Skill Checkup: Lumbar Puncture

Helmi L. Lutsep, MD

Disclosures

May 20, 2019

Lumbar puncture is performed to obtain information about cerebrospinal fluid (CSF). Usually used for diagnostic purposes, it is also sometimes used for therapeutic purposes. Lumbar puncture should be performed only after a neurologic examination but should never delay potentially life-saving interventions, such as the administration of antibiotics and steroids to patients with suspected bacterial meningitis.

A thorough discussion of lumbar puncture, including patient preparation, is also available.

Procedure

Wearing nonsterile gloves, locate the L3-L4 interspace by palpating the right and left posterior superior iliac crests and moving the fingers medially toward the spine. Palpate that interspace (L3-L4), the interspace above (L2-L3), and the interspace below (L4-L5) to find the widest space. Mark the entry site with a thumbnail or a marker. To help open the interlaminar spaces, ask the patient to practice pushing the entry site area out toward the practitioner.

Open the spinal tray, change to sterile gloves, and prepare the equipment. Open the numbered plastic tubes, and place them upright. Assemble the stopcock on the manometer, and draw the lidocaine into the 10-mL syringe. Use the skin swabs and antiseptic solution to clean the skin in a circular fashion, starting at the L3-L4 interspace and moving outward to include at least one interspace above and one below. Just before applying the skin swabs, warn the patient that the solution is very cold. Place a sterile drape below the patient and a fenestrated drape on the patient. Use the 10-mL syringe to administer a local anesthetic (see the video below).

Raise a skin wheal using the 25-gauge needle, then switch to the longer 20-gauge needle to anesthetize the deeper tissue. Insert the needle all the way to the hub, aspirate to confirm that the needle is not in a blood vessel, and then inject a small amount as the needle is withdrawn a few centimeters. Continue this process above, below, and to the sides very slightly (using the same puncture site).

This process anesthetizes the entire immediate area so that if redirection of the spinal needle is necessary, the area will still be anesthetized. For this reason, a 10-mL syringe may be more beneficial than the usual 3-mL syringe supplied with the standard lumbar puncture kit. The 20-gauge needle can also be used as a guide for the general direction of the spinal needle. In other words, the best direction in which to aim the spinal needle can be confirmed if the 20-gauge needle encounters bone in one direction but not in another.

Next, stabilize the 20- or 22-gauge needle with the index fingers, and advance it through the skin wheal using the thumbs (see the video below). Orient the bevel parallel to the longitudinal dural fibers to increase the chances that the needle will separate the fibers rather than cut them; in the lateral recumbent position, the bevel should face up, and in the sitting position, it should face to one side or the other.

Insert the needle at a slightly cephalad angle, directing it toward the umbilicus. Advance the needle slowly but smoothly. Occasionally, a characteristic "pop" is felt when the needle penetrates the dura. Otherwise, the stylet should be withdrawn after approximately 4-5 cm and observed for fluid return. If no fluid is returned, replace the stylet, advance or withdraw the needle a few millimeters, and recheck for fluid return. Continue this process until fluid is successfully returned.

For measurement of the opening pressure, the patient must be in the lateral recumbent position. After fluid is returned from the needle, attach the manometer through the stopcock, and note the height of the fluid column. The patient's legs should be straightened during the measurement of the open pressure, or a falsely elevated pressure will be obtained (see the video below).

Collect at least 10 drops of CSF in each of the 4 plastic tubes, starting with tube 1. If possible, the CSF that is in the manometer should be used for tube 1. If the CSF flow is too slow, ask the patient to cough or bear down (as in the Valsalva maneuver), or ask an assistant to press intermittently on the patient's abdomen to increase the flow. Alternatively, the needle can be rotated 90° so that the bevel faces cephalad.

Replace the stylet, and remove the needle (see the video below). Clean off the skin preparation solution. Apply a sterile dressing, and place the patient in the supine position.

Comments

3090D553-9492-4563-8681-AD288FA52ACE
Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.
Post as:

processing....