Proportional pressure support in acute lung injury

The use of partial ventilatory support in patients affected by Acute Respiratory Failure (ARF) due to Acute Lung Injury (ALI) let them to perform an active inspiration, while it acts in providing the amount of work that patient’s muscles are not able to achieve themselves. PPS is a partial ventilatory support that overcomes a patient’s respiratory system elastance (Ers) and resistance (Rrs), by applying pressure „proportional” to volume (volume assist, VA) and flow (flow assist, FA) respectively. The ventilator acts just an extension of patient’s inspiratory muscles, thus amplifying his inspiratory effort. Consequently he/she is able to breathe performing the pattern chosen by his/her control system. This translates itself in a variable breathing pattern in terms of tidal volume, respiratory rate and pressures applied to the airway openings: the patient is able to compensate variable respiratory workloads and/or minute ventilation requirements with a more physiologic strategy. This may be felt by the patient as more comfortable. Preliminary studies about the use of PPS in ALI patients showed an increase in arterial blood oxygenation. Although future technical improvements are advisable, such as smart alarms and systems able to continuously measure Ers and Rrs while on PPS and, accordingly, able to adjust VA and FA respectively, and if preliminary results about gas exchange will be confirmed by larger studies, the use of PPS in ALI patients might introduce variability during pressure assisted mechanical ventilation that mimics the variability seen ubiquitariously in physiologic signals from mammals and this may result in some advantages.