Influence of apneic oxygenation and minimal tidal volumes on ventilator-associated lung injury

Protective tidal volumes such as 6 mL/kg can still result in tidal hyperinflation and expose the lung to mechanical stress. Further reduction of tidal volume and apneic oxygenation might mitigate lung injury. We aimed to assess the influence of minimal tidal volumes and apneic oxygenation in combination with arterio-venous extracorporeal lung assist (av-ECLA) on ventilator-associated lung injury.

Acute respiratory distress syndrome was induced in swine (N.=24) by saline lavage. The animals were randomized into three groups, ventilated in a pressure-controlled mode with a tidal volume (VT) of 6 mL/kg, 3 mL/kg and 0 mL/kg body weight, respectively. The latter two groups were instrumented with an av-ECLA device. Lung injury was assessed by histological examination of lung tissue at the end of the 24 hour experiment and by gas exchange parameters.

Oxygenation was significantly lower in the 3 and 0 mL/kg groups, whereas CO2 remained in the targeted range in all groups. Histological examination revealed a reduction of tidal hyperinflation in the apical lung regions in the 3 and 0 mL/kg groups. In lower lung regions an increase of inflammation, intra-alveolar exudation and formation of atelectasis was shown in the animals ventilated with lower VTs.

In combination with highly effective CO2-removal, the reduction of tidal volumes up to 0 mL was feasible. Tidal hyperinflation could be reduced in the upper lung areas, yet inflammation in the lower lung was higher with low tidal volumes. This stresses the differing mechanical properties of inhomogeneous injured lungs.