The Optimal Angles and Point of Needle Insertion in Paramedian Spinal Anesthesia: an Ultrasonographic Study

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Nattaporn Songborassamee
Warita Chaiaroondeekul
Wirinaree Kampitak
Banchobporn Songthamwat
Chutikant Vichainarong


Background: Multiple attempts at needle placement in conventional paramedian spinal anesthesia are still often required to reach the subarachnoid space in some individuals. This study aims to assess the optimal angles and point of needle insertion for spinal anesthesia using neuraxial ultrasound scanning. Method: Neuraxial ultrasound scanning of the L2-L5 intervertebral spaces in 120 volunteers aged 20-79 years was performed. The optimal vertical and horizontal angles were analyzed using the Arccosine function. The baseline characteristics, neuraxial structural depth, and optimal needle insertion point were evaluated in transverse midline (TM) and paramedian sagittal oblique (PSO) views from ultrasound scanning. Results: At 1 cm caudal to spinous process, mean optimal needle-entry angle was 18.6±5.2°, 18.5±5°, and 18.7±4.9° in PSO view and 25±6.2°, 25.7±6.3°, and 28.1±6.9° in TM view at L2/3, L3/4 and L4/5 intervertebral space, respectively. The distance from midline to lateral for paramedian needle insertion was 1.7±0.4 cm at both L2/3 and L3/4, and 1.8±0.4 cm at L4/5 intervertebral space. There was significant inverse correlation between maximal vertical angle, age, and BMI at L2-5 (P < 0.05). Conclusion: The optimal angles of needle trajectory range for paramedian spinal anesthesia were 13-25° vertically and 17-35° medially off the sagittal plane in L2-L5 levels, and optimal point for needle insertion was 1.7-1.8 cm lateral from midline. Increased age and high BMI were associated with unfavorable parameters which may result in difficult spinal anesthesia.

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