**9. Lumbar puncture**

Lumbar puncture (LP) is a relatively common procedure performed in emergency department and the NICU as part of a complete sepsis evaluation. The LP is typically performed using the "blind" surface landmark guidance. Anecdotally, this technique is reported to be have a high percentage of success. However successful identification of landmarks has been shown to be accurate only 30% of the time [47]. Traumatic or unsuccessful LPs in this group have been documented in the pediatric literature in 30–50% of patients [48, 49]. This translates to increased difficulty in obtaining CSF and higher rate of complications such as local/ subdural/epidural hematoma, bloody tap and incomplete sepsis evaluation to name a few. Fluoroscopy guided LP is an alternative but challenges include limited availability, radiation exposure, need to transport critical patients for the procedure.

Use of POCUS for identification of key landmarks is a safe and easy alternative to the blind method [50–52]. In adults, using ultrasound for LP has been associated with a reduction in the number of attempts and interspaces accessed [51–55]. In neonates, the incompletely ossified spinous processes, minimal fat aids in interrogation of the space by ultrasound compared to older kids and adults. The good resolution of image, lack of ionizing radiation and potential for real time guidance makes ultrasound a valuable tool for performing LP in neonates [48, 56].

LP can be performed in the neonate without general anesthesia or sedation, using oral sucrose and local anesthesia. Patient can be in lateral decubitus position or sitting up. Using ultrasound to measure the interspinous space at L3-L4 and L4-L5 in varying positions, the lumbar spine is found to be maximally positioned in both neonates and children in the seated position with flexed hips versus the lateral decubitus position [57, 58]. The probe used is the 7–15 MHz hockey stick or equivalent linear array transducer. There is still very limited knowledge on ultrasound guided LP in neonates. There are two techniques described in literature, the transverse approach and longitudinal approach based on how the probe is held.

The first skill is to define the landmarks for the LP procedure. Using a surgical marker or pen one can delineate the location of midline and the position of the conus, the point where the spinal cord ends. There are no studies validating the guidance of the needle into the interspace and so this will require more studies before guidance by US is a routine procedure.
