Neurological Prognostication - Timeline and Workup
Neurological prognostication after cardiac arrest is challenging and uncertain. The introduction of therapeutic hypothermia alters the timeframe for neurological recovery and the interpretation of prognostic markers. Studies of neurological prognostication are hampered by heterogenous patient populations and variable definitions of “coma”. We will discuss the clinical predictors of recovery and available diagnostics – clinical exam, electrodiagnostic testing, and neuroimaging.
Timeframe post cardiac arrest diagnostics:
Day 1-2 Therapeutic hypothermia and rewarming
• Electroencephalography (EEG)
- Timing: started during TH and continued for 24 hours post normothermia.
- Poor prognosis: absence of EEG activity, seizures, burst suppression (Neurology 2013;80:339).
- Positive prognosis: continuous background pattern and reactivity at day 3 or later.
• Clinical exam
- Poor prognosis: Status myoclonus at <48 hours post cardiac arrest or normothermia. Defined as spontaneous, repetitive, unrelenting, generalized multifocal myoclonus involving the face, limbs and axial musculature. There may be no EEG correlate. Absent brainstem reflexes: bilateral pupillary, corneal, and oculocephalic reflexes. Absent brainstem reflexes, along with apnea and other criteria (depending on local guidelines), may signify brain death.
• Somatosensory evoked potentials (SSEP) – measurement of brain activity in reponse to somatosensory stimulation
- Timing: 48 hours post cardiac arrest or normothermia.
- Poor prognosis: Bilateral absence of N20, which reflects the integrity of thalamocortical projections.
• Neuron specific enolase (serum) – non-specific marker of neuronal injury (misnomer as it is found in RBC and platelets).
- Timing: 24-72 hours post cardiac arrest or nomothermia.
- Poor prognosis: >33 ug/l and increasing daily NSE levels (Neurology 2011;77:623). NSE is prognostic in the pretherapeutic hypothermia era but is not well validated in patients who received therapeutic hypothermia. Not part of MGH neuroprognostication guidelines.
• CT head, 48 hours post cardiac arrest or normothermia
- Poor prognosis: wide spread hypodensity, loss or reversal of grey-white differentiation.
• Brain MRI, 72 hours post cardiac arrest or normothermia
- Poor prognosis: DWI and ADC changes suggestive of ischemic injury. Quantitative ADC values may correlate with severity. MRI can be insensitive to lesions if not performed during normothermia.
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