The effect of combined high frequency ventilation with and without continuous positive airway pressure in...

Combined high frequency ventilation (CHFV) with 8 mmHg (1.0 kPa) continuous positive airway pressure (CPAP) and without CPAP (CHFV0) were compared to each other, and to continuous positive pressure ventilation (CPPV) with 8 mmHg (1.0 kPa) CPAP in pigs with oleic acid induced lung injury. The respiratory rate was 15 min-1 and the high frequency (HF) rate 360 min-1. Arterial carbon dioxide tension (PaCO2) was adjusted to 5 kPa and 25% oxygen was used. After CHFV, CPAP was briefly discontinued to allow the establishment of CHFV0 in order to examine the cardiovascular and pulmonary effects of combined high frequency ventilation alone. Mean arterial oxygen tension (PaO2) was 15.8 +/- 3.9 kPa during CPPV, 15.5 + 3.2 kPa during CHFV and 13.2 +/- 5.1 kPa during CHFV0 (ns). The peak airway pressure and the pericardiac pressure were lowest during CHFV0. CHFV provoked significant cardiovascular depression (mean arterial pressure, stroke index, left and right ventricle stroke work index). When compared to CPPV, a non-significant trend towards improved cardiovascular function was found during CHFV0. With similar mean airway pressures (during CHFV0) or the same CPAP (during CHFV) as during CPPV, no further improvement in oxygenation due to HF waves was found. Airway pressure was the major factor causing alterations in cardiovascular function, not the ventilation technique.