From the Guidelines
A lumbar puncture without imaging should be performed with careful attention to anatomical landmarks, using a landmark-based approach to identify the L3-L4 or L4-L5 interspace, after sterile preparation and local anesthesia, to minimize the risk of complications and ensure accurate diagnosis. This approach is supported by the guidelines for evaluation of new fever in critically ill adult patients, which recommend considering lumbar puncture in patients with unexplained altered consciousness or focal neurologic signs, unless there is a contraindication 1.
When performing a lumbar puncture without imaging, it is essential to position the patient in lateral decubitus with knees drawn to chest and spine flexed, or seated leaning forward, to facilitate access to the lumbar spine. The intercristal line, which connects the iliac crests and crosses the L4 spinous process, can be used to identify the L3-L4 or L4-L5 interspace. After sterile preparation and local anesthesia (1-2% lidocaine), a spinal needle with stylet should be inserted at the identified interspace, angled slightly cephalad toward the umbilicus. The needle should be advanced slowly until a "pop" is felt as the needle penetrates the dura, then the stylet should be removed to check for CSF flow.
Contraindications to lumbar puncture include increased intracranial pressure, infection at the puncture site, coagulopathy, and thrombocytopenia, as highlighted in the management of suspected viral encephalitis in adults guidelines 1. If the patient reports severe shooting pain down a leg during the procedure, the needle should be withdrawn and redirected. This landmark-based approach is reliable in most patients but may be challenging in those with obesity, scoliosis, or previous spinal surgery, where imaging guidance would be preferable.
Key considerations when performing a lumbar puncture without imaging include:
- Careful attention to anatomical landmarks to minimize the risk of complications
- Sterile preparation and local anesthesia to reduce discomfort and prevent infection
- Identification of contraindications, such as increased intracranial pressure or coagulopathy, to avoid potential harm
- Slow and careful advancement of the needle to avoid causing damage to surrounding tissues
- Collection of necessary samples and measurement of opening pressure, if indicated, to ensure accurate diagnosis.
It is also important to note that the guidelines for evaluation of new fever in critically ill adult patients recommend considering lumbar puncture in patients with unexplained altered consciousness or focal neurologic signs, unless there is a contraindication 1, and that the management of suspected viral encephalitis in adults guidelines highlight the importance of careful consideration of the risks and benefits of lumbar puncture in patients with suspected central nervous system infections 1.
From the Research
Procedure for Lumbar Puncture without Imaging
If imaging is unavailable, the best procedure to complete a lumbar puncture involves the use of ultrasound guidance, when possible, to increase the accuracy of the procedure and reduce complications.
- The use of ultrasound guidance for adult lumbar puncture is recommended by the Society of Hospital Medicine 2 to reduce the number of needle insertion attempts and increase overall procedure success rates.
- Ultrasound should be used to more accurately identify the lumbar spine level than physical examination in both obese and nonobese patients 2.
- A low-frequency transducer, preferably a curvilinear array transducer, should be used to evaluate the lumbar spine and mark a needle insertion site 2.
Alternative Methods
In the absence of ultrasound guidance, anatomical landmarks can be used to identify the correct level for lumbar puncture.
- The line connecting both iliac crests is commonly used as a landmark, which typically crosses the vertebra column at the level of the L4-L5 intervertebral space or L4 vertebra 3.
- However, this method can be misleading in more than 30% of cases, especially in patients with chronic orthopaedic disorders, chronic pain, overweight, or difficulties with positioning for lumbar puncture 3.
Considerations and Complications
Lumbar puncture is an important technique used to obtain cerebrospinal fluid, administer medications, and monitor intracerebral pressure.
- Clinicians should be familiar with the considerations, contraindications, procedures, and complications of lumbar puncture 4.
- Inappropriate sampling, inaccurate technique, and incomplete analysis can contribute to significant patient morbidity and reduce the amount of accurate information obtained 5.
- The use of ultrasound-guided techniques, such as the "transverse process-zygapophysis separation method," may be considered a therapeutic option in patients with chronic pain 6.