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LUMBAR PUNCTURE

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Lumbar puncture is considered the gold standard diagnostic procedure to assist clinicians with the evaluation of subarachnoid hemorrhage, meningitis, and other neurologic conditions. Anxiolytics, such as benzodiazepines, may be administered to improve patient comfort, relaxation, and cooperation. Contraindications to lumbar puncture are listed in Table 175–1.

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Table 175–1

Contraindications to Lumbar Puncture

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If an anxiolytic is used, give a short-acting agent to avoid clouding subsequent clinical assessment. Antiseptic technique should be strictly observed. Scrub the site with povidone-iodine and allow to dry thoroughly to avoid introduction of the chemical and the subsequent production of chemical arachnoiditis.

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In adults, a transverse line drawn between the iliac crests crosses the spine at the L4 spinous process. The L4-L5 interspace is the most commonly used interspace for lumbar puncture, although one can also select the L3-L4 interspace. Palpate the L4-L5 interspace while the patient is curled as tightly as possible in a fetal position. Alternatively, the patient may be seated on the edge of a bed or cart leaning over a tray stand. This latter technique is particularly useful when landmarks are uncertain due to body habitus.

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Use a 31/2-inch atraumatic 22-gauge needle in adults. Use of a needle larger than 20-gauge may double the incidence of post–lumbar puncture headache compared with a smaller needle. The use of an atraumatic or pencil-point needle (such as a Whitacre or Sprotte needle) is associated with fewer post–lumbar puncture headaches than a conventional cutting needle1,2 (Figure 175–1). Also, a smaller needle size using the stylet is associated with reduced frequency of post–lumbar puncture headaches.1

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FIGURE 175–1.

Two types of needle for lumbar puncture. The Quincke is a bevel-type needle, and the Whitacre is a pencil-point needle.

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TECHNIQUE

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Assemble all equipment. Then properly position the patient and identify the patient's L4-L5 interspace. Now put on your sterile gown, mask, and gloves. Next, apply povidone-iodine to the area and let dry. Apply sterile drapes. Anesthetize the skin with 1% lidocaine by raising a skin bleb, then directing the needle toward the umbilicus, and injecting the anesthetic in a fan-shaped area around the proposed lumbar puncture site. Make sure to pull back on the plunger to check for blood ...

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