Apnea test for brain death determination is able to perform easily with the method written in Japanese criteria (Brain death study group, Ministry of Health and Welfare, 1987) (Figure 3). PaCO2 is increased to more than 60 mmHg, by which respiratory center in the brain stem is stimulated enough. Hypoxemia may occur and is the most serious complication during apnea test. We examined O2 delivery methods either by a thin cannula inserted to near tracheal carina (Ordinary method, 6 l/min) or by constant flow using a ventilator (6 l/min, or 20 l/min). During 10 minutes apnea test, PaO2 and PaCO2 changed significantly from 429 to 264 mmHg and 43 to 90 mmHg, respectively. But there was no significance between the methods. During apnea test, we have to distinguish spinal reflex movement from spontaneous respiratory movement. It is better to keep body temperature near 37 degrees C, because low body temperature requires much longer duration to reach required PaCO2, 60 mmHg (y = 0.54x - 15.2, where x is body temperature, degrees C and y is delta PaCO2, mmHg/min). Hypoxemia during apnea test must be prohibited, because it may cause farther organ damage. Maintenance of oxygenation during apnea test is difficult in patients who have severe respiratory failure. Oxygenation is kept much higher by adding positive airway pressure (10 cm H2O) and continuous monitoring of oxygenation by a pulse oxymeter prepares much safer apnea test in these patients.