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LP

abbr.

lumbar puncture

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line pair (lp),

a factor that determines the spatial frequency of CT and radiographic images. It consists of two parallel lines or bars separated by a space. As the number of line pairs per centimeter increases, the fidelity of the image decreases.

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lumbar puncture (LP),

a diagnostic or therapeutic procedure in which a hollow needle and stylet are introduced into the subarachnoid space of the lumbar part of the spinal canal to obtain cerebrospinal fluid (CSF). Strict aseptic technique is used. Diagnostic indications include measuring of CSF pressure; obtaining CSF for laboratory analysis; and injecting oxygen or a radiopaque substance for radiographic visualization of the structures of the nervous system of the spinal canal and meninges and brain. Therapeutic indications for lumbar puncture include removing blood or pus from the subarachnoid space, injecting sera or drugs, withdrawing CSF to reduce intracranial pressure, introducing a local anesthetic to induce spinal anesthesia, and placing a small amount of the patient's blood in the subarachnoid space to form a clot to patch a hole in the dura to prevent leak of CSF into the epidural space.

method The skin over the interspace of the third and fourth lumbar vertebrae is cleansed. A fenestrated sterile drape is placed over the back, the window over the puncture site. The needle is inserted through the interspace to the subarachnoid space, and the stylet is withdrawn. If the needle is in the proper place, clear, straw-colored CSF will begin to drip out through the needle. Depending on the indication for the procedure, various techniques follow. The pressure of the CSF may be measured with a manometer attached to a catheter and stopcock, or fluid may be withdrawn, visually examined, and sent to the laboratory for chemical or bacteriologic analysis.

interventions The nurse may be responsible for obtaining the patient's written permission for the physician to perform a lumbar puncture. If the patient is apprehensive, he or she may be given a sedative one-half hour before the procedure. The techniques to be used and the treatments to be given or the information to be obtained are explained. The patient is placed in a lateral recumbent position, the back as near the edge of the bed as possible. The legs are flexed on the thighs, the thighs are flexed on the abdomen, and the head and shoulders are bent down, curving the spine convexly to afford the greatest space between the vertebrae. If the patient is excessively hairy, a dry shave of the lumbar area is performed before draping the area. After the procedure, significant signs to be observed by the nurse include pain, change in mentation or alertness, leakage of CSF from the puncture site, fever, and urinary retention. The patient is usually kept flat in bed, often in a prone position, for 1 hour after the procedure.

outcome criteria Lumbar puncture is contraindicated if intracranial tumor is suspected and there is evidence of greatly increased intracranial pressure, if there are signs of infection at the site of puncture, or (to avoid a second puncture) if encephalography or myelography is planned in the near future. Infection, leakage of CSF, headache, nausea, vomiting, dysuria, or signs of meningeal irritation occur in approximately 25% of patients.