpful for identifying landmarks
  • Possibly going to increase your confidence
  • Possibly going to increase your likelihood of success

 

References

  1. Neal, Jeffrey T., Summer L. Kaplan, Ashley L. Woodford, Krisha Desai, Joseph J. Zorc, and Aaron E. Chen. “The Effect of Bedside Ultrasonographic Skin Marking on Infant Lumbar Puncture Success: AÂ Randomized Controlled Trial.” Annals of Emergency Medicine (2016): n. pag. Web.
  2. Kim S, Adler DK. Ultrasound-assisted lumbar puncture in pediatric emergency medicine. J Emerg Med. 2014 Jul. 47(1):59-64. [Medline].
  3. Abo A, Chen L, Johnston P, Santucci K (2010) Positioning for lumbar puncture in children evaluated by bedside ultrasound. Pediatrics 125:e1149–e1153
  4. Bruccoleri RE, Chen L (2011) Needle‐entry angle for lumbar punc‐ture in children as determined by using ultrasonography. Pediatrics 127:e921–e926
  5. Nomura JT, Leech SJ, Shenbagamurthi S (2007) A randomized con‐trolled trial of ultrasound‐assisted lumbar puncture. J Ultrasound Med 26:1341–1348
  6. Nigrovic LE et al. Risk factors for traumatic or unsuccessful lumbar punctures in children. Ann Emerg Med. 2007 Jun;49(6):762-71
  7. Marin, Jennifer, and ALyssa Abo. ̶