Lumbar puncture (LP) is a common diagnostic and therapeutic procedure. It is most commonly performed to obtain a sample of cerebrospinal fluid (CSF) to help establish neurologic diagnoses. LP is the most accurate method for diagnosing central nervous system infection.
CSF is produced by the choroid plexus in the brain and circulates around the brain and spinal cord within the subarachnoid space. During an LP, the spinal needle penetrates the skin, subcutaneous tissue, spinal ligaments, dura, and arachnoid before entering the subarachnoid space. Four samples of CSF are usually obtained, and the usual studies include bacterial culture and Gram stain from tube 1, protein and glucose from tube 2, blood cell counts and differential cell counts from tube 3, and optional tests such as viral cultures, fungal cultures, countercurrent immunoelectrophoresis, India ink studies, or latex agglutination tests from tube 4. Common CSF findings are shown in Table 2-1.
TABLE 2-1. COMMON PROPERTIES OF CEREBROSPINAL FLUID
The indications for LP in neonates are not as clear as they once were. The once common practice of performing an LP in all ill newborns with suspected sepsis or respiratory distress is no longer recommended unless other findings suggest meningitis. LP is often reserved for babies who demonstrate hypothermia, hyperthermia, poor feeding 24 hours after birth, coma, or seizures. Bedside ultrasound scanning has largely replaced LP for the diagnosis of intracranial hemorrhage. Only about one half of LPs in newborns are successfully completed, and traumatic (bloody) taps are common.
The most common complication is the post-LP (spinal) headache, which occurs in 10% to 25% of patients. The headache often persists for days. The use of smaller-diameter needles, ensuring adequate hydration, and keeping the patient supine (or better, prone) after the procedure can reduce this complication. When the 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.
A more serious potential complication is brain herniation from elevated intracranial pressure that often is caused by a supratentorial mass. However, research has shown that severe meningitis also may cause elevated intracranial pressure and herniation. Before performing an LP, always check the optic fundi
for papilledema. If increased pressure due to a tumor or an intracranial bleed is suspected, an emergency computed tomography (CT) scan should be obtained before LP to reduce the potential of herniation. Inadvertent aspiration of nerve roots on needle withdrawal can be prevented by replacing the stylet before needle removal. Meningitis as a result of the procedure is a theoretical complication. Epidermoid spinal cord tumors have been associated with the performance of LP in infants with unstyletted needles.
Position the patient in the left lateral decubitus position, with the back near the edge of the bed or examination table and with the spine flexed and knees drawn toward the chest. Ensure 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 two large pillows in the patient's lap, with the spine flexed anteriorly.
(1) Position the patient in one of two ways: in a sitting position with patient leaning on a table with the spine flexed anteriorly or in the left lateral decubitus position with the patient's back near the edge of the bed, the spine flexed, and knees drawn to the chest.
PITFALL: Avoid forced flexion of the neck during the procedure because cardiorespiratory arrest may occur if a child's neck is excessively flexed.
Clean the back with povidone-iodine. Set up the sterile tray, remove the tops of the sample tubes, and don a mask and sterile gloves while the povidone-iodine air dries on the skin. Sterile draping typically is used for adult patients, but it can be omitted for the infant in favor of a wide prep to maximize landmark exposure and proper positioning. Inject a small amount (1–3 mL) of 1% lidocaine subcutaneously and into the area between the spinous processes.
(2) Inject a small amount (1–3 mL) of 1% lidocaine subcutaneously and into the area between the spinous processes.
The optimal needle insertion site is in the center of the spinal column, as defined by the spinous processes. The L3-4 interspace can be found where the line joining the superior iliac crests meets the spinous process of L4. Insertion is usually at the L3-4 interspace, but it may be performed one space above or below.
(3) Optimal needle insertion is usually obtained at the L3-4 interspace.
With the stylet in place, slowly insert the 22- or 20-gauge spinal needle midway between the two spinous processes. 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 a loss of resistance, a give, or a “pop” as the needle enters the subarachnoid space, and then advance the needle 1 to 2 mm farther. The pop may not be felt in younger children. Withdraw the stylus, and check the hub for fluid. If there is no fluid, replace the stylus, and advance another fraction before repeating.
(4) With the stylet in place, slowly insert a 22- or 20- gauge spinal needle midway between the two spinous processes.
PITFALL: Make sure the bevel of the needle enters and exits the dura parallel to the long axis of the spinal column. This may lower the incidence of spinal nerve root damage and postprocedure headache.
After fluid is obtained, obstruct the passage of fluid with the stylet or your thumb. Place the stopcock and manometer onto the hub of the needle. As the CSF rises in the manometer, observe the color of the fluid and the opening pressure (Table 2-1).
(5) Once fluid is obtained, obstruct the passage of fluid with the stylet, and place the stopcock and manometer onto the hub of the needle.
PITFALL: Have the patient relax his or her legs to prevent falsely elevating the opening pressure.
PITFALL: Accurate pressure measurements can only be made in the decubitus position.
Turn the stopcock to allow 2 to 3 mL of the CSF in children or 4 to 5 mL in adults to flow into each test tube. If desired, measure the closing pressure, but this has little value and removes additional CSF.
(6) Turn the stopcock to allow 2 to 3 mL of the CSF in children or 4 to 5 mL in adults to flow into each test tube.
PITFALL: Allow the fluid in the manometer tube to flow into the tubes first to lower the amount of CSF removed.
PITFALL: If the tubes are not prelabeled, make sure to place the tubes in order, so that you can easily identify and label each tube after the procedure.
Replace the stylus, and withdraw the needle. Wash off the povidone-iodine, and cover the puncture site with a sterile dressing. Have the patient turn to the supine position and remain horizontal for the next 2 hours.
(7) Replace the stylus, and withdraw the needle.
INSTRUMENT AND MATERIALS ORDERING
Spinal tray sets may be obtained through Arrow Medical Products, Ltd., 2400 Bernville Road, Reading, PA 19605 (phone: 800-233-3187;http://www.arrowintl.com/products/critical_care/).
Many kits and supplies from various companies, including Baxter and American Hospital Supply, can be obtained from Cardinal Health, Inc., 7000 Cardinal Place, Dublin, OH 43017 (phone: 800-234-8701; http://www.cardinal.com/ must register online) and from Owens and Minor, 4800 Cox Road, Glen Allen, VA 23060-6292 (phone: 804-747-9794; fax: 804-270-7281).
Chordas C. Post-dural puncture headache and other complications after lumbar puncture. J Pediatr Oncol Nurs 2001;18:244–259.
Errando CL, Peiro CM. Postdural puncture upper back pain as an atypical presentation of postdural puncture symptoms. Anesthesiology2002;96:1019–1020.
Flaatten H, Thorsen T, Askeland B, et al. Puncture technique and postural postdural puncture headache: a randomised, double-blind study comparing transverse and parallel puncture. Acta Anaesthesiol Scand 1998;42:1209–1214.
Grande PO, Myhre EB, Nordstrom CH, et al. Treatment of intracranial hypertension and aspects on lumbar dural puncture in severe bacterial meningitis. Acta Anaesthesiol Scand 2002;46:264–270.
Hasbun R, Abrahams J, Jekel J, et al. Computed tomography of the head before lumbar puncture in adults with suspected meningitis. N Engl J Med 2001;345:1727–1733.
Holdgate A, Cuthbert K. Perils and pitfalls of lumbar puncture in the emergency department. Emerg Med 2001;13:351–358.
Levine DN, Rapalino O. The pathophysiology of lumbar puncture headache. J Neurol Sci 2001;192:1–8.
Marton KI, Gean AD. The spinal tap: a new look at an old test. Arch Intern Med 1986;104:840—848.
Thoennissen J, Herkner H, Lang W, et al. Does bed rest after cervical or lumbar puncture prevent headache? A systematic review and meta-analysis. Can Med Assoc J 2001;165:1311–1316.
Thomas SR, Jamieson DR, Muir KW. Randomised controlled trial of atraumatic versus standard needles for diagnostic lumbar puncture.BMJ 2000;321:986–990.