7.2 Epidural Abscess

Question 1

You are asked to see a 67-year-old patient 8 hours after having a
cystectomy under general anaesthetic and an epidural block. The nurses in
the ward are concerned that she is unable to move her legs since admission
postoperatively.

What are the causes of non-receding motor block after epidural anaesthesia?

Answer 1

Factors related to neuraxial block
* Use of large volume of high concentration local anaesthetic
* Inadvertent subarachnoid placement
* Migration of the catheter into the subdural/subarachnoid space
* Direct nerve trauma
* Epidural haematoma
* Epidural abscess

Factors unrelated to neuraxial block
* Pregnancy, surgical, etc.
* Disc herniation
* Tumours
* Transverse myelitis
* Vascular and neurological disease
* Meningitis

Question 2

How can you prevent epidural abscess?

Answer 2

• Basic precautions—
  Surgical scrubbing and donning of gloves and mask.
  Operating department practitioner also wears a mask.
• Skin disinfectant—
  chlorhexidine (0.5%) in ethanol (70%) being
  fully bactericidal in 15 seconds.
• Catheter dressing—
  opsite spray, semipermeable clear dressing.
• Infusion systems—
  large volume reservoirs better than repeated
  changing of syringes; avoiding disconnection.
• Epidural filters.
• Identifying high-risk patients.

Question 3

What is the incidence of epidural abscess?

Answer 3

• Rare complication;
  different incidence in different studies
• 0.2–1.2/10 000 hospital admissions/year
  (not necessarily intervention related)
• 1:100 000–1:500 000 in one study
• 1:45 000 of all neuraxial blocks according to NAP 3

Question 4

What are the risk factors for the development of epidural abscess?

Answer 4

• Compromised immunity—
  diabetes, HIV, intake of alcohol,
  steroids, and immunosuppressants
• Disruption of spinal column—
  trauma, intervention, and surgery
• Source of infection—
  respiratory, urinary, etc.,
  prolonged duration of catheterisation

Question 5

What are the signs and symptoms?

Answer 5

• Back pain 90%
• Feeling unwell and fever
• Neurological deficits
• Signs of meningism
• Localised pain and temperature

Question 6

What are the most common causative organisms?

Answer 6

• Gram +ve cocci—
  Staphylococcus aureus and epidermidis,
  Streptococcus pneumonia
• Gram –ve rods—pyogenes
• Aspergillus and mycobacterium

Question 7

How would you manage it?

Answer 7

Diagnosis by clinical suspicion

• Blood tests and cultures—
  inflammatory markers and antibiotic sensitivity
• MRI—90% sensitivity

Management
* ABC approach

• Early surgical decompression
• Prolonged antibiotics (6–12 weeks)
• Conservative management only in cases without neurological complications

Question 8

Describe the epidural filter.

Answer 8

• It is disc-shaped with hydrophilic supported membrane.
• Filter pore size is usually 0.22 microns.
• It filters viruses, bacteria, and foreign bodies.

Question 9

What others filters do you know that you use every day at work?

Answer 9

Heat and Moisture exchanger/Filter (HMeF)
* Hygroscopic membrane pleated to decrease the dead space

• Mode of action—mechanical filters or electrostatic filters
• 0.2 microns pore size
  [relative size of organisms—
  HIV (0.14 μm), HCV (0.06 μm), and M. tuberculosis (0.4 μm)]
• 60%–70% relative humidity and adds up to 100 mls dead space
• Can increase positive end expiratory pressure

Filter needles
* Prevents particulate and organism contamination
* Size: 0.2 microns

Fluid filter
* 15 microns to prevent particulate contamination

Blood filter
* I generation: 170–250 microns; for whole blood

• II generation: 20–50 microns; 70%–80% of leucocytes depleted
• III generation: electrostatic filters (100% leucodepletion)

Filters used in renal haemofiltration