Sonographic evaluation of lumbar interlaminar space opening in a variety of patient body positions for optimal neuraxial anesthesia delivery.

OBJECTIVE: To find the position that provided the most comfort, as well as the widest L3-L4 interlaminar space opening.

DESIGN: Pilot study.

SETTING: Operating room.

PATIENTS: Thirty-two healthy volunteers.

INTERVENTIONS: L3-L4 interlaminar space was measured on volunteers assuming a baseline position (sitting upright) and 5 study positions: (1) sitting in fetal position, (2) sitting on a table tilted at 30°, (3) sitting while hugging an exercise ball, (4) sitting with midcalves on the table's edge, and (5) lying on one side in fetal position. Interlaminar spaces were measured to determine which position resulted in the largest interlaminar space compared with baseline. The comfort level of each position was rated by subjects using a visual analogue scale from 1 to 10.

MAIN RESULTS: The means of the interlaminar openings in all study positions were significantly different from baseline, with the "sitting fetal" having the greatest difference, (1.32mm, P<.001), followed by "hugging a ball" (0.94mm, P<.001) and "lying fetal" (0.92mm, P<.001). Alternatively, when using "sitting fetal" (a more commonly used position) as a comparative baseline, "hugging a ball" and "lying fetal" showed smaller but not significantly different interlaminar openings (Δ=-0.38mm, P value = .221 and Δ=-0.40mm, P value = .164, respectively)."Sitting on a tilted table" and "sitting midcalf" showed significantly smaller interlaminar openings (Δ=-0.52mm, P value = .025 and Δ=-0.72mm, P value < .001, respectively) when compared with the alternative baseline of "sitting fetal." Mean visual analogue scale scores for comfort showed that "hugging a ball" (7.8/10), "lying fetal" (7.5/10), and "sitting fetal" (7.2/10) positions had the highest ratings.

CONCLUSIONS: Ultrasonographic measurements carried out on 32 subjects showed that "sitting fetal," "lying fetal," and "hugging a ball" positions provided the widest L3-L4 interlaminar openings. These 3 positions were also found to be more comfortable.