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It may be done for diagnostic purposes to determine the pressure within the cerebrospinal cavities, to determine presence of an obstruction to flow of cerebrospinal fluid, to remove a specimen of cerebrospinal fluid for laboratory examination, or to inject air or other contrast medium into the spinal canal to take an x-ray of the cerebrospinal system.
The patient is positioned so that the knees and head are flexed as much as possible and is assisted in maintaining this position during the entire procedure. A local anesthetic is injected subcutaneously to anesthetize the skin and underlying tissues. The patient should be warned not to move suddenly and told there may be a slight feeling of pressure when the puncture needle is inserted.
Strict adherence to the rules of aseptic technique is necessary to avoid the possibility of introducing microorganisms into the spinal canal. The attendant may be asked to assist in the Queckenstedt test during the lumbar puncture. This test involves compression of the veins of the neck, first on one side, then on the other and finally on both sides at once. The cerebrospinal fluid pressure is measured each time the veins are compressed. This test determines whether there is an obstruction in the spinal canal. Care must be taken that the trachea is not constricted while the neck veins are being compressed.
After the procedure the patient is observed for signs of pulse changes, respiratory difficulty, or cyanosis. These rarely occur, but headache is common and may be partially relieved by keeping the patient flat in bed for 8 hours after the procedure. An ice cap and aspirin may help alleviate the discomfort.
lum·bar punc·ture (LP),
lumbar punctureSpinal tap Neurology A diagnostic procedure in which a very long needle is inserted into the subarachnoid space between the 3rd and 4th lumbar vertebrae in order to obtain CSF; an LP is used to measure intracranial pressure, which may be ↑ 2º to hemorrhage, tumors, or edema, measure CSF chemistries–eg, glucose, proteins, diagnose inflammation of the CNS, especially infections–eg, meningitis, and stroke, spinal cord tumors and metastases to the CNS, or inject a dye into the spine before myelography Complications Uncommon; meningitis, bleeding into spinal canal; if intracranial pressure is ↑, removal of CSF from spinal canal may cause fatal herniation of cerebellar tonsils. See Cerebrospinal fluid.
lum·bar punc·ture(lŭm'bahr pŭngk'shŭr)
lumbar punctureAbbreviation: LP
CAUTION!Postprocedure headache occurs in about half of all patients who undergo lumbar puncture. Rarely reported complications of the procedure include cerebral herniation, epidural infection, epidural bleeding, paraparesis, and subdural bleeding.
Informed consent for the procedure is obtained except in dire emergencies when clinical judgment prevails. Appropriate equipment is gathered: sterile gloves and mask for the operator, skin antiseptic (povidine-iodine solution), local anesthetic (1% lidocaine), and a lumbar puncture tray containing sterile gauze sponges, fenestrated drape and towel, needles and syringe for anesthesia, spinal needles, 4 collection tubes, 3-way stopcock and manometer; and a small adhesive bandage.
The procedure and expected sensations are explained, and the patient is asked to remain still when positioned and to breathe normally. The patient is typically placed on his or her left side at the right edge of the bed or examining table with knees drawn up to the abdomen and chin down to the chest, or in a sitting position with legs over one side of the table and buttocks at the other, bending head and chest toward the knees. Either of these positions exposes the back to the operator and provides spinal flexion, allowing easy access to the lumbar subarachnoid space. The assisting nurse holds the patient appropriately to secure this position (one arm around the neck, the other around the knees, or holding both shoulders bent forward). Draping provides warmth and privacy. Next, the patient's skin is prepared with antiseptic solution, and a sterile fenestrated barrier is placed over the proposed puncture site. Local anesthetic is injected, and then the spinal needle, with its stylet in place, is slowly advanced between the vertebra into and through the dura and arachnoid membranes. The stylet that fills the needle is removed, and initial measurements are made of the opening intracranial pressure (ICP) with a manometer. When the procedure is performed for diagnosis, about 8 to 10 ml of fluid are collected and sent promptly to the clinical laboratory for analysis of cell count, glucose, protein levels, cultures stains, and special studies. The closing pressure should then be read, the needle removed, and a small impervious adhesive dressing applied, sometimes with collodion to prevent CSF leakage. See: illustration
Pain at the puncture site, infection, bleeding, neurological injury, death, and post–spinal tap headaches are all potential complications. Of these, postural headache, caused by chronic leakage from the puncture site, is the complication most often brought to the attention of health care professionals. It may be treated with the injection of a small amount of the patient's own blood epidurally, to form a blood patch. See: cerebrospinal fluid
The nurse assists the operator throughout the procedure by numbering and capping specimen tubes for laboratory examination and by applying jugular vein pressure as directed. Reassurance and direction are provided to the patient throughout the procedure, and the patient is assessed for adverse reactions (elevated pulse rate, pain radiating into the limbs, pallor, clammy skin, or respiratory distress).
After the procedure, the nurse assesses vital signs and neurological status, particularly observing for signs of paralysis, weakness, or loss of sensation in the lower extremities. If CSF pressure is elevated, the patient’s neurological status should be assessed every 15 min for 4 hr, if normal, every hour for 2 hr, then every 4 hr or as ordered. The puncture site should be checked hourly for 4 hr, then every 4 hr for 24 hr, assessing for redness, swelling, and drainage. To decrease the chance of headache, oral intake (for spinal fluid replacement and equalization of pressures) is encouraged, and the patient should remain in bed in a supine position or with the head elevated no more than 30° for 4 to 24 hr (per operator or institutional protocol). The patient should not lift his or her head but can move it (and himself or herself) from side to side. Noninvasive pain relief measures and prescribed analgesia are provided if headache occurs.