Brain Death Determination: Apnea Test Criterion
The PaCO₂ increasing to 68 mmHg when off the ventilator for 8 minutes is the anticipated criterion that supports declaration of death by neurologic criteria, as it meets the required threshold of ≥60 mmHg with absence of respiratory effort. 1, 2
Why the Other Options Are Incompatible with Brain Death
The other clinical findings described in this case are inconsistent with brain death and would preclude the diagnosis:
Sluggishly reactive pupils: Brain death requires complete absence of pupillary light reflex, with pupils fixed in midsize or dilated position 3, 2, 4. Any pupillary reactivity, even if sluggish, indicates residual brainstem function.
Weak cough with suctioning: Brain death requires complete absence of the cough reflex to deep tracheal suctioning 3, 2, 4. Any cough response, regardless of strength, demonstrates intact brainstem reflexes.
Eyelid trembling with corneal stimulation: Brain death requires complete absence of corneal reflex 3, 2, 4. Any eyelid movement in response to corneal touch indicates preserved brainstem function.
Apnea Test Requirements for Brain Death
The apnea test is the definitive assessment of brainstem respiratory drive and must demonstrate specific physiologic thresholds 1, 2:
- PaCO₂ must reach ≥60 mmHg AND increase ≥20 mmHg above baseline 1, 2, 4, 5
- Complete absence of any respiratory effort throughout the test 1, 2, 4
- Prerequisites include core temperature >35°C, normotension, preoxygenation with 100% oxygen for 5-10 minutes, and normalized baseline PaCO₂ 1, 2
In this case, the PaCO₂ of 68 mmHg clearly exceeds the 60 mmHg threshold required by all major guidelines 3, 1, 2, 4, 5. The average rate of PaCO₂ rise during apnea is approximately 3.7 mmHg/min, though this can vary considerably from 0.5 to 10.5 mmHg/min 6.
Critical Pitfalls to Avoid
Any respiratory effort during apnea testing is absolutely inconsistent with brain death 2. Even irregular breaths or minimal respiratory effort when PaCO₂ >60 mmHg have been documented in patients who otherwise appeared to meet brain death criteria, and these patients cannot be declared brain dead 3.
Brain death should never be diagnosed when any brainstem reflexes are present, including pupillary, corneal, cough, or gag reflexes 3, 2, 4. The presence of these reflexes in this patient means brain death criteria are not met, regardless of the apnea test result.
Complete Clinical Examination Requirements
Brain death determination requires demonstration of 2, 4:
- Complete absence of arousal or awareness to maximal stimulation
- Fixed, nonreactive pupils (midsize or dilated)
- Absent corneal, oculocephalic, and oculovestibular reflexes
- No facial movement to noxious stimulation
- Absent gag and cough reflexes
- No brain-mediated motor responses
- Positive apnea test (PaCO₂ ≥60 mmHg with no respiratory effort)
Two complete examinations separated by an observation period are required, with 12-24 hours recommended for adults 2, 5. Death is declared only after the second examination confirms an unchanged and irreversible condition 2, 5.