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 +/- A SD, 51.4 +/- A
5.1% vs. 60.0 +/- A 2.5%, and 62.1 +/- A 9.0%, respectively; P a
parts per thousand currency sign 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 a parts per thousand
currency sign 0.04), and improved oxygenation versus HFO and CMV (P a
parts per thousand currency sign 0.04).
HFO-TGI improves oxygenation versus HFO and CMV through the recruitment
of previously nonaerated lower lung units