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LET T ER Open Access

Altering the mechanical scenario to decrease the driving pressure

João Batista Borges 1* , Göran Hedenstierna 2 , Anders Larsson 1 and Fernando Suarez-Sipmann 1

Abstract

Ventilator settings resulting in decreased driving pressure ( ΔP) are positively associated with survival.

How to further foster the potential beneficial mediator effect of a reduced ΔP? One possibility is promoting the active modification of the lung ’s “mechanical scenario ” by means of lung recruitment and positive end-expiratory pressure selection. By taking into account the individual distribution of the threshold- opening airway pressures to achieve maximal recruitment, a redistribution of the tidal volume from overdistended to newly recruited lung occurs. The resulting more homogeneous distribution of transpulmonary pressures may induce a relief of overdistension in the upper regions. The gain in lung compliance after a successful recruitment rescales the size of the functional lung, potentially allowing for a further reduction in ΔP.

Amato et al. [1] showed that ventilator settings resulting in decreased driving pressure (ΔP) were positively asso- ciated with survival. One may reason that ΔP scales the tidal volume in relation to the aerated lung size and the mechanical scenario created by the positive end- expiratory pressure (PEEP) being used, implying that a lung-protective ventilatory strategy may be adapted to the size of the aerated lung. The same was con- cluded based on the association of tidal hyperinflation with higher concentrations of inflammatory mediators and a lower number of ventilator-free days in acute respiratory distress syndrome patients who had larger amounts of collapse despite tidal volume and pressure

* Correspondence: joao.batista_borges@surgsci.uu.se

1

Hedenstierna Laboratory, Department of Surgical Sciences, Section of Anaesthesiology & Critical Care, Uppsala University, Hospital, 75185 Uppsala, Sweden

Full list of author information is available at the end of the article

limitations [2]. Experimental data emphasize the import- ance of unloading the small-aerated lung [3], which re- ceives most of ventilation, because strain hotspots concentrate as much as four times more in alveolar walls of aerated units that are overstretched.

How to further foster the potential beneficial mediator effect of a reduced ΔP? We think that an attractive alter- native possibility could consist of promoting the active modification of the lung’s “mechanical scenario” by means of lung recruitment and careful PEEP selection (Fig. 1). By stepwise challenging the lung, taking into account the in- dividual distribution of the threshold-opening airway pres- sures to achieve maximal recruitment, a redistribution of the tidal volume from overdistended to newly recruited lung occurs. The resulting more homogeneous distribu- tion of transpulmonary pressures through interdepend- ence properties may induce a relief of overdistension in the upper regions [4]. In addition, the gain in lung compli- ance after a successful recruitment rescales the size of the functional lung, potentially allowing for a further reduc- tion in ΔP without decreasing ventilation.

Lung recruitment is a complex process whose effects depend on the amount of recruitment achieved and the level of PEEP necessary to stabilize the lung. A recurrent concern regarding recruitment maneuvers is overdisten- sion. We stress the counterintuitive and opposite effects of partial/nonindividualized versus maximum/titrated re- cruitment strategies [4]. A partial recruitment may ex- acerbate local stretches because the persistence of lung collapse maintains the heterogeneous distribution of ventilation [2]. Any recruitment strategy should there- fore aim at the individual maximal possible recruitment to obtain its highest benefit.

Under the “newly created” circumstances of a fully re- cruited lung, it is essential to determine and maintain an end-expiratory pressure level above the closing pressure of the newly recruited lung and use the minimum possible ΔP. This not only sustains the improved mechanical sce- nario of a resized more homogeneous lung, but also atten- uates the derecruitment-associated lung injury [4].

© 2015 Borges et al. Open Access This 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.

Borges et al. Critical Care (2015) 19:342

DOI 10.1186/s13054-015-1063-x

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Abbreviations

PEEP: Positive end-expiratory pressure; ΔP: Driving pressure.

Competing interests

The authors declare that they have no competing interests.

Authors ’ contributions

JBB drafted the manuscript. GH, AL, and FS-S edited and helped to draft the manuscript. All authors read and approved the final manuscript.

Author details

1

Hedenstierna Laboratory, Department of Surgical Sciences, Section of Anaesthesiology & Critical Care, Uppsala University, Hospital, 75185 Uppsala, Sweden.

2

Hedenstierna Laboratory, Department of Medical Sciences, Clinical Physiology, Uppsala University, Hospital, 75185 Uppsala, Sweden.

References

1. Amato MBP, Meade MO, Slutsky AS, Brochard L, Costa ELV, Schoenfeld DA, et al. Driving pressure and survival in the acute respiratory distress syndrome. N Engl J Med. 2015;372:747 –55.

2. Terragni PP, Rosboch G, Tealdi A, Corno E, Menaldo E, Davini O, et al. Tidal hyperinflation during low tidal volume ventilation in acute respiratory distress syndrome. Am J Respir Crit Care Med. 2007;175:160 –6.

3. Borges JB, Costa ELV, Suarez-Sipmann F, Widström C, Larsson A, Amato M, et al. Early inflammation mainly affects normally and poorly aerated lung in experimental ventilator-induced lung injury. Crit Care Med. 2014;42:e279 –87.

4. Borges JB, Okamoto VN, Matos GFJ, Caramez MPR, Arantes PR, Barros F, et al. Reversibility of lung collapse and hypoxemia in early acute respiratory distress syndrome. Am J Respir Crit Care Med. 2006;174:268 –78.

Fig. 1 Representative data for a patient with early pulmonary acute respiratory distress syndrome (pneumonia) submitted to incremental positive end-expiratory pressure (PEEP) levels followed by an individualized recruitment maneuver (RM) and a subsequent decremental PEEP titration. The same PEEP levels were applied during the incremental and decremental phases. The patient was ventilated in a volume-controlled mode with a tidal volume of 6 ml/kg (predicted body weight). During the incremental phase, dynamic compliance (Cdyn) responded with an initial increase until PEEP 14 cmH

2

O and then remained constant with further incremental steps without any effects on oxygenation. This indicated a lack of any relevant recruitment effect during the incremental steps, which resulted in a constant driving pressure (Driving P). A new mechanical scenario was achieved after lung recruitment, confirmed by the increase in compliance and oxygenation already at the first decremental PEEP steps. As a consequence, ΔP decreased (lower panel, shaded area) despite ventilation at a similar tidal volume. The decreased ΔP was maintained until the beginning of lung collapse during the decremental PEEP steps, evidenced by the fall in oxygenation and compliance. This example illustrates how the modulatory effects of ΔP can be optimized when the mechanical scenario is modified while minimizing lung collapse by recruitment and PEEP titration. Appropriate ethics approval was obtained, as well as appropriate consents to publish from the participant (or legal parent or guardian for children) to report individual patient data. PaO

2

arterial partial pressure of oxygen, Pplat plateau pressure

Borges et al. Critical Care (2015) 19:342 Page 2 of 2

References

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