4 samples of CSF are usually obtained, and the usual studies include bacterial culture and Gram's stain from tube 1, protein and glucose from tube 2, blood cell counts and differential cell counts from tube 3, and optional tests—e.g., viral cultures, fungal cultures, countercurrent immunoelectrophoresis, India ink studies, or latex agglutination tests from tube 4.
Lumbar puncture (LP) for babies is often reserved for those who demonstrate hypothermia, hyperthermia, poor feeding 24 hrs after birth, coma, or seizures.
Bedside U/S scanning has largely replaced LP for diagnosis of intracranial hemorrhage.
The most common complication is post-LP (spinal) headache, which occurs in 10–25% of patients. Headache often persists for days.
Use of smaller-diameter needles, ensuring adequate hydration, and keeping the patient supine (or better, prone) after the procedure can reduce this complication.
When headache is persistent, an epidural blood patch may be applied by an anesthesiologist.
Traumatic (bloody) taps result from inadvertent puncture of the spinal venous plexuses and may rarely lead to spinal hematoma. Other temporary complications include shooting pains in the lower extremities and local pain in the back.
Before performing an LP, always check optic fundus for papilledema. If increased pressure due to tumor or intracranial bleed is suspected, obtain emergency CT scan before LP to reduce potential of herniation.
Inadvertent aspiration of nerve roots on needle withdrawal can be prevented by replacing the stylet before needle removal.
Indications⬆⬇
Suspected CNS infection
Suspected subarachnoid hemorrhage
Suspected neurosyphilis
Suspected Guillain-Barré syndrome
Support for diagnosis of pseudotumor cerebri (i.e., increased CSF pressure without infection)
Serial removal of CSF
Support for diagnosis of multiple sclerosis (i.e., elevated IgG level and oligoclonal banding on electrophoresis)
Contraindications⬆⬇
Dermatitis or cellulitis at insertion site
Raised intracranial pressure
Supratentorial mass lesions (evaluate with CT scan first)
Severe bleeding diathesis (relative)
Lumbosacral deformity (relative)
Uncooperative patient
Procedure⬆⬇
Position the patient in the left lateral decubitus position, with the back near the edge of the bed or exam table and with spine flexed and knees drawn toward chest. Ensure that the shoulders and back are perpendicular to the table. Place a pillow under the patient's head to keep the spine as straight as possible.
An alternative method is to place the patient in the sitting position, leaning on a bedside table or with 2 large pillows in the patient's lap, with the spine flexed anteriorly.
Optimal needle insertion site is in the center of the spinal column, as defined by the spinous processes. Insertion is usually at the L3–4 interspace (where the line joining the superior iliac crests meets the spinous process of L4), but it may be performed 1 space above or below (Fig. 2-1).
Clean the back with povidone-iodine. Set up a sterile tray, remove the tops of the sample tubes, and don mask and sterile gloves while povidone-iodine air-dries on the skin. Sterile draping typically is used for adult patients, but it can be omitted for infants in favor of a wide prep to maximize landmark exposure and proper positioning.
Inject a small amount (1–3 mL) of 1% lidocaine SC and into area between the spinous processes.
Pitfall: Avoid forced flexion of the neck during the procedure because cardiorespiratory arrest may occur if the child's neck is excessively flexed.
With stylet in place, slowly insert 22- or 20-gauge spinal needle midway between the 2 spinous processes (Fig. 2-2). The correct angle for the needle is approximately toward the umbilicus, along the sagittal midplane of the body.
If bone is encountered, withdraw the needle slightly and change its angle. Feel for loss of resistance, give, or "pop'' as needle enters subarachnoid space, and then advance needle 1–2 mm farther. The pop may not be felt in younger children.
Withdraw stylus and check hub for fluid. If there is no fluid, replace stylus and advance another fraction before repeating. After fluid is obtained, obstruct the passage of fluid with the stylet or your thumb.
Place stopcock and manometer onto the hub of the needle. As CSF rises in the manometer, observe the color of fluid and opening pressure (Table 2-1). Turn the stopcock to allow 2–3 mL of CSF in children or 4–5 mL in adults to flow into each test tube. If desired, measure closing pressure, but this has little value and removes additional CSF.
Pitfall: Make sure the bevel of the needle enters and exits the dura parallel to the long axis of the spinal column, which may lower the incidence of spinal nerve root damage and postprocedure headache.
Pitfall: Have the patient relax his or her legs to prevent falsely elevating the opening pressure. Accurate pressure measurements can only be made in the decubitus position.
Pitfall: Allow fluid in the manometer tube to flow into tubes first to lower the amount of CSF removed.
Pitfall: If tubes are not prelabeled, make sure to place tubes in order, so that you can easily identify and label each tube after the procedure.
Replace the stylus, and withdraw the needle (Fig. 2-3). Wash off povidone-iodine and cover the puncture site with sterile dressing. Have the patient turn to supine position and remain horizontal for the next 2 hrs.