Introduction:

The most commonly used technique to locate the intervertebral space L3-L4 for neuraxial blockade is palpation.

Objective:

To determine with ultrasound the ratio of adequate location of the L3-L4 space by palpation, setting the proportion of “level above” and “below”, and to evaluate the association between body mass index and inaccurate location.

Methods:

100 healthy volunteers aged 18 to 75 years were studied; in the left lateral decubitus, we proceeded to locate by manual palpation the intervertebral space L3-L4 and placed a mark; without moving the patient, with the linear ultrasound probe, the processes of T12 and the top edge of the sacrum were located, and counting the spinous processes, we identified the previously marked intervertebral space.

Results:

In 68% of the evaluations, the mark was adequate; in 75% of these, the landmark was a “level above”, and in 25%, a “level below”; the greater the body mass index, the greater the inaccuracy in locating this space.

Conclusions:

The location of the L3-L4 intervertebral space by manual palpation had a 32% inaccuracy confirmed by ultrasound. A higher body mass index increased the inaccuracy of the location of L3-L4 by palpation.