Skip to main content

Elastance-derived transpulmonary pressure may overestimate the risk of overdistension in severely obese patients

Dear editor,

During acute respiratory distress syndrome (ARDS), estimation of transpulmonary pressure (PL) using esophageal pressure has been proposed to customize the positive end-expiratory pressure (PEEP) in order to avoid alveolar collapse (i.e., positive end-expiratory PL [PL, exp]) while limiting the stress applied to the lung (i.e., limit end-inspiratory PL below 20–25 cmH2O) [1]. Regarding the latter, the calculation of end-inspiratory PL based on the elastance ratio method (PL,end-insp,ER) is usually preferred because it has been shown to better approximate the PL of the non-dependent areas than the direct method (PL,end-insp,direct) [2]. However, the elastance ratio method relies on the assumption that PL is zero at atmospheric pressure, which may be inappropriate in some patients. We herein report such an illustrative case.

A 30-year-old obese woman (BMI 52.5 kg.m−2) with past medical history of HIV infection was admitted to the Intensive Care Unit for a moderate ARDS related to undocumented community-acquired pneumonia. After intubation, tidal volume was set at 6.6 mL/kg of predicted bodyweight and respiratory rate at 34 cycles/min. With a PEEP of 6 cmH2O, the plateau pressure (PPLAT) was measured at 30 cmH2O. However, an airway opening pressure (AOP) of 16 cmH2O [3] was retrieved during low-flow insufflation. Chest CT-scan showed bilateral alveolar consolidations. To customize ventilator’s settings, an esophageal catheter was inserted and electrical impedance tomography (EIT, Enlight 1800, TIMPEL, São Paulo, Brazil) was recorded during decremental PEEP titration from 30 to 6 cmH2O, in steps of 2 cmH2O, with constant tidal volume and flow rate. Esophageal balloon (Nutrivent, Sidam, Italy) was filled with 4 mL of air. Proper position and filling were verified by chest radiograph, the presence of cardiac artifacts on PES recording, and a ΔPESPAW ratio induced by gentle chest compressions during end-expiratory occlusion at PEEP 18 cmH2O at 0.99 [1]. At each step, the following parameters were collected or calculated according to standard formulas: PPLAT (measured after 0.5 s end-inspiratory occlusion), total PEEP (PEEPTOT, measured after 2 s end-expiratory hold), lung driving pressure (ΔPL, computed as PL,end-insp,directPL,exp) and respiratory system driving pressure (ΔPRS, defined as PPLAT – end-expiratory alveolar pressure, where end-expiratory alveolar pressure was either PEEPTOT or AOP, whichever was greater), lung compliance (CL) and CRS, PL, exp (defined as end-expiratory alveolar pressure—Pes,exp, where end-expiratory alveolar pressure was either PEEPTOT or AOP, whichever was greater), PL,end-insp,direct, PL,end-insp,ER, stress index, and the percentage of collapse and overdistension estimated by EIT.

During the decremental PEEP titration, PPLAT, PL, exp, PL, end-insp, direct, PL, end-insp, ER, and the percentage of overdistension decreased, while the percentage of collapse increased. Consequently, both ΔPRS and ΔPL adopted a U-shaped pattern, with a nadir corresponding to a PEEP of 24 cmH2O. No significant hemodynamic changes were observed.

The PL, exp measurement and EIT assessment of the percentage of collapse resulted in a congruent estimate of the minimum PEEP required to minimize derecruitment: the lowest PEEP associated with positive PL, exp corresponded to the lowest PEEP associated with a percentage of collapse < 1% (Fig. 1).

Fig. 1
figure 1

Results of the PEEP titration. A collapse indices. Left Y axis, green curve: collapse determined by EIT. Right Y axis, blue curve: end-expiratory transpulmonary pressure. Blue-dashed horizontal line indicates 0 cmH2O. B Overdistension indices. Left Y axis, orange curve: overdistension determined by EIT. Left Y axis, red curve: transpulmonary driving pressure (ΔPL). Right Y axis, blue curve: end-inspiratory, elastance derived transpulmonary pressure (PL, end-insp, ER); Right Y axis, green curve: plateau pressure (PPLAT). Blue horizontal-dashed line indicates 25 cmH2O. On each graph, green vertical-dashed line indicates airway opening pressure; blue vertical-dashed line indicates the highest set PEEP with elastance derived transpulmonary pressure < 25 cmH2O; grey vertical-dashed line indicates set PEEP with lowest transpulmonary driving pressure; red vertical-dashed line indicates the lowest level of set PEEP associated with positive end-expiratory transpulmonary pressure, and the lowest level of set PEEP associated with minimal collapse by EIT (defined as collapse < 1%)

In contrast, PL, end-insp, ER appeared to overestimate the risk of overdistension, according to EIT assessment: PL, end-insp, ER reached the upper limit of 20–25 cmH2O for a PEEP of 6–18 cmH2O, respectively. However, between 18 and 24 cmH2O, we found no other marker of overdistension: ΔPRS and ΔPL decreased continuously, the stress index remained below 1, and overdistension measured by EIT was kept negligible (Fig. 1). Conversely, PL, end-insp, direct appeared to underestimate the risk of overdistension. In fact, as ΔPL increased between PEEP 24 and 30 cmH2O and EIT revealed significant overdistension at PEEP 30 cmH2O (17%), PL, end-insp, direct increased from eight to 14 cmH2O between these two levels of PEEP, suggesting a safe range.

Based on this overall assessment, the PEEP was adjusted to 24 cmH2O to mitigate the risk of both collapse and overdistension. Two prone sessions were performed and the patient was weaned from mechanical ventilation on day-16.

We herein report a case illustrating that estimating end-inspiratory PL using esophageal pressure may significantly misjudge the risk of overdistension in obese patients. Two non-mutually exclusive explanations could account for the discrepancy between PL, end-insp, ER and overdistension estimated by EIT in this patient. Firstly, since EIT estimates distension and collapse from the relative change in pixel-level compliance calculated from pixel intratidal variation of impedance and driving pressure, the percentage of overdistension can be altered when the PEEP is set below AOP. In the current case, overdistension estimated by EIT started several levels of PEEP above AOP, lending support to the second explanation, which is that obesity is associated with significantly higher end-expiratory pleural pressure [4], a situation where the conditions for PL, end-insp, ER interpretation are no longer met [5]. In that case, EIT assessment may help adjusting PEEP to limit both derecruitment and overdistension. Further studies are needed to determine the consistency of such an observation.

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.



Acute respiratory distress syndrome


Electrical impedance tomography


Positive end-expiratory pressure


  1. Mauri T, Yoshida T, Bellani G, Goligher EC, Carteaux G, Rittayamai N, et al. Esophageal and transpulmonary pressure in the clinical setting: meaning, usefulness and perspectives. Intensive Care Med. 2016;42(9):1360–73.

    Article  PubMed  Google Scholar 

  2. Yoshida T, Amato MBP, Grieco DL, Chen L, Lima CAS, Roldan R, et al. Esophageal manometry and regional transpulmonary pressure in lung injury. Am J Respir Crit Care Med. 2018;197(8):1018–26.

    Article  PubMed  Google Scholar 

  3. Chen L, Del Sorbo L, Grieco DL, Junhasavasdikul D, Rittayamai N, Soliman I, et al. Potential for lung recruitment estimated by the recruitment-to-inflation ratio in acute respiratory distress syndrome. A clinical trial. Am J Respir Crit Care Med. 2020;201(2):178–87.

    Article  PubMed  Google Scholar 

  4. Behazin N, Jones SB, Cohen RI, Loring SH. Respiratory restriction and elevated pleural and esophageal pressures in morbid obesity. J Appl Physiol. 2009;108(1):212–8.

    Article  PubMed  PubMed Central  Google Scholar 

  5. Grieco DL, Chen L, Brochard L. Transpulmonary pressure: importance and limits. Ann Transl Med. 2017;5(14):285–285.

    Article  PubMed  PubMed Central  Google Scholar 

Download references



Author information

Authors and Affiliations



ST was involved in study design, data collection, analysis, and interpretation, and script writing. EM was involved in data collection, analysis, and interpretation. MAB was involved in data analysis and interpretation. AFH was involved in data analysis and interpretation. AMD was involved in data analysis and interpretation, and script writing. GC was involved data analysis and interpretation, and script writing. All authors read and approved the final manuscript.

Corresponding author

Correspondence to Samuel Tuffet.

Ethics declarations

Ethics approval and consent to participate

The data presented here were collected in the setting of usual care.

Consent for publication

Consent for publication has been obtained from the patient.

Competing interests

The authors declare that they have no competing interests.

Additional information

Publisher's Note

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

Rights and permissions

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit The Creative Commons Public Domain Dedication waiver ( applies to the data made available in this article, unless otherwise stated in a credit line to the data.

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Tuffet, S., Moncomble, E., Boujelben, M.A. et al. Elastance-derived transpulmonary pressure may overestimate the risk of overdistension in severely obese patients. Crit Care 27, 168 (2023).

Download citation

  • Received:

  • Accepted:

  • Published:

  • DOI: