The purpose of this study is to determine if performing an ultrasound to identify the space to insert the needle before performing a lumbar puncture will improve success of the procedure and patient safety.

The investigators are conducting a single-center, prospective two-arm parallel group randomized clinical trial in an urban pediatric emergency department to determine if performing an ultrasound prior to lumbar puncture procedure improves success of the procedure.

Patients will be block-randomized into two groups to receive procedural interspace selection via 1) standard anatomic palpation technique or 2) visualization with pre-procedural ultrasound (experimental group).

1. Standard Anatomic Palpation Technique:

   Participants randomized to this group will receive standard of care treatment with providers using the palpation technique to select an interspace. As variations on the palpation technique exist, the investigators will provide a standardized educational cognitive aid that clinicians can use for this approach.

2. Pre-Procedural Ultrasound:

Clinicians will first use the standard palpation technique to select an interspace for ultrasound evaluation. A select group of pediatric emergency medicine attendings and fellows who have already trained to a mastery standard with the ultrasound protocol will then conduct the pre-procedural ultrasound. The clinicians performing the lumbar puncture will be provided the following information to conduct the lumbar puncture:

i. Assessment for fluid at the level selected (and the number of interspaces above that have fluid without conus present)

ii. Measurements of appropriate angle and depth

iii. Evaluation of any overlying vasculature

Post-Lumbar Puncture:

After the lumbar puncture, infants randomized to both groups will receive a post-procedural ultrasound scan performed by one of the mastery trained ultrasound physicians.

Inclusion Criteria:

• Patient is less than 90 days old.
• Patient is receiving a lumbar puncture

Exclusion Criteria:

• Patient is clinically unstable
• Patient had a previous lumbar puncture in the past 24 hours
• An outside consultant (not working in ED) is performing the LP
• Patient has developmental delay or neurological impairment
• There is no legal guardian present
• The legal guardians speak neither English nor Spanish
• There is no ultrasound personnel available to enroll