Reduced CO2-elimination during combined high-frequency ventilation compared to conventional pressure-controlled...

Combined high-frequency ventilation (CHFV) combines a conventional low-frequency component with super-imposed high-frequency jet pulses. The intention is to overcome the limited CO2-elimination of high-frequency ventilation, and to decrease airway pressures and enhance hemodynamic performance by reducing the conventional component. The present study was performed to compare the effects of conventional continuous positive-pressure ventilation (CPPV) on gas exchange, airway pressures and cardiac output to those of CHFV at matched minute volume (MV) and mean airway pressure (MPAW).

Sixteen anaesthetised piglets with lavage-induced surfactant deficiency were ventilated with CPPV, with positive end-expiratory pressure (PEEP) set to obliterate the lower inflection point of the inspiratory pressure-volume loop. This setting was compared to CHFV during which 50% of the total MV was applied as superimposed jet pulses of 20 Hz at otherwise unchanged settings, and to CPPV at a PEEP level which was reduced (CPPVred) until MPAW matched MPAW during CHFV. Gas exchange, airway pressures and hemodynamics were measured after the ventilatory setting had been applied for 20 min.

MPAW decreased from (median) 2.7 kPa with CPPV to 2.4 kPa with CHFV (P < or = 0.05). Peak inspiratory pressure was 3.6 kPa with CPPV, 3.2 kPa with CHFV, and 3.2 kPa with CPPVred (P < or = 0.05 for differences to CPPV), respectively. PaCO2 was comparable during CPPV (5.9 kPa), CPPVred and CHFVCO2, while it increased during CHFV (6.8 kPa, (P < or = 0.05)). Cardiac output did not differ significantly between the settings.

In the porcine lavage model, CO2-elimination is reduced during CHFV compared to CPPV at matched minute volume. At matched mean airway pressure, CHFV fails to reduce peak inspiratory airway pressure and to improve hemodynamic performance compared to CPPV.