Effect of table tilt and spine flexion–rotation on the acoustic window of the lumbar spine in pregnant women

STUDY OBJECTIVE: The purpose of this study was to assess whether application of dorsal table tilt and body rotation to a parturient seated for neuraxial anesthesia increased the size of the paramedian target area for neuraxial needle insertion. SETTING: Labor and Delivery Room. PATIENTS: Thirty term pregnant women, ASA I–II, scheduled for an elective C-section delivery. INTERVENTIONS: Lumbar ultrasonography was performed in four seated positions: (F) lumbar flexion; (FR) as in position F with right shoulder rotation; (FT) as in position F with dorsal table-tilt; (FTR) as in position F with dorsal table-tilt combined with right shoulder rotation. MEASUREMENTS: For each position, the size of the ‘target area’, defined as the visible length of the posterior longitudinal ligament was measured at the L3-L4 interspace. MAIN RESULTS: The mean posterior longitudinal ligament was 18.4 ± 4 mm in position F, 18.9 ± 5.5 mm in FR, 19 ± 5.3 mm in FT, and 18 ± 5.2 mm in FTR. Mean posterior longitudinal ligament length was not significantly different in the four positions. CONCLUSIONS: These data show that the positions studied did not increase the target area as defined by the length of the posterior longitudinal ligament for the purpose of neuraxial needle insertion in obstetric patients. The maneuvers studied will have limited use in improving spinal needle access in pregnant women.