High Frequency Percussive Ventilation in Viral Bronchiolitis: Do We Need a Standardized Approach to HFPV Management?

High-frequency percussive ventilation (HFPV) is a pneumatically powered, time-cycled pressure mode of ventilation. HFPV is considered an advanced mode of ventilation delivered by the Volumetric Diffusive Respirator (VDR-4, Percussionaire, Sandpoint, Idaho), which combines the principles of high-frequency ventilation with those of conventional mechanical ventilation. The VDR-4 uses a Phasitron to deliver percussive breaths to propel secretions to the mainstem airways. HFPV has shown success in treating adults and neonatal and pediatric patients with ventilation and oxygenation failure.^1–4

The study in this issue of Respiratory Care by White et al⁵ adds to the HFPV literature by evaluating how HFPV affects gas exchange in subjects with acute bronchiolitis and who are intubated. More specifically, these investigators hypothesized that HFPV would improve both oxygenation and ventilation without negative hemodynamic effects or complications. In this single-center, prospective study, they transitioned 35 subjects with the primary diagnosis of bronchiolitis to HFPV.⁵ The subjects were placed on HFPV for 1 of 4 indications: (1) ventilation failure (n = 21), (2) mixed oxygenation and ventilation failure (n = 5), (3) secretion management (n = 5), and (4) oxygenation failure (n = 4).⁵ The management of HFPV, sedation, and supportive treatments were left up to the discretion of the clinicians. The primary outcome measure was the improvement in CO₂ at lower peak inflating pressures. The improvement in gas exchange was not accompanied by an increase in barotrauma and/or vasopressor use. As demonstrated in previous studies, HFPV was associated with significant improvement in ventilation, but evidence of improved oxygenation was mixed despite an increase in mean airway pressure within the first 4 h of initiation.^3,6–8

We commend the authors for designing and implementing a prospective HFPV study, an area of the literature that is scant at best. Where the investigators fall short is not with the use of HFPV but with the varied approach to the management described. Despite including an unvalidated guide to suggested HFPV settings in the study's Supplemental Figure 1, both conventional mechanical ventilation and ventilator escalation to HFPV were subject to the clinician's discretion. As a single-center study with a small sample size, a comparison with a control group would have been ideal in determining if HFPV made a difference in outcomes. Ninety-four percent of the subjects enrolled in the study were given a neuromuscular blockade, but it remains unclear if the subjects were given neuromuscular blockade before pre–HFPV data collection; neglecting to differentiate this could skew the results. With bronchiolitis being the primary diagnosis of the subjects enrolled in the study, it is interesting that only 5 subjects were enrolled for secretion management, given the potential therapeutic benefit of HFPV in populations with a high secretion burden.^6,9,10

Thus, it overall remains unclear from this study if using HFPV for bronchiolitis truly made a clinical impact. Notably, HFPV was discontinued in 11% of subjects due to failure to have improved ventilation, oxygenation, or secretion burden. It is unclear why these subjects did not show clinical improvement, but one wonders if there would have been a more marked improvement in ventilation, and possibly with oxygenation, if settings were tailored more to the subjects' needs. The mean percussive rate and mean convective rate were 500 and 20 breaths/min, respectively, and optimization of either parameter could plausibly improve a given subject's gas exchange. Limiting the maximum peak inspiratory pressure to 30 cm H₂O and starting at a peak inspiratory pressure 2–4 cm H₂O lower than conventional settings could also contribute to the 11% failure rate and 12% of subjects progressing to extracorporeal membrane oxygenation.

There is little evidence that supports cuff deflation for patients with oxygenation failure. Deflation of the cuff, allowing for audible leak, could lead to unintended consequences because position changes might adversely affect the leak, either causing the peak pressures to increase to dangerous levels or by providing inadequate distending pressures. A cuff leak with patients on HFPV should only be needed to quickly remove secretions or to allow for more CO₂ clearance in the event that manipulations of the VDR-4 have proven unsuccessful, with close attention paid to what that maneuver does to the resulting other pressures. Despite optimization of settings, the lack of improvement in oxygenation failure with this study may be due to the cuff deflation.¹¹

This study offers useful experience with regard to the use of HFPV on a common diagnosis in the neonatal and pediatric population. However, we will never grow as a field in using this device if we do not share a common approach to management when using HFPV. In the future, we would like to see more discussion about the operation of the VDR-4. Data on which Phasitron configuration (traditional Phasitron at the airway vs a distal Phasitron, also known as the TurboHub) would be essential. Differences in the properties of the traditional versus the TurboHub circuits may have an influence on maintaining target tidal volume delivery as well as humidification and would be important to call out in HFPV research.

It is also important for investigators to share best practices on the use of HFPV: how settings are selected, titration of settings, and when transition back to conventional ventilation occurs. Also, future studies should focus on establishing the premise for large multi-center prospective randomized controlled trials that evaluate the utility of HFPV in neonatal and pediatrics. To that end, it becomes important to identify how HFPV is currently practiced; for which indications; with what range of settings considered typical; and what criteria for initiation, weaning, transition, and failure are deemed acceptable for the community.

This present study confirms that practitioners seem to consider HFPV during times of hypercarbia, obstructive physiology, and high secretion burden. More detailed assessment of how and why HFPV is used will prove informative for designing a useful efficacy trial.

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