A narrative review of advanced ventilator modes in the pediatric intensive care unit

Abstract

Respiratory failure is a common reason for pediatric intensive care unit admission. The vast majority of children requiring mechanical ventilation can be supported with conventional mechanical ventilation (CMV) but certain cases with refractory hypoxemia or hypercapnia may require more advanced modes of ventilation. This paper discusses what we have learned about the use of advanced ventilator modes [e.g., high-frequency oscillatory ventilation (HFOV), high-frequency percussive ventilation (HFPV), high-frequency jet ventilation (HFJV) airway pressure release ventilation (APRV), and neurally adjusted ventilatory assist (NAVA)] from clinical, animal, and bench studies. The evidence supporting advanced ventilator modes is weak and consists of largely of single center case series, although a few RCTs have been performed. Animal and bench models illustrate the complexities of different modes and the challenges of applying these clinically. Some modes are proprietary to certain ventilators, are expensive, or may only be available at well-resourced centers. Future efforts should include large, multicenter observational, interventional, or adaptive design trials of different rescue modes (e.g., PROSpect trial), evaluate their use during ECMO, and should incorporate assessments through volumetric capnography, electric impedance tomography, and transpulmonary pressure measurements, along with precise reporting of ventilator parameters and physiologic variables.

The Physiological Basis of High-Frequency Oscillatory Ventilation and Current Evidence in Adults and Children: A Narrative Review

“…Although lung protective ventilation can certainly be achieved through carefully conducted conventional mechanical ventilation (CMV), the lower V T , lower alveolar pressure swings, and higher mean airway pressure (mPaw) generally employed during various forms of high frequency ventilation make these modalities theoretically well suited for lung protection ( Figure 2 ). There are four types of high frequency ventilation in clinical use: HFOV, high frequency jet ventilation, high-frequency percussive ventilation, and high frequency flow interruption ( Keszler et al, 2015 ; Miller A. G. et al, 2021 ). This review will focus on the physiologic rationale for the use of HFOV in patients with acute respiratory failure, summarize data from relevant bench and animal models, and discuss the potential use of HFOV as a primary and rescue mode in adults and children with severe respiratory failure.…”

“…HFOV is a form of MV that uses a constant distending pressure, usually reported as the mPaw, coupled with sinusoidal or square flow oscillations at supra-physiologic respiratory frequencies ( Rettig et al, 2015 ; Miller A. G. et al, 2021 ). Respiratory frequencies used in clinical practice range from 5 to 15 Hz (i.e., 300 to 900 breaths per minute) with a small delivered V T , generally around 1–3 ml/kg, or lower than the anatomic dead space ( Rettig et al, 2015 ; Miller A. G. et al, 2021 ). The constant distending pressure allows for alveolar recruitment while avoiding repetitive opening and closing of alveoli (atelectrauma), and has been shown to improve oxygenation ( Rettig et al, 2015 ; Meyers et al, 2019 ).…”

“…HFOV differs from CMV and high frequency jet ventilation in that both inspiration and expiration are active ( Miller A. G. et al, 2021 ; Miller A. G. et al, 2021 ). Oxygenation and ventilation are fairly independent during HFOV with oxygenation being controlled by FiO 2 and mPaw while ventilation is controlled by V T (amplitude) and frequency (f) ( Kneyber et al, 2012 ; Miller A. G. et al, 2021 ).…”

“…HFOV differs from CMV and high frequency jet ventilation in that both inspiration and expiration are active ( Miller A. G. et al, 2021 ; Miller A. G. et al, 2021 ). Oxygenation and ventilation are fairly independent during HFOV with oxygenation being controlled by FiO 2 and mPaw while ventilation is controlled by V T (amplitude) and frequency (f) ( Kneyber et al, 2012 ; Miller A. G. et al, 2021 ). Various mechanisms contribute to gas exchange during HFOV; these include gas flow turbulence in large airways, bulk convection, turbulent flow with radial mixing, pendelluft, asymmetric inspiratory and expiratory velocity profiles, Taylor dispersion, collateral ventilation, and cardiogenic mixing ( Slutsky and Drazen, 2002 ; Pillow, 2005 ) ( Figure 3 ).…”

“…V T is inversely proportional to frequency and directly proportional to amplitude ( Sedeek et al, 2003 ; Miller A. G. et al, 2021 ). Therefore, the higher the frequency, the lower the V T ; the higher the amplitude, the higher the V T ( Sedeek et al, 2003 ; Miller A. G. et al, 2021 ). Similarly, a higher inspiratory time percentage results in increased ventilation due to higher V T ( Miller A. G. et al, 2021 ).…”