Expiratory flow limitation in intensive care: prevalence and risk factors

Ultrasonographic Assessment of the Diaphragm

Mechanical ventilation injures not only the lungs but also the diaphragm, resulting in dysfunction associated with poor outcomes. Diaphragm ultrasonography is a noninvasive, cost-effective, and reproducible diagnostic method used to monitor the condition and function of the diaphragm. With advances in ultrasound technology and the expansion of its clinical applications, diaphragm ultrasonography has become increasingly important as a tool to visualize and quantify diaphragmatic morphology and function across multiple medical specialties, including pulmonology, critical care, and rehabilitation medicine. This comprehensive review aims to provide an in-depth analysis of the role and limitations of ultrasonography in assessing the diaphragm, especially among critically ill patients. Furthermore, we discuss a recently published expert consensus and provide a perspective for the future.

Expiratory flow limitation during mechanical ventilation: real-time detection and physiological subtypes

BACKGROUND

Tidal expiratory flow limitation (EFLT) complicates the delivery of mechanical ventilation but is only diagnosed by performing specific manoeuvres. Instantaneous analysis of expiratory resistance (Rex) can be an alternative way to detect EFLT without changing ventilatory settings. This study aimed to determine the agreement of EFLT detection by Rex analysis and the PEEP reduction manoeuvre using contingency table and agreement coefficient. The patterns of Rex were explored.

METHODS

Medical patients ≥ 15-year-old receiving mechanical ventilation underwent a PEEP reduction manoeuvre from 5 cmH2O to zero for EFLT detection. Waveforms were recorded and analyzed off-line. The instantaneous Rex was calculated and was plotted against the volume axis, overlapped by the flow-volume loop for inspection. Lung mechanics, characteristics of the patients, and clinical outcomes were collected. The result of the Rex method was validated using a separate independent dataset.

RESULTS

339 patients initially enrolled and underwent a PEEP reduction. The prevalence of EFLT was 16.5%. EFLT patients had higher adjusted hospital mortality than non-EFLT cases. The Rex method showed 20% prevalence of EFLT and the result was 90.3% in agreement with PEEP reduction manoeuvre. In the validation dataset, the Rex method had resulted in 91.4% agreement. Three patterns of Rex were identified: no EFLT, early EFLT, associated with airway disease, and late EFLT, associated with non-airway diseases, including obesity. In early EFLT, external PEEP was less likely to eliminate EFLT.

CONCLUSIONS

The Rex method shows an excellent agreement with the PEEP reduction manoeuvre and allows real-time detection of EFLT. Two subtypes of EFLT are identified by Rex analysis.

TRIAL REGISTRATION

Clinical trial registered with www.thaiclinicaltrials.org (TCTR20190318003). The registration date was on 18 March 2019, and the first subject enrollment was performed on 26 March 2019.

Effect of expiratory flow limitation on ventilation/perfusion mismatch and perioperative lung function during pneumoperitoneum and Trendelenburg position

BACKGROUND

Laparoscopic surgery and Trendelenburg position may affect the respiratory function and alter the gas exchange. Further the reduction of the lung volumes may contribute to the development of expiratory flow limitation (EFL). The latter is associated with an increased risk of postoperative pulmonary complications. Our aim was to investigate the incidence of EFL and to evaluate its effect on pulmonary function and intraoperative V/Q mismatch.

METHODS

This is a prospective study on patients undergoing elective laparoscopic gynecological surgery. We evaluated respiratory mechanics, V/Q mismatch and presence of EFL after anesthesia induction, during pneumoperitoneum and Trendelenburg position and at the end of surgery. Intraoperative gas exchange and hemodynamic were also recorded. Clinical data were collected until seven days after surgery to evaluate the onset of pulmonary postoperative complications (PPCs).

RESULTS

Among the 66 patients enrolled, 25/66 (38%) exhibited EFL during surgery, of whom 10/66 (15%) after anesthesia induction, and the remaining 15 patients after pneumoperitoneum and Trendelenburg position. Median PEEP able to reverse flow limitation was 7 [7-10] cmH2O after anesthesia induction and 9 [8-15] cmH2O after pneumoperitoneum and Trendelenburg position. Patients with EFL had significantly higher shunt (17 [2-25] vs. 9 [1-19]; P=0.05), low V̇/Q̇ (27 [20-70] vs. 15 [10-22]; P=0.05) and high V̇/Q̇ (10 [7-14] vs. 6 [4-7]; P=0.024). At the end of surgery, only high V/Q was significantly higher in EFL patients. Further, they exhibited higher incidence of postoperative pulmonary complication (48% (12/25) vs. 15% (6/41), P=0.005), hypoxemia and hypercapnia (80% [20/25] vs. 32% [13/41]; P<0.001).

CONCLUSIONS

Expiratory flow limitation is a common phenomenon during gynecological laparoscopic surgery associated with worsen gas exchange, increased V/Q mismatch and altered lung mechanics. Our study showed that patients experiencing EFL during surgery showed a higher risk for PPCs.

Lung-protective ventilation during Trendelenburg pneumoperitoneum surgery: A randomized clinical trial

Study objective To assess the effects of a protective ventilation strategy during Trendelenburg pneumoperitoneum surgery on postoperative oxygenation.

DESIGNS

Parallel-group, randomized trial.

SETTING

Operating room of a university hospital, Italy.

PATIENTS

Morbidly obese patients undergoing Trendelenburg pneumoperitoneum gynaecological surgery.

INTERVENTIONS

Participants were randomized to standard (SV: tidal volume = 10 ml/kg of predicted body weight, PEEP = 5 cmH₂O) or protective (PV: tidal volume = 6 ml/kg of predicted body weight, PEEP = 10 cmH₂O, recruitment maneuvers) ventilation during anesthesia.

MEASUREMENTS

Primary outcome was PaO₂/FiO₂ one hour after extubation. Secondary outcomes included day-1 PaO₂/FiO₂, day-2 respiratory function and intraoperative respiratory/lung mechanics, assessed through esophageal manometry, end-expiratory lung volume (EELV) measurement and pressure-volume curves.

MAIN RESULTS

Sixty patients were analyzed (31 in SV group, 29 in PV group). Median [IqR] tidal volume was 350 ml [300-360] in PV group and 525 [500-575] in SV group. Median PaO₂/FiO₂ one hour after extubation was 280 mmHg [246-364] in PV group vs. 298 [250-343] in SV group (p = 0.64). Day-1 PaO₂/FiO_2, day-2 forced vital capacity, FEV-1 and Tiffenau Index were not different between groups (all p > 0.10). Intraoperatively, 59% of patients showed complete airway closure during pneumoperitoneum, without difference between groups: median airway opening pressure was 17 cmH₂O. In PV group, airway and transpulmonary driving pressure were lower (12 ± 5 cmH₂O vs. 17 ± 7, p < 0.001; 9 ± 4 vs. 13 ± 7, p < 0.001), PaCO₂ and respiratory rate were higher (48 ± 8 mmHg vs. 42 ± 12, p < 0.001; 23 ± 5 breaths/min vs. 16 ± 4, p < 0.001). Intraoperative EELV was similar between PV and SV group (1193 ± 258 ml vs. 1207 ± 368, p = 0.80); ratio of tidal volume to EELV was lower in PV group (0.45 ± 0.12 vs. 0.32 ± 0.09, p < 0.001).

CONCLUSIONS

In obese patients undergoing Trendelenburg pneumoperitoneum surgery, PV did not improve postoperative oxygenation nor day-2 respiratory function. PV was associated with intraoperative respiratory mechanics indicating less injurious ventilation. The high prevalence of complete airway closure may have affected study results.

TRIAL REGISTRATION

Prospectively registered on http://clinicaltrials.govNCT03157479 on May 17th, 2017.

Association Between Acute Kidney Injury During Invasive Mechanical Ventilation and ICU Outcomes and Respiratory System Mechanics

Compare ICU outcomes and respiratory system mechanics in patients with and without acute kidney injury during invasive mechanical ventilation.

Circulating Skeletal Troponin During Weaning From Mechanical Ventilation and Their Association to Diaphragmatic Function: A Pilot Study

Background: Patients with acute respiratory failure (ARF) may need mechanical ventilation (MV), which can lead to diaphragmatic dysfunction and muscle wasting, thus making difficult the weaning from the ventilator. Currently, there are no biomarkers specific for respiratory muscle and their function can only be assessed trough ultrasound or other invasive methods. Previously, the fast and slow isoform of the skeletal troponin I (fsTnI and ssTnI, respectively) have shown to be specific markers of muscle damage in healthy volunteers. We aimed therefore at describing the trend of skeletal troponin in mixed population of ICU patients undergoing weaning from mechanical ventilation and compared the value of fsTnI and ssTnI with diaphragmatic ultrasound derived parameters.

Methods: In this prospective observational study we enrolled consecutive patients recovering from acute hypoxemic respiratory failure (AHRF) within 24 h from the start of weaning. Every day an arterial blood sample was collected to measure fsTnI, ssTnI, and global markers of muscle damage, such as ALT, AST, and CPK. Moreover, thickening fraction (TF) and diaphragmatic displacement (DE) were assessed by diaphragmatic ultrasound. The trend of fsTnI and ssTnI was evaluated during the first 3 days of weaning.

Results: We enrolled 62 consecutive patients in the study, with a mean age of 67 ± 13 years and 43 of them (69%) were male. We did not find significant variations in the ssTnI trend (p = 0.623), but fsTnI significantly decreased over time by 30% from Day 1 to Day 2 and by 20% from Day 2 to Day 3 (p < 0.05). There was a significant interaction effect between baseline ssTnI and DE [F₍₂₎ = 4.396, p = 0.015], with high basal levels of ssTnI being associated to a higher decrease in DE. On the contrary, the high basal levels of fsTnI at day 1 were characterized by significant higher DE at each time point.

Conclusions: Skeletal muscle proteins have a distinctive pattern of variation during weaning from mechanical ventilation. At day 1, a high basal value of ssTnI were associated to a higher decrease over time of diaphragmatic function while high values of fsTnI were associated to a higher displacement at each time point.

Three bedside techniques to quantify dynamic pulmonary hyperinflation in mechanically ventilated patients with chronic obstructive pulmonary disease

BACKGROUND

Dynamic pulmonary hyperinflation may develop in patients with chronic obstructive pulmonary disease (COPD) due to dynamic airway collapse and/or increased airway resistance, increasing the risk of volutrauma and hemodynamic compromise. The reference standard to quantify dynamic pulmonary hyperinflation is the measurement of the volume at end-inspiration (Vei). As this is cumbersome, the aim of this study was to evaluate if methods that are easier to perform at the bedside can accurately reflect Vei.

METHODS

Vei was assessed in COPD patients under controlled protective mechanical ventilation (7 ± mL/kg) on zero end-expiratory pressure, using three techniques in a fixed order: (1) reference standard (Vei_reference): passive exhalation to atmosphere from end-inspiration in a calibrated glass burette; (2) ventilator maneuver (Vei_maneuver): measuring the expired volume during a passive exhalation of 45s using the ventilator flow sensor; (3) formula (Vei_formula): (Vt × P_plateau)/(P_plateau - PEEP_i), with Vt tidal volume, P_plateau is plateau pressure after an end-inspiratory occlusion, and PEEP_i is intrinsic positive end-expiratory pressure after an end-expiratory occlusion. A convenience sample of 17 patients was recruited.

RESULTS

Vei_reference was 1030 ± 380 mL and had no significant correlation with P_plateau (r² = 0.06; P = 0.3710) or PEEP_i (r² = 0.11; P = 0.2156), and was inversely related with P_drive (calculated as P_plateau -PEEP_i) (r² = 0.49; P = 0.0024). A low bias but rather wide limits of agreement and fairly good correlations were found when comparing Vei_maneuver and Vei_formula to Vei_reference. Vei remained stable during the study period (low bias 15 mL with high agreement (95% limits of agreement from - 100 to 130 mL) and high correlation (r² = 0.98; P < 0.0001) between both measurements of Vei_reference).

CONCLUSIONS

In patients with COPD, airway pressures are not a valid representation of Vei. The three techniques to quantify Vei show low bias, but wide limits of agreement.

A quantitative analysis of extension and distribution of lung injury in COVID-19: a prospective study based on chest computed tomography

Background

Typical features differentiate COVID-19-associated lung injury from acute respiratory distress syndrome. The clinical role of chest computed tomography (CT) in describing the progression of COVID-19-associated lung injury remains to be clarified. We investigated in COVID-19 patients the regional distribution of lung injury and the influence of clinical and laboratory features on its progression.

Methods

This was a prospective study. For each CT, twenty images, evenly spaced along the cranio-caudal axis, were selected. For regional analysis, each CT image was divided into three concentric subpleural regions of interest and four quadrants. Hyper-, normally, hypo- and non-inflated lung compartments were defined. Nonparametric tests were used for hypothesis testing (α = 0.05). Spearman correlation test was used to detect correlations between lung compartments and clinical features.

Results

Twenty-three out of 111 recruited patients were eligible for further analysis. Five hundred-sixty CT images were analyzed. Lung injury, composed by hypo- and non-inflated areas, was significantly more represented in subpleural than in core lung regions. A secondary, centripetal spread of lung injury was associated with exposure to mechanical ventilation (p < 0.04), longer spontaneous breathing (more than 14 days, p < 0.05) and non-protective tidal volume (p < 0.04). Positive fluid balance (p < 0.01), high plasma D-dimers (p < 0.01) and ferritin (p < 0.04) were associated with increased lung injury.

Conclusions

In a cohort of COVID-19 patients with severe respiratory failure, a predominant subpleural distribution of lung injury is observed. Prolonged spontaneous breathing and high tidal volumes, both causes of patient self-induced lung injury, are associated to an extensive involvement of more central regions. Positive fluid balance, inflammation and thrombosis are associated with lung injury.

Trial registration Study registered a priori the 20th of March, 2020. Clinical Trials ID NCT04316884.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-021-03685-4.

Associations Between Expiratory Flow Limitation and Postoperative Pulmonary Complications in Patients Undergoing Cardiac Surgery

OBJECTIVES

To determine whether driving pressure and expiratory flow limitation are associated with the development of postoperative pulmonary complications (PPCs) in cardiac surgery patients.

DESIGN

Prospective cohort study.

SETTING

University Hospital San Raffaele, Milan, Italy.

PARTICIPANTS

Patients undergoing elective cardiac surgery.

MEASUREMENTS AND MAIN RESULTS

The primary endpoint was the occurrence of a predefined composite of PPCs. The authors determined the association among PPCs and intraoperative ventilation parameters, mechanical power and energy load, and occurrence of expiratory flow limitation (EFL) assessed with the positive end-expiratory pressure test. Two hundred patients were enrolled, of whom 78 (39%) developed one or more PPCs. Patients with PPCs, compared with those without PPCs, had similar driving pressure (mean difference [MD] -0.1 [95% confidence interval (CI), -1.0 to 0.7] cmH₂O, p = 0.561), mechanical power (MD 0.5 [95% CI, -0.3 to 1.1] J/m, p = 0.364), and total energy load (MD 95 [95% CI, -78 to 263] J, p = 0.293), but they had a higher incidence of EFL (51% v 38%, p = 0.005). Only EFL was associated independently with the development of PPCs (odds ratio 2.46 [95% CI, 1.28-4.80], p = 0.007).

CONCLUSIONS

PPCs occurred frequently in this patient population undergoing cardiac surgery. PPCs were associated independently with the presence of EFL but not with driving pressure, total energy load, or mechanical power.

Management of Intraoperative Mechanical Ventilation to Prevent Postoperative Complications after General Anesthesia: A Narrative Review

Mechanical ventilation (MV) is still necessary in many surgical procedures; nonetheless, intraoperative MV is not free from harmful effects. Protective ventilation strategies, which include the combination of low tidal volume and adequate positive end expiratory pressure (PEEP) levels, are usually adopted to minimize the ventilation-induced lung injury and to avoid post-operative pulmonary complications (PPCs). Even so, volutrauma and atelectrauma may co-exist at different levels of tidal volume and PEEP, and therefore, the physiological response to the MV settings should be monitored in each patient. A personalized perioperative approach is gaining relevance in the field of intraoperative MV; in particular, many efforts have been made to individualize PEEP, giving more emphasis on physiological and functional status to the whole body. In this review, we summarized the latest findings about the optimization of PEEP and intraoperative MV in different surgical settings. Starting from a physiological point of view, we described how to approach the individualized MV and monitor the effects of MV on lung function.

Bench Assessment of Expiratory Valve Resistance of Current ICU Ventilators in Dynamic Conditions

BACKGROUND

We hypothesized that the lack of benefit of setting a low versus a high PEEP in patients with ARDS may be due in part to differences in the dynamic behavior of the expiratory valve in ventilators. We tested this hypothesis by conducting a bench comparison of the dynamic behavior of expiratory valves on ICU ventilators currently in use.

METHODS

We attached 7 ICU ventilators (C5, C6, Carescape, PB980, ServoU, V500, and V680) to the ASL 5000 lung model (passive condition with compliance 20 mL/cm H₂O and resistance 5 cm H₂O/L/s) and set in volume controlled mode (tidal volume 0.8 L, breathing frequency 10 breaths/min). Flow and pressure were measured just before the exhalation valve. At PEEP of 5, 10, and 15 cm H₂O, the median instantaneous expiratory resistance, the time to valve opening, and the pressure time products above or below the values of PEEP (expressed in cm H₂O × s) were determined.

RESULTS

Median instantaneous expiratory resistance values differed between the ventilators and PEEP settings with a significant interaction: at PEEP 5 cm H₂O, the median (interquartile range) expiratory resistance values were 3.9 (3.5-4.7), 3.0 (3.0-3.1), 20.9 (15.8-24.9), 27.4 (26.5-43.2), 13.8 (13.6-13.9), 4.4 (4.0-4.6), and 34.3 (33.7-33.8) cm H₂O/L/s, for the C5, C6, Carescape, PB980, ServoU, V500, and V680, respectively. For all the PEEP settings, the corresponding times to valve opening were 0.080 (0.077-0.082), 0.082 (0.080-0.085), 0.110 (0.105-0.110), 0.100 (0.085-1.05), 0.072 (0.062-0.072), 0.145 (0.115-0.150), and 0.075 (0.070-0.080) s, respectively, and pressure-time products were 2.8 (2.1-7.4), 6.8 (6.7-7.3), 2.4 (2.1-2.4), 3.5 (2.7-3.6), 1.8 (1.8-2.1), 2.8 (2.7-2.9), and 5.7 (5.4-5.9) cm H₂O × s, respectively.

CONCLUSIONS

The resistance of active expiratory valves differed significantly between the 7 ICU ventilators tested.

Non-interventional monitoring of expiratory flow limitation during experimental mechanical ventilation

Background

Expiratory flow limitation (EFL) is common among patients in the intensive care unit under mechanical ventilation (MV) and may have significant clinical consequences. In the present study, we examine the possibility of non-interventional detection of EFL during experimental MV.

Methods

Eight artificially ventilated New Zealand rabbits were included in the experiments. EFL was induced during MV by application of negative expiratory pressure (−5, −8 and −10 hPa) and detected by the negative expiratory pressure technique. Airway pressure (P_aw) and gas flow (V′) were digitally recorded and processed off-line for the evaluation of respiratory mechanics. The method is based on the computation and monitoring of instantaneous respiratory resistance R_rs(t). The resistive pressure (P_aw,res(t)) is calculated by subtracting from P_aw its elastic component and the end-expiratory pressure, as assessed by linear regression. Then, R_rs(t) is computed as the instant ratio P_aw,res(t)/V′(t).

Results

Two completely different patterns of expiratory R_rs(t) separate the cases with EFL from those without EFL. Small and random fluctuations are noticed when EFL is absent, whereas the onset of EFL is accompanied by an abrupt and continuous rise in R_rs(t), towards the end of expiration. Thus, EFL is not only detected but may also be quantified from the volume still to be expired at the time EFL occurs.

Conclusion

The proposed technique is a simple, accurate and non-interventional tool for EFL monitoring during MV.

Respiratory system resistance in expiratory flow limitation during mechanical ventilationhttps://bit.ly/34hU6Bv

Respiratory physiology of COVID-19-induced respiratory failure compared to ARDS of other etiologies

BACKGROUND

Whether respiratory physiology of COVID-19-induced respiratory failure is different from acute respiratory distress syndrome (ARDS) of other etiologies is unclear. We conducted a single-center study to describe respiratory mechanics and response to positive end-expiratory pressure (PEEP) in COVID-19 ARDS and to compare COVID-19 patients to matched-control subjects with ARDS from other causes.

METHODS

Thirty consecutive COVID-19 patients admitted to an intensive care unit in Rome, Italy, and fulfilling moderate-to-severe ARDS criteria were enrolled within 24 h from endotracheal intubation. Gas exchange, respiratory mechanics, and ventilatory ratio were measured at PEEP of 15 and 5 cmH2O. A single-breath derecruitment maneuver was performed to assess recruitability. After 1:1 matching based on PaO2/FiO2, FiO2, PEEP, and tidal volume, COVID-19 patients were compared to subjects affected by ARDS of other etiologies who underwent the same procedures in a previous study.

RESULTS

Thirty COVID-19 patients were successfully matched with 30 ARDS from other etiologies. At low PEEP, median [25th-75th percentiles] PaO2/FiO2 in the two groups was 119 mmHg [101-142] and 116 mmHg [87-154]. Average compliance (41 ml/cmH2O [32-52] vs. 36 ml/cmH2O [27-42], p = 0.045) and ventilatory ratio (2.1 [1.7-2.3] vs. 1.6 [1.4-2.1], p = 0.032) were slightly higher in COVID-19 patients. Inter-individual variability (ratio of standard deviation to mean) of compliance was 36% in COVID-19 patients and 31% in other ARDS. In COVID-19 patients, PaO2/FiO2 was linearly correlated with respiratory system compliance (r = 0.52 p = 0.003). High PEEP improved PaO2/FiO2 in both cohorts, but more remarkably in COVID-19 patients (p = 0.005). Recruitability was not different between cohorts (p = 0.39) and was highly inter-individually variable (72% in COVID-19 patients and 64% in ARDS from other causes). In COVID-19 patients, recruitability was independent from oxygenation and respiratory mechanics changes due to PEEP.

CONCLUSIONS

Early after establishment of mechanical ventilation, COVID-19 patients follow ARDS physiology, with compliance reduction related to the degree of hypoxemia, and inter-individually variable respiratory mechanics and recruitability. Physiological differences between ARDS from COVID-19 and other causes appear small.

Expiratory Resistances Prevent Expiratory Diaphragm Contraction, Flow Limitation, and Lung Collapse

Rationale: Tidal expiratory flow limitation (tidal-EFL) is not completely avoidable by applying positive end-expiratory pressure and may cause respiratory and hemodynamic complications in ventilated patients with lungs prone to collapse. During spontaneous breathing, expiratory diaphragmatic contraction counteracts tidal-EFL. We hypothesized that during both spontaneous breathing and controlled mechanical ventilation, external expiratory resistances reduce tidal-EFL.Objectives: To assess whether external expiratory resistances 1) affect expiratory diaphragmatic contraction during spontaneous breathing, 2) reduce expiratory flow and make lung compartments more homogeneous with more similar expiratory time constants, and 3) reduce tidal atelectasis, preventing hyperinflation.Methods: Three positive end-expiratory pressure levels and four external expiratory resistances were tested in 10 pigs after lung lavage. We analyzed expiratory diaphragmatic electric activity and respiratory mechanics. On the basis of computed tomography scans, four lung compartments-not inflated (atelectasis), poorly inflated, normally inflated, and hyperinflated-were defined.Measurements and Main Results: Consequently to additional external expiratory resistances, and mainly in lungs prone to collapse (at low positive end-expiratory pressure), 1) the expiratory transdiaphragmatic pressure decreased during spontaneous breathing by >10%, 2) expiratory flow was reduced and the expiratory time constants became more homogeneous, and 3) the amount of atelectasis at end-expiration decreased from 24% to 16% during spontaneous breathing and from 32% to 18% during controlled mechanical ventilation, without increasing hyperinflation.Conclusions: The expiratory modulation induced by external expiratory resistances preserves the positive effects of the expiratory brake while minimizing expiratory diaphragmatic contraction. External expiratory resistances optimize lung mechanics and limit tidal-EFL and tidal atelectasis, without increasing hyperinflation.

Lung and chest wall mechanics in patients with acute respiratory distress syndrome, expiratory flow limitation, and airway closure

Tidal expiratory flow limitation (EFL), which may herald airway closure (AC), is a mechanism of loss of aeration in ARDS. In this prospective, short-term, two-center study, we measured static and dynamic chest wall (Est,cw and Edyn,cw) and lung (Est,L and Edyn,L) elastance with esophageal pressure, EFL, and AC at 5 cmH₂O positive end-expiratory pressure (PEEP) in intubated, sedated, and paralyzed ARDS patients. For EFL determination, we used the atmospheric method and a new device allowing comparison of tidal flow during expiration to PEEP and to atmosphere. AC was validated when airway opening pressure (AOP) assessed from volume-pressure curve was found greater than PEEP by at least 1 cmH₂O. EFL was defined whenever flow did not increase between exhalation to PEEP and to atmosphere over all or part of expiration. Elastance values were expressed as percentage of normal predicted values (%N). Among the 25 patients included, eight had EFL (32%) and 13 AOP (52%). Between patients with and without EFL Edyn,cw [median (1st to 3rd quartiles)] was 70 (16-127) and 102 (70-142) %N (P = 0.32) and Edyn,L338 (332-763) and 224 (160-275) %N (P < 0.001). The corresponding values for Est,cw and Est,L were 70 (56-88) and 85 (64-103) %N (P = 0.35) and 248 (206-348) and 170 (144-195) (P = 0.02), respectively. Dynamic E_L had an area receiver operating characteristic curve of 0.88 [95% confidence intervals 0.83-0.92] for EFL and 0.74[0.68-0.79] for AOP. Higher Edyn,L was accurate to predict EFL in ARDS patients; AC can occur independently of EFL, and both should be assessed concurrently in ARDS patients.NEW & NOTEWORTHY Expiratory flow limitation (EFL) and airway closure (AC) were observed in 32% and 52%, respectively, of 25 patients with ARDS investigated during mechanical ventilation in supine position with a positive end-expiratory pressure of 5 cmH₂O. The performance of dynamic lung elastance to detect expiratory flow limitation was good and better than that to detect airway closure. The vast majority of patients with EFL also had AC; however, AC can occur in the absence of EFL.