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Critical Care

, 23:178 | Cite as

Are we really preventing lung collapse with APRV?

  • Ryota SatoEmail author
  • Natsumi Hamahata
  • Ehab G. Daoud
Open Access
Letter
  • 464 Downloads

Keywords

Airway pressure release ventilation APRV Trans-pulmonary pressure Esophageal balloon 

Abbreviations

APRV

Airway pressure release ventilation

Auto-PEEP

Intrinsic PEEP

PEEP

Positive end-expiratory pressure

PEF

Peak expiratory flow

PHigh

The value of the high pressure (inspiratory pressure)

PLow

The value of the low pressure (release pressure)

PTP

Trans-pulmonary pressure

THigh

Time spent at high-pressure phase

TLow

Time spent at low-pressure phase

Letter to the editor

APRV is an inverse ratio, pressure-controlled, intermittent mandatory ventilation without the restriction of spontaneous breathing, and it is based on the principle of the open-lung approach [1]. A recent meta-analysis reported beneficial effects of APRV on ventilator-free days and in-hospital mortality in acute hypoxic respiratory failure; however, the quality of evidence was low [2]. Therefore, it has been still controversial whether APRV is truly beneficial or not.

The main settings of APRV include PHigh, PLow, THigh, and TLow. There are numerous suggested ways for setting TLow to prevent alveolar collapse, e.g., setting TLow to create auto-PEEP empirically in a range of 0.2–0.8 s or to achieve 50–75% of peak expiratory flow or according to a certain time constant, and for a certain volume per release [1]. However, it has been unclear whether APRV truly stabilizes the alveoli and reduces lung stress and strain [3] since it is uncertain how much auto-PEEP we are creating and whether it is enough to prevent alveolar collapse especially in the setting of elevated alveolar elastance.

The measurement of trans-pulmonary pressure (PTP) using an esophageal balloon is a physiological way to detect and prevent lung stress and strain. Using that strategy has shown improved oxygenation and compliance, and trend towards improved mortality [4].

Recently, we reported that PTP in patients undergoing APRV was in the negative values (< 0 cmH2O) at all levels (0.1 to 0.8 s) of TLow suggesting the alveolar collapse but was actually positive after the application of an end-expiratory occlusion maneuver to measure total and auto-PEEP (the gold standard for measuring total PEEP) [5]. This case report demonstrates a new method to adjust TLow, also highlights the need to quantify the actual total PEEP at the end of TLow, and enforces the beneficial knowledge gained by esophageal balloon in APRV. The expiratory flow decay and the resultant auto-PEEP during APRV are variable among different ventilator manufacturer [1], and using a time constant may not be reliable as well. Recently, it was suggested that the use of tracheal pressure at the end of TLow as the amount of auto-PEEP might not be accurate either [3].

In conclusion, without the knowledge of end release trans-pulmonary pressure, we are driving blind not knowing how often we are causing alveolar collapse with APRV. Therefore, there is an emergent need for more research about its settings given its rising popularity.

Notes

Acknowledgements

Not applicable

Funding

None

Availability of data and materials

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Authors’ contributions

RS and ED were responsible for the conception of the letter. All authors drafted the manuscript. All authors read and approved the final manuscript.

Authors’ information

RS and NH are internal medicine residents in the USA. ED is a board-certified intensivist in the USA.

Ethics approval and consent to participate

Not applicable

Consent for publication

Not applicable

Competing interests

The authors declare that they have no competing interests.

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Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

References

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Copyright information

© The Author(s). 2019

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

Authors and Affiliations

  1. 1.Department of Internal Medicine, John A. Burns School of MedicineUniversity of Hawaii at ManoaHonoluluUSA
  2. 2.Respiratory Care ProgramKapiolani Community CollegeHonoluluUSA
  3. 3.Critical Care DepartmentKuakini Medical CenterHonoluluUSA

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