Principles of Neuraxial Anaesthesia

This section discusses factors common to spinal and epidural anaesthesia.

Indications

  • Analgesia
  • Anaesthesia

Contraindications

Absolute contraindications:

  • Patient refusal
  • Anaphylaxis to local anaesthetics
    True allergy is rare.
  • Anticoagulants
    Covered in detail in principles of neuraxial anaesthesia.
  • Localised infection at insertion site
  • Sepsis
    • Risk of infected blood/haematoma in the epidural or subarachnoid space
    • Exaggerated hypotension due to pre-existing vasodilation
    • Coagulopathy

Relative contraindications:

  • Immunocompromise
  • Coagulopathy
    • Epidural should be withheld in patients with pre-existing coagulopathy where intraoperative heparin administration is planned.
  • Raised ICP
  • Leukocytosis
    WCC >20×109/L.
  • Infection
    • Chorioamnionitis
    • Usually safe to insert if temperature is < 38°C and patient is on antibiotics.
  • CVS disease:
    • AS
      Afterload reduction results in ↓ LV perfusion pressure.
    • Pulmonary hypertension
      Afterload reduction results in ↓ RV perfusion pressure.
    • Hypotension/hypovolaemia/shock states
      Exacerbated by drop in SVR.
  • Anxiety/behavioural concern
  • Lack of expertise in the technique and management of potential complications

Coagulopathy

In general:

  • Coagulation studies should be performed prior to insertion if there is any concern
    Any abnormality of coagulation is always a relative contraindication.
  • Risk of haematoma exists on a continuum - a platelet count of 79 is not substantially more risky than a platelet count of 81
    Decision needs to be based upon a risk-benefit analysis for this particular patient.
  • Risk varies depending on technique
    Paravertebral is less risky than a spinal, which is less risky than a single-shot epidural, which is less risky than an epidural catheter.
  • Absolute thresholds will vary depending on the centre; one particular set of numbers is:
    • Normal APTT
    • INR <1.5
    • Platelets >80×109/L
      Institutional policy may vary.
      • Above 100 is ideal
      • <70 can be considered an absolute contraindication
      • Beware patients whose platelet counts are falling
  • Strong history of bleeding
    Even in presence of normal coagulation studies.

Anticoagulants

Drug Time between last dose and epidural insertion/adjustment/removal Time before next dose
Heparin
5,000 Units S/C		 6 hours. 2 hours.
Heparin Infusion 6 hours since cessation, and a normal APTT 2 hours
Enoxaparin (prophylactic) 12 hours, 24 hours post-operative 4 hours
Enoxaparin (therapeutic) 24 hours 4 hours
Warfarin INR < 1.5 prior to insertion. Warfarin cannot be used with an epidural in situ - use UFH. INR < 1.5 prior to removal. 6 hours
Aspirin 2-3 days prior to cervical/thoracic epidural placement. -
NSAIDs - -
Clopidogrel 7 days for insertion, can consider 5 days if high cardiac risk. 12-24 hours following catheter removal (24 hours if loading dose to be given).
Ticagrelor 5 days 24 hours
Prasugrel 7-10 days 24 hours
Dabigatran Ideally 4 days 24 hours
Rivaroxaban/Apixaban At least 2 days, ideally 3 days 24 hours
Tirofiban 8-24 hours 8-12 hours
Thrombin inhibitors including bivalirudin, lepirudin Avoid. Seek expert advice. Seek expert advice.
Thrombolytics 10 days. Measure fibrinogen level prior to removal. Seek expert advice.
Herbal including garglic, gingseng, and gingo bilboa - -

Anatomy

Layers of the back include:

  • Skin
  • Subcutaneous tissue
  • Longitudinal ligament
  • Interspinous ligament
  • Ligamentum flavum
  • Epidural space
    The epidural space:
    • Bounded:
      • Anteriorly by the posterior longitudinal ligament
        Remember the epidural space forms a ring around the dural sac.
      • Superiorly by the skull
        At the foramen magnum.
      • Inferiorly by the sacrococcygeal ligament
      • Posteriorly by the ligamentum flavum
    • Contains fat, valveless veins, nerve roots, as well as the posterior and anterior spinal arteries and the artery of Adamkiewicz
    • Has different properties in different areas of the spine:
      • Lumbar
        • At an average of 5cm (3-8 in 90%)
        • Usually catheterised between L2 and L5 interspaces
      • Thoracic
        • Narrow, avoid midline approach between T5 and T8
      • Cervical
        • Thin and soft ligamentum flavum leads to poor appreciation of LoR
        • Space is ~ 1.5-2mm deep at C7, ↑ to 3-4mm with neck flexion
  • Dura and arachnoid
  • Subarachnoid space

Complications

Divided into:

  • Physiological
    Arising due to effect of the drugs:
    • Hypotension
    • LAST
    • Narcosis
  • Procedural
    • Permanent nerve injury
    • Bleeding
      • Epidural haematoma
    • Infection
      • Epidural abscess
    • Drug error
      • Antiseptic injection
    • PDPH
  • Failure/Incomplete analgesia

References

  1. Narouze S, Benzon HT, Provenzano D, Buvanendran A, De Andres J, Deer T, Rauck R, Huntoon MA. Interventional Spine and Pain Procedures in Patients on Antiplatelet and Anticoagulant Medications (Second Edition): Guidelines From the American Society of Regional Anesthesia and Pain Medicine, the European Society of Regional Anaesthesia and Pain Therapy, the American Academy of Pain Medicine, the International Neuromodulation Society, the North American Neuromodulation Society, and the World Institute of Pain. Reg Anesth Pain Med. 2018 Apr;43(3):225-262.
  2. ANZCA. PS03: Guidelines for the Management of Major Regional Analgesia.