Materials

Technique

1- Place the patient in the lateral decubitus position lying on the edge of the bed and facing away from operator. Place the patient in a knee-chest position with the neck flexed. The patient's head should rest on a pillow, so that the entire cranio-spinal axis is parallel to the bed. Sitting position is the second choice because there may be a greater risk of herniation and CSF pressure cannot be measured

2- Find the posterior iliac crest and palpate the L4 spinous process, and mark the spot with a fingernail. Prepare the skin by starting at the puncture site and working outward in concentric circles. Put on sterile gloves. Drape the patient

3- Anesthetize the skin using the 1% lidocaine in the 5 mL syringe with the 25-gauge needle. Change to 22-gauge needle before anesthetizing between the spinous process. Insert in the midline with the needle parallel to the floor and the point directed toward the patient's umbilicus

4- Advance slowly about 2 cm or until a "pop'' (piercing a membrane of the dura) is heard. Then withdraw the stylet in every 2- to 3-mm advance of the needle to check for CSF return. If the needle meets the bone or if blood returns (hitting the venous plexus anterior to the spinal canal), withdraw to the skin and redirect the needle. If CSF return cannot be obtained, try one disk space down

5- When cerebrospinal fluid begins to flow from the needle, discard the first few drops. Do not aspirated cerebrospinal fluid, because a nerve root may be trapped against the needle and injuried

6- Measure the opening pressure with a manometer; allow the patient to relax, and check for good respiratory variation of the fluid level in the manometer to ensure that the needle is properly positioned.

8- Remove the manometer and allow 1 to 2 cc of CSF to flow into each of the three sterile tubes. Send the first for glucose and protein, the second for Gram stain and culture and sensitivity (C&S), and the third for cell count and differential. A fourth tube, when indicated, is collected for viral titer or cultures, India ink preparation, Cryptococcus antigen, VDRL, or cytology

9- Withdraw the needle without replacing the stylet

Complications

A. Postlumbar puncture headache occurs in 10% to 30% of patients within 1 to 3 days and lasts 2 to 7 days. The pain is relieved by lying flat. Treatment consists of bed rest and fluid with simple analgesics.

Bibliography

1-Hayward RA, Shapiro MF, Oye RK: Laboratory testing on cerebrospinal fluid: A repappraisal. Lancet 1987;1:1-4.

2-Marton KI, Gean AD,: The spinal tap: A new look at an old test. Annals of Internal Medicine 1986;104:840-48.

3-Charles E. Saunders, Mary T. Ho(eds): In Current Emergency Diagnosis and Treatment. Fourth edition, 1992.