Tools for protective lung ventilation. The elastic pressure-volume curve and aspiration of dead space

Abstract: Ventilator-induced lung injury (VILI) may contribute to morbidity and mortality of acute lung injury (ALI). Lung protective ventilation (LPV), that reduces VILI, may involve low tidal volume (Vt). Particularly low Vt is possible if dead space ventilation is reduced e.g. by aspiration of dead space gas (ASPIDS). ASPIDS implies that gas rich in CO2 during expiration is aspirated through a separate channel from the tracheal tube and replaced by fresh gas injected in the inspiratory line. The elastic pressure volume (Pel/V) curve of the respiratory system is recommended as a guideline to set the ventilator so as to reduce VILI. The Vt should be confined to the linear segment of the Pel/V curve, to avoid lung collapse below this zone, and hyperinflation above it. However, the understanding of physiological phenomena behind the Pel/V curve is limited. The objectives were to increase our comprehension of the Pel/V curve, to enhance its potential clinical usefulness, and to develop and test ASPIDS, in an approach aiming at LPV. A computer controlled Servo Ventilator 900 C allowed accurate recording of the Pel/V curve and control of the ASPIDS system. ASPIDS allowed isocapnic ventilation of pigs and humans with low Vt, and higher PEEP levels in ALI patients. In pigs and humans recruitment was shown to start below the lower inflection point and to continue far above it. Pel/V curves recorded from different PEEP levels allowed evaluation of lung collapse and guidance in setting PEEP. New concepts will hopefully increase the feasibility of LPV.