Imposed Work of Breathing During High-Frequency Oscillatory Ventilation in Spontaneously Breathing Neonatal and Pediatric Models

BACKGROUND: High-frequency oscillatory ventilation (HFOV) is used in cases of neonatal and pediatric acute respiratory failure, sometimes even as the primary ventilatory mode. Allowing patients (at least neonates) on HFOV to breathe spontaneously soon after intubation has been shown to be feasible, and this is becoming a more generally used approach for infants and small children. However, such an approach may increase the imposed work of breathing (WOB), raising the question of whether the imposed WOB varies with the use of newer-generation HFOV devices, which operate according to different functional principles.

METHODS: A bench test was designed to compare the pressure-time product (PTP), a surrogate marker of the imposed WOB, produced with the use of 7 HFOV devices. Scenarios corresponding to various age groups (preterm newborn [1 kg], term newborn [3.5 kg], infant [10 kg], and child [25 kg]) and 2 respiratory system conditions (physiologic and pathologic) were tested.

RESULTS: The PTP varied between devices and increased with the oscillation frequency for all devices, independent of the respiratory system condition. Furthermore, the PTP increased with age and was higher for physiologic than for pathologic respiratory system conditions. We considered a change of ≥ 20% as being of clinically relevant; the effect of oscillation frequency was the most important parameter influencing imposed WOB during spontaneous breathing.

CONCLUSIONS: Variations in imposed WOB, as expressed by PTP values, during spontaneous breathing depend mainly on the oscillator frequency, respiratory system condition, and, though to a lesser extent, on the device itself.