Counting interspaces during lumbar neuraxial ultrasound

When counting interspaces to determine the target intervertebral level for neuraxial anesthesia, start by identifying the sacrum and the L5-S1 interspace. The vertical ultrasound line corresponds to the midpoint of the long edge of the ultrasound transducer and appears on many ultrasound machines when the M-mode or M/D cursor function is turned on. Slide the transducer cephalad centering the vertical ultrasound line in the midpoint of each interlaminar space, making horizontal skin markings until the desired interspace is reached. For further detail refer to UpToDate content on neuraxial ultrasound for anesthesia.