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Transpulmonary pressures to predict the percentage of alveolar collapse and overdistension in acute respiratory distress syndrome

This study demonstrates that end-expiratory and end-inspiratory transpulmonary pressures accurately predict critical thresholds of alveolar collapse and overdistension in ARDS patients, yet EIT-guided PEEP titration yields higher pressures and improved recruitment compared to esophageal pressure-guided strategies, albeit with a trade-off of increased non-dependent overdistension.

Original authors: Clément Brault, Yoann Zerbib, Romain Vallee, Rosalie Schoux, Alexis Lambour, Benjamin Swinyard, Valentin Dambrine, Julien Demaiter, Loay Kontar, Julien Maizel, Michel Slama

Published 2026-07-03

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CC BY 4.0

Original authors: Clément Brault, Yoann Zerbib, Romain Vallee, Rosalie Schoux, Alexis Lambour, Benjamin Swinyard, Valentin Dambrine, Julien Demaiter, Loay Kontar, Julien Maizel, Michel Slama

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the lungs of a patient with Acute Respiratory Distress Syndrome (ARDS) as a crowded, unevenly packed suitcase. Some parts of the suitcase are squished flat (collapsed), while other parts are stuffed so tight they might rip (overdistended). The goal of the doctors is to find the "Goldilocks" pressure to keep the suitcase open just enough to let air in, without crushing the clothes or tearing the fabric.

This study, conducted by researchers at Amiens-Picardie University Hospital, tried to figure out how to measure that perfect pressure using two different tools: esophageal pressure sensors (which act like a pressure gauge inside the chest) and Electrical Impedance Tomography (EIT) (which acts like a real-time X-ray camera showing how air moves).

Here is the breakdown of what they found, using simple analogies:

1. The Two Problems: The "Flat Tire" and the "Balloon"

In ARDS, the lungs suffer from two opposite problems at the same time:

Collapse (Atelectrauma): Like a flat tire. The tiny air sacs (alveoli) collapse and stick together. If they stay closed, the patient can't get oxygen.
Overdistension (Volutrauma): Like a balloon being blown up too hard. The air sacs that are open get stretched so thin they risk bursting.

The doctors need to find the right amount of PEEP (Positive End-Expiratory Pressure). Think of PEEP as a "backstop" pressure that keeps the suitcase slightly open even when the patient breathes out, preventing the flat tires from going flat again.

2. The Two Tools: The "Gauge" vs. The "Camera"

The researchers compared two ways to decide how much pressure to use:

The Gauge (Esophageal Pressure): They put a balloon in the patient's esophagus to measure the pressure surrounding the lungs. They calculated a number called Transpulmonary Pressure ( $P_L$ $P_{L}$ ).
- $P_{L,e}$ (End-Expiratory): The pressure when the patient breathes out.
- $P_{L,i}$ (End-Inspiratory): The pressure when the patient breathes in.
The Camera (EIT): A belt around the chest that creates a live map of the lungs, showing exactly which parts are collapsed and which are over-stretched.

3. The Big Discovery: The Gauge Predicts the Camera

The main finding is that the Gauge and the Camera tell the same story.

The "Flat Tire" Rule: When the end-expiratory pressure ( $P_{L,e}$ ) dropped below 2.0, the "camera" showed that more than 10% of the lung had collapsed. It's like a warning light: "If the pressure drops below this line, the suitcase is getting too squished."
The "Balloon" Rule: When the end-inspiratory pressure ( $P_{L,i}$ ) went above 18.4, the "camera" showed that more than 10% of the lung was over-stretched. It's like a warning light: "If the pressure goes above this line, the suitcase is getting too tight."

Essentially, the pressure numbers from the gauge are reliable "surrogates" (stand-ins) for seeing the actual state of the lung tissue.

4. The Conflict: Two Different "Best" Settings

Here is where it gets interesting. When the doctors used the two tools to decide the perfect pressure setting, they got different answers:

The Camera Strategy (EIT-guided): The camera said, "We need higher pressure (around 12 cmH₂O)."
- Result: This opened up more of the collapsed "flat tires." The air was distributed more evenly. However, it did cause a slight increase in the "over-stretched" areas in the top parts of the lung.
The Gauge Strategy (Esophageal-guided): The gauge said, "We only need lower pressure (around 8 cmH₂O)."
- Result: This kept the top parts of the lung safe from over-stretching, but it allowed more of the bottom parts of the lung to collapse.

The Trade-off: The "Camera" approach was better at opening up the collapsed lungs (recruitment), but the "Gauge" approach was slightly more conservative to avoid over-stretching.

5. The "Gray Zone" Warning

The researchers found that while the numbers (2.0 and 18.4) are good guides, they aren't perfect magic numbers for everyone. There is a "gray zone" in the middle where you can't be 100% sure what the lung is doing just by looking at the pressure number.

Because every patient's "suitcase" is packed differently (some have more fat, some have different lung stiffness), the study concludes that doctors should treat each patient individually. The pressure numbers are helpful tools, but they shouldn't be used as rigid rules for everyone.

Summary

This study proves that measuring the pressure inside the chest (Transpulmonary pressure) is a reliable way to guess if a patient's lungs are collapsing or over-stretching, even without a special camera. However, relying on pressure numbers alone might lead to a different treatment plan than using a live lung camera. The best approach seems to be using these tools to find a personalized balance for each patient, rather than following a single strict rule.

Technical Summary: Transpulmonary Pressures to Predict Alveolar Collapse and Overdistension in ARDS

Problem Statement
In the management of Acute Respiratory Distress Syndrome (ARDS), determining the optimal Positive End-Expiratory Pressure (PEEP) remains a critical clinical challenge. The goal is to maximize alveolar recruitment (preventing collapse) while minimizing overdistension, both of which contribute to Ventilator-Induced Lung Injury (VILI). While Electrical Impedance Tomography (EIT) offers real-time, non-invasive visualization of regional ventilation to estimate collapse and overdistension, its widespread clinical adoption is limited. Conversely, esophageal pressure monitoring allows for the calculation of transpulmonary pressure ( $P_L$ ), a surrogate for the distending pressure applied to the lung parenchyma. However, the definitive relationship between transpulmonary pressures ( $P_{L,e}$ at end-expiration and $P_{L,i}$ at end-inspiration) and the actual extent of alveolar collapse and overdistension as measured by EIT has not been fully established. This study investigates whether transpulmonary pressures can serve as reliable physiologic surrogates for regional lung stress and predict critical thresholds of alveolar collapse and overdistension.

Methodology
The study was a physiological investigation conducted at Amiens University Hospital involving 38 mechanically ventilated patients with moderate-to-severe ARDS (Berlin criteria).

Protocol: Patients underwent a decremental PEEP trial, starting at 20 cmH₂O (or 16 cmH₂O in two cases due to hemodynamics) and reducing in 2 cmH₂O steps down to 4 cmH₂O.
Measurements: Simultaneous recordings were made using:
- EIT (PulmoVista 500): To quantify regional ventilation distribution and calculate percentages of alveolar collapse and overdistension at each PEEP level.
- Esophageal Manometry (Nutrivent): To measure esophageal pressure ( $P_{eso}$ $P_{eso}$ ) and calculate transpulmonary pressures.
  - End-expiratory transpulmonary pressure ( $P_{L,e}$ ) was derived from direct esophageal pressure measurements in middle-to-dependent lung regions.
  - End-inspiratory transpulmonary pressure ( $P_{L,i}$ ) was estimated in non-dependent regions using the elastance ratio method.
Strategies Compared: Two PEEP selection strategies were compared:
1. EIT-guided: The PEEP level achieving the best compromise (crossing point) between collapse and overdistension curves.
2. Esophageal pressure-guided ( $P_{eso}$ -guided): The lowest PEEP yielding a positive $P_{L,e}$ .
Statistical Analysis: Correlations were assessed using Spearman's coefficients and repeated-measures correlation (rmcorr). Receiver Operating Characteristic (ROC) curves determined the predictive value of $P_{L,e}$ and $P_{L,i}$ for critical collapse and overdistension (defined as >10%).

Key Results

Correlations: Strong correlations were found between transpulmonary pressures and alveolar status.
- $P_{L,e}$ showed a strong negative correlation with alveolar collapse ( $r = -0.68$ , $p < 0.001$ ).
- $P_{L,i}$ showed a strong positive correlation with alveolar overdistension ( $r = 0.60$ , $p < 0.001$ ).
- Within-subject analysis confirmed these relationships, with each 1 cmH₂O decrease in $P_{L,e}$ associated with a 3.0% increase in collapse, and each 1 cmH₂O increase in $P_{L,i}$ associated with a 1.9% increase in overdistension.
Predictive Thresholds: ROC analysis identified specific cut-off values with high specificity (≥80%):
- Collapse: A $P_{L,e} < 2.0$ cmH₂O predicted alveolar collapse >10% (AUC = 0.84). Conversely, a $P_{L,e} > 9.0$ cmH₂O predicted collapse <10%.
- Overdistension: A $P_{L,i} > 18.4$ cmH₂O predicted overdistension >10% (AUC = 0.80). Conversely, a $P_{L,i} < 9.2$ cmH₂O predicted overdistension <10%.
Strategy Comparison:
- The EIT-guided strategy resulted in significantly higher PEEP levels (median 12.0 cmH₂O) compared to the $P_{eso}$ -guided strategy (median 8.0 cmH₂O).
- The EIT-guided approach significantly reduced alveolar collapse (6% vs. 16%) and improved ventilation distribution to dependent lung regions.
- However, the EIT-guided strategy led to a slight but significant increase in overdistension (10% vs. 4%) and reduced compliance in the non-dependent lung. Global respiratory system compliance remained similar between strategies.
- Subgroup analysis indicated the correlation between $P_{L,i}$ and overdistension was significantly stronger in obese patients.

Significance and Claims
The authors conclude that end-expiratory ( $P_{L,e}$ ) and end-inspiratory ( $P_{L,i}$ ) transpulmonary pressures accurately identify clinically relevant thresholds for alveolar collapse and overdistension, respectively. These pressures can serve as physiologic surrogates for regional lung stress in ARDS, offering a potential alternative when EIT is unavailable or contraindicated (e.g., due to pacemakers or burns).

The study highlights that while transpulmonary pressures are predictive, the strategies derived from them differ fundamentally from EIT-guided titration. Specifically, relying solely on esophageal pressure to maintain a positive $P_{L,e}$ results in lower PEEP levels that may fail to prevent significant alveolar collapse compared to EIT-guided optimization. The authors emphasize the existence of "gray zones" in these thresholds, supporting an individualized approach to PEEP setting rather than rigid adherence to universal cut-offs. The findings suggest that targeting a slightly positive $P_{L,e}$ (around 2 cmH₂O) may prevent critical collapse, while monitoring $P_{L,i}$ is crucial to avoid excessive overdistension, particularly in obese patients.