Procedural Steps
Patient Positioning
Site Preparation
Local Anesthesia
Needle Insertion
Collection of CSF
Removal of Needle
Post-procedural Care
Interpretation of Results
CSF Pressure

LP Pressure Quick Guide

A lumbar puncture can be performed using any of the L3-L4, L4-L5, or L5-S1 interspaces. The spinal cord ends at L1 in adults, thus the risk of cord damage is insignificant. At these levels, the subarchnoid space contains the nerve roots of the cauda equine floating free in the CSF. The nerve roots are brushed aside by the penetrating LP needle.

To make a landmark visible throughout the procedure: at the proposed point of needle insertion, press the skin with a blunt object such as the base of a pen or a man’s wedding ring for several seconds.

To avoid damaging the spinal cord, do not go above the
L2-L3 space.

The posterior iliac crests are easily palpated in most patients. A line drawn between the superior border of the posterior iliac crests will intersect the L4 spinous process (see image). Using this surface landmark, the L3-L4-L5 interspaces can be localized. Identify the L4-L5 interspinous process space midline as your needle insertion site. If insertion at this space is unsuccessful, try the L3-L4 space.

The L4-L5 interspace is likely the largest when the spine is flexed, and therefore this space should be attempted first.

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