Which test is used to check spontaneous respirations?

• A. Apnea test
• B. Cold caloric test
• C. Pupillary light reflex test
• D. Corneal reflex

Answer: (A)

The key idea is measuring whether the brainstem can drive spontaneous breathing. The test that directly assesses this is the apnea test. In this test, the patient is prepared on ventilation with good oxygenation, then ventilation is temporarily withheld to let carbon dioxide levels rise. If there are no spontaneous breaths despite hypercapnia (often reaching a specified PaCO2 threshold), it indicates a lack of respiratory drive from the brainstem. This finding, considered alongside other brainstem tests and clinical criteria, helps determine brain death. If spontaneous breathing occurs, the apnea test is not completed as part of brain-death confirmation and the evaluation continues with other assessments.

Other tests do not evaluate spontaneous respiration. The cold caloric test probes the vestibulo-ocular reflex by irrigating the ear with cold water to elicit eye movements. The pupillary light reflex tests the optic and oculomotor nerves by checking pupil constriction in response to light. The corneal reflex assesses trigeminal and facial nerve pathways by observing blinking in response to corneal stimulation.