Brain death criteria

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Prerequisites - Setting the Stage

  • Irreversible Cause: Establish a known, irreversible cause for the coma.
  • Exclusion of Confounders: Must rule out conditions that mimic brain death.
    • Temperature: Core body temperature > 36°C (>97°F).
    • Hemodynamics: Systolic blood pressure ≥ 100 mmHg (or age-appropriate level).
    • Toxins/Drugs: No evidence of sedatives, anesthetics, or neuromuscular blockers.
    • Metabolic: No severe electrolyte, acid-base, or endocrine abnormalities.

⭐ The cause of coma must be definitively established and irreversible before brain death testing can be initiated.

Clinical Exam - The Bedside Verdict

  • Unresponsive Coma: No purposeful motor response to maximal noxious stimuli.
  • Absent Brainstem Reflexes: Must have normal core temperature (>36°C) and be free of CNS depressants or neuromuscular blockers.
    • Pupils: Fixed and dilated (4-9 mm), no response to bright light.
    • Ocular Movement: No oculocephalic (doll's eyes) or vestibulo-ocular (cold caloric) reflexes.
    • Facial Sensation/Motor: No corneal reflex; no grimacing to deep pressure.
    • Pharyngeal/Tracheal: No gag or cough reflex.

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⭐ Spinal reflexes (e.g., deep tendon reflexes) may still be present and do not rule out brain death as they are mediated by the spinal cord.

Apnea Test - The CO2 Challenge

  • Goal: To prove the absence of a brainstem respiratory drive by inducing hypercapnia.
  • Procedure:
    • Pre-oxygenate with 100% O₂ to a $PaO₂$ > 200 mmHg.
    • Disconnect ventilator; provide passive oxygenation (e.g., tracheal cannula).
    • Observe for respiratory movements for 8-10 minutes.
    • Abort if the patient becomes hemodynamically unstable or hypoxemic.

Key Endpoint: The test confirms apnea if there are no respiratory movements and the final arterial $PaCO₂$ is ≥ 60 mmHg or has risen by ≥ 20 mmHg from a normal baseline.

Ancillary Tests - Calling for Backup

  • Used when clinical exam or apnea test is inconclusive or contraindicated (e.g., severe facial trauma, chronic CO₂ retention).
  • Confirmatory Findings:
    • Cerebral Angiography: No intracerebral filling.
    • EEG: Electrocerebral silence (no activity >2 µV).
    • Transcranial Doppler: Small systolic peaks, no diastolic flow.
    • Nuclear Scintigraphy: "Hollow skull sign" (no isotope uptake).

⭐ Cerebral angiography is the gold-standard ancillary test, definitively showing absence of cerebral blood flow.

High‑Yield Points - ⚡ Biggest Takeaways

  • Brain death is legally and medically equivalent to cardiopulmonary death.
  • It signifies the irreversible loss of all brain function, including the brainstem.
  • The diagnosis is clinical; ancillary tests (EEG, cerebral angiography) are confirmatory, not mandatory.
  • Core exam findings: unresponsive coma, absent brainstem reflexes, and a positive apnea test.
  • Apnea test: No respiratory effort despite a PaCO2 > 60 mmHg.
  • Rule out confounding factors: severe hypothermia (<36°C), intoxicants, or neuromuscular blockade.
  • Spinal reflexes may still be present and do not preclude the diagnosis.

Practice Questions: Brain death criteria

Test your understanding with these related questions

A 22-year-old man is brought to the emergency department by ambulance 1 hour after a motor vehicle accident. He did not require any circulatory resuscitation at the scene, but he was intubated because he was unresponsive. He has no history of serious illnesses. He is on mechanical ventilation with no sedation. His blood pressure is 121/62 mm Hg, the pulse is 68/min, and the temperature is 36.5°C (97.7°F). His Glasgow coma scale (GCS) is 3. Early laboratory studies show no abnormalities. A search of the state donor registry shows that he has registered as an organ donor. Which of the following is the most appropriate next step in evaluation?

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Flashcards: Brain death criteria

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EF < _____% and MI within _____ months are absolute contraindications to non-cardiac surgery

TAP TO REVEAL ANSWER

EF < _____% and MI within _____ months are absolute contraindications to non-cardiac surgery

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