Summary:
Purpose: In acute respiratory distress syndrome (ARDS), combined high-frequency
oscillation (HFO) and tracheal gas insufflation (TGI) improves oxygenation vs.
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 (CT) tomography to determine
whether HFO-TGI vs. HFO improves the recruitment of the lower lung, and
especially of its dependent region, where loss of aeration is maximized in
ARDS.
Methods: We enrolled 15 patients who had ARDS for 96 hours, and pulmonary
infiltrates in 3 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 (Ptr) of CMV. During HFO/HFO-TGI, mean airway pressure was
titrated to CMV Ptr-level. Gas-exchange and intra-arterial pressure/heart rate
were determined for each ventilatory technique.
Results: Regarding total lung parenchyma, HFO-TGI vs. 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, P0.04); this was due to HFO-TGI-induced
recruitment of nonaerated tissue in the dependent and nondependent lower lung.
HFO-TGI increased normally aerated tissue vs. CMV (P=0.04) and poorly aerated
tissue vs. HFO and CMV (P0.04), and improved oxygenation vs. HFO and CMV (P0.
04).
Conclusions. HFO-TGI improves oxygenation vs. HFO and CMV through the
recruitment of previously nonaerated lower lung units.
Keywords:
Acute respiratory distress syndrome, Adult, Respiration, High frequency oscillatory ventilation, Computed tomography
