Brain death is the permanent and irreversible cessation of all functions of the entire brain, including the brainstem. For NEET PG, focus on the “Triad of Brain Death”.
The Clinical Triad
- Coma: Unresponsiveness to all forms of external stimulation (visual, auditory, tactile).
- Absence of Brainstem Reflexes: All brainstem-mediated reflexes must be absent.
- Apnea: Absence of spontaneous respiratory effort in the setting of hypercarbia.
Neurological Examination (Brainstem Reflexes)
| Reflex | Afferent Nerve | Efferent Nerve |
|---|---|---|
| Pupillary Light Reflex | CN II | CN III |
| Corneal Reflex | CN V | CN VII |
| Gag Reflex | CN IX | CN X |
| Cough Reflex | CN X | CN X |
| Oculocephalic (Doll’s Eyes) | CN VIII | CN III, VI |
High-Yield NEET PG Pearls:
- Prerequisites: Rule out confounders like hypothermia (Temp < 36°C), drugs (sedatives/NMJ blockers), and severe metabolic/electrolyte disturbances.
- Apnea Test: The definitive test. Positive if PaCO2 ≥ 60 mmHg (or 20 mmHg rise from baseline) with no respiratory effort.
- Spinal Reflexes: Can persist in brain death (e.g., deep tendon reflexes, flexion withdrawal); they do NOT invalidate the diagnosis.
- Confirmatory Tests: Indicated if the clinical exam is inconclusive or impossible. Includes 4-vessel angiography, radionuclide scintigraphy, or TCD.
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