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Lumbar puncture (shown) is a procedure often performed in the emergency department for either therapeutic or diagnostic purposes. Most commonly, lumbar puncture is employed as a diagnostic procedure to diagnose meningitis, subarachnoid hemorrhage, or other infectious/inflammatory conditions. Lumbar puncture may be used to reduce the volume of cerebrospinal fluid (CSF) and thus mitigate the symptoms and/or effects of pseudotumor cerebri or normal pressure hydrocephalus.[1]
Image courtesy of Wikipedia Commons.
Shown is the leg of a 9-month-old infant in septic shock and disseminated intravascular coagulation with a rapidly evolving purpuric rash due to suspected meningococcal meningitis. Early bacterial meningitis may be difficult to diagnose based on history and physical examination alone as many viral processes can cause similar symptoms (eg headache, neck/back pain and fever). Lumbar puncture should be performed only after a neurologic examination and an assessment of intracranial pressure, but should never delay potentially life-saving interventions such as the administration of antibiotics and steroids to patients with suspected bacterial meningitis.
Image courtesy of Medscape/ D. Scott Smith, MD.
Brain CT scanning (shown) should be obtained before a lumbar puncture in patients with clinical history, symptoms or physical exam signs of elevated intracranial pressure. Elevated intracranial pressure (ICP) may result from space occupying lesions, hemorrhage or significant edema. Patients with elevated ICP may manifest papilledema, detectable on funduscopic examination. Common symptoms suggesting elevated ICP include vomiting, anisocoria, severe headache, altered mental status, or a focal neurological exam. Elevated ICP may be more common in patients who are known to be immunocompromised (and thus more susceptible to cerebral space occupying lesions such as abscesses or tumors), and in patients with suspected subarachnoid hemorrhage (SAH) because a significant intracranial mass effect might be present in awake and alert patients with only subtle neurologic abnormalities. A study in the British Medical Journal showed that a non-contrast brain CT performed within 6 hours of headache onset is nearly 100% sensitive for SAH.[2]
Image courtesy of Medscape.
This CT scan of the brain demonstrates a hyperdense collection in the circle of Willis consistent with SAH. Indications for lumbar puncture include suspicion of SAH, suspicion of CNS infection, therapeutic relief of pseudotumor cerebri, and suspicion of central nervous system disease, such as Guillain-Barré, multiple sclerosis and carcinomatous meningitis. Relative contraindications to lumbar puncture include the following: increased intracranial pressure (ICP), coagulopathy, and brain abscess (arrow).[1]
Image courtesy of Wikipedia Commons/James Heilman, MD.
Note that absolute contraindications to lumbar puncture are the presence of infected skin over the needle entry site and the presence of unequal pressures between the supratentorial and infratentorial compartments. The latter is usually inferred by the following characteristic findings on CT: midline shift, loss of suprachiasmatic and basilar cisterns, posterior fossa mass, loss of the superior cerebellar cistern, and loss of the quadrigeminal plate cistern.[1] Avoid lumbar puncture in patients in whom the disease process has progressed to impending cerebral herniation (deteriorating level of consciousness, brainstem signs including pupillary changes such as anisocoria [shown], posturing, irregular respirations and very recent seizure).[3]
Other relative contraindications to LP include neutropenia (as the risk of introducing a central nervous system infection is theoretically higher) and coagulopathy or thrombocytopenia (as the risk of bleeding and/or hematoma formation is more significant, and may lead to mass effect and potentially devastating neurologic injury). Presence of a brain abscess is also a relative contraindication to lumbar puncture.
Indications for performing brain CT scanning before lumbar puncture in patients with suspected meningitis include the following[1,3]:
Image courtesy of Wikipedia Commons.
Prior to obtaining a lumbar puncture, explain the procedure, benefits, risks, complications, and alternative options to the patient or the patient's representative, and obtain a signed informed consent. Warn patients that the procedure is sometimes technically difficult and despite the significant discomfort of the procedure and the best efforts of the physician, the procedure may be unsuccessful.
The potential complications of lumbar puncture include: pain, bleeding, infection (either at the skin site or of the meninges) and damage to adjacent structures such as the nerves of the cauda equina. These complications are quite rare and LP is generally considered to be a safe procedure. The most common complication of LP is post-LP headache and may occur in 10-40% of patients.[4] In the pediatric population, the incidence is likely underreported among younger patients; however, using a 25G or 27G needle and taking a little more time to collect the CSF may reduce the occurrence to 1%-4%.[5] Post-LP headache is thought to result from a persistent leak of CSF from the site of the initial tap.[6]
While post-LP headache is not dangerous, it may be severe and resistant to most common methods of analgesia such as opioid analgesics. An epidural blood patch can help to seal the leak and provide relief. During a blood patch procedure, a physician removes a quantity of venous blood from the patient via normal venipuncture. This blood is then re-introduced into the epidural space of the patient via epidural needle, with the hope being that this blood then coagulates and plugs the leak of CSF. The rate of post-LP headache is higher in technically difficult LPs in which multiple passes are required or when larger bore needles are used.[7] The use of smaller gauge, pencil point, 'atraumatic' needles has as well been associated with a lower rate of post-LP headache (~5%).[6,8]
Shown are magnetic resonance myelography images of post-puncture CSF leakage in two patients (arrows). One patient remained asymptomatic despite the leakage, however, the second patient had a headache that persisted for six days.
Image courtesy of Sakurai K, Matsukawa N, Okita K, et al. Lumbar puncture-related cerebrospinal fluid leakage on magnetic resonance myelography: is it a clinically significant finding? BMC Anesthesiol. 2013; 13: 35.
A spinal or lumbar puncture tray (shown) should include the following items: sterile dressing, sterile gloves, sterile drape, antiseptic solution with skin swabs, lidocaine 1% without epinephrine, 3-mL syringe, 20 and 25 gauge spinal needles, 3-way stopcock, manometer, and 4 numbered plastic test tubes with caps. Optional: Syringe, 10 mL. Additional local anesthetic agents, such as 1%-2% lidocaine, may be used to increase patient comfort during the procedure (most commercial trays include only a small volume vial). A smaller (27 gauge, 1-1/4 inch) needle may be used for initial skin infiltration. Smaller needles are shown to be associated with less pain during local anesthesia.
Image courtesy of Medscape/Gil Z Shlamovitz, MD.
As discussed, the smaller the gauge of the needle used for the lumbar puncture, the lower the risk of the patient developing a post-lumbar puncture headache. However, fluid flow will be slower with smaller gauge needles. Obtaining opening pressures may be more difficult with these smaller needles.
Image courtesy of Wikipedia Commons.
Positioning for lumbar puncture is critically important and poor positioning can lead to a failed procedure. The target is the space between the 2nd and 3rd lumbar vertebrae or the space between the 3rd and 4th lumbar vertebrae. Palpate that interspace (L3-L4) as well as the one above (L2-L3) and the one below (L4-L5) to find the widest space. The pelvic crest can be palpated as this is approximately lateral to the L3-4 interlaminar space. Mark the entry site with a needle cap or a marker (shown). To help open the interlaminar spaces, the patient can be asked to practice pushing the entry site area out toward the practitioner.
Image courtesy of Medscape.
Two possible patient positions are utilized for lumbar puncture. In the lateral recumbent position (shown), place the patient with the hips, knees, and chin flexed toward the chest to open the interlaminar spaces. A pillow can be used to support the head. The thumb in this image is pushing on the area where the needle will be inserted in the interspace between the third and fourth lumbar vertebrae. Notice the other hand on the top of the pelvis bone identifying the iliac crest.
Image courtesy of Medscape/Gil Z Shlamovitz, MD.
Alternatively, the sitting position (shown) may be preferable in obese patients. To open the interlaminar spaces, the patient should be asked to lean forward. A support, such as a Mayo stand with a pillow on it, can be used to support the upper body. The patient should be urged to arch his/her back outwards (backwards, towards the operator, similar to the image of a 'scared cat'). If difficulty is encountered in one position, changing position during the procedure is possible, although the spinal needle should be removed.
Image courtesy of Medscape/Gil Z Shlamovitz, MD.
The use of bedside ultrasonography (shown) for the identification of the lumbar spinous process (arrows) for lumbar puncture is a helpful alternative to the previously discussed blind technique, especially in patients without good surface landmarks. A sagittal ultrasound view demonstrates the spinous processes (arrows) with the interspinous space located and visualized between them. Ultrasonography is safe and painless, without concern for ionizing radiation. If available, fluoroscopic-guided lumbar puncture may also be performed, however, fluoroscopy does expose the patient to small amounts of radiation and is generally performed in the radiology suite, requiring transportation and potential delay.[9]
Image courtesy of Medscape.
After the target interlaminar space has been identified and the patient has been positioned, the proceduralist should don sterile gloves and other personal protective equipment and prepare his/her tray to reduce the amount of manipulation of equipment required after the needle has been inserted. Open the numbered plastic tubes and place them upright (shown), assemble the stopcock on the manometer, and draw the lidocaine into the 10-mL syringe.
Image courtesy of Medscape/Gil Z Shlamovitz, MD.
Use bacteriocidal skin swabs and antiseptic solution to clean the skin, swabbing in a circular fashion, starting at the target site in the L2-3 or L3-4 interspace and moving outward to include at least 1 interspace above and below (shown). Warn the patient prior to the application of the antiseptic solution as it can be cold and cause discomfort.
Image courtesy of Medscape/Gil Z Shlamovitz, MD.
Place a sterile drape below the patient and a fenestrated drape on the patient (shown) making sure to allow for continued identification of anatomical landmarks. Most spinal trays contain fenestrated drapes with an adhesive tape that secures the drape in place.
Image courtesy of Medscape/Gil Z Shlamovitz, MD.
Use the 10-mL syringe to administer local anesthesia, usually in the form of subcutaneous lidocaine (shown). Raise a skin wheal to anesthetize the nerve-rich superficial dermal layers using the 25-gauge needle and then change to a longer needle (usually included in most kits) to anesthetize the deeper tissue. Insert the needle along the pathway you plan to advance the spinal needle. Aspirate prior to depressing the syringe plunger to confirm that the needle is not in a blood vessel, and then inject a small amount of lidocaine as the needle is withdrawn a few centimeters. Withdraw the needle nearly to the surface of the skin and then continue this process above, below, and to the sides very slightly (using the same puncture site so as to stick the patient only a single time). This process anesthetizes the entire area immediate to the planned site such that, if redirection of the spinal needle is necessary, laterally, inferiorly, or superiorly, adequate anesthesia should be present.
Image courtesy of Medscape/Gil Z Shlamovitz, MD.
Stabilize the needle (20 or 22 gauge) with the index fingers, and advance it through the skin wheal using the thumbs (shown). Orient the bevel parallel to the longitudinal dural fibers to increase the chances of the needle separating the fibers rather than cutting them (bevel facing up in the lateral recumbent position and facing to either side in the sitting position). Insert the needle at a slightly cephalad angle and insert toward the umbilicus. Advance the needle slowly but smoothly.
Image courtesy of Medscape/Gil Z Shlamovitz, MD.
The needle should be advanced. If bone is encountered, withdraw the needle and re-orient, keeping in mind the lumbar spine anatomy. Occasionally, the practitioner will feel a characteristic "pop" or "give" when the needle penetrates the dura. Otherwise, the stylet should be withdrawn after approximately 4-5 cm in average size adults and observed for fluid return (shown). If no fluid returns, replace the stylet, advance or withdraw the needle a few millimeters, and recheck for fluid return. Continue this process until fluid is successfully returned.
Image courtesy of Medscape/Gil Z Shlamovitz, MD.
To measure the opening pressure, the patient must be in the lateral recumbent position. After fluid returns from the needle, attach the manometer through the stopcock, and note the height of the fluid column. The patient's legs should be straightened when measuring the open pressure or a falsely elevated pressure will be obtained. Normal opening pressure is 5-20 cm water.
Image courtesy of Simon Fraser / RVI, Newcastle upon Tyne / Science Source.
Collect at least 10 drops of CSF in each of the 4 plastic tubes, starting with tube 1. The total volume of fluid to be collected should be projected ahead of time based on what laboratory tests are needed. If the volume of fluid obtained is limited, tests may need to be prioritized. The CSF that is in the manometer should be used (if possible) for tube 1. If the CSF flow is too slow, ask the patient to cough, hum, or bear down as in the Valsalva maneuver, or ask an assistant to intermittently press on the patient's abdomen to increase the flow. Alternatively, the needle can be rotated 90 degrees so that the bevel faces cephalad.[1]
Image courtesy of Simon Fraser / RVI, Newcastle upon Tyne / Science Source.
Replace the stylet and remove the needle (shown). Clean off the skin preparatory solution with a wet and then dry towel. Apply a sterile dressing, and place the patient in the supine position. Prophylactic bed rest following lumbar puncture to avoid post-LP headache or other complications has not been shown to be of benefit and should not be recommended.[10,11]
Image courtesy of Medscape/Gil Z Shlamovitz, MD.
CSF should be clear and colorless (shown). Assuming the CSF has been collected under sterile conditions, microbiologic studies can be performed. Stains, cultures, and immunoglobulin titers can be obtained. Classically, CSF tubes 1-4 are sent for the following studies: cell count and differential (tube 1), glucose and protein levels, gram stain, culture and sensitivity, cell count, and differential (repeated for tube 4).
Image courtesy of Wikimedia Commons/ James Heilman, MD.
A greater than normal number of white blood cells (WBC), including neutrophils (shown), suggests an infection. Classically, bacterial infections are associated with a predominance of polymorphonuclear leukocytes, but viral meningitis and encephalitis in the acute phase may have a similar appearance. A lymphocytic predominance of CSF white blood cells may suggest viral meningitis, or tubercular infection. Other causes of elevated WBCs are vasculitis, leukemic infiltration, and a traumatic tap. Approximately 1 WBC per 1000 RBCs may be seen in a traumatic tap.[12]
Image courtesy of Wikipedia Commons.
The CSF glucose level normally approximates 60% of the peripheral blood glucose level at the time of the tap. A simultaneous measurement of blood glucose (especially if the CSF glucose level is likely to be low) is recommended. A low CSF glucose level is usually associated with bacterial infection.[12] Red blood cells (RBCs) in the CSF are commonly the result of needle trauma.[1] Ordering a cell count from tubes 1 and 4 can allow comparisons of the RBC count after time and drainage of CSF. There should be a reduction in RBC quantity from tube 1 to tube 4, although the number of RBCs may not reach zero. This is contrasted with the findings of a SAH (shown) in which the RBC count remains stable from tube 1 to 4. No absolute number or ratio of RBC decline from the first to the last tube can be used to rule out an underlying SAH.[13]
Image courtesy of Medscape.
Blood from ruptured aneurysms rapidly disseminates throughout the subarachnoid space, with large numbers of RBCs present in the lumbar theca within 2-4 hours. The development of xanthochromia, the yellowish hue (arrow) resulting from hemoglobin catabolism into oxyhemoglobin, methemoglobin, and bilirubin, requires more time. The presence of xanthochromia indicates that the CSF contains blood that has undergone in vivo enzymatic degradation to bilirubin, implying true SAH. Xanthochromia can be measured visually (although the sensitivity is very low) or by spectrophotometry.[9]
Image courtesy of Medscape.
This gram stain shows meningococci from a culture showing gram negative bacteria in pairs (arrows). Assessment of CSF protein level, while nonspecific, can provide a clue to otherwise unsuspected neurologic disease. The high protein levels in demyelinating polyneuropathies (such as multiple sclerosis (MS), or postinfectious states, can be informative. A traumatic tap can also introduce protein into the CSF. An approximation of 1 mg of protein per 750 RBCs may be used, but a repeat tap is preferable.[1] The gram stain should be clear of any organisms.
Image courtesy of Centers for Disease Control and Prevention/Dr. Brodsky.
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