Lumbar Puncture

Potential Indications

1. Suspected Meningitis / Encephalitis
2. Suspected Subarachnoid Haemorrhage after 12 hours following symptom onset, before 2 weeks have passed (no longer sensitive)
3. Suspected Idiopathic Intracranial Hypertension
4. Other requirements for urgent diagnostic CSF sampling, eg Guillain Barré Syndrome (diagnosis supported if raised protein with no cells), probable Multiple Sclerosis (looking for oligoclonal bands)
5. Other requirements for urgent therapeutic CSF drainage, eg IIH with visual impairment

Contraindications

1. Absolute
   • Symptoms or signs of raised Intracranial pressure – mandatory neuroimaging (CT/MRI head scan) prior to lumbar puncture to exclude this
   • Altered GCS
   • Focal Neurological signs
   • Recent seizures (within 1 week)
   • Papilloedema
2. Relative: the Balance of risks and benefits are dependent upon the indication for the relative contraindications, there may be solutions to improve the risk to benefit ratio
   • Respiratory compromise where unable to lie horizontally (respiratory muscle weakness) – seek ICU support if necessary
   • Skin infection or suspected epidural abscess at site of LP – alternative sites / methods may be possible – seek senior / Anaesthetic or ICU support
   • Agitated or confused patient – seek senior / ICU support
   • Significant bleeding risk on haematological testing – INR more than or equal to 1.5, or PLT count <75 (<40 in experienced hands (Blood Transfusion / BSH guidance) – take advice from Haematologists if needed.
   • Significant bleeding risk from anticoagulants or antiplatelet agents – see page Lumbar Puncture, Antiplatelet and Anticoagulant Drugs to determine risk / options on reversal / delayed procedure

Considerations

1. Equipment and Practitioner
   • Access to resuscitation equipment including suction
   • Competent practitioner performing the procedure
   • Appropriate assistant available for entire procedure
   • Where supervision is or assistance if needed
2. Indication
   • Is the test needed
   • Is it needed at this time point (or delay appropriately with covering treatment dependent on the indication),
   • Are there any contraindications – it is worth checking bloods and drug administration kardex for timings yourself if you are the practitioner
3. Patient
   • The patient’s capacity to consent
   • They have been consented (or Power of Attorney where there is incapacity)
   • They have been informed of the intended benefits versus the risks and complications (see patient information leaflet but you must talk through these as part of the consent process)
   • They have been given advice on alternatives to the test (with risks of these and any delay in performing them versus the LP)
   • Laboratory liaison for urgent processing and how to contact them once samples taken

Complications for Consenting

1. Post-dural puncture headache – postural headache, nausea, vomiting – frequency 5-30% (common)
2. Backache at puncture site – mild – frequency 17-25% (common)
3. Infection (wound site) – frequency not well established
4. Infection (meningo-encephalitis) – pyrexia, photophobia, meningism, confusion, altered GCS – frequency <0.01-0.2%(rare-very rare)
5. Infection (discitis) – frequency very rare (case reports only)
6. Spinal / epidural haematoma (main risk factor is coagulopathy). Persistent severe back pain and tenderness with lower limb/perineal neurology – frequency unknown but rare with 4% of known spinal haematomas are due to Lumbar Puncture.
7. Cerebral herniation (reduced conscious level, coma, dilated pupil(s):
   • Occurs in 5% of bacterial meningitides who have an LP – accounts for 30% mortality
   • Care required in patients with risk factors for this – even a normal CT Head may not exclude this risk. Risk factors:
     • GCS <11
     • Brainstem signs
     • Recent seizure
     • Arnold-Chiari malformation

Anatomical Considerations

1. The ideal insertion point of the spinal needle should be either in the interspinous area between L4 and L5 or L3 and L4. Using these landmarks will avoid inadvertent damage to the spinal cord, which typically terminates at L1/2.
2. Palpation of landmarks along the back of the patient is used to locate the ideal insertion point for the needle. Certain conditions such as obesity, scoliosis, and degenerative disc disease may make palpation of landmarks more difficult.
3. A line should be drawn between the superior aspects of the iliac crests. This line is referred to as the intercristal line or Tuffier line. This line typically intersects the spine along the L4 spinous process.
4. Insertion of the spinal needle just above the intercristal line will usually take you to the L3/L4 interspace.  If you aim for just below the intercristal line you will likely enter the L4/L5 interspace
5. Once the interspinous space is palpated, use a skin marking pen to mark the area of needle insertion.
6. The lateral decubitus position is best – patient in foetal position flexing knees towards chest with back along edge of the bed.  Lateral decubitus position is important if you need to measure opening pressure as in IIH.  Remember if you are doing this to straighten the legs before recording the pressure.
7. Upright position may be preferred for patients in whom a lateral technique is not possible or feasible, for example patients with high BMI. The upright position should be with patients still in as foetal position as possible to allow the intervertebral spaces to open posteriorly. The upright position will prevent the ability to measure opening pressure.
8. More elderly / patients with vertebral arthritic conditions may prove challenging with smaller gauge needles. Anaesthetic / ICU team support for alternative approaches may be needed if the perpendicular method fails.
9. It is always difficult finding a space between vertebrae in patients who are significantly overweight.  Consider asking for anaesthetic help before attempting LP in patients with BMI >30 (typically patients with suspected idiopathic intracranial hypertension)
10. Consider reviewing an annotated model of the layers of the spine at: Annotated Lumbar Puncture & Layers of the Spine – 3D model by University of Dundee, CAHID (@anatomy_dundee) [fa7a84d] (sketchfab.com)

Equipment

1. Competent practitioner and assistant
2. Chair / stool for practitioner
3. Chair/stool for patient if upright (for legs to rest upon to maintain high knee/foetal position)
4. Inco-pads for bed sheet protection
5. Sharps bin
6. Surgical gown, sterile gloves, FFP2R surgical mask surgical hat
7. Procedure trolley
8. Sterile pack to include liquid container, cotton swabs
9. Sterile sheet / drape with adhesive tape to keep sheet position
10. Antiseptic solution (0.5% Chlorhexidine ‘Chlorprep’)
11. Lignocaine 1 or 2%. Likely 5ml ampoule needed only (NB toxic dose is over 3mg/kg)
12. 5ml syringe
13. Drawing up needle (red / filter needle)
14. 1 orange, 1 green needle for lignocaine infiltration of skin
15. NR fit (yellow packaging) Spinal needles x2 (orange 25g or purple 24g as first line – black 22g reserved if significant calcification)
16. NR fit (yellow packaging) Manometer if in lateral position
17. 3-4 Universal containers (3 for meningoencephalitis, 4 for SAH, 4 for antibody/oligoclonal bands)
18. Equipment to take paired serum glucose (yellow tube)

Technique

1. Prepare patient in optimal position, identify appropriate level, prepare equipment
2. Clean skin with Chlorprep sponge, allow skin to dry before moving to next step
3. Use sterile drape on bed and patient (preferably with procedure ‘hole’ in middle)
4. Apply local anaesthetic to skin and superficial skin structures
5. In right position, insert introducer in midline and aim towards umbilicus, insert introducer ‘under/caudal to the spinous process above’ at 90º to skin only to the resistance of first ligament
6. Insert spinal needle gently keeping perpendicular position
7. If no resistance changes felt on progress of spinal needle, check for CSF by withdrawing the stylet frequently after each small advance of needle, replace before advancing further
8. If the needle hits bone, withdraw, ensure the position is in the midline and redirect
9. May ‘pop’ or lose resistance when needle penetrates ligamentum flavum
10. When fluid returns attach the manometer and stopcock
11. Take the opening pressure first – allowing the meniscus in the manometer to stabilise, then take samples afterwards
12. Assistant to help position universal container under the needle and take 20 drops for each sample container (approx 1ml). Label the sample containers 1, 2, 3, 4 in the order samples were taken.
13. Xanthochromia for SAH measurement should be collected from the last sample (container 4) and immediately protected from light in a dark/brown envelope or similar to prevent degradation
14. Once samples taken, re-insert stylet into spinal needle and then remove all needles from patient’s lumbar area
15. Cover with adhesive dressing.
16. Document your procedure as though someone reading it could replicate the procedure the way you did it. Document all important initial results eg colour of CSF, opening pressure, any procedural difficulties / complications.
17. There is no standard advice for post-lumbar puncture management in terms of needing to remain supine/horizontal for a set period. Some clinicians may advise an hour of rest before mobilising. Ensure patients have a source of fluid to drink following the procedure.

Sample Management

1. Samples 1 and 3 should be sent to Microbiology for cell count, C&S (sample 1) and  PCR (sample 3)
2. Samples 2 and if required sample 4 should be sent to Biochemistry for Protein, glucose (sample 2) and Xanthochromia (sample 4).

• • NB xanthochromia if negative will be reported by the biomedical scientist out of  hours as negative, if the sample may be positive, this will need validated in hours by another member of their clinical team
  • NB 1ml required for Xanthochromia (20 drops)

1. Samples should be walked to the laboratory (not podded/pneumatic tube) with both laboratory technicians (Micro and Biochemistry) pre-alerted to the sample being delivered.
2. Other sample volumes required:
   • TB – minimum 7ml
   • Pathology – 5ml if malignancy considered
   • Oligoclonal bands – remember to send serum protein as well as glucose

Normal Values for Reference

1. Opening pressure 10-25 cm CSF (95% reference interval)
   • NB can be increased in anxiety, SAH, infection, SOL, IIH, CCF, Cerebral venous thrombosis
2. No Red Cells (in setting of traumatic tap, repeat cell count of sample 3 and comparison to sample 1 – if reducing count, probably traumatic tap, if same RCC, likely bleed in CSF.
3. Lymphocytes <6
4. Neutrophils 0 (one WCC permitted for every 500 RCC in a bloody tap)
5. Protein <0.4g/l)
6. Glucose 2.5-4.0 (2/3 of serum glucose)

Links

1. Medical MED Mastery Skills Pathway, University of Edinburgh [pdf]

Content by Dr Alex McDonald