Brain death

Prerequisites

• Irreversible etiology known (e.g., severe TBI, anoxia, massive ICH).
• Core Temp: $\ge 36^{\circ }\mathbf{C}$ ($96.8^{\circ }\text{F}$).
• Hemodynamics: $\text{SBP}\ge 100\text{ mmHg}$, $\text{MAP}\ge 60\text{ mmHg}$.
• Toxic/Metabolic: Discontinue CNS depressants/paralytics ($\ge 5$ half-lives, TOF 4/4); correct severe electrolyte/endocrine derangements.

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Clinical Neurologic Exam

• Coma: No response to central noxious stimuli.
• Absent Brainstem Reflexes:
  • Pupils: Fixed, nonreactive ($4-9\text{ mm}$).
  • Corneal: Absent bilaterally.
  • Oculocephalic (Doll’s eyes): Absent (no eye movement on head turn).
  • Oculovestibular (Cold calorics): No deviation after ice-water irrigation.
  • Gag & Cough: Absent to pharyngeal/tracheal suction.

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Apnea Test

• Procedure: Pre-oxygenate with $100\%{\text{FiO}}_2$ $\to$ normalize ${\text{PaCO}}_2$ $\to$ disconnect ventilator $\to$ deliver passive ${\text{O}}_2$ via tracheal cannula $\times 8-10\text{ min}$.
• Positive (Confirms Brain Death):
  • No respiratory effort AND
  • $\mathbf{PaC}{\mathbf{O}}_2\ge 60\text{ mmHg}$ (or $\ge 20\text{ mmHg}$ increase from baseline).
• Abort Criteria (hypotension $\text{SBP}<90$, ${\text{SpO}}_2<85\%$, arrhythmia) $\to$ reconnect ventilator $\to$ obtain ancillary test.

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Ancillary Tests (Used only if exam/apnea test inconclusive)

• Cerebral Angiography: Absent intracerebral blood flow (Gold Standard).
• Radionuclide Perfusion (SPECT): “Hollow skull” sign (no intracranial uptake).
• EEG: Isoelectric (flatline) $\ge 30\text{ min}$.

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High-Yield USMLE Pearls

• Spinal Reflexes Preserved: Deep tendon reflexes, Babinski, triple flexion (hip/knee/ankle), and Lazarus sign originate from the spinal cord $\to$ do NOT rule out brain death. c
• Central DI: Common complication (polyuria, hypernatremia, low urine Osm) $\to$ treat with Desmopressin (DDAVP).
• Legal/Ethics:
  • Brain death = Legal death; family consent/court order is not required to withdraw mechanical ventilation.
  • Notify Organ Procurement Organization (OPO) before terminal extubation.
  • Family cannot override a registered donor’s consent.