Frequency dependence of lung volume changes during superimposed high-frequency jet ventilation and high-frequency jet ventilation

Background. Superimposed high-frequency jet ventilation (SHFJV) has proved to be safe and effective in clinical practice. However, it is unclear which frequency range optimizes ventilation and gas exchange. The aim of this study was to systematically compare high-frequency jet ventilation (HFJV) with HFJV by assessing chest wall volume variations (Delta EEVCW) and gas exchange in relation to variable high frequency. Methods. SHFJV or HFJV were used alternatively to ventilate the lungs of 10 anaesthetized pigs (21-25 kg). The low-frequency component was kept at 16 min(-1) in SHFJV. In both modes, high frequencies ranging from 100 to 1000 min(-1) were applied in random order and ventilation was maintained for 5 min in all modalities. Chest wall volume variations were obtained using opto-electronic plethysmography. Airway pressures and arterial blood gases were measured repeatedly. Results. SHFJV increased Delta EEVCW compared with HFJV; the difference ranged from 43 to 68 ml. Tidal volume (V-T) was always >240 ml during SHFJV whereas during HFJV ranged from 92 ml at the ventilation frequency of 100 min(-1) to negligible values at frequencies >300 min(-1). We observed similar patterns for Pa-O2 and Pa-CO2. SHFJV provided generally higher, frequency-independent oxygenation (Pa-O2 at least 32.0 kPa) and CO2 removal (Pa-CO2 similar to 5.5 kPa), whereas HFJV led to hypoxia and hypercarbia at higher rates (Pa-O2 < 10 kPa and Pa-CO2 > 10 kPa at f(HF) > 300 min(-1)). Conclusions. In a porcine model, SHFJV was more effective in increasing end-expiratory volume than single-frequency HFJV, but both modes may provide adequate ventilation in the absence of airway obstruction and respiratory disease, except for HFJV at frequencies >= 300 min(-1).