aka Neurological Mind-boggler 006
Remember the patient from Microbial Mystery 005? If not, make sure you read that post before this one!
A 20 year-old girl with a pre-existing spinal cord injury (C5 ASIA A) from an MVA at the age of 2, returns to ICU post-op following drainage of a large epidural abscess. She had presented with systemic sepsis 4 days previously and an MRI had demonstrated the epidural abscess. She has a long and complex medical history, including a sub-rectus sheath intrathecal baclofen pump inserted 2 years ago, several spinal fixation operations for spinal stability (the last 5 years ago), and chronic excoriation of both flanks from scratching.
The operation had gone smoothly, with the surgeons satisfied they had drained the collection. The anaesthetic had also been unremarkable and the patient had been awake and lucid in recovery.
After she had been in ICU for 15 minutes, you are called to see her, as her level of consciousness has suddenly decreased and her right pupil is much larger than the left….
Q1. What’s the differential for the decreased level of consciousness?
There are many ways to break this down into a logical sieve. This is a modified version of the apporach described by Bala Venkatesh in Oh’s Intensive Care Manual:
Differential Diagnosis of Coma
|Category||Specific Disorder||Clinical features||Key investigation|
||Risk factors for CVA||CT|
|Trauma||Look signs of base-of-skull fracture||CT|
|Space occupying lesion:
||Look for ENT and dental sources of infection
Past history of cancer
|Sub-arachnoid haemorrhage||‘Worst headache ever’
SAH risk factors
|No focal signs or meningism(MESOT)||Metabolic causes:
|Seizures (including eclampsia)||?witnessed
CT for SOL
History/exam findings of liver disease
? paracetamol OD
||Toxicology risk assessment||ABG analysis
Specific drug levels
|Pseudocoma||history of mental illness
history of sleep disorder
|Diagnosis of exclusion|
This, of course, is a very generic approach. Immediately post op, you can also think of causes as being:
- Related to the anaesthetic
- Related to the surgery
- Related to post-operative events
Q2. And differential for the asymmetrical pupils?
As discussed in Ophthalmological Befuddler 001 there are two possible causes of anisocoria (unequal pupillary size)
- one pupil is abnormally small or constricted (miotic)
- one pupil is abnormally large or dilated (mydriatic)
Again, an approach modified from that of Bala Venkatesh in Oh’s Intensive Care Manual is shown::
Local pathology/ trauma
Damage to sympathetics
Drug ingestion, eg.
|CN3 stretched on petroclinoid ligament
CN3 nucleus damage
|Bilateral fixed pupils||Bilat uncal herniation
Massive midbrain bleed
Bilateral CN3 damage
Q3. What investigations would you do now?
In addition to a close review of what happened in the operating theatre and recovery, the following investigations may help:
- ABG including glucose and lactate
- Blood tests (see Q2 above)
- CT brain +/- MRI brain +/- spine
All of the investigations listed in Q2 were done — they were all unremarkable!
Q7. So what’s the explanation?
The currently held belief is that as the epidural abscess was drained, canal compression was released and CSF flow was altered. A bolus of intrathecal baclofen (from the pump, which had always been running) then reached the brain in high concentration, and caused coma.
The anisocoria was also attributed to the baclofen overdose, although this usually causes bilateral pupillary dilation. It is difficult to explain why only one pupil was affected — perhaps there was a degree of post-operative Horner’s syndrome affecting the side of the ‘small’ pupil?
With supportive treatment complete neurological recovery occurred over the next 48 hours.
Read Wall et al (2006) for an open access case report of a baclofen overdose in a different context, with a literature review.
Over the next week, fevers and raised inflammatory markers persisted.
Q8. What could explain this and what would you do?
Is antimicrobial chemotherapy inadequate?
- check that current antibiotic dosing is adequate for the MIC of cultured organism
- re-culture everything, empirically broaden cover and narrow when you get a new organism
Is there an ongoing source of sepsis?
- Was all the abscess drained? Re-drain & washout.
- Is the metal work infected? Remove it if suspected and its possible.
- Is the baclofen pump infected? Remove it!
- Look for ventilator associated pneumonia (VAP): CXR, blind tracheal aspirate & non-quantitative culture — see Canadian Clinical Trials Group (2006).
- Look for endocarditis (TTE +/- TOE depending on the TTE result)
- Look for collections elsewhere
Antibiotic cover was increased to vancomycin & meropenem. An echocardiogram showed no vegetations. A further MRI showed evidence of remaining collection. In OT, the internal fixation was removed, the intrathecal baclofen pump was removed and the abscess drained. The only organism isolated was the MSSA and long term (at least 6 weeks) IV benzyl penicillin was all that was needed. The MSSA presumably came from her scratched skin and seeded to her metal rods/epidural space.
Of course, other complications occurred but I won’t bore you with them!
- Bersten AD, Soni N. Oh’s Intensive Care Manual (6th edition). Butterworth-Heinemann, 2008.
- Canadian Critical Care Trials Group. A randomized trial of diagnostic techniques for ventilator-associated pneumonia. N Engl J Med. 2006 Dec 21;355(25):2619-30. PMID: 17182987.
- Jeff Mann’s EM Guidemaps. Coma and Anisocoria.
- Poser JB, et al. Plum and Posner’s Diagnosis of Stupor and Coma (4th edition), Oxford university Press, 2007.
- Wall GC, Wasiak A, Hicklin GA. An initially unsuspected case of baclofen overdose. Am J Crit Care. 2006 Nov;15(6):611-3. PMID: 17053268. [free fulltext]