Briefly discuss the information (including clinical features / investigations) that may help determine the prognosis of patients following cardiac arrest.

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College Answer
 

Prognostication after cardiac arrest may be very difficult and involve a number of modalities.

It involves consideration of:

History

  • Underlying cause of the arrest
  • Co-morbidities
  • Use of therapeutic hypothermia
  • Features of the arrest – down time, CPR, ROSC

Clinical assessment

Timing:
Neurological assessment timing will be determined by the use of therapeutic hypothermia and the duration and type of medication for sedation but is most reliably performed day 3 without therapeutic hypothermia – probably day 5 with TH. Suggestion is to wait 72 hours after return of normothermia.
With new TTM trial suggesting 36C then 72 hours post arrest may again be appropriate.
 

Examination:
Clinical – off sedation and neuromuscular blocking agents
Cranial nerve abnormalities – absence of pupillary response and corneal reflexes are bad prognostic indicators.
Best Motor response at 72 hours with absent or extensor response associated with poor outcome.
Status / Generalised and repetitive myoclonus (as opposed to sporadic myoclonus)

Biochemical parameters

  • Neurone specific enolase >33mcg/L at days 1-3 indicates poor outcome
  • S100, CSF CKBB not accurate enough for prognostication

Electrophysiological features

EEG: generalised suppression, burst suppression or generalised periodic complexes strongly associated with poor outcome.
SSEPs: Bilateral absence of N20 component of SSEP with median nerve stimulation within 1-3 days is strongly associated with poor outcome.

Imaging

 CT appearance – catastrophic changes with obvious pathology. Diffuse oedema has not been formally assessed as an indicator.
MRI may be more sensitive

Predictors of better outcome are:

Recovery of brainstem reflexes within 48 hours
Return of purposeful response within 24 hours
Hypothermia at the time of arrest
Young age

Discussion

The tabulated summary below is based on the most recent ERC/ESICM statement (Sandroni et al, 2014). A vast and riduculous discussion of prognostication after cardiac arrest is also carried out in the Cardiac Arrest and Resuscitation section of this site.

Predictors of Poor Outcome in Comatose Survivors of Cardiac Arrest
Predictive sign or investigation Predictive utility Confounding factors
Absent pupillary reflex

 0% false positive rate at 72 hours, irrespective of cooling

  • Sedation
  • Hypothermia
  • Paralysis
  • Presence of shock
  • Metabolic derangements, eg. acidosis
Absent corneal reflex  0-15% false positive rate at 72 hours
Extensor motor response, or worse May be associated with poor outcomes
  • High false positive rate (~50%)
Myoclonic status epilepticus Persisting myoclonic status epilepticus has a 0% false positive rate within the first 24 hours
  • Interpreter-dependent
  • Findings may be subtle
  • Paralysis interferes with interpretation
Somatosensory evoked potentials:
absence of the N20 component
Absence of N20 predicts poor outcome with a0% false positive rate.

Presence of N20 does not rule out a poor outcome.

N20 responses may disappear on repeat testing.

N20 responses may reappear, but this does not suggest a good prognosis.

Burst suppression on EEG May be associated with poor outcome  Poor predicitive value; 
cannot be used for prognostication.
Absence of EEG reactivity Low false positive rate (0-5%) Confounded by sedation
Neuron-specific enolase NSE over 33μg/L at 1-3 days post CPR predicts poor outcome with a 0% false positive rate

NSE may be elevated for reasons other than brain injury; for instance, it may be secreted by neuroendocrine tumours

CT brain On CT, an inversed gray/white matter ratio in Hounsfield units was found in patients who failed to awaken after cardiac resuscitation. However, the predictive value of CT findings is not known

If performed too early, the CT may not demonstrate any findings.

References

References

Engdahl, Johan, et al. "Can we define patients with no and those with some chance of survival when found in asystole out of hospital?." The American journal of cardiology 86.6 (2000): 610-614.

Bunch, T. Jared, et al. "Outcomes and in-hospital treatment of out-of-hospital cardiac arrest patients resuscitated from ventricular fibrillation by early defibrillation." Mayo Clinic Proceedings. Vol. 79. No. 5. Elsevier, 2004.

Levine, Robert L., Marvin A. Wayne, and Charles C. Miller. "End-tidal carbon dioxide and outcome of out-of-hospital cardiac arrest." New England Journal of Medicine 337.5 (1997): 301-306.

Rea, Thomas D., et al. "Temporal Trends in Sudden Cardiac Arrest A 25-Year Emergency Medical Services Perspective." Circulation 107.22 (2003): 2780-2785.

Carew, Heather T., Weiya Zhang, and Thomas D. Rea. "Chronic health conditions and survival after out-of-hospital ventricular fibrillation cardiac arrest." Heart 93.6 (2007): 728-731.

Goldberger, Zachary D., et al. "Duration of resuscitation efforts and survival after in-hospital cardiac arrest: an observational study." The Lancet (2012).

Wijdicks, E. F. M., et al. "Practice Parameter: Prediction of outcome in comatose survivors after cardiopulmonary resuscitation (an evidence-based review) Report of the Quality Standards Subcommittee of the American Academy of Neurology."Neurology 67.2 (2006): 203-210.

Rogove, Herbert J., et al. "Old age does not negate good cerebral outcome after cardiopulmonary resuscitation: analyses from the brain resuscitation clinical trials."Critical care medicine 23.1 (1995): 18-25.

LEVY, DE, et al. "Predicting Outcome from Hypoxic-Ischemic Coma." Survey of Anesthesiology 30.2 (1986): 93.

Sandroni, Claudio, et al. "Prognostication in comatose survivors of cardiac arrest: an advisory statement from the European Resuscitation Council and the European Society of Intensive Care Medicine." Resuscitation 85.12 (2014): 1779-1789.