What on earth is APRV?

Airway pressure release ventilation (APRV) was described more than 20 years ago [1] as a mode that allows spontaneous breathing throughout the ventilation cycle. APRV is a time-cycled alternant between two levels of positive airway pressure, with the main time on the high level and a brief expiratory release to facilitate ventilation. As such, APRV may be considered a partial ventilatory support modality that has the ability to deliver the full work of breathing if needed. Although it seems that APRV is well defined, the characteristics are surprisingly unspecific, as is the way APRV is used.Different perceptions of this mode may exist around the globe. While 'APRV' is common to users in North America, a very similar mode, biphasic positive airway pressure (BIPAP), was introduced in Europe [2]. The term APRV has also been used in American journals where, from the ventilation characteristics, BIPAP would have been the more adequate terminology [3]. To further confusion, BiPAP？ (with a small 'i') is a registered trade-mark for a noninvasive ventilation mode in a specific ventilator (Respironics Inc.). Other names (BILEVEL, DUOPAP) have been created for legal reasons. Although similar in modality, these terms share the same shortcomings: they describe how a mode is intended to inflate the lung, rather than defining the characteristics of synchronization or the way spontaneous breathing efforts are supported.The perceived differences between APRV and BIPAP have been described previously [4,5]. Essentially, APRV has a longer time phase on the high pressure level, while BIPAP usually does not exceed an inspiration:expiration time ratio of 1:1 [5]. Expiratory lung collapse is prevented in APRV by creating intrinsic positive end-expiratory pressure (PEEP) during the short expiration, while in BIPAP the PEEP is directly set with the lower pressure level. BIPAP can be applied in different ways: with unsynchronized, unsupported interfacing of spontaneous breaths ('genuine' BIP