Changes in PaO2, PaCO2 and pH during the apnea test

: Changes in PaCO2, PaO2 and arterial pH were monitored during a 10 min apnoea test in nine clinically brain dead subjects. The patients were preoxygenated for 15 min with 100% O2. During the apnoea test they were oxygenated by tracheal cannulation with 5 l O2 per min. PaCO2 rose 1.3-2.1 kPa during the first two minutes of apnoea. Patients with PaCO2 greater than or equal to 5.5 kPa at the beginning of apnoea all had PaCO2 greater than 8 kPa after 5 min of apnoea for five minutes. With one exception, all of the patients were sufficient oxygenated during the apnoea test. If patients are ventilated to a PaCO2 greater than or equal to 5.5 kPa then 5 min of apnoea testing will increase PaCO2 above 8 kPa. As a few patients may develop hypoxemia, patients should be monitored with pulseoximetry.