Lumbar puncture (LP) is a common procedure in the Emergency Department (ED) performed to obtain cerebrospinal fluid (CSF). Common indications include evaluating for infection of the central nervous system, establishing the diagnosis of idiopathic intracranial hypertension, and identifying the presence of subarachnoid hemorrhage [[1], [2], [3]]. Traditionally, LPs are performed without ultrasound guidance, requiring the operator to rely solely on external anatomical landmarks. Consequently, procedural success rates have been variable [[4], [5], [6]] and failed attempts often necessitate fluoroscopy-guided lumbar punctures. The frequency of LP in emergency medicine (EM) practice has also been decreasing [[7], [8], [9]] which can result in reduced proficiency amongst physicians.

Notably, most invasive ED procedures involving needle insertion, such as peripheral and central venous access or paracentesis, are now routinely performed under active ultrasound guidance [[10], [11], [12]]. Despite this, lumbar punctures are often still performed via landmark approaches, perhaps due to the difficulty in establishing a technique where active needle visualization is feasible.

Currently, the two most common approaches for performing lumbar punctures are the landmark-based and static ultrasound-assisted techniques. In the landmark-based approach, the operator identifies the L4–L5 intervertebral space by palpating the midline between the iliac crests, then advances a spinal needle with a stylet until CSF flow is obtained. However, this method can be inaccurate in patients with atypical anatomy, obesity, or spinal deformities such as scoliosis [5,13,14], all of which decrease procedural success rates. To mitigate these challenges, some clinicians have adopted an ultrasound-assisted technique in which the interspinous space and midline are identified and marked prior to needle insertion. This approach has seen mixed results, with potential benefit being demonstrated in certain studies and others showing minimal to no benefit [[15], [16], [17], [18]]. This lack of consistent benefit is likely due to the procedure remaining a “static” technique, wherein the operator must still advance the needle without visualization, and relying on tactile feedback.

A dynamic, active ultrasound-guided (USG) LP is feasible in the paramedian approach. This involves sliding the probe slightly off of midline where there is ample space for needle guidance. The spinal canal openings are also wider in this approach. Prior work in the Anesthesia literature has seen significant benefit in the paramedian ultrasound-guided spinal approach [[19], [20], [21], [22]].

Our objective was to explore the dynamic paramedian LP amongst a cohort of EM physicians. We conducted a single-center randomized controlled trial using soft-embalmed cadavers to compare the success rates of two ultrasound-guided lumbar puncture techniques: the static midline lumbar puncture (SMLP) and the dynamic paramedian lumbar puncture (DPLP).