Chapter S9: Technique of Lumbar Puncture

In experienced hands lumbar puncture (LP) is usually a safe procedure. Major complications are extremely uncommon but can include cerebral herniation, injury to the spinal cord or nerve roots, hemorrhage (spinal hematoma), or infection. Minor complications occur with greater frequency and can include backache, post-LP headache, and radicular pain or numbness.

Patients with an altered level of consciousness, a focal neurologic deficit, new-onset seizure, papilledema, or an immunocompromised state are at increased risk for potentially fatal cerebellar or tentorial herniation following LP. Neuroimaging should be obtained in these patients prior to LP to exclude a focal mass lesion or diffuse swelling. Imaging studies should include the spine in patients with symptoms suggesting spinal cord compression, such as back pain, leg weakness, urinary retention, or incontinence. In patients with suspected meningitis who require neuroimaging prior to diagnostic LP, administration of antibiotics, preferably following blood culture, should precede the neuroimaging study.

LP should not be performed through infected skin, as organisms can be introduced into the subarachnoid space (SAS).

Patients with coagulation defects including thrombocytopenia are at increased risk of post-LP spinal subdural or epidural hematomas, either of which can produce permanent nerve injury and/or paralysis. If a bleeding disorder is suspected, the platelet count, international normalized ratio (INR), and partial thromboplastin time (PTT) should be checked prior to LP. There are no data available to assess the safety of LP in patients with low platelet counts; a count of <20,000/μL is considered to be a contraindication to LP, and some institutions recommend that the platelet count be >40,000 prior to LP. Bleeding complications rarely occur in patients with platelet counts ≥50,000/μL and an INR ≤1.5.

GUIDELINES FOR PATIENTS RECEIVING ANTICOAGULANT OR ANTIPLATELT MEDICATIONS

There is an increased risk of bleeding complications if an LP is performed in a patient receiving antiplatelet or anticoagulant medications. The risk is further increased when multiple anticoagulant medications are used or when the level of anticoagulation is high. The most common site of bleeding is the epidural space. Symptoms of bleeding following an LP can include a sensory or motor deficit and/or bowel/bladder dysfunction; back pain occurs less commonly. For serious deficits such as paraparesis, immediate surgical intervention, ideally within 8 h of onset of weakness, is important to minimize permanent disability; surgical intervention after 24 h is associated with a poor outcome.

Only limited data are available to guide decisions about performing LPs in patients receiving anticoagulant drugs. Information about managing antiplatelet and anticoagulation drugs during invasive surgical procedures is available from the prescribing information provided by the drug manufacturer. Evidence-based guidelines for management of regional anesthetic procedures including spinal and epidural blocks and for management of interventional spine and pain procedures in patients receiving anticoagulation have been developed by the American Society of Regional Anesthesia and Pain (ASRA); these guidelines can help guide decisions by physicians considering LP. Management of these patients can be complex and needs to consider both the risk of LP-related hemorrhage as well as the risk of reversing therapeutic anticoagulation prior to LP. Guidelines for some commonly used anticoagulants are summarized below.

Unfractionated Heparin (UFH), Therapeutic Dosing

The ASRA 2010 Practice Advisory recommends discontinuing UFH 2–4 h prior to removal of spinal or epidural catheters to minimize risk of hematoma. Similar guidelines are reasonable for patients undergoing LP: discontinue UFH 2–4 h prior to LP; document normal PTT prior to the procedure; and document a normal platelet count in patients who have received heparin for 4 days or longer because of the risk of heparin-induced thrombocytopenia (HIT). The half-life of heparin is 60–90 min.

UFH, Prophylactic Dosing

There have been case reports of spinal hematoma resulting from spinal or epidural anesthetic procedures in patients receiving low-dose subcutaneous UFH. The 2010 ASRA guidelines for regional anesthetic procedures stated that there is no contraindication to the use of these techniques for anesthesia in patients receiving prophylactic UFH at a dose of 5000 U subcutaneously twice daily. However, the 2015 ASRA guidelines for interventional spine and pain procedures recommend discontinuing subcutaneous heparin for 8–10 h before a planned neuraxial procedure. Similar precautions to prevent bleeding should be taken prior to LP in patients receiving 5000 U of UFH subcutaneously twice daily: document a normal PTT prior to the LP; document a normal platelet count in patients who have received heparin for 4 days or longer; and perform the LP 1–2 h prior to the next heparin dose, when the heparin effect should be minimal. Subcutaneous heparin can be usually resumed 2 h after an uncomplicated procedure.

Low-Molecular-Weight Heparin (LMWH), Therapeutic Dose (e.g., Enoxaparin 60 mg Subcutaneously q12h)

Patients receiving LMWH are at increased risk of post-LP spinal or epidural hematoma. LMWH dose should be held for at least 24 h before the procedure.

LMWH, Prophylactic Dose (e.g., Enoxaparin 30 mg Subcutaneously q12h)

Patients receiving prophylactic dose LMWH have altered coagulation. ASRA guidelines recommend waiting at least 10–12 h after a prophylactic dose of LMWH before inserting a spinal or epidural catheter to minimize the risk of spinal or epidural hematoma. Similar guidelines are reasonable for patients undergoing LP.

Warfarin

Spinal puncture is contraindicated during warfarin therapy. Warfarin should be stopped 4–5 days prior to the LP, and for urgently needed procedures, warfarin’s effect can be reversed with fresh frozen plasma. The INR should be within the normal range at the time of the procedure.

Aspirin and Nonsteroidal Anti-inflammatory Drugs (NSAIDs)

ASRA guidelines conclude that use of these drugs does not appear to be associated with a significant added risk of spinal bleeding in patients having spinal or epidural anesthesia. Similarly, LP in patients receiving one of these drugs is unlikely to cause bleeding. Reversal of drug effect on platelet function requires stopping the drug for ~10 days for aspirin, 4 days for naproxen, and 24 h for ibuprofen.

Ticlopidine/Clopidogrel

ASRA guidelines developed for regional anesthetic procedures suggest discontinuing ticlopidine 14 days prior to a spinal or epidural procedure and discontinuing clopidogrel 7 days prior to the procedure. Similar guidelines are reasonable for performing LP.

Abciximab, Eptifibatide, and Other Platelet Glycoprotein IIb/IIIa Inhibitors

The risk of spinal hematoma with these drugs is unknown. Platelet aggregation remains abnormal for 24–48 h following discontinuation of abciximab and 4–8 h following discontinuation of eptifibatide. ASRA guidelines for regional anesthetic procedures recommend avoiding spinal or epidural procedures until platelet function is normal. Similar guidelines are reasonable for performing LP.

Direct Thrombin Inhibitors (e.g., Dabigatran)

Pradaxa^® prescribing information includes a boxed warning about the risk of epidural or spinal hematoma in patients treated with Pradaxa who are receiving neuraxial anesthesia or undergoing spinal puncture. For medium- and high-risk interventional pain procedures, where the risk of bleeding may be similar to LP, ASRA guidelines recommend an interval of 4–5 days between discontinuation of dabigatran and the interventional pain procedure, and an interval between the procedure and resumption of dabigatran of 24 h. Similar guidelines for performing LP are not available. For emergency situations in which rapid reversal of the anticoagulant effect of dabigatran is indicated, idarucizumab, a humanized monoclonal antibody fragment, is U.S. Food and Drug Administration (FDA) approved as a specific reversal agent for dabigatran. The half-life of dabigatran is 8 h after a single dose and 17 h after multiple doses.

Oral Factor Xa Inhibitors

RIVAROXABAN

Xarelto^® prescribing information includes a boxed warning about the risk of spinal/epidural hematoma with spinal puncture. LP should be avoided in patients receiving this drug. The half-life of rivaroxaban is 9–13 h. Xarelto^® prescribing information states that indwelling epidural or intrathecal catheters not be removed before at least 2 half-lives have elapsed, i.e., 18 h in young patients aged 20–45 years and 26 h in elderly patients aged 60–76 years, after the last administration of rivaroxaban. Rivaroxaben should not be resumed earlier than 6 h after removal of the catheter. If traumatic puncture occurs, resumption of rivaroxaban should be delayed for 24 h. Similar guidelines are reasonable for performing LP.

APIXIBAN

Eliquis^® prescribing information includes a boxed warning about the risk of spinal/epidural hematoma with spinal puncture. LP should be avoided in patients receiving this drug. The effect of apixiban is expected to last for at least 24 h after the last dose, i.e., for about 2 drug half-lives. Eliquis^® prescribing information recommends that indwelling epidural or intrathecal catheters not be removed earlier than 24 h after the last administration of apixiban. Apixiban should not be resumed earlier than 5 h after removal of the catheter. If traumatic puncture occurs, resumption of apixiban should be delayed for 48 h. Similar guidelines are reasonable for performing LP.

FONDAPARINUX

Arixtra^® prescribing information includes a boxed warning about the risk of spinal/epidural hematoma with neuraxial anesthesia or spinal puncture. ASRA guidelines for interventional spine and pain procedures recommend stopping fondaparinux for 3–4 days before a medium- or high-risk pain procedure. Similar guidelines are reasonable for performing LP.

Anxiety and pain can be minimized prior to beginning the procedure. Anxiety can be allayed by the use of lorazepam, 1–2 mg given PO 30 min prior to the procedure or IV 5 min prior to the procedure. Topical anesthesia can be achieved by the application of a lidocaine-based cream. Lidocaine 4% is effective when applied 30 min prior to the procedure; lidocaine/prilocaine requires 60–120 min. The cream should be applied in a thick layer so that it completely covers the skin. An occlusive dressing is used to keep the cream in place, for example Tegaderm^® or Press’n Seal^®.

Proper positioning of the patient is essential. The procedure should be performed on a firm surface; if the procedure is to be performed at the bedside, the patient should be positioned at the edge of the bed and not in the middle. The patient is asked to lie on his or her side, facing away from the examiner, and to “roll up into a ball.” The neck is gently ante-flexed and the thighs pulled up toward the abdomen; the shoulders and pelvis should be vertically aligned without forward or backward tilt (Fig. S9-1). The spinal cord terminates at approximately the L1 vertebral level in 94% of individuals. In the remaining 6%, the conus extends to the L2–L3 interspace. LP is therefore performed at or below the L3–L4 interspace. A useful anatomic guide is a line drawn between the posterior superior iliac crests, which corresponds closely to the level of the L3–L4 interspace. The interspace is chosen following gentle palpation to identify the spinous processes at each lumbar level.

An alternative to the lateral recumbent position is the seated position. The patient sits at the side of the bed, with feet supported on a chair. The patient is instructed to curl forward, trying to touch the nose to the umbilicus. It is important that the patient not simply lean forward onto a bedside tabletop, as this is not an optimal position for opening up the spinous processes. LP is sometimes more easily performed in obese patients if they are sitting. A disadvantage of the seated position is that measurement of opening pressure is not accurate. In situations in which LP is difficult using palpable spinal landmarks, particularly in obese patients, fluoroscopic or computed tomography (CT)-guided needle placement may be necessary. Bedside ultrasound to guide needle placement is also an option.

Once the desired site for needle insertion has been identified, the examiner should put on sterile gloves. A mask is worn if the clinician will be injecting material into the spinal or epidural space to prevent droplet spread of oral flora during the procedure. After cleansing the skin with povidone-iodine or similar disinfectant, the area is draped with a sterile cloth; the needle insertion site is blotted dry using a sterile gauze pad. Proper local disinfection reduces the risk of introducing skin bacteria into the SAS or other sites. Local anesthetic, typically 1% lidocaine, 3–5 mL total, is injected into the subcutaneous tissue; in nonemergency situations, a topical anesthetic cream can be applied (see above). When time permits, pain associated with the injection of lidocaine can be minimized by slow, serial injections, each one progressively deeper than the last, over a period of ~2 min. Approximately 0.5 mL of lidocaine is injected at a time; the needle is not usually withdrawn between injections. A pause of ~15 s between injections helps to minimize the pain of the subsequent injection. The goal is to inject each mini-bolus of anesthetic into an area of skin that has become numb from the preceding injection. Approximately 5–10 mini-boluses are injected, using a total of ~2–5 mL of lidocaine.

If possible, the LP should be delayed for 10–15 min following the completion of the injection of anesthetic; this significantly decreases and can even eliminate pain from the procedure. Even a delay of 5 min will help to reduce pain.

The LP needle (typically 20- to 22-gauge) is inserted in the midline, midway between two spinous processes, and slowly advanced. The bevel of the needle should be maintained in a horizontal position, parallel to the direction of the dural fibers and with the flat portion of the bevel pointed upward; this minimizes injury to the fibers as the dura is penetrated. When LP is performed in patients who are sitting, the bevel should be maintained in the vertical position. In most adults, the needle is advanced 4–5 cm (1–2 in.) before the SAS is reached; the examiner usually recognizes entry as a sudden release of resistance, a “pop.” If no fluid appears despite apparently correct needle placement, then the needle may be rotated 90–180°. If there is still no fluid, the stylet is reinserted and the needle is advanced slightly. Some examiners halt needle advancement periodically to remove the stylet and check for flow of cerebrospinal fluid (CSF). If the needle cannot be advanced because it hits bone, if the patient experiences sharp radiating pain down one leg, or if no fluid appears (“dry tap”), the needle is partially withdrawn and reinserted at a different angle. If on the second attempt the needle still hits bone (indicating lack of success in introducing it between the spinous processes), then the needle should be completely withdrawn and the patient should be repositioned. The second attempt is sometimes more successful if the patient straightens the spine completely prior to repositioning. The needle can then be reinserted at the same level or at an adjacent one.

Once the SAS is reached, a manometer is attached to the needle and the opening pressure measured. The examiner should look for normal oscillations in CSF pressure associated with pulse and respirations. The upper limit of normal opening pressure with the patient supine is 180 mmH₂O in adults but may be as high as 200–250 mmH₂O in obese adults.

CSF is allowed to drip into collection tubes; it should not be withdrawn with a syringe. Depending on the clinical indication, fluid is obtained for studies including: (1) cell count with differential; (2) protein and glucose concentrations; (3) culture (bacterial, fungal, mycobacterial, viral); (4) smears (e.g., Gram’s and acid-fast stained smears); (5) antigen tests (e.g., latex agglutination); (6) polymerase chain reaction (PCR) amplification of DNA or RNA of microorganisms; (7) antibody levels against microorganisms; (8) immunoelectrophoresis for determination of γ-globulin level and oligoclonal banding; and (9) cytology. Although 15 mL of CSF is sufficient to obtain all of the listed studies, the yield of fungal and mycobacterial cultures and cytology increases when larger volumes are sampled. In general, 20–30 mL may be safely removed from adults.

A bloody tap due to penetration of a meningeal vessel (a “traumatic tap”) may result in confusion with subarachnoid hemorrhage (SAH). In these situations, a specimen of CSF should be centrifuged immediately after it is obtained; clear supernatant following CSF centrifugation supports the diagnosis of a bloody tap, whereas xanthochromic supernatant suggests SAH. In general, bloody CSF due to the penetration of a meningeal vessel clears gradually in successive tubes, whereas blood due to SAH does not. In addition to SAH, xanthochromic CSF may also be present in patients with liver disease and when the CSF protein concentration is markedly elevated (>1.5–2 g/L [150–200 mg/dL]).

Prior to removing the LP needle, the stylet is reinserted to avoid the possibility of entrapment of a nerve root in the dura as the needle is being withdrawn; entrapment could result in a dural CSF leak, causing headache. Some practitioners question the safety of this maneuver, with its potential risk of causing a needle-stick injury to the examiner. Injury is unlikely, however, given the flexibility of the small-diameter stylet, which tends to bend, rather than penetrate, on contact. Although patients are often advised to remain recumbent for 30–60 min following LP to prevent headache, this is unnecessary because it does not appear to affect the development of headache (see below).

The principal complication of LP is headache, occurring in 10–30% of patients. Younger age and female gender are associated with an increased risk of post-LP headache. Headache usually begins within 48 h but may be delayed for up to 12 days. Head pain is dramatically positional; it begins when the patient sits or stands upright; there is relief upon reclining or with abdominal compression. The longer the patient is upright, the longer the latency before head pain subsides. The pain is usually a dull ache but may be throbbing; its location is occipitofrontal. Nausea and stiff neck often accompany headache, and occasionally, patients report blurred vision, photophobia, tinnitus, and vertigo. In more than three-quarters of patients, symptoms completely resolve within a week, but in a minority they can persist for weeks or even months.

Post-LP headache is caused by a drop in CSF pressure related to persistent leakage of CSF at the site where the needle entered the SAS. Loss of CSF volume decreases the brain’s supportive cushion, so that when a patient is upright there is probably dilation and tension placed on the brain’s anchoring structures, the pain-sensitive dural sinuses, resulting in pain. Although intracranial hypotension is the usual explanation for severe LP headache, the syndrome can occur in patients with normal CSF pressure.

Because post-LP headache usually resolves without specific treatment, care is largely supportive with oral analgesics (acetaminophen, NSAIDs, opioids [Chap. 10]) and antiemetics. Patients may obtain relief by lying in a comfortable (especially a recumbent or head-down Trendelenburg) position. For some patients, caffeine tablets or beverages with caffeine can provide temporary pain relief. Other drugs shown to decrease pain severity scores include gabapentin, hydrocortisone, and theophylline.

For patients with persistent pain an epidural blood patch may be effective. This is accomplished by injection of 15 mL of autologous whole blood; the injection is directed at the epidural space at the level of the initial LP. This procedure is most often performed by a pain specialist or anesthesiologist. The blood patch has an immediate effect, making it unlikely that sealing off a dural hole with blood clot is its sole mechanism of action. The acute benefit may be due to compression of the CSF space by the clot, increasing CSF pressure. Some clinicians reserve epidural blood patch for patients who do not respond to caffeine, while others prefer to use blood patch as initial management for unremitting post-LP symptoms.

Strategies to decrease the incidence of post-LP headache are listed in Table S9-1. Use of an atraumatic needle (“pencil point,” Sprotte, Whitacre) reduces the risk of headache compared to use of a traditional traumatic or cutting tip needle (Quincke) (Fig. S9-2). Needle gauge does not appear to correlate with the risk of PDPH: studies comparing higher and lower gauges of atraumatic and traumatic needles showed no significant differences in terms of the development of PDPH. Atraumatic needles are more difficult to use and more attempts may be required to perform the LP; this may increase the risk of PDPH. There is a low risk of needle damage, e.g., breakage, with the Sprotte atraumatic needle.

Other strategies to decrease the incidence of headache include performing the LP in the lateral decubitus position, as opposed to the sitting position, and replacing the stylet before removing the LP needle.

Patients are often advised to remain in a recumbent position for up to an hour following LP to prevent PDPH. However, a meta-analysis of the effects of bed rest following dural puncture showed no benefit in terms of reducing the incidence of headache. The customary practice of remaining in a recumbent position post-LP is unnecessary. Another approach to preventing headache, administering extra fluids, also appears ineffective in reducing headache incidence.

In uninfected CSF, the normal white blood cell count is fewer than five mononuclear cells (lymphocytes and monocytes) per μL (Table S9-2). Polymorphonuclear leukocytes (PMNs) are not found in normal unconcentrated CSF; however, rare PMNs can be found in centrifuged or concentrated CSF specimens such as those used for cytologic examination. Red blood cells (RBCs) are not normally present in CSF; if RBCs are present from a traumatic tap, their number decreases as additional CSF is collected. CSF glucose concentrations <2.2 mmol/L (<40 mg/dL) are abnormal. The protein concentration varies in CSF sampled from lumbar, cisternal and ventricular regions (Table S9-2); the normal lumbar protein concentration is >50 mg/dL.