Adult Critical Care Specialty (ACCS) Practice Exam

What is the significance of having a PaCO2 of 70 torr during an apnea test?

1. It indicates respiratory acidosis

2. It suggests impaired respiratory function

3. It confirms cerebral autoregulation

4. It supports diagnosis of brain death

The correct answer is: It supports diagnosis of brain death

A PaCO2 level of 70 torr during an apnea test is highly significant in the context of diagnosing brain death. The apnea test is performed to assess the patient's ability to initiate a breath in response to elevated carbon dioxide levels in the blood. In a healthy individual, an increase in PaCO2 typically stimulates the respiratory center in the brain to trigger spontaneous breathing. Therefore, if a patient is unable to breathe despite a PaCO2 level of 70 torr, which is considerably elevated, it indicates that the brainstem, where the respiratory center is located, is not functioning. This finding supports the diagnosis of brain death, as it signifies a complete and irreversible loss of all brain function. While elevated PaCO2 does indicate respiratory acidosis and suggests impaired respiratory function, the definitive conclusion drawn in the context of the apnea test is that it provides critical evidence to support the diagnosis of brain death by demonstrating the absence of neural respiratory drive. Hence, the presence of a PaCO2 of 70 torr directly correlates with the criteria needed to confirm brain death in a clinical setting.