Coma in a spinal patient

aka Neurological Mind-boggler 006

Remember the patient from Microbial Mystery 005? If not, make sure you read that post before this one!

Let’s recap:

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….

Questions

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
Focal signs CVA:

  • Ischemic
  • Haemorrhagic
Risk factors for CVA CT
Trauma Look signs of base-of-skull fracture CT
Space occupying lesion:

  • Infective
  • non-infective
Look for ENT and dental sources of infection
Past history of cancer
Immunosuppression
CT
Meningism Meningitis or
menigoencephalitis
Fever
Meningococcal rash
LP
CT
Sub-arachnoid haemorrhage ‘Worst headache ever’
Subhyaloid hemorrhages
SAH risk factors
LP
CT
No focal signs or meningism(MESOT) Metabolic causes:

  • Hypoxia
  • Hypercapnoea
  • Hyponatraemia
  • Hyperglycaemia
  • Hypoglycaemia
  • Hypo/hyperthermia
  • Hypo/hyperosmolarity
History essential SO2
ABG
ETCO2
UEC
BSL
Temperature
ketones
Endocrine:

  • Adrenal insufficiency
  • Hypopituitarism
  • Hypothyroidism
  • Diabetic coma
Time course
Steroid medications
Phenotype
TFT
free T3/4
Temperature
BSL
UEC
Ca, PTH
Cortisol
Seizures (including eclampsia) ?witnessed
?post-ictal
?non-convulsive epilepsy
EEG
CT for SOL
Organ Failure

  • Renal: uraemia
  • Liver: PSE
Urine output
History/exam findings of liver disease
? paracetamol OD
EUC
LFTs, NH3
INR
Toxins/drugs, especially:

  • Sedatives
  • Narcotics
  • Alcohol
  • Psychotropics
  • Carbon monoxide
  • Many other poisons!
Toxicology risk assessment ABG analysis
Specific drug levels
Osmolality
ECG
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)
    OR
  • 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::

Pupillary abnormality Cause Pathology
Miosis (<2mm)
Unilateral Horner’s Syndrome
Local pathology/ trauma
Sympathetic paralysis
Damage to sympathetics
Bilateral Pontine lesion
Thalamic haemorrhage
Metabolic encephalopathy
Senile miosis
Argyll-Robertson pupils
Holmes-Adie pupils
Drug ingestion, eg.

  • Organophosphate
  • Barbiturate
  • Narcotics
Sympathetic paralysisMechanisms:

  • Cholinesterase inhibition
  • Central effects
Mydriasis (>5mm)
Unilateral Uncal herniation
Midbrain lesion
CN3 stretched on petroclinoid ligament
CN3 nucleus damage
Bilateral fixed pupils Bilat uncal herniation
Massive midbrain bleed
Hypoxic injuryDrugs:

  • Atropine
  • Tricyclics
  • Sympathomimetics
Brain herniation
Bilateral CN3 damage
Mesencephalic damageMechanisms:

  • Parasympathetic paralysis
  • TCA’s pevent reuptake of catecholamines by nerve endings
  • Sympathetic stimulation

For further review read Neurological Mind-boggler 002 on the causes of coma with small pupils, and Ophthalmological Befuddler 001 for the causes of a dilated pupil.

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
  • EEG

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!

References

  • 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]
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