Lumbar Puncture

• In suspected meningitis:
  • Lumbar puncture (LP) can confirm or exclude meningitis.
  • In 8% cases CSF appears normal on microscopy but is later found to be positive for meningococcus.¹
  • Initial Gram staining shows organism in 68-80% of cases of meningitis.
  • Also allows identification of uncommon pathogens and viruses by polymerase chain reaction (PCR).
• Suspected intracranial bleeding:
  • Establishes diagnosis but CT is more valuable.
• To check for subarachnoid haemorrhage (SAH):
  • Performed after normal CT scan (a significant minority of SAHs cannot be detected on CT).
• Also used to establish diagnosis following status epilepticus:
  • In confusional states, meningeal malignancies, demyelinating disorders, CNS vasculitis, multiple sclerosis.
• Occasionally used to treat idiopathic intracranial hypertension:
  • By draining CSF.

• Skin infection overlying puncture area.
• Any suspicion of cerebral herniation with raised intracranial pressure:
  • Glasgow Coma Scale (GCS <8)
  • Abnormal pupil size and reaction
  • Absent doll's eye movements
  • Abnormal tone
  • Tonic posturing
  • Abnormal respiration (hyperventilation, Cheyne-Stokes breathing, apnoea, respiratory arrest - in this instance, a CT scan should be performed to look for evidence of cerebral herniation before proceeding to LP.)
• Thrombocytopenia:
  • Only perform LP if urgently needed when platelets <50 x 10⁹/l (give platelet transfusion if <20 x 10⁹/l or rapidly dropping).

Before

• Explain to patient what you want to do, and why you need to do it. Obtain explicit consent and use appropriate consent form. Tell them that co-operation is important and that they can talk to you at any time.
• Explain that you will numb the area with local anaesthetic, which will involve a sharp scratch and then some stinging which will quickly settle. With children over 6 months, if there is time, a topical local anaesthetic cream can be used before infiltration.
• Advise that, subsequently, there should be no pain. However, they may feel sensations down a lower limb and there could be a pulling/pressure sensation and mild discomfort.
• Discuss possible complications (see below under Complications of lumbar puncture), give patient an opportunity to ask questions and remember to document this in the clinical record when you make your notes.

Procedure

Preparing your equipment and patient properly will save time in the long run and ensure full co-operation.
Place patient on left side with back exactly vertical, aligned with edge of bed, with spine fully flexed - knees up to chin. If you are left-hand dominant, the right lateral position may be easier.

• Mark intervertebral space L4/5 or L3/4 (at same height as iliac crest) with gentle skin indentation using thumbnail or object like a pen top.
• Wash hands thoroughly and put on mask and sterile gloves. From this point on you must observe strict aseptic technique. Place sterile towels from pack beneath patient and over their side, to isolate your sterile field.
• Open your sterile LP pack and make sure your needle, sample bottles (preferably labelled '1, 2, 3' in the order you will use to collect samples) and manometer are set up and immediately to hand.
• Spinal needles are available in varying sizes for different ages from 30 mm-90 mm usually. Extra long needles are occasionally required for very large adults.
• Sterilise area with iodine-based antiseptic unless allergic. If you are using a fenestrated sterile adhesive drape, the sterile field can be isolated at this point.
• Anaesthetise skin with 1% lidocaine. Use a small gauge needle to minimise pain. Let a minute pass, then infiltrate lidocaine into the interspinous area; in bigger patients use a longer, larger gauge needle if required. ALWAYS aspirate before injecting lidocaine to avoid intravascular injection.
• After 1 minute, insert 22G spinal needle with stylet in place, horizontally through mark, aiming towards umbilicus with needle bevel facing upwards.
• Make sure that you are in the midline between the iliac crests and in the interspinous space. Feel resistance from spinal ligaments and then dura, and feel 'give' as needle enters subarachnoid space.
• Withdraw stylet and wait for CSF to appear at needle cuff.
• Measure CSF pressure with manometer. Connect tubing from manometer to needle cuff and hold gauge upright. When meniscus settles, gently tap tube, if no movement then read pressure in cm H₂O from scale. Pressure is normally 5-20 cm H₂O. May be up to 25 cm H₂O in very obese patients.²
• Collect fluid in 5 numbered bottles (<5-10 ml in total). Usually 5-10 drops for each sample is sufficient. 3 bottles go to microbiology, 1 to virology, 1 to biochemistry.
• Reinsert stylet to halt CSF flow. There is evidence that leaving the stylet in situ when removing the needle may reduce the incidence of headache due to dural disruption.^3,4
• Clean, then dress, site.

Refer to separate Cerebrospinal Fluid record for detail on interpretation of findings.

• Prescribe simple analgesia as required in case of headache.
• There is no evidence that prolonged bed rest after LP has any effect on reducing the incidence of headache.⁵
• Document the procedure, taking care to note that you explained possible complications to the patient, used aseptic technique and what gauge/type of needle was used. It is also useful to document how easy or difficult the procedure was (particularly if repeat LP needed), and whether it was a bloody tap, as this can effect the results.

• Headache is commonest, lasting 2-8 days in around 25% of patients.⁶ It is caused by low CSF pressure due to fluid leakage through hole (so-called 'dural tap'). Typically presents in upright position and quickly relieved by lying down. The headache is aggravated by coughing or straining and can be associated with nausea, vomiting or tinnitus. Neck and low backache are also common.
  • The diagnosis can be confirmed by slowly squeezing the waist of the patient from behind when sitting, which quickly relieves the headache by compressing the inferior vena cava. This causes the epidural veins to become engorged and displaces CSF into the head.
  • Treat with bed rest & pain relief and oral fluids. Caffeine is anecdotally reported to be helpful. Can use IV fluids (no convincing evidence to support their use but may help when headache is causing nausea).
  • If still persists, use extradural blood patch. This is where 10-20 ml of patient's blood is injected into the extradural space.
  • Incidence of headache can be reduced to 5% by using 22G blunt-tipped (atraumatic) needles that separate dural fibres instead of cutting them.^7,8 However, they are more expensive.
• LP can worsen brain herniation (see above), spinal cord compression, subarachnoid bleeding, diplopia, backache and radicular symptoms.

1. Ragunathan L, Ramsay M, Borrow R, et al; Clinical features, laboratory findings and management of meningococcal meningitis in England and Wales: report of a 1997 survey. Meningococcal meningitis: 1997 survey report. J Infect. 2000 Jan;40(1):74-9. [abstract]
2. Seehusen DA, Reeves MM, Fomin DA; Cerebrospinal fluid analysis. Am Fam Physician. 2003 Sep 15;68(6):1103-8. [abstract]
3. Deibel M, Jones J, Brown M; Best evidence topic report: reinsertion of the stylet before needle removal in diagnostic lumbar puncture. Emerg Med J. 2005 Jan;22(1):46. [abstract]
4. Yentis S; Lumbar puncture and headache. Replacing the stylet before withdrawing the needle may help to prevent headache. BMJ. 1998 Mar 28;316(7136):1018.
5. Thoennissen J, Herkner H, Lang W, et al; Does bed rest after cervical or lumbar puncture prevent headache? A systematic review and meta-analysis. CMAJ. 2001 Nov 13;165(10):1311-6. [abstract]
6. Evans RW; Complications of lumbar puncture. Neurol Clin. 1998 Feb;16(1):83-105. [abstract]
7. Kleyweg RP, Hertzberger LI, Carbaat PA; Significant reduction in post-lumbar puncture headache using an atraumatic needle. A double-blind, controlled clinical trial. Cephalalgia. 1998 Nov;18(9):635-7; discussion 591. [abstract]
8. Cooper N; Evidence-based lumbar puncture: best practice to prevent headache. Hosp Med. 2002 Oct;63(10):598-9. [abstract]

• Sucholeiki R, Waldman AL; Lumbar Puncture (CSF Examination). eMedicine, 2009.