What is the apnea test?
Apnea test is an essential test for the cessation of brain stem function. It stimulates the respiratory centers in the brain stem by inducing hypercarbia.
One technique requires ventilating the patient with 100% oxygen for 10 to 30 minutes (depending on the severity of any underlying lung injury) followed by disconnection from the respirator and administration of 100% oxygen through a catheter in the trachea or via a T-piece at a flow rate of 6 L/min.
Absence of spontaneous respiratory effort with a PaCO 2 of above 60 mm Hg or >20 mm above baseline confirms clinical apnea.
Arterial blood gas should be checked before and after the withdrawal of ventilation.
Sometimes the test cannot be completed because of ventricular arrhythmias or hypotension. In that situation, the diagnosis of irreversible brain stem dysfunction is made by cerebral blood flow test or other appropriate confirmatory test.
The American Academy of Neurology has published an evidence-based practice guideline for determining brain death in adults that provides additional important information.