High-frequency oscillatory ventilation: a better tool for lung protection?

Objective

This study was performed to compare the efficacy of high-frequency oscillatory ventilation (HFOV) with conventional mechanical ventilation (CV) in patients with acute respiratory distress syndrome (ARDS).

Method

Ten patients with ARDS were enrolled to the study. Gas exchange and hemodynamic parameters were measured during initial phase of the mechanical ventilation (tidal volume [TV] ≤ 6–8 ml/kg, positive end expiratory pressure [PEEP] = 10 cmH₂O, f = 12/min, I/E = 0.5, FIO₂ = 1). Then patients were randomized into CV or HFOV groups. The upper inflection point (UIP) and closing pressures (CP) were approximated according to blood gases response to PEEP/continuous distending pressure (CDP) titration. The lung protective ventilation strategy was followed for both groups. Ventilatory settings were CDP = CP + 5 cmH₂O, f = 5 Hz, bias flow = 20 l/min for HFOV and PEEP = CP + 2 cmH₂O, f = 12/min, TV ≤ 6–8 ml/kg for CV. FIO₂ was set to keep on the SaO₂ over 90%. After 3 hours ventilation with each setting, groups were switched from HFOV to CMV or vice versa. For each group, the recruitment maneuver was applied with a pressure of 2 cmH₂O below the UIP for 40–60 s at the beginning and after all disconnections. Gas exchange and hemodynamic parameters in addition to ventilatory settings were recorded at 10, 60 and 120 min of each setting. Results were mentioned as the median. The Mann–Whitney U test was used for the comparisons.

Results

The lung injury (LIS), APACHE II and multiple organ dysfunction scores of the patients were 2.6, 23.5 and 9, respectively. The median recruitment pressure was 41.5 cmH₂O. Peak, mean, end-expiratory pressures and tidal volumes in CV were 28, 20, 16 cmH₂O, and 6.4 ml/kg, respectively. CDP of HFOV was 25.5 cmH₂O. There was no significant difference in gas exchange and hemodynamic parameters between the two groups except PaCO₂ values. PaCO₂ values were significantly lower in HFOV (P < 0.05) (Fig. 1). In spite of statistically insignificant differences in the PaO₂/FIO₂ ratio between groups, this ratio improved during successive measurements in HFOV while deteriorating in CV (Fig. 1). No complication occurred in both groups during study.

Figure 1

Values are expressed as median and interquartile range.

Conclusion

CO₂ removal capacity of HFOV may not only be related with its active expiration feature, but also related with its capability to prevent derecruitment better than CV ventilation, as shown with an improvement in PaO₂/FIO₂ ratios. Therefore, HFOV may be a better tool to follow lung protective ventilation.