BiPAP

BiPAP, bilevel positive airway pressure, is a close cousin of CPAP that breathes with you instead of holding one steady pressure. It delivers a higher pressure while you inhale and a lower pressure while you exhale. If CPAP is a constant prop holding the airway open, BiPAP is a prop that also gives the lungs a gentle push on the way in and eases off on the way out.

The two pressure levels do two jobs. The lower expiratory pressure keeps the airway from collapsing and makes breathing out against the flow more comfortable; the higher inspiratory pressure adds a boost to each breath that increases the volume of air moved and helps clear carbon dioxide. The difference between the two pressures is essentially a measure of the ventilatory support being given.

Because of this, BiPAP is used where CPAP is not enough: when ventilation itself is failing and carbon dioxide is rising, as in obesity hypoventilation syndrome, COPD with carbon dioxide retention, or neuromuscular weakness; for non-invasive ventilation of acute respiratory failure; and for patients who cannot tolerate exhaling against a single high CPAP pressure. Advanced modes can even deliver a backup breath if the patient pauses.

BiPAP shares CPAP's practical hurdles — mask fit, leak, dryness, and the need for consistent use — and adds the requirement of correctly setting two pressures, usually by a clinician. It is not automatically better than CPAP for ordinary obstructive sleep apnea; for simple obstruction, CPAP is first-line, and BiPAP is reserved for when a single pressure proves inadequate or poorly tolerated.