Bilevel positive airway pressure. A type of noninvasive ventilation that helps with breathing by providing a flow of air delivered through a face mask. The air is pressurized by a machine, which delivers it to the face mask through long, plastic tubing. The machine delivers the air at two different pressures which alternate: A higher pressure to breathe in (called inspiratory positive airway pressure, or IPAP) and a lower pressure for breathing out (called expiratory positive airway pressure, or EPAP).