The brain death criteria include assessment of the following: normothermia; cause of brain death; unresponsiveness; absence of brainstem reflexes; and apnea. The presence of withdrawal reflexes, typically seen in the lower extremities, do not preclude the diagnosis of brain death given that withdrawal reflexes can be spinally mediated. The absence of brainstem reflexes includes pupillary responses, eye movements, and lower brainstem reflexes such as response to tracheal stimulation. Apnea testing is performed to demonstrate lack of respiratory effort, even in the presence of elevated pCO2 levels. When no respiratory effort is made during the apnea test and the other criteria have been met, the patient may be pronounced dead. The diagnosis of brain death is not without controversy. For instance, thermoregulation is regarded as a brainstem function; therefore, some argue that those patients who maintain their body temperature cannot be declared brain dead.