Frequency, Tidal Volume, and Mean Airway Pressure Combinations that Provide Adequate Gas Exchange and Low Alveolar Pressure during High Frequency Oscillatory Ventilation in Rabbits

Abstract

ABSTRACT. We studied healthy and saline lavaged rabbits during high frequency oscillatory ventilation to determine what combination of frequency (0, tidal volume (V,), and mean airway pressure (Fa,) produced the lowest peakto-peak alveolar pressure amplitude (Pal,) 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 (P,,) was measured through a tracheal catheter and alveolar pressure amplitude was measured in a capsule glued to the right lower lobe. Paoz, Pacoz, P,,, and Pa,, were measured at the following settings: Fi02 = 0.5, frequency 2-28 Hz, V, 1-3 mL/kg (50 150% dead space) and Paw 5-15 cm H20. Many combinations of frequency and V, resulted in the same Pa02 and Paco2. Paw had a large effect on Pal, and minimal effect on blood gas tensions. In lavaged rabbits, the composite variable f X V : described the trends in Pa,, and blood gas tensions. As the product of f x V : increased, Paoz initially increased and then decreased, whereas Pacoz decreased and Pal,increased. No single combination of frequency, V, and Paw simultaneously provided the lowest Pal, and physiologic blood gas tensions. Adequate blood gas tensions and low Pa,, were o b t a i~d at frequencies less than 12 Hz, a V, of 2 mL/kg and a Pa, of 10 cm HzO. 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. Pa,, tended to be greater in lavaged rabbits. (Pediatr Res 27: 64-69,1990) Abbreviations f, frequency V,, tidal volume -Paw, mean airway pressure P,,, peak-to-peak tracheal pressure amplitude Selected effects off, V,, and paw on gas exchange and pressure amplitude have been studied previously in healthy and lung damaged animal models during HFOV. Oxygenation and ventilation have been shown to depend on frequency and V, (1, 2). Previous work indicating there is a relationship between C 0 2 elimination and the product of oscillatory frequency and Vt [VC02 = a(Qb(V,)" where a, b, c are constants] (3, 4) led us to evaluate the relationship of arterial blood gas tensions to the product f x V? (5). We observed that many combinations of frequency and V, produced equivalent blood gas tensions and that the composite variable f x V : was a good descriptor of our mean arterial blood gas tensions during HFOV in healthy rabbits. Others have found that different combinations of frequency, V, and Paw can produce equivalent blood gas tensions (3, 4) but the resultant pressure swings in the trachea and alveolus may not be equivalent. Near the resonant frequency of the respiratory system, pressure swings in the alveolus may exceed those at the airway opening during HFOV (8, 9). Allen et al. (10) reported that the ratio, Pa,,/P,,, increased as &, increased near the resonant frequency in excised rabbit lungs. Although increasing Paw has not been shown to improve gas exchange in healthy animals (1 1) it does improve oxygenat...

The effect of airway pressure and oscillation amplitude on ventilation in pre-term infants

“…Previous studies have shown that an increase in pressure amplitude increases the Vosc measured at the airway opening [6][7][8]. This study shows that this increase in Vosc can also be detected at the regional pulmonary level using EIT.…”

“…It has been suggested that ventilation and oxygenation during HFOV can be controlled independently by adjusting, respectively, the oscillation amplitude or frequency, and the continuous distending pressure (CDP) or the fraction of inspired oxygen (FI,O 2 ) [2][3][4][5][6]. An increase in oscillation amplitude at a fixed frequency will increase the oscillatory volume measured at the airway opening and improve carbon dioxide removal [7][8][9]. An increase in CDP at a fixed FI,O 2 will increase lung volume by alveolar recruitment in atelectatic lung diseases and improve oxygenation by reducing the intrapulmonary right-to-left shunt [5,10].…”

New Generation Neonatal High Frequency Ventilators: Effect of Oscillatory Frequency and Working Principles on Performance

“…There is no consensus about the ideal V T for HFOV, but studies in animals 17,18 and pre-term neonates 19 have shown that a V T of 2-3 mL/kg allows optimal gas exchange during HFOV. Although the use of these new generation neonatal ventilators is intended for the neonatal population unlike the 3100A (a ventilator that can be used with patients larger than neonates), some of them might not have sufficient power to deliver required V T for adequate gas exchange, especially when used in full-term infants at high oscillatory frequencies.…”

Dependence of Intrapulmonary Pressure Amplitudes on Respiratory Mechanics during High-Frequency Oscillatory Ventilation in Preterm Lambs

“…The experimental evidence supporting the generation of small ⌬P A during HFOV was obtained in healthy adult rabbits (1) and excised adult dog lungs (2). Only one study has obtained direct measurements of ⌬P A in both a normal and abnormal lung model (3). Although the primary focus of that study was to determine whether ventilation settings could be optimized during HFOV, Kamitsuka et al (3) made an incidental observation that higher alveolar pressure amplitudes were observed during HFOV in rabbits after saline lung lavage than in the nonlavage group.…”