The combination of external high-frequency oscillation and pressure support ventilation in acute respiratory failure

Effective gas exchange can be maintained in animals by using external high-frequency oscillation (EHFO). The present study evaluates the effect of relatively long-term duration EHFO combined with pressure support ventilation (PSV) in patients with acute respiratory failure.

Twelve patients were ventilated with EHFO combined with PSV for 8 h at 60 oscillations.min-1, with a cuirass pressure of 36 cm H2O: -26 to +10 cm H2O (27 mm Hg: -19.5 to +7.5 mm Hg) and an inspiratory-to-expiratory ratio of 1:1. Blood gas values and hemodynamic parameters were measured.

Significant increases were noted in cardiac index (3.0 +/- 0.7 to 3.2 +/- 0.7 1.min-1.m-2, P < 0.05) and stroke volume index (32 +/- 14 to 35 +/- 13 ml.m-2, P < 0.05) without changes in pulmonary artery wedge pressure at 1 h after EHFO. PaO2 (kPa)/FiO2 and PaCO2 improved from 21.9 +/- 7.5 to 26.8 +/- 8.0 (P < 0.05) at 2 h and from 6.9 +/- 1.7 to 6.1 +/- 0.9 (P < 0.01) at 30 min after EHFO, respectively. Breath sounds could be heard well throughout the lung fields after institution of EHFO. The mucous rales also decreased.

As a method of ventilation for patients with acute respiratory failure, EHFO combined with PSV may have potential advantages over conventional mechanical ventilation when drainage of secretions if facilitated. Beneficial effects of EHFO may appear after several hours.