ICU · Respiratory / ventilation

APRV, Bilevel & Airway-Pressure Release Ventilation

Also known as APRV · Airway pressure release ventilation · Bilevel · BiVent · Duo-PAP · Open lung ventilation · P-high · P-low · Release ventilation · Inverse ratio ventilation · T-high · T-low · Continuous positive airway pressure with release · BiPhasic positive airway pressure

Airway pressure release ventilation (APRV) is a pressure-controlled, time-cycled mode that applies two levels of CPAP — a high pressure (P-high) set from the plateau or peak inspiratory pressure of the preceding conventional mode and held for a long T-high, and a brief release to a low pressure (P-low, commonly 0 cmH2O) for a short T-low terminated when expiratory flow reaches 75 per cent of its peak — allowing spontaneous breathing throughout the cycle. The high mean airway pressure maintains alveolar recruitment and oxygenation (an open-lung strategy), while the intermittent release clears CO2 and the spontaneous breaths improve cardiac index and venous return and reduce sedation. The extreme inverse I:E ratio keeps the lung inflated most of the time and derecruits only partially on each brief release. APRV is used selectively in moderate-severe ARDS as a rescue or an alternative to conventional ventilation, and in refractory hypoxaemia; systematic reviews and a COVID-era RCT show improved oxygenation without a clear mortality benefit, so it is not the standard first-line. Contraindications are obstructive airway disease (CO2 retention, air-trapping) and profound shock (the elevated intrathoracic pressure). Bilevel (BiVent/Duo-PAP) is the generalised two-level mode with a more conventional ratio and set mandatory breaths; APRV is its extreme, inverse-ratio, spontaneous-breathing form.