Bringing back the old: time to reevaluate the high-frequency ventilation strategy

Abstract

Objective:

To examine the role of frequency in high-frequency ventilation (HFV) on carbon-dioxide (CO₂) elimination and lung injury, independent of its effect on tidal volume.

Study Design:

An anatomically representative lung model was attached to a mechanical ventilator capable of providing HFV with a constant volume. CO₂ was infused directly into the lung, and a commercially available end-tidal CO₂ detector was used to determine CO₂ elimination. CO₂ elimination and amplitude of pressure transmissions were evaluated using frequencies ranging from 5 to 15 Hz. The pressure–volume index (PVI) was described as the product of the volume and pressures delivered to the lung, a surrogate for lung injury.

Result:

The use of increasing frequencies directly correlated with improved CO₂ clearance when keeping the tidal volume fixed, expressed as percent CO₂ remaining in the lung at 25 s (66.5 (±1.1)%, 50.5 (±0.1)% and 37.8 (±0.3)% at 5, 10 and 15 Hz, respectively, P<0.05). With a fixed tidal volume, there was a decrease in pressure amplitudes transmitted to the lung with a decline in the PVI (53.9 (±2.7) mmHg ml⁻¹, 41.1 (±0.9) mmHg ml⁻¹ and 23.4 (±3.6) mmHg ml⁻¹, at 5, 10 and 15 Hz, respectively, P<0.05).

Conclusion:

Frequency has a direct relationship with CO₂ elimination when tidal volume is fixed. Using low delivered tidal volumes and high frequencies may allow for improved ventilation efficacy, while minimizing lung injury.