US-guided LP (Basics)
① Choosing right probe
-Linear probe
>Better resolution, limited penetration (4-6cm)
>Best for non-obese patients
-Curvilinear or phase array probe
>Lower resolution, deeper penetration (>6cm)
>Best for patients with higher BMI
②Finding the midline
-Place ultrasound probe in transverse plane
-Locate the spinous process (hyperechoic line with shadow below)
-Mark skin with a vertical line
③Finding the interspinous space
-Rotate probe 90 degrees to put probe in longitudinal plane
-Identify spinal levels by starting from the sacrum and sliding the probe upwards
-Locate the interspinous space (valley between humps)
-Mark skin with a horizontal line
④Estimate needle depth
-Identify the ligamentum flavum either on transverse or longitudinal plane (hyper echoic line that can be seen below the spinous process or the interspinous space) and measure distance from the skin
⑤Locate needle entry target
-Connect both horizontal and vertical lines until they intersect
>US-assisted: insert needle at the intersection point using landmarks
>US-guided: insert needle while using ultrasound
