Outline the value of the following in determining prognosis for neurological recovery in an adult patient admitted to ICU, after successful cardiovascular resuscitation from an out-of-hospital cardiac arrest:
a) Peri-arrest data
b) Clinical examination
c) Neuro-imaging
d) Neurophysiology
e) Biomarkers
a. Peri-arrest data:
Initial rhythm, bystander CPR, time to ROSC intuitively helpful and commonly considered, but have not been shown to correlate with individual outcome. Co-morbidities and pre- arrest performance status may determine overall survival.
b. Clinical Examination:
Unreliable and of no predictive value before 24 hours, clinical assessment at ≥ 72 hours conventional
• Appropriate pre-conditions: absence of sedation/relaxants, adequate CVS
resuscitation, normothermia, corrected biochemistry etc.
• All data pertains to studies before the common use of therapeutic hypothermia, and the effect of this intervention unknown. May need longer than 72 hours to obtain reliable data from CNS examination in patients treated with induced hypothermia
• GCS < 4, absent corneal response, absent pupillary response to light indicative of poor prognosis
• myoclonus not sufficiently predictive to be reliable in isolation but myoclonic status epilepticus is a poor prognostic feature
c. Neuro-imaging:
• CT may be performed early to exclude a CNS cause of arrest
• CT signs of poor prognosis include qualitative assessment, and quantitative assessment of white matter Houndsfield unit ratio. Optimum timing not clear
• MRI demonstration of diffuse cortical lesions or sub-cortical lesions is associated with poor outcome
d. Neurophysiology:
• No neurophysiology study reliably predicts outcome at < 24 hours
• EEG findings of: diffuse suppression to < 20 mV, burst suppression, generalised seizures, diffuse periodic complexes indicate poor prognosis
• EEG shown to have increased false positive prediction for poor outcome after induced hypothermia
• SSEP: bilaterally absent cortical responses to median nerve stimulation seems highly accurate (0% False Positive Rate), not studied after induced hypothermia
e. Biomarkers:
• Neurone specific enolase (NSE) most studied, some studies show 0% FPR for poor outcome, but cut-off levels vary, studies small
With the exception of the "peri-arrest data" section, this question closely resembles Question 4 from the second paper of 2013.
The table from Question 4 is thus reproduced below, with the peri-arrest data section added, sans the confounding factors column. The whole peri-arrest data issue is better discussed in the chapter on prognostication of neurological recovery following a cardiac arrest.
Peri-arrest data:
| Predictive sign or investigation | Predictive utility | Confounding factors |
| Absent pupillary reflex |
0% false positive rate at 72 hours, irrespective of cooling |
|
| Absent corneal reflex | 0-15% false positive rate at 72 hours | |
| Extensor motor response, or worse | May be associated with poor outcomes |
|
| Myoclonic status epilepticus | Persisting myoclonic status epilepticus has a 0% false positive rate within the first 24 hours |
|
| 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. |
The key features of the college answer one would be wise to remember include the following:
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Tapia, F. J., et al. "Neuron-specific enolase is produced by neuroendocrine tumours." The Lancet 317.8224 (1981): 808-811.
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