October 2025 POCUS Case of the Month: Lung Ultrasound

The two most common types of ventilators used today are ascending bellows and pistons. Ascending bellows, which rise during expiration, are generally considered safer than descending or “hanging” bellows because they will not ascend if there is a leak in the system. Ascending bellows rely on pneumatic control as inspiration is driven pneumatically by the introduction of pressurized oxygen or air into the ventilator casing, which compresses the bellows in order to deliver a mechanical breath. Piston ventilators use an electric motor to drive a piston within a cylinder in order to deliver a mechanical breath. Piston ventilators are generally considered more accurate because of the precise control over piston positioning, delivering greater precision of both volume and pressure. Piston ventilators also lack intrinsic PEEP.