What finding demonstrates lack of medullary function?

• A. Absent pupillary light reflex; no response to pain.
• B. Absent corneal reflex; absent inducible eye movements (ice water).
• C. Apnea test shows no ventilatory movements in setting of maximal CO2.
• D. No spontaneous respirations.

Answer: (C)

Medullary respiration is the automatic drive to breathe. The apnea test directly assesses this by letting CO2 rise (hypercapnia) and watching for any spontaneous ventilatory effort. If there are no ventilatory movements despite high CO2, it indicates the medullary respiratory center is not functioning, demonstrating lack of medullary function. The other findings involve other brainstem regions or are non-specific (for example, reflexes like the pupillary or corneal responses test parts of the midbrain or pons, and not the medulla; absence of spontaneous respirations alone can be caused by factors such as sedation or severe coma).