Normocapnic High Frequency Oscillatory Hyperventilation Increases Oxygenation in Pigs

Abstract

High frequency oscillatory ventilation (HFOV), contrary to conventional ventilation, enables a safe increase in tidal volume (VT) without endangering alveoli by volutrauma or barotrauma. The aim of the study is to introduce the concept of normocapnic high frequency oscillatory hyperventilation and to assess its effect upon oxygen gain under experimental conditions. Laboratory pigs (n=9) were investigated under total intravenous anesthesia in three phases. Phase 1: Initial volume controlled HFOV period. Phase 2: Hyperventilation – VT was increased by (46±12) % when compared to normocapnic VT during phase 1. All other ventilatory parameters were unchanged. A significant increase in PaO2 (by 3.75±0.52 kPa, p<0.001) and decrease in PaCO2 (by –2.05±0.31 kPa, p<0.001) were obtained. Phase 3: Normocapnia during hyperventilation was achieved by an iterative increase in the CO2 fraction in the inspiratory gas by a CO2 admixture. All ventilatory parameters were unchanged. A significant increase in PaO2 (by 3.79±0.73 kPa, p<0.001), similar to that which was observed in phase 2, was preserved in phase 3 whereas normocapnia was fully re-established. The concept of high frequency normocapnic hyperventilation offers a lung protective strategy that significantly improves oxygenation whilst preserving normocapnia.