Ventilator disconnexion alarm failures. The role of ventilator and breathing system accessories

Pressure-sensitive ventilator disconnexion alarms do not always alarm during disconnexion of a discharging compliance ventilator such as Manley Blease, unless accurately adjusted. High flows during disconnexion result in significant pressure generation caused by outflow resistance of catheter mounts, heat and moisture exchangers, capnometer cuvettes, and angled connectors; this may lead to alarm failure because of incorrectly adjusted pressure alarm limits. The exact position of the disconnexion is critical and if the alarm's pressure sensor is placed in either the inspiratory or expiratory limb of the ventilator it makes no difference to its correct function. Nine different heat and moisture exchanges were compared in the same breathing system. Those with 15-mm male connectors generate the highest pressures on disconnexion (1.1 kPa). It is suggested that the low pressure alarm limit is set only marginally below the peak inspiratory pressure, and that it is readjusted for every patient and after every change in ventilation. Most importantly, the alarm should be shown to be functional by a trial disconnexion at the tracheal tube.