From the Guidelines
The aiming point for a lumbar puncture (LP) is the L3-L4 or L4-L5 interspace, with the needle inserted midway between the spinous processes, at a 90-degree angle to the skin 1.
Key Considerations
- The patient should be positioned in a lateral decubitus position with their knees flexed and back arched, or in a sitting position with their back arched 1.
- The skin should be cleaned and disinfected with chlorhexidine or povidone-iodine, and local anesthesia with 1% lidocaine may be used to minimize discomfort 1.
- A 22-gauge or 25-gauge needle is typically used, and the procedure should be performed under sterile conditions 1.
Important Factors
- The use of atraumatic needles is recommended to reduce the risk of post-LP headache and other complications 1.
- The volume of CSF withdrawn should be less than 30 mL, and passive rather than active withdrawal of CSF is recommended when feasible 1.
- The patient's age, weight, and medical history should be taken into account when selecting the needle size and type, and when determining the volume of CSF to be withdrawn 1.
From the Research
Aiming Point for Lumbar Puncture
The aiming point for a lumbar puncture (LP) is typically between the spinous processes of two adjacent lumbar vertebrae, usually at the L3-L4 or L4-L5 interspace.
- The optimal position for LP is with the patient in a sitting position with flexed hips, as this maximizes the interspinous space 2.
- The angle of needle entry for LP varies with age, with more acute angles used for infants and more obtuse angles used for older children 3.
- The depth of needle penetration can be estimated using formulas based on body mass index (BMI) or weight, with more accurate estimates provided by formulas that take into account both BMI and weight 4.
- Ultrasound guidance can be used to determine the optimal aiming point and needle trajectory for LP, with the transverse-axis approach providing a smaller puncture depth and greater puncture angle than the longitudinal-axis approach 5.
- The distance between the puncture point and the spinous process, as well as the angle of the needle, can be measured using ultrasound images and correlated with cadaver measurements to ensure accurate and safe needle placement 5.