A 52-year-old man is brought to the emergency department after collapse at home. CPR is initiated by bystanders. After 20 minutes of resuscitation, the team suspects prolonged cardiac arrest with possible cerebral hypoxia. Which investigation is most appropriate to assess the severity of global cerebral ischemia and predict neurological outcome?

Explanation

## Assessment of Cerebral Injury Post-Cardiac Arrest ### Role of Biomarkers in Prognostication **Key Point:** Serum neuron-specific enolase (NSE) and S-100B protein are the most validated biochemical markers for predicting neurological outcome after cardiac arrest. NSE is released from damaged neurons and correlates with the extent of cerebral ischemia; S-100B reflects astrocytic injury. Their combined use provides robust prognostic information about the severity of global cerebral ischemia. **High-Yield:** NSE levels >33 μg/L at 48–72 hours post-arrest are associated with high specificity (approximately 80–95%, per European Resuscitation Council 2021 guidelines) for poor neurological outcome (cerebral performance category 3–5). S-100B is more sensitive but less specific; combined use improves prognostication accuracy. ### Comparison of Investigations | Investigation | Timing | Sensitivity | Specificity | Clinical Use | |---|---|---|---|---| | NSE + S-100B | 24–72 hrs post-arrest | High (NSE ~80%) | High (NSE ~80–95% at cutoff) | Prognostication, outcome prediction | | CT head | Immediate | Moderate | Moderate | Rule out structural lesion, hemorrhage | | EEG at 24 hrs | 24 hrs post-arrest | Moderate | Moderate | Assess seizure activity, burst suppression | | Transcranial Doppler | Immediate–early | Low–moderate | Low | Assess cerebral perfusion, not prognostic | **Clinical Pearl:** The multimodal approach to prognostication includes clinical examination (pupillary reflex, corneal reflex, motor response), NSE/S-100B, EEG patterns (burst suppression, status epilepticus), and imaging. NSE >33 μg/L is one of the strongest biochemical predictors of poor outcome and is recommended in international guidelines (European Resuscitation Council 2021; Nolan et al., Resuscitation 2021). **Why not EEG at 24 hours?** While EEG is a valuable component of multimodal prognostication — particularly for detecting seizures, burst suppression, and malignant patterns — it provides functional (electrical) information rather than a direct quantitative measure of the *severity* of global cerebral ischemia. EEG findings at 24 hours can also be confounded by sedation and hypothermia protocols. Serum biomarkers (NSE/S-100B) directly quantify neuronal and glial cell death and are the most appropriate *investigation* for assessing severity of ischemic injury and predicting neurological outcome. **Warning:** CT head is useful to rule out acute structural pathology (hemorrhage, infarction) but does NOT quantify the degree of global cerebral ischemia. Transcranial Doppler assesses cerebral blood flow but lacks standalone prognostic power for neurological outcome prediction. ### Timing and Clinical Context In a patient with prolonged cardiac arrest (20 minutes), serum biomarkers drawn at 24–72 hours provide the most robust biochemical evidence of neuronal and glial injury and allow clinicians to counsel families on likelihood of meaningful neurological recovery, consistent with ERC 2021 and AHA post-cardiac arrest care guidelines.