Manual Palpation versus Ultrasound to Identify the Intervertebral Space for Spinal Anesthesia in Infants

Awake spinal anesthesia continues as an alternative to general anesthesia for infants. Standard clinical practice includes the manual palpation of surface landmarks to identify the desired intervertebral space for lumbar puncture (LP). The current study investigates the accuracy of manual palpation for identifying the intended intervertebral site for LP, using ultrasonography for confirmation and to determine the interspace where the conus medullaris ends.

After informed parental consent, patients less than one year of age undergoing spinal anesthesia for lower abdominal, urologic, or lower extremity surgical procedures were included. Patients were held in the seated position and an attending pediatric anesthesiologist or pediatric anesthesiology fellow declared the vertebral interspace intended for needle insertion, palpated surface landmarks, and placed a mark at the site. A research anesthesiologist then determined the actual vertebral interspace of the marked site and the location of the conus medullaris using ultrasonography. The time to complete both techniques (manual palpation and ultrasonography) was recorded.

The study cohort included 50 infants (median age of 7 months). Sixteen vertebral interspaces (32%) were inaccurately marked. One was marked two spaces higher than intended, ten were marked one space higher than intended, and five were marked one space lower than intended. In one patient, the intended vertebral interspace for the lumbar puncture overlaid the conus medullaris. The median time required was 25 seconds (IQR 14.3, 32) for palpation and 39 seconds (IQR 29, 63.8) for ultrasonography.

Manual palpation of surface landmarks to determine the correct interspace for LP for spinal anesthesia in infants is inaccurate. The time required to perform spinal ultrasonography in infants for determination of the optimal site for LP is brief and may be useful in ensuring accurate identification of the correct interspace and the location of the conus medullaris.