Identification of the L3-L4 Intervertebral Space in Obese Parturients at Term in the Sitting and Lateral Positions: Manual Palpation (Tuffier's Line Method) Versus Ultrasound Imaging

For years now, anesthesiologists have used anatomical landmarks to guide neuraxial anesthesia and analgesia techniques in obstetric patients. Traditionally, Tuffier's line (intercristal line) has been used as a reference and corresponds to a horizontal line drawn between the upper part of the iliac crests that is thought to intersect the spine at the level of the L4 spinous process or the L4-L5 intervertebral space. However, many studies have found this anatomical landmark to be unreliable reporting the Tuffier's line to intersect the spine at levels ranging from the L3-L4 to L5-S1 intervertebral spaces. Regarding the obstetrical population, the anatomical position of the Tuffier's line was found to be even higher presumably due to the exaggerated lordosis of pregnancy.

Neuraxial techniques used for obstetrical anesthesia and analgesia include epidurals, spinals and combined epidural-spinal (CSE) techniques. The correct identification of the intervertebral space for neuraxial analgesia and anesthesia is very important especially if using a spinal injection such as is done when performing a CSE.

Neuraxial techniques can be done in the sitting or the lying lateral position. When expecting a more challenging technique, such as in an obese patient, anesthesiologists will usually choose to perform the technique with patients in the sitting position. But the lateral position is preferred in certain conditions such as in premature rupture of membranes where there is a risk of umbilical cord prolapse, in women experiencing a vasovagal response caused by the needle insertion or upon assuming the sitting position, or because of the anesthesiologist's preference.

US-guided regional techniques are gaining popularity both for the general population as well as for the pregnant women. It has been shown to be a more reliable tool than the palpation method in identifying a specific lumbar intervertebral level. The use of US imaging for neuraxial techniques in pregnant women has been shown to reduce the numbers of attempts, improve the comfort of the patient during the procedure and increase the precision in identifying the intervertebral space at which the technique is being performed. Obesity can make regional techniques extremely challenging and US imaging becomes a valuable tool in this setting.

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