Ultrasound guided LP


Equipment needed:

–       high-frequency (small parts linear probe) for patients with normal weight

–       low-frequency 2-4 MHZ probe (abdominal curvilinear probe) for obese patients

–       transducer gel

–       skin marking pen

–       LP tray


Positioning: left lateral decubitus or seated position



1-   Identify spinous process which signifies the midline of the spine. Probe must be in transverse position, probe marker to clinician’s left side, at level of iliac crest. Spinous process looks like cresent shape hyperechoic structure with posterior acoustic shadowing.





2-   Mark the midline with a skin marking pen at the center of the probe. Drag the probe superiorly (head) and inferiorly (feet) and again mark the midline of the spine.

3-   Rotate the transducer to the sagittal (longitudinal) plane, with probe marker pointed at patient’s head. The probe should be parallel with patients spine and in between spinous processes previously marked.  The spinous processes again appear as hyperechoic cresent shapes.






4. Mark the space between the two spinous processes which is the interspinous space, on left and right side of probe.

5. The point of intersection represent the middle of the interspace and most ideal place for LP needle insertion.



6. Proceed with LP as you usually would. Instruct patient not to move as this may obscure landmarks and skin markings.


Reference: http://emedicine.medscape.com/article/1458641-overview#showall   Written by our very own Sinai EM attending’s Suzie Bentley and Danny Duque!