FREQUENCY, TIDAL VOLUME, AND MEAN AIRWAY PRESSURE COMBINATIONS THAT PROVIDE ADEQUATE GAS-EXCHANGE AND LOW ALVEOLAR PRESSURE DURING HIGH-FREQUENCY OSCILLATORY VENTILATION IN RABBITS

We studied healthy and saline lavaged rabbits during high frequency oscillatory ventilation to determine what combination of frequency (f), tidal volume (Vt), and mean airway pressure (Paw) produced the lowest peak-to-peak alveolar pressure amplitude (Paiv) and physiologic blood gas tensions. Sinusoidal volume changes were delivered through a tracheostomy by a piston pump driven by a linear motor. Tracheal pressure amplitude (Ptr) was measured through a tracheal catheter and alveolar pressure amplitude was measured in a capsule glued to the right lower lobe. Pao2, Paco2, Ptr, and Pai» were measured at the following settings: Fi02 = 0.5, frequency 2-28 Hz, Vt 1-3 mL/kg (50 150% dead space) and Pa„ 5-15 cm H20. Many combinations of frequency and V, resulted in the same Pa02 and PaC02. Paw had a large effect on Paiv and minimal effect on blood gas tensions. In lavaged rabbits, the composite variable f X V,2 described the trends in Pa)v and blood gas tensions. As the product of f x V,2 increased, Pao2 initially increased and then decreased, whereas Paco2 decreased and Paiv increased. No single combination of frequency, Vt and Paw simultaneously provided the lowest Paiv and physiologic blood gas tensions. Adequate blood gas tensions and low Paiv were obtained at frequencies less than 12 Hz, a V, of 2 mL/kg and a Palv of 10 cm H20. In healthy and lavaged rabbits Pao2 increased and Paco2 decreased as frequency increased at lower V, Pao2 decreased as frequency increased at higher V, in lavaged rabbits only. P, iv tended to be greater in lavaged rabbits. © 1990 International Pediatric Research Foundation, Inc.