Ventilation requirements during high frequency ventilation.

This study was undertaken to investigate ventilatory requirements during high frequency ventilation (HFV). Six anesthetized dogs were ventilated with bird M-2 or Emerson 2-V ventilators at respiratory rates (RRs) ranging from 13-1300 breath/min. PaCO2 was maintained within normal range at all rates by tidal volume (VT) adjustment. Required minute volume (VE) increased linearly with rate while VT decreased exponentially and approached a plateau at rates above 200. Airway pressure was inversely proportional to rate at rates below 80 but increased with rate thereafter. A method is provided to estimate required ventilatory volume during HFV based on the results of this study. It was concluded that gas exchange during HFV can be explained by conventional concepts of ventilation and with an unvented nonrebreathing system no benefit accrues from respiratory rates above 200 inasmuch as neither airway pressure nor VT can be reduced in the face of increasing VE requirements.