EditorialEditor's Choice

Airway and Transpulmonary Driving Pressure by End-Inspiratory Holds During Pressure Support Ventilation

Joaquin Pérez, Javier H Dorado, Matías Accoce and Gustavo A Plotnikow
Respiratory Care November 2023, 68 (11) 1483-1492; DOI: https://doi.org/10.4187/respcare.10802

Abstract

BACKGROUND: The precision of quasi-static airway driving pressure (ΔP) assessed in pressure support ventilation (PSV) as a surrogate of tidal lung stress is debatable because persistent muscular activity frequently alters the readability of end-inspiratory holds. In this study, we used strict criteria to discard excessive muscular activity during holds and assessed the accuracy of ΔP in predicting global lung stress in PSV. Additionally, we explored whether the physiological effects of high PEEP differed according to the response of respiratory system compliance (CRS).

METHODS: Adults with ARDS undergoing PSV were enrolled. An esophageal catheter was inserted to calculate lung stress through transpulmonary driving pressure (ΔPL). ΔP and ΔPL were assessed in PSV at PEEP 5, 10, and 15 cm H2O by end-inspiratory holds. CRS was calculated as tidal volume (VT)/ΔP. We analyzed the effects of high PEEP on pressure-time product per minute (PTPmin), airway pressure at 100 ms (P0.1), and VT over PTP per breath (VT/PTPbr) in subjects with increased versus decreased CRS at high PEEP.

RESULTS: Eighteen subjects and 162 end-inspiratory holds were analyzed; 51/162 (31.5%) of the holds had ΔPL ≥ 12 cm H2O. Significant association between ΔP and ΔPL was found at all PEEP levels (P < .001). ΔP had excellent precision to predict ΔPL, with 15 cm H2O being identified as the best threshold for detecting ΔPL ≥ 12 cm H2O (area under the receiver operating characteristics 0.99 [95% CI 0.98–1.00]). CRS changes from low to high PEEP corresponded well with lung compliance changes (R2 0.91, P < .001) When CRS increased, a significant improvement of PTPmin and VT/PTPbr was found, without changes in P0.1. No benefits were observed when CRS decreased.

CONCLUSIONS: In subjects with ARDS undergoing PSV, high ΔP assessed by readable end-inspiratory holds accurately detected potentially dangerous thresholds of ΔPL. Using ΔP to assess changes in CRS induced by PEEP during assisted ventilation may inform whether higher PEEP could be beneficial.

Introduction

Lung stress induced by tidal volume (VT) is one of the main determinants of ventilator-induced lung injury in ARDS.1,2 Under controlled mechanical ventilation, lung stress can be estimated by transpulmonary driving pressure (ΔPL) and calculated as the difference between airway driving pressure (ΔP) and esophageal driving pressure (ΔPes). Nonetheless, Pes monitoring is rarely used in clinical settings because it requires expertise and considerable time for interpretation.3,4 Therefore, ΔP has been proposed as a feasible way to indirectly estimate tidal lung stress.5,6 During fully controlled ventilation, ΔP was shown to be moderately correlated with ΔPL and to be able to predict high total lung stress with sufficient accuracy at different PEEP levels.6

Since it has been shown that spontaneous breathing can induce or worsen lung damage, assessing respiratory mechanics during assisted ventilation has become imperative.7–9 In this setting, obtaining quasi-static measurements of plateau pressure (Pplat) and ΔP in pressure support ventilation (PSV) is possible by performing end-inspiratory holds.7,10 However, the precision of ΔP to estimate ΔPL in PSV has been argued because expiratory muscle activity is frequent during the maneuver, making holds unreadable. This fact is clinically meaningful because high monitored ΔP may overestimate the real ΔPL.11 Consequently, certain acceptability criteria have been proposed to improve hold readability.7,12 By applying these criteria, it was shown that Pplat and ΔP can be reliably measured and can be used to compute quasi-static respiratory system compliance (CRS) during patient-triggered breaths.12 However, whether these criteria may help to overcome the maneuver's limitations in predicting ΔPL has not been evaluated. Moreover, if ΔP accurately reflects ΔPL, monitoring the response of CRS to different ventilatory interventions (eg, setting higher PEEP) might serve as a noninvasive way to monitor the response of lung compliance (CL). Accordingly, if lung mechanics improve, an improved physiology of spontaneous breathing activity is expected. This is important because no current methods have been proposed to identify PEEP response during assisted ventilation.

In this study, we analyzed previous physiological data collected from a convenience sample of subjects with ARDS at different PEEP levels with 2 main objectives: (1) to assess whether, by using end-inspiratory holds fulfilling acceptability criteria, ΔP can accurately predict ΔPL during assisted ventilation in PSV; our primary hypothesis was that high ΔP correctly identifies risky thresholds of ΔPL when the hold maneuvers are acceptable; and (2) to explore if a different physiological response to high PEEP during assisted ventilation can be identified by changes in CRS calculated in PSV. We hypothesized that enhancement in CRS with high PEEP is related to improvement in CL, and this will be associated with optimization of work of breathing (WOB), respiratory drive, and neuromuscular ventilatory coupling (NMVC).

QUICK LOOK

Current knowledge

The noninvasive assessment of airway driving pressure (ΔP) by quasi-static end-inspiratory holds is feasible during pressure support ventilation (PSV), but the accuracy of these maneuvers to predict lung stress is controversial because readable traces without excessive muscular activity are challenging to achieve.

What this paper contributes to our knowledge

In this small sample of subjects recovering from ARDS, ΔP assessed by readable end-inspiratory holds performed in PSV had an excellent precision to predict transpulmonary driving pressure (ΔPL), with a value of 15 cm H2O being identified as the best threshold for detecting ΔPL ≥ 12 cm H2O. In addition, using ΔP to compute respiratory system compliance (CRS) changes to high PEEP enabled us to follow lung compliance changes and to identify physiological benefits in subjects who improved CRS with higher PEEP. When end-inspiratory holds are readable, the noninvasive monitoring of ΔP in PSV might be helpful to identify thresholds of lung stress and to guide PEEP settings during patient triggered ventilation.

Methods

This is an ancillary report of an ongoing prospective physiological trial carried out in Sanatorio Anchorena San Martín, Buenos Aires, Argentina (ClinicalTrials.gov NCT04524091). The original trial enrolled adults ≥ 18 y old with intubation time > 48 h who fulfilled Berlin ARDS criteria and transitioned from controlled to assisted ventilation in PSV for ≥ 2 h, and it was expected them to remain under mechanical ventilation > 24 h after enrollment. Exclusion criteria were contraindications for esophageal catheter insertion (eg, platelets < 1003), pregnancy, previous chronic obstructive disease or neuromuscular disease affecting respiratory muscles, non-resolved pneumothorax, or persistent bronchopleural fistula. We eliminated subjects without acceptable/readable end-inspiratory holds in all the PEEP steps. The original protocol was approved by the local review board (code number 08–2019), and the subjects or their next of kin signed the informed consent.

The subjects were ventilated using Servo-i ventilators (Getinge, Solna, Sweden) in PSV mode. An esophageal balloon (MBMed-BA-A-008, non-latex, MBMed, Buenos Aires, Argentina) was inserted and filled with 1 mL of air according to manufacturer recommendations. Briefly, the esophageal catheter was passed through the nostrils and progressively pushed down 50–60 cm to the stomach. Afterward, it was gently withdrawn 15–20 cm until cardiac artifacts and negative esophageal pressure (Pes) deflections were observed. An occlusion test was performed to assess the proper balloon placement in the lower third of the esophagus, considering as acceptable a relationship between airway and esophageal pressure of 0.8–1.2.13,14 Airway pressure (Paw), flow, volume, and Pes were recorded by a dedicated system (FluxMed, MBMed) connected to a computer. Transpulmonary pressure (PL) was quantified by instantaneous real-time digital subtraction of Pes from Paw.

In the original study protocol, the pressure support level, FIO2, and cycling criteria were adjusted at the discretion of the attending physician and remained unchanged during all the measurements. Thereafter, the subjects were submitted to a stepwise non-randomized incremental PEEP evaluation consisting of 3 PEEP levels (5, 10, and 15 cm H2O), each lasting 10 min. Subsequently, at least 3 end-inspiratory and 3 end-expiratory holds were performed to obtain Pplat and PEEP total (PEEP set + intrinsic PEEP), and the following parameters were calculated (Fig. 1):

  1. ΔP = Pplat − PEEP total

  2. ΔPes = (end-inspiratory Pes − end-expiratory Pes)

  3. ΔPL = (end-inspiratory PL − end-expiratory PL)

  4. CRS = VT/ΔP

  5. CL = VT/ΔPL

  6. Chest wall compliance (CCW) = VT/ΔPes

Fig. 1.
Fig. 1.

Airway pressure (Paw), esophageal pressure (Pes), transpulmonary pressure (PL), and flow tracing during an end-inspiratory hold performed during pressure support ventilation. As can be observed, there is a first part of the inspiratory hold where Paw, Pes, and PL waveforms are flat and readable. Contrarily, at the end of the hold, a new inspiratory effort occurs, making all measurements unreadable from that point onward. Paw = airway pressure; ΔP = airway driving pressure; Pes = esophageal pressure; PL = transpulmonary pressure; ΔPL = transpulmonary driving pressure.

Each hold maneuver was separated from the next for 30 s to avoid discomfort. The measurements were suspended if any of the following safety-stopping criteria were met at any time during the protocol: heart rate > 140 beats/min, sustained hypotension (systolic blood pressure < 90 mm Hg) or hypertension (systolic blood pressure > 180 mm Hg), clear use of accessory muscles with thoracoabdominal paradox, hemodynamic instability (new arrhythmias, increase noradrenaline > 0.1 μg/kg/h), or pulse oxygen saturation < 90% with FIO2 1.0.

The holds were considered acceptable/readable if previously established criteria were met (Fig. 1): (1) time to reach a stable Pplat < 800 ms, (2) Pplat duration of at least 1–2 s, and (3) stable Pplat defined as Paw variation < 0.6 cm H2O/s.7,12 Additionally, the Pes signal during the hold maneuvers was observed to discard excessive expiratory activity. Two independent evaluators (JP and JHD) revised all the waveform traces offline to ensure acceptability of the end-inspiratory holds. In case of discordance between evaluators' judgment, it was solved by consensus. All the traces not fulfilling acceptability/readability criteria were discarded.

To explore PEEP effects, we analyzed the changes from low to high PEEP of the following indexes: a) the pressure-time product per minute (PTPmin), obtained from the multiplication of PTP per each breath (PTPbr) and breathing frequency (f) (software FluxMed, MBMed); b) the Paw during the first 100 ms of an expiratory occlusion (P0.1), obtained from the average of 3 end-expiratory occlusions; c) the relationship between VT and PTPbr (VT/PTPbr), as representative variables of WOB, respiratory drive, and NMVC, respectively. To investigate the differential physiological response according to the behavior of respiratory system mechanics when increasing PEEP, the changes of these indexes were analyzed in subjects in whom CRS increased versus decreased at high PEEP (15 cm H2O) compared with low PEEP (5 cm H2O). The average of the following parameters was calculated with respiratory cycles of last 30–60 s considered stable of each PEEP step, and it was used to compute the aforementioned indexes: VT (time integral of flow), f, neural inspiratory time, and Pes swings. Waveform signals were analyzed using Biopac Student Lab PRO 3.7.7 software (BIOPAC Systems, Goleta, California).

Continuous data are presented as mean ± SD or median [25–75% interquartile range [IQR]] according to the distribution checked by visual inspection of histograms and Shapiro-Wilk test. Categorical variables are reported as number of presentations (proportion). Comparisons between variables of respiratory monitoring derived from Pes, PL, and Paw obtained during holds were assessed by one-way analysis of variance (ANOVA) or non-parametric Friedman test, as appropriate. The association between respiratory system and lung mechanics was assessed by simple linear regressions and expressed by R2 using the average of the holds available per each subject performed at each PEEP step. The accuracy of ΔP to estimate ΔPL ≥ 12 cm H2O was assessed with the area under the curve of the receiver operating characteristic (AUROC). This threshold of lung stress was selected based on previous studies suggesting it as potentially injurious and associated with patient's outcomes.13,15 The optimal cut-off point of ΔP was selected according to the Youden index. To build the ROC curve, we fitted a generalized linear mixed model using lme4 package,16 with an individual patient random effect due to intra-patient variation, as recommended by previous studies.17,18 A internal cross-validation 10 k-folds procedure was applied using performance package19 to evaluate the validity of the model.20 For all these analyses, we decided to use the measurements of all 3 PEEP levels evaluated in the original protocol to account for the possible modifications that PEEP may have on lung and chest wall–distending pressures and, consequently, in the relationship between ΔP and ΔPL.2

To assess the differential effects of PEEP, we analyzed subject's response in subgroups based on CRS changes (increase or decrease) induced by high PEEP. To ease the interpretation of the results, we analyzed the response between low (5 cm H2O) and high (15 cm H2O) PEEP. The comparisons of physiological variables at these 2 PEEP levels were evaluated by 2-way ANOVA. A linear mixed-effects regression model for repeated measures was used to assess interaction between PEEP and CRS change. P values for multiple comparisons were adjusted by Bonferroni post hoc correction. A 2-tailed P < .05 was considered statistically significant. The analysis was performed with R software 4.1.3 (R Foundation for Statistical Computing, Vienna, Austria).

Results

Between April 2020–September 2022, the complete data set of 24 subjects was available and included for waveform analysis. Of them, 6 subjects were eliminated because of inability to obtain at least one readable end-inspiratory hold maneuver in all the PEEP steps. Persistent expiratory muscle activation evidenced by continuous increase in Pplat was the cause of unreadability in 100% of these maneuvers (maneuvers discarded: no. = 54). The traces of 18 subjects were finally analyzed (Table 1). Overall, the mean ± SD age of the sample was 58 ± 13 y old; Simplified Acute Physiology Score at admission was 34 [29–43] points. All the subjects required neuromuscular blockers, and 12/18 had at least one prone positioning session before transitioning from controlled to assisted ventilation. The ICU mortality was 33.0%.

View this table:
Table 1.

Characteristics of the Subjects (N = 18)

At the time of inclusion, subjects were recovering from ARDS in PSV mode, with a mean ± SD level of pressure support of 8.4 ± 2.5 cm H2O and FIO2 of 0.40 ± 0.10. No adverse events were registered during the protocol. A total of 162 end-inspiratory holds with paired ΔP and ΔPL was analyzed for the primary end point. Each subject had 3 [2–3] readable holds analyzed during each PEEP step, and 51/162 (31.5%) of the included holds had a ΔPL ≥ 12 cm H2O.

Table 2 depicts the main respiratory parameters collected from airway, esophageal, and transpulmonary monitoring during the holds. As expected, ΔP was, on average, 2–3 cm H2O > ΔPL, and this difference kept constant at increasing PEEP (mean difference between ΔP and ΔPL 2.69 [95% CI 1.95–3.44] cm H2O at PEEP 5; 2.68 [2.17–3.16] cm H2O at PEEP 10; and 2.74 [1.19–4.28] cm H2O at PEEP 15, P = .41). There was a very tight association between the absolute values ΔP and ΔPL (Fig. 2). Furthermore, ΔP was shown to have an excellent accuracy to estimate ΔPL, with 15 cm H2O being identified as the best threshold to detect the presence of ΔPL ≥ 12 cm H2O (AUROC 0.99 [95% CI 0.98–1.00], sensitivity 0.94, specificity 1.00) (Fig. 3). After applying the internal 10 k-folds cross-validation, ΔP de-monstrated a similar precision for predicting high lung stress (AUROC 0.95, standard error 0.09).

Fig. 2.
Fig. 2.

Association between airway and transpulmonary driving pressure assessed in pressure support ventilation at different PEEP levels. ΔPL = transpulmonary driving pressure; ΔP = airway driving pressure.

Fig. 3.
Fig. 3.

Accuracy of airway driving pressure to detect transpulmonary driving pressure ≥ 12 cm H2O. The black dot in the left-upper corner of the curve indicates the best cut-off point according to Youden index.

View this table:
Table 2.

Main Parameters Collected During End-Inspiratory and End-Expiratory Holds in Pressure Support Ventilation

The physiological response of subjects differed according to the effects exerted by high PEEP on respiratory system mechanics. Overall, we identified 11 subjects in whom CRS increased (12.5 ± 5.7 mL/cm H2O; 33.8 ± 16.7%) and 7 subjects in whom CRS decreased (−8.5 ± 3.4 mL/cm H2O; −25.7 ± 12.1%) when PEEP was increased from 5 cm H2O to 15 cm H2O. The changes in CL from low to high PEEP were well reflected by the changes in CRS (R2 = 0.91, P < .001). The main dynamic parameters collected in both groups are shown in Table 3. A significant interaction was found between PEEP and CRS change regarding to the effects on PTPmin (P = .046) and VT/PTPbr (P = .005) but not regarding to P0.1 (P = .09). Of note, when CRS increased, a significant optimization of WOB and NMVC was observed (Fig. 4, left panels). On the contrary, when CRS decreased with high PEEP (Fig. 4, right panels), all these indexes remained unchanged.

Fig. 4.
Fig. 4.

Individual physiological response of subjects who increased (right panels) and decreased (left panels) respiratory system compliance with high PEEP. (A) work of breathing, (B) respiratory drive, (C) neuromuscular ventilatory coupling. CRS = respiratory system compliance; PTPmin = pressure-time product per minute; P0.1 = airway pressure decay during the first 100 ms of an expiratory occlusion; VT/PTPbr = relationship tidal volume and pressure-time product per each breath; In (A), the scale of y axis was rescaled by square root function to improve visualization.

View this table:
Table 3.

Main Dynamic Parameters of Subjects According to the Response of Respiratory Mechanics to High PEEP

Discussion

In this physiological study performed in subjects recovering from ARDS, we showed that high ΔP obtained by readable end-inspiratory holds in PSV allowed the accurate identification of risky thresholds of ΔPL ≥ 12 cm H2O. In addition, the response of CRS to high PEEP was useful to differentiate physiological responses of subjects to higher PEEP and might possibly help to guide PEEP settings during assisted ventilation.

Previous studies have challenged the validity of ΔP assessed by end-inspiratory holds to approach lung mechanics during PSV.11 The main limitation of this method is that persistent expiratory muscle activity may affect the readability of the maneuvers. To account for this, we analyzed only those holds considered acceptable according to predefined criteria proposed by previous studies.7,12 Of note, these criteria may serve to make the Paw a better reflection of PL. Accordingly, we observed a strong association between ΔP and ΔPL, which improved at increasing PEEP. This could be explained by the fact that the CCW and the relationship between lung and respiratory system elastance (EL/ERS) tended to be higher at increasing PEEP, making the respiratory system behavior a closer reflection of lung behavior. In addition, high ΔP correctly identified high ΔPL. Indeed, under strict circumstances of relaxed muscular activity (eg, during passive ventilation), the close relationship between these variables is expectable given that ΔP is mostly explained by the lung component in absence of pathologies affecting CCW.6,21,22 Even though we cannot definitely rule out the presence of expiratory muscles activity during the hold, these results show that when clear acceptability criteria are met the precision of Paw to estimate PL is not affected. Moreover, only 25% of the maneuvers analyzed were discarded because of unreadability, highlighting that most of end-inspiratory holds may be usable in clinical practice.

The physiological rationale behind the ΔPL safety threshold is supported by the stress/strain concepts. When VT is applied, a change in lung volume (ΔV) occurs; the ratio between this ΔV and the pre-inflation state, (ie, functional residual capacity) is called strain. The lung-distending force opposing the VT is called stress and is represented by the ΔPL.2,13 When stress is close to 20–24 cm H2O, tidal inflation occurs close to total lung capacity and has been shown to induce significant lung injury within 24 h.23,24 Given that the lungs of patients with ARDS are not homogeneous, ΔPL values differ along the cephalocaudal axis. Indeed, the presence of stress raisers may regionally double ΔPL.25 Consequently, it has been suggested to target a global ΔPL < 12 cm H2O to maintain regional ΔPL < 24 cm H2O.13,15 However, measuring ΔPL is not simple in daily clinical practice, and ΔP may serve as surrogate. Amato et al5 observed an exponential increase in mortality beyond ΔP ≥ 15 cm H2O in a large analysis of ARDS trials. These findings were further confirmed by other studies.3,15 Even though strict targets for quasi-static measurements of ΔP and ΔPL are lacking in spontaneous assisted ventilation, some data suggest that ΔP ≥ 15 cm H2O may also be associated with worse outcomes.26 Additionally, Bellani et al7 recently reported that increasing ΔP during assisted ventilation was independently associated with mortality in subjects with ARDS. Our results indicated that increasing ΔP is mostly explained by increasing ΔPL. Furthermore, we observed that high ΔP can accurately identify a ΔPL ≥ 12 cm H2O. Taken together, these findings may support the independent association observed by the above studies.7,26 Interestingly, as previously found during passive controlled ventilation,5 our analysis showed that the best threshold of ΔP to detect potentially dangerous lung stress was 15 cm H2O. Of note, as ΔPL depends on EL/ERS relation and most of the subjects under mechanical ventilation without abdominal or thoracic disease present EL/ERS ≈ 0.8,2,13 we believe that this ΔP cut-off point could be a reasonable target in most of the subjects even during assisted spontaneous breathing when holds are acceptable/readable (ie, ΔPL = 15 cm H2O × 0.8 = 12 cm H2O). However, special attention should be paid to cases where alterations of chest wall mechanics are suspected.

Some experimental studies have suggested that high PEEP is preferable to reduce inspiratory effort, avoid pendelluft, and dampen local lung overstretch.27 However, a recent clinical study showed that PEEP response is highly heterogeneous and may depend on its effects on lung mechanics.28 In the present study, we aimed to test if noninvasive quasi-static calculations of CRS in PSV would permit trending of CL behavior during PEEP settings and possibly identify responders and non-responder to high PEEP. Indeed, we observed that CRS changes closely followed CL changes. In addition, WOB decreased and NMVC improved only when high PEEP was accompanied by improvement in CRS. These results support previous reasonings and suggest that high PEEP might only be clinically indicated in selected patients in whom better lung protection is achieved. Further, the behavior of respiratory drive when modifying PEEP levels deserves special attention. In a previous physiological study, Mauri et al29 observed that higher PEEP did not alter the absolute values of P0.1. In contrast, Spinelli et al30 recently reported an independent association between lower PEEP and higher P0.1 in subjects with hypoxemic respiratory failure undergoing PSV. Based on these findings, we believe that the interpretation of the changes of P0.1 when modifying PEEP levels deserves further investigation and should be integrated together with other parameters to decide if high PEEP could provide benefits.

Our findings may have clinical implications: First, to the best of our knowledge, the capacity of quasi-static noninvasive measurement of ΔP to predict ΔPL during patient-triggered breath has not been evaluated before. Despite our small sample size, the results suggest that when clear holds acceptability criteria are met a Paw-based monitoring in PSV might provide similar information as during controlled ventilation regarding lung protection and possibly enable to control the risk of lung injury without invasive techniques. Nonetheless, given the high inter-individual variability of EL/ERS, a detailed case-by-case evaluation is further warranted. Second, observing changes in CRS during incremental PEEP steps may provide a close estimations of CL behavior without the necessity of invasive techniques and might potentially help to decide whether a higher PEEP is a feasible option to optimize lung and diaphragm protection.

Our study presents several limitations. Our sample size is small, and the analyzed data stem from a secondary analysis of a study originally designed for another purpose. Moreover, even though performing internal validation of models is strongly recommended and our sample size is similar to other studies carrying out this procedure,9 the minimum number of observations necessary for internal validation is unclear; consequently, our results should be considered as hypothesis generating awaiting for confirmation. Most of the subjects had pulmonary ARDS, and the results may be different in subjects with ARDS of non-pulmonary origin or other pathologies. A threshold of ΔPL ≥ 12 cm H2O was considered as potentially injurious in our study, and lower safe limits around 10 cm H2O have been previously proposed.31 Even though the best ΔPL target is unknown, we based the selection of this threshold on the largest prospective clinical study reporting a direct association between this ΔPL limit and mortality during controlled ventilation.15 We believe that future studies should be specifically designed for elucidating the causal relationship between a certain ΔPL value and subject's outcomes. We did not obtain arterial blood gases during PEEP changes to account for possible modifications in determinants of control of breathing (eg, PaCO2, pH). Some of the included subjects were obese, which could have affected CCW. However, in line with previous studies, we did not observe significant chest wall mechanics alterations in our sample,32,33 suggesting that the results may be similar to normal weighted individuals. Finally, it is worth to note that the quasi-static measurements of ΔPL reported in our study may better represent the average stress experienced by non-dependent lung regions, whereas the risk of dependent zones may be underestimated.34 In this sense, other noninvasive dynamic methods have been proposed to quantify more closely the tidal lung stress of dependent zones.9 Even though some experimental data suggest that quasi-static ΔPL might be more relevant than dynamic ΔPL,35 it is still unknown whether a lung-protective strategy should target quasi-static, dynamic, or both lung-distending pressures during assisted ventilation. In the meantime, both methods may give complementary information about the risk of patient self-inflicted lung injury and should be used to strictly control lung stress at the bedside.36

Conclusions

In subjects recovering from ARDS undergoing patient-triggered ventilation, high values of ΔP assessed by readable quasi-static end-inspiratory holds in PSV accurately detected potentially dangerous thresholds of ΔPL. Finally, assessing compliance response to high PEEP may inform whether higher PEEP levels may reduce WOB and improve NMVC during patient-triggered breaths. Future studies should be conducted to further validate our results.

Acknowledgments

We would like to thank to Emiliano Navarro PT (Instituto de Efectividad Clínica y Sanitaria, Ciudad Autónoma de Buenos Aires, Argentina) for his valuable advice regarding statistical analysis of data.

Footnotes

  • Correspondence: Joaquin Pérez PT, Calle 422 4100, Villa Elisa, Buenos Aires, Argentina. E-mail: licjoaquinperez{at}hotmail.com

  • Mr Plotnikow discloses relationships with Vapotherm USA and Medtronic Argentina, Panamá, Costa Rica, and México. The remaining authors have disclosed no conflicts of interest.

  • See the Related Editorial on Page 1606

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