Hazard of a ruptured exhalation mushroom diaphragm

In most breathing circuits, ventilation of a patient requires some device to occlude the expiratory limb during inflation. Usually one or another modification of a mushroom exhalation valve is employed. Such valves are found in the Bourns Bear 1 ventilator, the Bennett MA-1 and MA-2 ventilators, and the Emerson postoperative ventilator, as well as in the Frumen valve for manual ventilation. Recently, the authors observed a defect that might cause permanent occlusion, raising the patient's airway pressure to the level of the limiting safety pop-off and effectively applying a prolonged Valsalva maneuver without ventilation. The defect responsible for this malfunction was a half-centimeter laceration in the mushroom valve. Although the defect occurred on a Bourns Bear 1 ventilator, the authors were able to reproduce it on other ventilators of different manufacturers.