Scanographic comparison of high frequency oscillation with versus without tracheal gas insufflation in acute respiratory distress syndrome

Abstract

In acute respiratory distress syndrome (ARDS), combined high frequency oscillation (HFO) and tracheal gas insufflation (TGI) improves oxygenation versus standard HFO, likely through TGI-induced lung recruitment. Experimental data suggest that steady flows such as TGI favor the filling of the lower (i.e., subcarinal) lung. We used whole-lung computerized tomography (CT) to determine whether HFO-TGI versus HFO improves the recruitment of the lower lung, and especially of its dependent region, where loss of aeration is maximized in ARDS. We enrolled 15 patients who had ARDS for 96 h or less, and pulmonary infiltrates in at least three chest X-ray quadrants. Patients were subjected to whole-lung CT after lung-protective conventional mechanical ventilation (CMV) and after 45 min of HFO and 45 min of HFO-TGI. HFO/HFO-TGI were employed in random order. CT scans were obtained at a continuous positive airways pressure equal to the mean tracheal pressure (P (tr)) of CMV. During HFO/HFO-TGI, mean airway pressure was titrated to the CMV P (tr) level. Gas exchange and intra-arterial pressure/heart rate were determined for each ventilatory technique. Regarding total lung parenchyma, HFO-TGI versus HFO and CMV resulted in a lower percentage of nonaerated lung tissue (mean ± SD, 51.4 ± 5.1% vs. 60.0 ± 2.5%, and 62.1 ± 9.0%, respectively; P≤0.04); this was due to HFO-TGI-induced recruitment of nonaerated tissue in the dependent and nondependent lower lung. HFO-TGI increased normally aerated tissue versus CMV (P=0.04) and poorly aerated tissue versus HFO and CMV (P≤0.04), and improved oxygenation versus HFO and CMV (P≤0.04). HFO-TGI improves oxygenation versus HFO and CMV through the recruitment of previously nonaerated lower lung units.