cmH₂O (Centimeters of Water Pressure)

The pressure unit used for CPAP and BiPAP prescriptions — the amount of air pressure, measured in centimeters of water displacement, delivered to keep the airway open.

Typical CPAP prescriptions range from 4–20 cmH₂O. BiPAP prescriptions specify two separate numbers: IPAP (inhale pressure) and EPAP (exhale pressure), since bi-level devices deliver different pressure for each phase of breathing.