The safe limits of mechanical factors in the apnea testing for the diagnosis of brain death

Apneic oxygenation is an apnea testing method in the diagnosis of brain death. In this method, oxygen (O-2) is delivered into the trachea via an O-2 catheter (O2C). However, barotrauma may develop during O-2 insufflation into the trachea. Oxygen catheter diameters, O-2 catheter tip position in the trachea, and O-2 flow rate have been proposed as causes of barotrauma. This study was designed to highlight the airway pressure changes during apneic oxygenation in a model consisting of an anesthesia bag, which was connected to a pressure transducer and to an endotracheal tube (ETT). The pressure of the system was monitored while delivering O-2 continuously to the system through O2C of different diameters, which were placed in the ETT. Tested variables were ETT/O2C ratio, O2C tip position in ETT (proximal 1/3 of the ETT, mid point of the ETT, and distal 1/3 of the ETT) and O-2 flow rate (6, 8, and 10 L min(-1)). The increase in the airway pressure significantly correlated with O2C tip position in ETT (p = 0.017). ETT/O2C ratio smaller than 1.75 caused significantly high airway pressures (p < 0.05). The pressure was significantly higher at the flow rate of 10 L min(-1) O-2 compared with the flow rate of 6 L min(-1) O-2 (p < 0.01). Thus, ETT/O2C ratio, O2C tip position in ETT and O-2 flow rate are the important factors that determine the airway pressure in the trachea during O-2 insufflation. In conclusion, overlooked mechanical factors dangerously increase airway pressure during apnea testing.