Evaluating infant positioning for lumbar puncture using sonographic measurements.

Objectives: Hypoxia has been observed when infants undergo lumbar puncture in a tight flexed lateral recumbent position. This study used sonographic measurements of lumbar interspinous spaces to investigate the anatomic necessity and advantage derived from this tight flexed positioning in infants.

Methods: This was a brief, prospective, observational study of a convenience sample of patients. Twenty-one healthy infants under 1 month of age were scanned in two positions: prone in a spine-neutral position and lateral recumbent with their knees bent into their chest and their neck flexed. In each position, a 5- to 10-MHz linear array transducer was used to scan midline along the lumbar spinous processes in the sagittal plane. The distances between the spinous processes were measured near the ligamentum flavum using the ultrasound machine's calipers. Pulse oximetry was monitored on all infants during flexed positioning.

Results: In the spine-neutral position, all studied interspinous spaces were much wider than a 22-gauge spinal needle (diameter 0.072 cm). The mean (±SD) interspinous spaces for L3-4, L4-5, and L5-S1 in a spine-neutral position were 0.42 (±0.07), 0.37 (±0.06), and 0.36 (±0.11) cm, respectively. Flexing the infants increased the mean lumbar interspinous spaces at L3-4, L4-5, and L5-S1 by 31, 51, and 44%, respectively.

Conclusions: This study verified that tight, lateral flexed positioning substantially enhances the space between the lumbar spinous processes and that a spine-neutral position also allows for a large enough anatomic interspinous space to perform lumbar puncture. However, further clinical research is required to establish the feasibility of lumbar puncture in a spine-neutral position.