FRCA Notes

Epidural Abscess

Resources

  • The annual incidence of epidural abscesses is 1 in 50,000 - 63,000/yr
  • It can cause permanent neurological damange

Patient factors Procedural factors
Immunocompromise inc. diabetes Difficult insertion or bloody tap
Local or systemic infection Long duration of epidural in situ
Disrupted spinal column e.g. surgery, trauma Prolonged hospital stay
Long-term vascular access
IVDU

Reducing risk

  • Insertion in as sterile a fashion as possible
    • If using an ultrasound ensure it is properly cleaned and use a single-use sterile transducer cover
    • Guidelines recommend skin preparation with 0.5% chlorhexidine gluconate in 70% alcohol and allowing adequate time to dry
    • 2% chlorhexidine offers no greater antimicrobial benefit but increases risk of neurotoxicity
    • Turns out we're not all that good at adhering to a totally aseptic technique
  • Avoid using catheters in peripheral nerve blocks (as higher rate of infection than single shot block)
  • Remove epidural catheter ASAP, ideally after ≤72hrs
  • Regular catheter-site checks
  • Regular temperature monitoring
  • Neuro-observations for those with epidural in situ

  • S. aureus is the major culprit (57 - 90%)

  • Other bacteria:
    • Streptococci of various species (18%)
    • Enterococcus
    • Gram - negative bacilli (13%) e.g. E. coli, Proteus, Enterobacter, Salmonella, Klebsiella
    • Mycobacteria

  • Fungi e.g. Aspergillus
  • Parasites

Symptoms and signs

  • Clinical features usually begin several days following neuraxial intervention
  • The classic triad of features is only fully present in 13% of individuals:
  1. Pyrexia (66%)

  2. Back pain (75%)

  3. Progressive lower limb neurological abnormality
    • Tends to occur later, with sensory changes, flaccid then spastic paralysis
    • The neurological damage is polyfactorial in its pathophysiology:
      • Direct compression from expanding abscess
      • Vascular compromise from ischaemia/thrombosis
    • The degree of neurological deficit does not correlate to the radiological degree of cord compression
    • Once muscle weakness is present, only 20% regain full muscle function even after surgery
    • Thoracic abscesses tend to lead to more severe disability than lumbar
  • Other features include:
    • Meningism
    • Pain on palpation of the spine
    • Paravertebral sensory loss
    • Generally unwell

Investigations

  • The most important action when suspected is to organise a gadolinium-enhanced whole spine MRI to identify the abscess and help decide whether open or percutaneous drainage should be used

  • A raised WCC (approx. 2/3rds patients) and CRP may be present but normal values do not exclude spinal infection and they are non-specific even if raised
  • ESR is more consistently raised
  • Raised CSF protein and WCC

  • One is going to need the early input of Radiologists, Neurosurgeons, Neurologists and Microbiologists ± Obstetricians if occurring post-partum

Interventions

  • Stop epidural infusion if still running
  • Remove epidural catheter if still present, and send the tip for MC&S

  • Full septic screen with blood cultures etc.
  • Early surgical decompression e.g. posterior laminectomy and sending of samples for MC&S, AFB culture and tissue histology

  • Typically requires 4-6 weeks of intravenous antibiotics, followed by a prolonged course of oral antibiotics
  • Often multi-agent therapy is indicated
  • The response is monitored by serial assessment of inflammatory markers, back pain and neurology

  • NB steroids are contraindicated

  • Poor prognostic markers include:
    • Finding granulation tissue at time of surgery (as opposed to pus)
    • Increased age; risk of poor outcome doubles for every additional decade
    • Large degree of thecal compression
    • Duration of neurological symptoms >36hrs

  • Mortality is variably described; possibly as high as 15%

Infection from peripheral nerve blockade

  • Naturally, single-shot techniques have less risk of introducing infection than catheter-based techniques
  • Some sites are at higher risk e.g. femoral, axillary
  • Patients with immunocompromised states are at higher risk
  • Infective risks include:
Infective complication Frequency
Localised inflammation ≤14%
Infection ≤2%
Abscess formation <1%
Sepsis Rare

Meningitis

  • <1 in 200,000
  • Due to contaminated equipment, haematogenous bacterial seeding or droplet spread of nasopharyngeal commensals
  • Symptoms develop 24-48hrs post-blockade
  • Treaed with antibiotics as standard; good prognosis if early antibiotics

Arachnoiditis

  • Unintentional presence of chlorhexidine in the intrathecal space e.g. inadequate drying time, on operator's gloves, use of 2% chlorhexidine solutions
  • Causes lower back pain and non-dermatomally distributed dysaesthesia & paraesthesia