Apnoea test is used for diagnosis of:

A neurologist, neurosurgeon, or intensivist generally performs the clinical brain death examination. Two examinations consistent with brain death 12 hours apa, or one examination consistent with brain death followed by a consistent confirmatory study generally is sufficient to declare brain death. Documentation of no brain stem function requires the following: nonreactive pupils; lack of corneal blink, oculocephalic (doll's eyes), oculovestibular (cold calorics) reflexes; and loss of drive to breathe (apnea test). The apnea test demonstrates no spontaneous breathing even when PaCO2 is allowed to rise above 60 mmHg. Ref: Schwaz's principle of surgery 9th edition, chapter 42.