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LetterCorrespondence

PEEP and Mechanical Ventilation: We Are Warned, We Cannot Ignore

Lorenzo Appendini, Antonio Esquinas, Nicola Launaro and Andrea Purro
Respiratory Care May 2016, 61 (5) 720-721; DOI: https://doi.org/10.4187/respcare.04795
Lorenzo Appendini
Respiratory Intensive Care Unit Presidio Ospedaliero di Saluzzo Saluzzo, Italy
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Antonio Esquinas
Intensive Care Unit Hospital Morales Mesenguer Murcia, Spain
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Nicola Launaro
Respiratory Intensive Care Unit Presidio Ospedaliero di Saluzzo Saluzzo, Italy
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Andrea Purro
Emergency and Critical Care Presidio Sanitario Gradenigo Torino, Italy
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To the Editor:

In an interesting study recently published in Respiratory Care, Natalini et al1 analyzed in 186 subjects receiving mechanical ventilation (settings chosen by the attending physician) several potential causes of dynamic hyperinflation and intrinsic PEEP (auto-PEEP). Both intrinsic and extrinsic2 auto-PEEP determinants as well as differences between low and high auto-PEEP cohorts (cutoff: 5 cm H2O) were assessed. The results showed that expiratory flow limitation, the ratio between the expiratory time and the time constant of the respiratory system (TE/τRS), the inspiratory resistance (RRS), and body mass index not only were independently associated with auto-PEEP levels but also represented the strongest risk factors associated with auto-PEEP >5 cm H2O. Surprisingly, TE did not. The authors concluded that the ventilator settings play a marginal role in auto-PEEP generation in the absence of subjects' predisposing factors. As a clinical consequence, the authors suggested that auto-PEEP can be effectively reduced by acting on patients' respiratory mechanics impairment, with little/no additional effect obtained by breathing pattern manipulation.

We are indebted to the authors for several reasons. First, they pointed out the key role played by expiratory flow limitation in generating dynamic hyperinflation and auto-PEEP. As a matter of fact, their data show that <50% of actual auto-PEEP was accounted for by elastic and resistive properties of the respiratory system alone (comparing actual with theoretical auto-PEEP [ie, 1/maximum CRS × trapped expiratory volume computed according to longest τRS]; data from Table 3). This reinforces the role of application of adequate CPAP levels to counterbalance auto-PEEP in the presence of expiratory flow limitation.3 Second, they stressed the importance of treating patients receiving mechanical ventilation with medical therapy. In our experience, too many physicians forget that mechanical ventilation has no therapeutic role in improving patients' respiratory mechanics impairment4; it only equilibrates the imbalance between respiratory muscle force-generating capacity and increased respiratory work load,4,5 providing time to recover from respiratory illness, facts that warrant concomitant bronchodilator use. Third, they suggest considering TE/τRS ratio instead of TE alone when setting the ventilator. In this line, we suggest that τRS should be directly measured4 to account also for expiratory flow limitation, when present. In our opinion, few physicians recognize the relevance of setting TE according to τRS. As a matter of fact, the breathing pattern was similar in both low and high auto-PEEP cohorts also in the present study.

This last fact is the cause of our major criticism of this worthy paper. The lack of relationship between auto-PEEP and TE forced the authors to conclude that “manipulation of the breathing pattern might only have a negligible effect on the overall auto-PEEP value.” However, this result depended mainly on the quite constant TE imposed by the attending physicians in the face of a wide range of auto-PEEP levels.1 To test auto-PEEP response to changing TE, ad hoc protocols are necessary (eg, different TE values tested in the same patient). Thus, the claim that breathing pattern manipulation has negligible effects on auto-PEEP sounds wrong and misleading and conflicts with the authors' seminal observation that TE should be chosen according to τRS.

In conclusion, also thanks to Natalini et al,1 enough knowledge is currently available to identify patients prone to develop significant auto-PEEP during mechanical ventilation, to treat its intrinsic causes (pharmacologically), and to prevent/attenuate its onset by manipulating the ventilator settings. We are warned, we cannot ignore…

Footnotes

  • The authors have disclosed no conflicts of interest.

  • Copyright © 2016 by Daedalus Enterprises

References

  1. 1.↵
    1. Natalini G,
    2. Tuzzo D,
    3. Rosano A,
    4. Testa M,
    5. Grazioli M,
    6. Pennestrì V,
    7. et al
    . Assessment of factors related to auto-PEEP. Respir Care 2016;61(2):134–141.
    OpenUrlAbstract/FREE Full Text
  2. 2.↵
    1. Rossi A,
    2. Polese G,
    3. Brandi G,
    4. Conti G
    . Intrinsic positive end-expiratory pressure (PEEPi). Intensive Care Med 1995;21(6):522–536.
    OpenUrlCrossRefPubMed
  3. 3.↵
    1. Appendini L,
    2. Patessio A,
    3. Zanaboni S,
    4. Carone M,
    5. Gukov B,
    6. Donner CF,
    7. Rossi A
    . Physiologic effects of positive end-expiratory pressure and mask pressure support during exacerbations of COPD. Am J Respir Crit Care Med 1994;149(5):1069–1076.
    OpenUrlCrossRefPubMed
  4. 4.↵
    1. Appendini L,
    2. Purro A,
    3. Patessio A,
    4. Zanaboni S,
    5. Carone M,
    6. Spada E,
    7. et al
    . Partitioning of inspiratory muscle workload and pressure assistance in ventilator-dependent COPD patients. Am J Respir Crit Care Med 1996;154(5):1301–1309.
    OpenUrlPubMed
  5. 5.↵
    1. Goldstone J,
    2. Moxham J
    . Weaning from mechanical ventilation. Thorax 1991;46(1):56–62.
    OpenUrlFREE Full Text
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Respiratory Care: 61 (5)
Respiratory Care
Vol. 61, Issue 5
1 May 2016
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PEEP and Mechanical Ventilation: We Are Warned, We Cannot Ignore
Lorenzo Appendini, Antonio Esquinas, Nicola Launaro, Andrea Purro
Respiratory Care May 2016, 61 (5) 720-721; DOI: 10.4187/respcare.04795

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PEEP and Mechanical Ventilation: We Are Warned, We Cannot Ignore
Lorenzo Appendini, Antonio Esquinas, Nicola Launaro, Andrea Purro
Respiratory Care May 2016, 61 (5) 720-721; DOI: 10.4187/respcare.04795
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