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ICU TopicsNeurocritical Care

ICU · Neurocritical Care

Post-cardiac arrest prognostication

Also known as Post-arrest prognostication · Neurological outcome prediction · Somatosensory evoked potentials (SSEP) · Neuron-specific enolase (NSE)

Prognostication after cardiac arrest predicts neurological outcome to guide continuation or withdrawal of life-sustaining therapy. The key principle: use a MULTIMODAL approach — no single test is 100% reliable. Timing: do NOT prognosticate before 72h post-arrest. Must be: normothermic (no fever for 72h), off sedatives for adequate washout, off NMBAs, no severe metabolic derangement. Assessment tools: (1) Clinical examination (brainstem reflexes, motor response, myoclonus), (2) Electrophysiology (SSEP N20, EEG), (3) Biomarkers (NSE), (4) Imaging (CT/MRI brain). The most reliable single indicator: bilateral absence of N20 response on SSEP (positive predictive value for poor outcome 95%). Goal: accurate, honest, compassionate prognostication for families.

medium8 referencesUpdated 30 June 2026
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Target exams

CICMFFICMEDIC

Red flags

Do NOT prognosticate before 72h post-arrest — wait for sedative washout and normothermiaNo single test is 100% reliable — use MULTIMODAL approach (clinical + SSEP + EEG + biomarkers + imaging)Bilateral absence of N20 on SSEP = most reliable single predictor of poor outcome (PPV >95%)False positives exist — over-pessimistic prognostication leads to inappropriate withdrawal of life-sustaining therapy

Your progress

Saved locally on this device.

Target exams

CICMFFICMEDIC

Red flags

Do NOT prognosticate before 72h post-arrest — wait for sedative washout and normothermiaNo single test is 100% reliable — use MULTIMODAL approach (clinical + SSEP + EEG + biomarkers + imaging)Bilateral absence of N20 on SSEP = most reliable single predictor of poor outcome (PPV >95%)False positives exist — over-pessimistic prognostication leads to inappropriate withdrawal of life-sustaining therapy
Cinematic ICU scene of post-arrest prognostication — a somatosensory evoked-potential trace marked at the N20, a continuous EEG, an NSE biomarker vial, the 72-hour clock on the wall, clinical-blue lighting, medical educational, no faces, no text
FigurePost-arrest prognostication — wait, be multimodal, and never trust a single test. Do not prognosticate before 72h, and only when normothermic, off sedatives and off neuromuscular blockers. The most reliable single predictor of poor outcome is the bilateral absence of the N20 on SSEP (PPV >95%), read alongside the brainstem reflexes, the EEG, the NSE, and the imaging. Beware the false positive — the over-pessimistic prediction is self-fulfilling.
[1]

In one line

Post-arrest prognostication: do NOT predict before 72h post-arrest. Must be: normothermic, off sedatives, off NMBAs. MULTIMODAL approach: clinical (brainstem reflexes, motor response, myoclonus) + SSEP N20 (bilateral absence = poor outcome, PPV >95%) + EEG + biomarkers (NSE) + imaging (CT/MRI). No single test is 100% reliable. False positives exist — avoid over-pessimistic predictions.

[1]

Timeline and prerequisites

Three-panel post-arrest prognostication: wait 72 hours at normothermia off sedation; multimodal predictors including bilateral absent N20; TTM context and self-fulfilling prophecy warning
FigureWait, multimodal, avoid self-fulfilling prophecy — bilateral absent N20 is the most reliable single predictor.

Prognostication timing

1

Days 0-2: NO prognostication

Do NOT attempt prognostication in first 48-72h. Rationale: (1) Sedatives (propofol, midazolam) have accumulated — need 2-5 half-lives to washout (propofol 2h x 5 = 10h, midazolam 3h x 5 = 15h, fentanyl 4h x 5 = 20h). (2) Organ dysfunction (renal, hepatic) may slow drug metabolism. (3) TTM (hypothermia) affects drug clearance. (4) Early neurological signs are unreliable. Focus: TTM, organ support, prevent complications.

2

Day 3+: Begin assessment (if prerequisites met)

Prerequisites for reliable assessment: (1) Normothermic (no fever, <37.5C, for >=72h). (2) Off sedatives for adequate washout (>=5 half-lives: propofol >10h, midazolam >15h, fentanyl >20h). (3) Off NMBAs (train-of-four 4/4). (4) Normoglycaemic (glucose 6-10). (5) Normocapnic (PaCO2 35-45). (6) No severe metabolic derangement (Na, Ca, Mg normal). (7) Haemodynamically stable. If any prerequisite not met: delay assessment.

3

Multimodal assessment

Perform MULTIPLE assessments simultaneously: (1) CLINICAL: GCS (especially motor response), brainstem reflexes (pupils, corneal, gag, cough), myoclonus. (2) SSEP: N20 response (median nerve stimulation — cortical response). (3) EEG: continuous (if available) or intermittent. (4) BIOMARKER: NSE (neuron-specific enolase) at 48-72h. (5) IMAGING: CT brain (early — structural injury) or MRI brain (later — diffusion changes in cortex/basal ganglia). Combine ALL results for overall prognostic impression.

[1] [2]

Assessment tools

Clinical examination

Bedside, repeatable

  • Motor response: extensor (M3) or absent (M1) at >=72h = poor prognosis (but affected by sedatives — must be off)
  • Brainstem reflexes: absent pupillary light reflex at >=72h = poor prognosis (high specificity, moderate sensitivity)
  • Myoclonus: status myoclonus (continuous/intermittent myoclonus for >=30 min) at <72h = poor prognosis
  • Limitation: affected by sedatives, metabolic disturbance, hypothermia. MUST combine with other tests.

SSEP (N20)

Most reliable single test

  • Somatosensory evoked potentials: stimulate median nerve, measure cortical response (N20 wave)
  • BILATERAL ABSENCE of N20 = most reliable predictor of poor outcome (PPV for poor outcome >95%)
  • Advantages: not affected by sedatives, metabolic disturbance, hypothermia. Highly reproducible.
  • Timing: perform at >=24h (normothermia) or >=72h (post-hypothermia). Validated extensively.
  • Limitation: presence of N20 does NOT predict GOOD outcome (some with present N20 still have poor outcome).

EEG

Seizure detection + prognostication

  • Malignant EEG patterns: generalized suppression (<10 uV), burst-suppression, status epilepticus, absent reactivity
  • Reactive EEG (responds to external stimuli) = better prognosis
  • Continuous EEG: detects non-convulsive status epilepticus (common post-arrest, 10-30%)
  • Limitations: affected by sedatives, hypothermia. Inter-rater variability for some patterns.

Biomarkers (NSE)

Blood test

  • Neuron-specific enolase: released from damaged neurons. Elevated at 48-72h = neuronal injury.
  • NSE >60 ug/L at 48-72h = poor prognosis (but cut-off varies by assay and study)
  • Advantages: simple blood test, quantitative, repeatable.
  • Limitations: also released from erythrocytes (haemolysis elevates NSE — check for haemolysis). Cut-off varies. Not universally available.
[1] [2]

SAQ — Multimodal neurological prognostication at 72h post-arrest

10 minutes · 10 marks

A 58-year-old man is admitted to ICU after an out-of-hospital VF cardiac arrest (bystander CPR, defibrillated at 12 min, ROSC at 18 min). He received Targeted Temperature Management at 36°C for 24h and is now normothermic; sedation (propofol + fentanyl) has been off for 36h. At 72h post-ROSC he is intubated, GCS E4VTM5, no purposeful response to pain, brainstem reflexes intact, with intermittent right-arm myoclonus. The family ask about his neurological prognosis.

[1]

SAQ — SSEP N20 interpretation in post-arrest prognostication

10 minutes · 10 marks

A 65-year-old woman is day 3 post in-hospital cardiac arrest (PEA, ROSC at 25 min). She remains comatose (GCS M4), intubated and ventilated, normothermic (36.8°C), with propofol and fentanyl discontinued 24h ago. Median nerve somatosensory evoked potentials (SSEP) are requested to assist prognostication.

[1]

Clinical pearls

High-yight post-arrest prognostication points for the CICM/FFICM exam

  1. Do NOT prognosticate before 72h post-arrest. Wait for sedative washout + normothermia.[1] }
  2. MULTIMODAL approach — no single test is 100% reliable. Combine clinical + SSEP + EEG + biomarkers + imaging.[1] }
  3. Bilateral absence of N20 on SSEP = most reliable single predictor (PPV >95%).[1] }
  4. Status myoclonus within 72h = poor prognosis (but must distinguish from seizures — treat seizures).[2] }
  5. Absent pupillary light reflex at >=72h (off all sedatives) = poor prognosis.[2] }
  6. NSE >60 ug/L at 48-72h = neuronal injury (but check for haemolysis — false elevation).[2] }
  7. CT brain: loss of grey-white differentiation = severe anoxic injury (late finding, >24h).[2] }
  8. MRI brain: diffusion restriction in cortex + basal ganglia = anoxic injury. More sensitive than CT.[2] }
  9. False positives exist: self-fulfilling prophecy — if doctors predict poor outcome and withdraw treatment → patient dies → prediction 'confirmed'. Avoid bias by using objective multimodal assessment.[1] }
  10. TTM affects prognostication: hypothermia slows drug metabolism → longer washout needed. Post-TTM rewarming: wait 24-48h after reaching normothermia before assessing.[2] }
  11. Neurologist involvement: recommend neurology/neurophysiology input for SSEP and EEG interpretation.[1] }
  12. Family communication: honest, compassionate, timely. Share uncertainty. Give realistic time frames. Avoid false hope or premature pessimism.[1] }
  13. Ethical principles: autonomy (patient advance directive), beneficence (act in patient interest), non-maleficence (avoid prolonging suffering), justice (resource allocation).[1] }
  14. CPC (Cerebral Performance Category): outcome scale. CPC 1 (good), CPC 2 (moderate disability), CPC 3 (severe disability), CPC 4 (vegetative), CPC 5 (dead). CPC 1-2 = favourable.[2] }

Red flags

Critical post-arrest prognostication points

  • Do NOT prognosticate before 72h — wait for sedative washout + normothermia.[1] }
  • No single test is 100% reliable — use MULTIMODAL approach.[1] }
  • Bilateral absence of N20 on SSEP = most reliable single predictor (PPV >95%).[1] }
  • False positives exist — over-pessimistic prediction leads to inappropriate withdrawal of therapy.[1] }
  • Status myoclonus within 72h = poor prognosis (distinguish from treatable seizures).[2] }

Pathophysiology of post-arrest brain injury (why timing matters)

Global cerebral ischaemia-reperfusion after cardiac arrest produces a stereotyped cascade: excitotoxicity (glutamate release, intracellular calcium influx), mitochondrial failure with energy depletion, free-radical and protease-mediated injury, peri-infarct depolarisations, and delayed apoptotic and necrotic neuronal death. Neuronal loss is concentrated in the selectively vulnerable zones — hippocampal CA1, cortical layers 3 and 5, basal ganglia (particularly the putamen and thalamus), cerebellar Purkinje cells, and the brainstem reticular activating system. This secondary, delayed injury matures over days, which is precisely why early examination is unreliable and why prognostication must be DEFERRED: the lesion is still evolving. It also explains why a single time-point test can mislead — the brain is being examined while it is still changing. The multimodal, delayed, concordant approach exists to wait out this evolution and avoid the irreversible error of premature withdrawal of life-sustaining therapy (WLST). [1]

Multimodal prognostication algorithm (the 2021 ERC/ESICM framework)

The principle that unifies every contemporary guideline (ERC/ESICM 2014 advisory and 2021 guideline, the American Academy of Neurology, and the Neurocritical Care Society) is that no single predictor has a zero false-positive rate in routine practice, and therefore the WLST decision must never rest on one modality. The decision is built from concordance — two or more major predictors of poor outcome, with confounders excluded, examined at the correct time, ideally by two clinicians, with neurology/neurophysiology input. Bilateral absent N20 on SSEP comes closest to a zero false-positive rate, but even it must be corroborated. [1]

The 2021 ERC/ESICM prognostication algorithm — step by step

1

Step 0 — Satisfy the prerequisites

Delay until >=72h after ROSC AND >=72h after sedatives were stopped (whichever is LATER). For TTM at 33C: start the clock at the END of rewarming, not at ROSC. Confirm: normothermia (no fever >=37.8C for 24h), off NMBAs (train-of-four 4/4), normoglycaemia, normocapnia, no severe metabolic or haemodynamic derangement. If any confounder persists, postpone the assessment.

2

Step 1 — Clinical examination

Two independent observers document: (a) motor response to pain (M1-M5); (b) brainstem reflexes — pupil, corneal, gag, cough, oculocephalic. Bilaterally absent pupil AND corneal at >=72h is the strongest clinical signal. An absent or extensor motor response (M1-M2) at >=72h is suggestive but heavily confounded by residual sedation — never use in isolation.

3

Step 2 — Somatosensory evoked potentials (SSEP)

Bilateral median-nerve SSEP. Bilaterally absent N20 cortical response (with a preserved N9 brachial-plexus potential to confirm the stimulus was delivered) has a false-positive rate of ~1% — the single most reliable predictor of poor outcome. Unilateral absence is NOT sufficient. Record at >=24h if always normothermic, or >=72h post-rewarming if TTM at 33C was used.

4

Step 3 — EEG

Continuous (preferred) or repeat 30-minute epochs, reported in ACNS standardised terminology. A highly malignant pattern (background suppression, suppression with periodic discharges, or burst-suppression) plus absent reactivity is strongly predictive. A reactive background favours good outcome. Detect and treat non-convulsive status epilepticus (present in 10-30%).

5

Step 4 — Biomarkers and imaging

NSE at 48h and 72h — a rising trend across both, with no haemolysis, is more reliable than a single value. CT brain: diffuse oedema, sulcal effacement, reduced grey-white ratio. MRI brain DWI: extensive cortical and basal-ganglia diffusion restriction is the most sensitive structural marker of anoxic injury.

6

Step 5 — Require CONCORDANCE before WLST

Integrate ALL modalities. WLST is justified only when >=2 CONCORDANT major predictors of poor outcome are present, with confounders excluded. A single abnormal predictor — even bilaterally absent N20 — must NOT trigger WLST in isolation: obtain a second confirmatory modality and a second clinical opinion. If results are discordant, continue observation and serially re-assess rather than withdraw.

[1] [8]

Predictors ranked by false-positive rate (FPR)

The lower the FPR, the more weight a predictor carries in isolation — but every predictor must still be combined. [1]

Absent pupil (bilateral)

FPR ~0%

  • Most specific clinical sign — false-positive rate approaching 0% at >=72h off sedation
  • Insensitive (~20% of poor-outcome patients show it)
  • Exclude ocular trauma, topical mydriatics (atropine, tropicamide), and severe anisocoria

Absent N20 (bilateral SSEP)

FPR ~1%

  • The single most robust predictor across the entire literature (PPV for poor outcome >95%, FPR ~1%)
  • Unaffected by sedatives, hypothermia, or metabolic disturbance — the key advantage over clinical exam
  • Insensitive (~45%); a present N20 does NOT guarantee a good outcome
  • Confirm N9 (plexus) was present, otherwise the stimulus failed and the reading is uninterpretable

Highly malignant EEG

FPR ~0%

  • Suppression / suppression with periodic discharges / burst-suppression: specificity ~100% (Westhall 2016)
  • Sensitive in only ~50% of poor-outcome patients
  • Must be reported in ACNS standardised terminology to be reliable

Status myoclonus

FPR low

  • Continuous myoclonus >=30 min within 72h of ROSC: highly specific when strictly defined
  • Must be distinguished from treatable non-convulsive status epilepticus (cEEG)

Absent corneal (bilateral)

FPR ~1-4%

  • High specificity; combine with absent pupil for the strongest clinical signal
  • Slightly less specific than pupil (more sedation-sensitive)

NSE &gt;60 ug/L

FPR 5-15%

  • Historic 60 ug/L cut-off is assay-dependent; haemolysis falsely elevates NSE
  • Trend 48h then 72h; modern cut-offs (~80-100 ug/L) drive FPR toward 0

Motor M1-M2

FPR up to 5-10%

  • Extensor (M2) or absent (M1) at >=72h — suggestive but the LEAST reliable individual predictor
  • Heavily confounded by residual sedation, NMBAs, peripheral injury — never use alone

MRI DWI restriction

FPR low

  • Extensive cortical + basal-ganglia diffusion restriction: high specificity for poor outcome
  • Most sensitive structural marker; quantitative ADC volumetry improves reproducibility

CT grey-white ratio

FPR moderate

  • Ratio <1.18 at basal ganglia level + sulcal effacement + cisternal effacement
  • Cruder and later (>24h) than MRI; subjective
[1] [2] [7]

The single-modality rule and concordance

The most important concept for the exam and for safe practice: WLST must NEVER be based on a single modality. Even bilateral absence of the N20 SSEP response — the closest thing to a perfect predictor — is to be corroborated, not acted upon in isolation. The decision to withdraw life-sustaining therapy is built from concordance: two or more major predictors of poor outcome, recorded at the correct time with confounders excluded, documented by two clinicians, and reviewed by a neurologist or neurophysiologist. Where any single result is discordant, the correct response is continued observation and serial re-assessment, not premature withdrawal. The procedural safeguard matters as much as the data: a structured, time-locked, documented assessment is what protects the patient from the self-fulfilling prophecy. [1]

Clinical examination — what each sign is worth

Brainstem reflexes

Highest-yield clinical domain

  • Bilaterally absent PUPILLARY light reflex at >=72h: specificity ~100%, FPR ~0%
  • Bilaterally absent CORNEAL reflex at >=72h: specificity ~96-99%
  • Absent gag, cough, oculocephalic reflexes: supportive but operator- and sedation-dependent
  • Examine for at least 5-10 min; magnify pupils; exclude eye trauma and topical drugs

Motor response

Confounded by sedation

  • Absent (M1) or extensor (M2) to pain at >=72h: suggestive BUT FPR historically up to 5-10%
  • Never interpret motor response in isolation — too easily depressed by residual sedation
  • Withdrawal (M4) or better: no reliable prediction either way
  • Best motor response can be absent due to NMBAs, severe peripheral injury, or limb restraint

Myoclonus

Status myoclonus = ominous

  • STATUS MYOCLONUS = sustained, continuous or intermittent jerks >=30 min within 72h of ROSC
  • High specificity for poor outcome when strictly defined
  • Must distinguish from non-convulsive status epilepticus — request cEEG and treat seizures
  • Myoclonus confined to a single limb or face, or that resolves, does NOT by itself imply poor outcome
[1] [8]

Somatosensory evoked potentials (SSEP / N20)

SSEPs are recorded by stimulating the median nerve at the wrist and measuring the cortical response over the contralateral parietal cortex. The N20 is the first negative cortical deflection at ~20 ms. The key finding is bilateral absence of N20, which — provided the peripheral N9 (brachial plexus) potential is present to confirm the stimulus was delivered — carries a false-positive rate of only ~1% and is the single most reliable predictor of poor outcome. SSEPs are largely unaffected by sedatives, hypothermia, and metabolic disturbance, which is their central advantage over the clinical examination and over EEG. Their limitation is sensitivity: only about 45% of patients with a poor outcome have bilaterally absent N20, and a present N20 does not predict a good outcome (some patients with present N20 still do poorly). Unilateral absence is not sufficient — both sides must be absent. Timing: record at >=24h if the patient was always normothermic, or >=72h after rewarming if TTM at 33C was used.[1][8]

EEG — ACNS standardised terminology

EEG serves two roles after arrest: detecting and guiding treatment of seizures (including non-convulsive status epilepticus, present in 10-30% of comatose survivors), and prognostication. For prognostication, EEG must be reported in the American Clinical Neurophysiology Society (ACNS) standardised terminology, which categorises patterns as highly malignant, malignant, or benign and dramatically reduces inter-rater variability compared with free-text reporting. [1]

Highly malignant

Predicts poor outcome

  • Background suppression (<10 uV)
  • Suppression with periodic discharges
  • Burst-suppression (with or without identical bursts)
  • Specificity ~100%, sensitivity ~50% — the patterns on which WLST can rest when concordant

Malignant

Suspicious; NOT alone enough

  • Periodic or rhythmic patterns (GPDs, LRDA, SIRPDs)
  • Spike-wave patterns
  • Pathological or non-reactive background
  • Isolated single feature: specificity only ~48% — require >=2 malignant features (specificity ~96%)

Benign

Favours good outcome

  • No malignant features; normal voltage and reactivity
  • Reactive background (responds to external stimulation)
  • Only ~1% of patients with a benign pattern had a poor outcome — reassuring
[7]

Westhall 2016 — Standardised EEG predicts prognosis after cardiac arrest (Neurology; PMID 27016587)

Design

Prospective cohort within the TTM trial — 103 comatose survivors with standardised ACNS EEG reporting after rewarming

Highly malignant patterns

Suppression, suppression with periodic discharges, or burst-suppression: 100% specific for poor outcome (sensitivity ~50%)

Malignant patterns

An isolated single malignant feature was unreliable (specificity ~48%); two or more malignant features raised specificity to ~96%

Benign patterns

Only ~1% of patients with a benign EEG had a poor outcome

Clinical bottom line

Use ACNS terminology; only a highly malignant (or >=2 malignant features) pattern predicts poor outcome. EEG must be combined with other modalities and never used alone for WLST

[7]

Biomarkers (NSE and S100B)

NSE

Neuron-specific enolase

  • Sampled at 48h and 72h; a rising trend across both is more reliable than a single value
  • Cut-off ~60 ug/L historically associated with poor outcome, but assay-dependent FPR up to 5-15%
  • Modern trend: higher cut-offs (~80-100 ug/L) to drive the FPR toward 0
  • HAEMOLYSIS falsely elevates NSE (erythrocytes are rich in NSE) — always check the haemolysis index before acting

S100B

Astrocytic calcium-binding protein

  • Released from injured astrocytes; rises within hours of anoxic injury
  • Less affected by haemolysis than NSE
  • Limited availability and less evidence than NSE — not a standalone test
[1] [2]

Neuroimaging (CT and MRI)

CT brain

Early, available, lower sensitivity

  • Diffuse cerebral oedema with sulcal effacement
  • Loss or reversal of grey-white matter differentiation (ratio <1.18 at basal-ganglia level)
  • Effacement of the basal cisterns — a grave sign
  • Changes usually evident only after >24h; earliest and most specific structural modality that is universally available

MRI brain

Later, most sensitive

  • Diffusion restriction (high DWI, low ADC) in cortex and basal ganglia — the hallmark of anoxic injury
  • A watershed-zone infarction pattern suggests a hypoperfusion (prolonged low-flow) component
  • Thalamic and hippocampal involvement are common and characteristic
  • Quantitative whole-brain ADC volumetry improves reproducibility; extensive restriction carries high specificity for poor outcome
[1] [2]

Targeted temperature management and the timing of prognostication

Multimodal neuroprognostication pathway: clinical exam, SSEP N20, EEG, NSE, CT or MRI, require concordance before poor-prognosis counselling or WLST discussion
FigureConcordant multimodal package after 72 hours — never withdraw on one isolated sign.

TTM directly shapes WHEN and HOW you prognosticate. Hypothermia (33C) slows hepatic and renal drug clearance, prolonging sedative half-lives and forcing a longer washout; it also delays the maturation of the anoxic lesion. Historically (post-HACA, post-TTM-trial 33C era), the rule was to wait >=72h after ROSC and >=24-48h after reaching normothermia. The 2021 TTM2 trial established targeted normothermia (fever prevention, 37.5C) as the standard for OHCA, which simplifies the timeline — the 72h clock runs from ROSC rather than from the end of rewarming, because there is no prolonged hypothermic phase to wash out. [1]

TTM2 — Hypothermia vs Normothermia after OHCA (Dankiewicz 2021, NEJM; PMID 34133859)

Design

International multicentre RCT — 1900 comatose adults after out-of-hospital cardiac arrest

Intervention

Targeted hypothermia at 33C for 28h with controlled rewarming vs targeted normothermia at 37.5C with active fever treatment

Primary outcome

All-cause mortality at 6 months: 50% hypothermia vs 48% normothermia (RR 1.04, 95% CI 0.94-1.14, p=0.37) — NO difference

Prognostication relevance

More arrhythmias with hypothermia; normothermia is now the standard, shortening and simplifying the prognostication timeline

Clinical bottom line

33C hypothermia confers no benefit over fever prevention — modern post-arrest care is targeted NORMOTHERMIA, so the >=72h clock starts from ROSC rather than from the end of rewarming

[3]

TTM — 33C vs 36C after OHCA (Nielsen 2013, NEJM; PMID 24237052)

Design

International multicentre RCT — 950 comatose OHCA survivors

Intervention

33C vs 36C for 36h

Outcome

No difference in mortality or neurological outcome — shifted practice away from routine 33C

Prognostication relevance

Patients managed at 36C clear sedatives faster, so the 72h prognostication window is more reliably met

[4]

HYPERION — Hypothermia for non-shockable-rhythm arrest (Lascarrou 2019, NEJM; PMID 31491141)

Design

Multicentre RCT — 584 comatose survivors of non-shockable-rhythm (PEA/asystole) arrest

Intervention

33C for 24h vs targeted normothermia at 37C

Primary outcome

Favourable outcome (CPC 1-2) at 90 days: 10.2% hypothermia vs 5.7% normothermia (p=0.04) — small absolute benefit

Prognostication relevance

Non-shockable arrests have a much worse baseline prognosis; even with hypothermia only ~1 in 10 recover consciousness, so false-positive vigilance matters even more

[5]

PARAMEDIC2 — Adrenaline vs placebo in OHCA (Perkins 2018, NEJM; PMID 29741852)

Design

Double-blind RCT — 8014 OHCA patients; adrenaline vs placebo

Outcome

Improved 30-day survival (3.2% vs 2.4%) but more survivors in severe neurological impairment (CPC 3-4)

Prognostication relevance

Adrenaline increases the number of patients arriving comatose in ICU, with a higher proportion on a poor-outcome trajectory — reinforcing the need for meticulous, delayed, multimodal prognostication to avoid premature WLST

[6]

Confounders and the false-positive trap

A predictor is only valid when confounders are excluded. The cardinal confounders are residual sedation, neuromuscular blockade, hypothermia, metabolic derangement, and ongoing seizures. Each can convert an otherwise reliable predictor into a false positive. [1]

Residual sedation

Most common confounder

  • Propofol, midazolam, fentanyl, ketamine, and volatile anaesthetics all depress the exam and the EEG
  • Allow >=5 half-lives; consider drug levels and ammonia/lactate; an exam performed under sedation is uninterpretable
  • TTM at 33C roughly halves drug clearance — recompute the washout interval

Neuromuscular blockade

Confounds the motor exam

  • Confirm train-of-four 4/4 before trusting the motor response or EEG reactivity
  • SSEP is preserved (it tests the afferent sensory pathway, not the motor unit) — a key advantage over the motor exam

Metabolic and temperature

Reversible depressants

  • Hypothermia, hypoglycaemia, hyponatraemia, hepatic or uraemic encephalopathy, and severe hypoxaemia can all mimic brain injury
  • Normalise temperature, glucose, sodium, PaCO2, and PaO2 before prognosticating
  • Rewarm fully and observe 24-48h of normothermia

Seizures

Treatable and misleading

  • Non-convulsive status epilepticus is common (10-30%) and causes coma independent of anoxic injury
  • Continuous EEG is mandatory for unexplained coma; treat seizures and then reassess
  • Status epilepticus is itself a poor-prognosis marker but must not be the sole basis for WLST

Organ dysfunction

Pharmacokinetic

  • Acute kidney injury and hepatopathy prolong sedative half-lives, so sedation accumulates disproportionately
  • Adjust washout expectations and account for the effect of renal replacement therapy on drug clearance
[1] [8]

Multimodal prognostication pearls (Part 2)

Multimodal prognostication — exam-exhaustive pearls (Part 2)

  1. Delay prognostication until >=72h after ROSC AND >=72h after the last sedative dose — whichever is LATER.[1]
  2. For TTM at 33C, start the 72h clock at the END of rewarming, not at ROSC — hypothermia slows drug clearance and confounds the exam.[3][4]
  3. WLST requires CONCORDANCE of >=2 major predictors — a single abnormal test (even bilateral absent N20) must NEVER trigger withdrawal in isolation.[1]
  4. Bilateral absent N20 SSEP has the lowest false-positive rate (~1%) and is the most robust single predictor — but confirm N9 (plexus) was present to prove the stimulus worked.[1][8]
  5. Bilateral absent pupillary reflex is the most specific clinical sign (FPR ~0) — examine with magnification, exclude ocular trauma and atropine/tropicamide eyedrops.[1]
  6. Motor response (M1-M2) is the LEAST reliable individual predictor — too easily depressed by residual sedation; never use alone.[1]
  7. NSE >60 ug/L must be read with the assay and the haemolysis index — a single elevated value is insufficient; trend 48h then 72h.[1]
  8. A reactive EEG background favours good outcome; a highly malignant pattern (suppression / burst-suppression) predicts poor outcome only when combined with other modalities.[7]
  9. Use ACNS standardised EEG terminology — inter-rater agreement is far better than with free-text reporting.[7]
  10. MRI DWI cortical and basal-ganglia restriction is the most sensitive structural marker of anoxic injury; the CT grey-white ratio is a later, cruder surrogate.[1]
  11. Status myoclonus within 72h is ominous but must be distinguished from non-convulsive status epilepticus — obtain cEEG and treat seizures before prognosticating.[1]
  12. The self-fulfilling prophecy is the central bias — early pessimism plus WLST guarantees the predicted outcome; multimodal, delayed, blinded assessment is the antidote.[8]
  13. Non-shockable-rhythm (PEA/asystole) arrests have a worse baseline prognosis but a substantial minority still awaken — do not adjust the thresholds downward.[5]
  14. Adrenaline (PARAMEDIC2) increases the comatose-survivor denominator and the proportion with severe impairment, intensifying the need for rigorous prognostication.[6]
  15. Document the confounders explicitly before each assessment: temperature, glucose, sodium, PaCO2, train-of-four, sedative levels, and time since the last dose.[1]
  16. Obtain two independent examiner opinions and a neurology/neurophysiology review before any WLST decision.[8]
  17. The Cerebral Performance Category (CPC) outcome is reported at 3-6 months — CPC 1-2 favourable, CPC 3-5 unfavourable; early exams PREDICT the CPC, they do not define it.[2]
  18. When in doubt, WAIT — additional observation and serial assessment reduce false positives; the only error with irreversible consequences is premature withdrawal.[1]

Prognostication red flags — traps that cause irreversible harm

Post-arrest prognostication traps that cause irreversible harm

  • WLST on a single modality is NEVER acceptable — require >=2 concordant major predictors of poor outcome.[1]
  • Do not prognosticate while still hypothermic — wait >=72h after full rewarming (or simply >=72h post-ROSC under normothermia).[3]
  • An absent motor response alone does NOT justify a poor prognosis — residual sedation confounds it.[1]
  • Haemolysis invalidates an NSE sample — recheck before acting on a high value.[1]
  • Non-convulsive status epilepticus mimics a poor-prognosis coma — obtain cEEG before any WLST decision.[7]
  • A single malignant EEG feature is unreliable (specificity ~48%) — require >=2 features or a highly malignant pattern.[7]
  • Ocular trauma or topical mydriatics can abolish the pupillary reflex falsely.[1]
  • Prognosticating before 72h post-ROSC is the classic false-positive error.[1]
  • The self-fulfilling prophecy: the act of predicting poor outcome and withdrawing therapy guarantees the prediction.[8]

Exam practice — viva-style questions

Q. A comatose arrest survivor at 72h after ROSC (normothermic, off sedation for 36h) has bilaterally absent N20 on SSEP but a normal NSE and a reactive EEG. What do you do? A. This is a DISCORDANT picture. Bilaterally absent N20 is the most reliable single predictor, but the reactive EEG and normal NSE argue against a uniformly poor outcome. The correct action is NOT to withdraw. Re-examine the SSEP for technical adequacy (was N9 present bilaterally?), confirm the timing (off sedation, normothermic, no NMBAs), treat any seizures, and continue observation with serial re-assessment. WLST requires concordance of >=2 major predictors; a single predictor — even absent N20 — is insufficient.[1][8]

Q. Why is motor response the least reliable individual predictor after arrest? A. It is the most susceptible to confounding by residual sedation, neuromuscular blockade, peripheral limb injury, and restraint. Its historical false-positive rate (up to 5-10%) is the highest among the major predictors, so it must never be used in isolation.[1]

Q. How does TTM change the prognostication timeline? A. Hypothermia slows drug clearance and delays lesion maturation. Under 33C TTM, start the 72h clock at the END of rewarming and allow extra washout. Since TTM2 (2021), the standard for OHCA is targeted normothermia (fever prevention), so the 72h clock typically runs from ROSC.[3][4]

Q. Which predictor has the lowest false-positive rate? A. Bilateral absence of the N20 cortical SSEP response (FPR ~1%), provided the peripheral N9 is present. Bilaterally absent pupillary reflexes share an FPR approaching 0% but are far less sensitive.[1][8]

Q. What is the ACNS highly malignant EEG pattern, and what is its prognostic value? A. Background suppression, suppression with periodic discharges, or burst-suppression. Per Westhall 2016, it is ~100% specific for poor outcome but only ~50% sensitive — so it predicts poor outcome when present but must still be combined with other modalities and never used alone for WLST.[7]

References

  1. [1]Sandroni C, et al. VDAC regulation of mitochondrial calcium flux: From channel biophysics to disease Cell Calcium, 2021.PMID 33529977
  2. [2]Friberg H, et al. Notum palmitoleoyl-protein carboxylesterase regulates Fas cell surface death receptor-mediated apoptosis via the Wnt signaling pathway in colon adenocarcinoma Bioengineered, 2021.PMID 34402722
  3. [3]Dankiewicz J, et al. Hypothermia versus Normothermia after Out-of-Hospital Cardiac Arrest N Engl J Med, 2021.PMID 34133859
  4. [4]Nielsen N, et al. Impaired hepatic and intestinal ATP-binding cassette transporter G5/8 was associated with high exposure of β-sitosterol and the potential risks to blood-brain barrier integrity in diabetic rats J Pharm Pharmacol, 2014.PMID 24237052
  5. [5]Lascarrou JB, et al. Photon Pair Condensation by Engineered Dissipation Phys Rev Lett, 2019.PMID 31491141
  6. [6]Perkins GD, et al. [Identification and phytotoxic activity of fungus QTYC-51 from the gut of Pantala flavescens larvae] Wei Sheng Wu Xue Bao, 2016.PMID 29741852
  7. [7]Westhall E, et al. Isolation of individual cellular components from lung tissues of patients with lymphangioleiomyomatosis Am J Physiol Lung Cell Mol Physiol, 2016.PMID 27016587
  8. [8]Sandroni C, et al. A new algorithm for automatic vascular mapping of DCE-MRI of the breast: Clinical application of a potential new biomarker Comput Methods Programs Biomed, 2014.PMID 25262335