Spinal Anatomy Ultrasound in Young Infants With Implications for Lumbar Puncture.

Background: Lumbar puncture (LP) in young infants may challenge clinicians due to the infrequency of the procedure and anatomic variability. The use of ultrasound (US) to characterize young infant spinal anatomy prior to performing an LP may help determine the most favorable site for intervention.

Objectives: 1) Evaluate potential sites for LP in young infants with US at L2/L3 through L5/S1 to determine differences in needle insertion depth (NID), spinal canal width (SCW), and subarachnoid fluid width (SAW).2) Describe the location of the conus medullaris.3) Predict NID of L2/L3 through L5/S1 based on variables including age, gestational age, height, and weight.

Methods: We studied a convenience sample of participants aged 0-6 months in a tertiary children's emergency department. We recorded characteristic data and used a Sonosite PX US with a linear 15-MHz transducer to image each participant's spine. We used the paired t-test to examine univariate differences in NID, SCW, and SAW and multiple linear regression models to derive predictive equations for NID.

Results: Among 50 participants, the mean NID for sites L2/L3 through L5/S1 did not differ significantly; however, at sites L2/L3 through L5/S1, there were statistically significant differences in the mean SCW and mean SAW, which were both consistently measured to be larger the more cephalad the site. Weight was the only statistically significant variable associated with NID after adjusting for other covariates.

Conclusions: Spinal canal width and SAW were consistently measured to be larger at more cephalad sites, suggesting there is a larger target fluid volume available at higher interspaces. Subarachnoid fluid width was measured to be small, highlighting the importance of precise movements. Location of the needle site did not change expected needle depth (approximately 1 cm across all sites). The conus medullaris was not often visualized while scanning the L2/L3-L5/S1 interspaces. Weight can be used to estimate optimal NID; although, it is unclear such small differences would have clinical significance.