Question 2

Outline the approach to neurological prognostication of a patient post out-of-hospital cardiac arrest (OOHCA). Your answer should include the following headings:
a) General principles.    (2 marks)
b) Clinical factors.    (2.5 marks)
c)  Imaging.    (2.5 marks)
d) Neurophysiological studies.    (2 marks)
e) Biomarkers.    (1 mark)

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Syllabus topic/section:

2.1.4    Cardiovascular Intensive Care – L1.

Aim:

To demonstrate knowledge of neuro-prognostication post OOHCA.

Discussion:

A detailed understanding of neuro prognostication is a core competency for Intensivists. Given its frequency in the examination process a high standard of detail was required. Good candidates outlined appropriate timing of multimodal assessment with reference to common confounding factors and clinical evaluation (specifically motor score, pupillary light and corneal reflexes, other brainstem reflexes and myoclonus), specifying utility in neuro prognostication.
Discussion of imaging (CT and MRI), Neurophysiological studies (EEG, SSEPs) and biomarkers (NSE) with exploration of expected findings and utility was expected. Reference to evidence and existing guidelines was limited in many answers. Several publications provide guidance to this complex area (e.g. ERC/ESICM). The application of neurophysiological testing and biomarkers was generally explored only superficially by many candidates who would benefit from clinical exposure or further reading in this area.
Candidates did less well if they:

1.    Misunderstood the question and focused on brain death testing.
2.    Provided generic answers.

For example, a motor score of < 3 is a marker of severity, however context is crucial to accurately assess the utility of the motor score. Outlining the time frame, the setting of clinical findings and the potential confounders would give more depth of knowledge to the answer, provide necessary context and allow the candidate to demonstrate competency.

Discussion

The 2023 NCS "Guidelines for Neuroprognostication in Comatose Adult Survivors of Cardiac Arrest" came out in March 2023, which means it is possible that the SAQ-writers used the newest version of the guidelines, but as the changes were subtle, it should not have mattered.

  • General principles of neuroprognostication following cardiac arrest:
    • Multimodal assessment: use several techniques concurrently to help form an opinion
    • Timing: not before 24 hours; ideally at 72-120 hours
    • Clinical features are especially susceptible to time context, i.e. need to exclude the effects of sedation and hypothermia
  • Clinical features associated with a poor outcome:
    • History: 
      • Initial rhythm (PEA or asystole)
      • unwitnessed
      • delayed CPR
      • CPR for longer than 20 minutes
    • Examination:
      • Unreactive pupils
      • Absent corneal reflex 
      • Status myoclonus
      • GCS motor score < 3
    • High false positive rate with clinical examination alone
    • Confounded by sedation and cooling
  • Imaging findings associated with a poor outcome:
    • CT: loss of grey-white differentiation (inversed gray/white matter ratio in Hounsfield units)
      • Early (<24hr) CT may fail to demonstrate these findings; poor negative predictive value (i.e. a normal CT does not rule out a bad outcome)
    • MRI: early increased signal intensity on DWI and diffusion restriction on ADC
      •  Good positive and negative predictive value at days 2-7
  • Neurophysiological studies associated with a poor outcome:
    • EEG: Absence of reactivity, burst suppression, suppressed background, or status epilepticus within the first 72 hrs
      • False positive rate 0-7%
    • SSEP: absence of the N20 component with median nerve stimulation
      • Very low false positive rate (close to 0%) even in cooled patients
  • Biomarkers associated with a poor outcome:
    • NSE over 33μg/L at 1-3 days post CPR
      • No uniformly accepted threshold 
    • S100 calcium-binding protein B
      • Remains largely experimental