[Experimental results of using the "open lung concept"].

Several elements of the "open lung concept", like ventilation with small tidal volumes, were incorporated into various ventilatory strategies. Our study demonstrates how the whole concept can be applied in an animal model using a standardized protocol with the following possible results. Eighteen pigs weighing between 30 and 45 kg were anaesthetized, tracheotomized and ventilated. Acute lung injury was induced by surfactant washout. Blood gases were monitored via a continuous arterial sensor system (Trendcare system). After washout, the ventilatory pattern of the American "ARDS Network study" was applied (PEEP = 9 cmH2O, volume controlled mode with a tidal volume of 6 ml/kg body weight and a respiratory rate of 25 breaths per minute). Afterwards, the opening pressure and the pressure at which the lung collapses were titrated. Both levels were used as the basis for adjusting the recruitment pressure and PEEP, which was necessary to keep the lung open. The respiratory rate was chosen in such a way that at a low intrapulmonary pressure difference between inspiration and expiration as well as normocapnia was reached. After induction of an acute lung injury by surfactant washout, the oxygenation index (OI) dropped from 556 +/- 54 to 176 +/- 89 mmHg. In the "ARDS Network" mode, OI increased to 285 +/- 49 mmHg. After alveolar recruitment with a peak pressure of 53 +/- 7 cmH2O and application of a median PEEP of 17 +/- 3 cmH2O, oxygenation returned close to baseline. A pCO2 of 33 +/- 4 mmHg resulted after using a respiratory rate of 39 breaths per minute. The median tidal volume was 8 ml/kg body weight. Despite a short arterial systolic blood pressure drop of 23 +/- 11 mmHg during recruitment, no significant difference was detectable afterwards compared to the baseline. Using low tidal volumes alone, complete reopening was not achieved in an experimentally induced acute lung injury. After recruitment manoeuvres, it was possible to reopen the lung and keep it open by application of a sufficient PEEP.