lumbar puncture (LP)

see also:

• meningitis
• subarachnoid haemorrhage (SAH)
• interpretation of CSF findings
• post LP headaches (PLPH)
• Seupaul, R Perform an LP and analyze the results to dx bacterial meningitis. Emergency Physicians Monthly August 2008.
• RCH guideline - lumbar puncture (LP)
• Emedicine.com - lumbar puncture
• Youtube demo LP tutorial

• most patients with suspected meningitis require the diagnosis to be confirmed by LP as confirmation will not only aid diagnosis but assist in determining duration and type of ongoing antibiotic Rx.
• patients with atypical presentations of meningitis in whom tuberculosis (TB) is possible, should be considered for 10ml CSF sent for TB cultures in addition to usual CSF studies.
• in the patient with suspected meningitis, unless the risk of an intracranial mass lesion (eg. abscess, subdural empyema) is very low (eg. previously well young adult or child with illness < 24hrs), a CT brain is usually recommended prior to performing a LP.

• shock
• widespread rash
• evidence of coagulopathy - see minimum coagulation parameters for safe invasive procedures in the ED
• drowsiness / impaired consciousness
• signs of raised ICP (bradycardia, hypertension, papilloedema, periodic breathing)
• focal neurology
• mass lesion on CT scan
• possible hydrocephalus on CT scan
• if LP is contraindicated due to possible raised intracranial pressure, neurosurgical consultation may be indicated to consider a diagnostic ventricular tap.

• most are adapted from Ben Butson and Paul Kwa. EMA (2014) 26,500-501.
• spinal needle choice
  • atraumatic needles reduce post-puncture headache incidence by creating a smaller dural hole and thus reduced CSF leak
  • if one must use a standard spinal needle (eg. Quincke), use a smaller gauge such as 22G instead of 20G and ensure it is oriented to reduce the size of hole by ensuring the bevel faces laterally and thus separate the vertically running dural fibers rather than cutting them
  • ensure the stylet is fully inserted within the needle whenever the needle is being inserted or withdrawn.
    • the stylet minimises risk of the lumen of the needle becoming clogged with debris, and the risk of epithelial tissue being introduced into the spinal canal which may result in an epidermoid tumour
• patient should be asked to arch back like an angry cat and remain still during procedure
• avoid neck flexion as only increases discomfort
• monitor SaO2 in young children as hyperflexed position may impede ventilation
• sitting position
  • maximises the interspinous distance and may make identifying the midline easier in obese patients, however, no evidence of improved success or reduced traumatic taps
  • cannot be used if one wishes to measure CSF pressure
• lateral decubitus position:
  • place pillow under patient's head and between the knees to prevent lateral flexion of the spine
  • both hips and shoulders should be vertically aligned and the back flush with the bed
  • if operator is right handed, place patient in left lateral position as gives more natural aim at umbilicus
• performing the lumbar puncture
  • have line of vision level with the insertion site which should be at L3-L4 or L4-L5 level noting that the L4 spinous process is at the level of the top of the iliac crests
  • using a standard 25G needle inject lignocaine LA under the skin at the selected entry site and then pass the needle in a cephalad direction to inject a further 1-2mL of LA
  • switch to a 22-25G longer needle to infiltrate a further 3-5mL of LA deeper into the interspinous gap ensuring you aspirate first to ensure you are not about to give an intravascular injection
  • pierce the skin with a 18-20G beveled needle to allow easier passage through the skin of the atraumatic spinal needle
  • insert the spinal needle in a cephalad direction aiming towards the umbilicus or epigastrium (if flexion of the spine is limited) to avoid hitting the superior aspect of the spinous process below the spinous gap which would occur if you passed the needle perpendicular to the skin
  • if hit bone, ask patient if it feels like left, right or middle
  • every 5mm of advancement, stop and withdraw stylet to see if CSF drains, if not, replace stylet fully and advance further
• US may be helpful, but will only locate relevant landmarks in 75% of obese patients
• fluoroscopic guided LP reduces traumatic tap rate from 18% to 12%
• measure CSF opening pressure:
  • normal adult: 10-25cm CSF
  • normal child: 10-28cm CSF (don't bother in very young children or if crying)
  • ensure patient is relaxed and legs straightened slightly to avoid abdominal compression
  • measure CSF meniscus when it stops rising and begins to swing with respiration or arterial pulsations
  • use the fluid in the tube to fill the first tube
• tubes:
  • 10-20 drops per tube = 15-20ml total CSF removed which will be regenerated in ~1hr
  • replace stylet into needle before withdrawing it to avoid withdrawing a spinal nerve rootlet through the needle tract