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BACKGROUND: Retention of airway secretions is a common and serious problem in ventilated patients. Treating or avoiding secretion retention with mucus thinning, patient-positioning, airway suctioning, or chest or airway vibration or percussion may provide short-term benefit. METHODS: In a series of laboratory experiments with a test-lung system we examined the role of ventilator settings and lung-impedance on secretion retention and expulsion. Known quantities of a synthetic dye-stained mucus simulant with clinically relevant properties were injected into a transparent tube the diameter of an adult trachea and exposed to various mechanical-ventilation conditions. Mucussimulant movement was measured with a photodensitometric technique and examined with imageanalysis software. We tested 2 mucus-simulant viscosities and various peak flows, inspiratoryl expiratory flow ratios, intrinsic positive end-expiratory pressures, ventilation waveforms, and impedance values. RESULTS: Ventilator settings that produced flow bias had a major effect on mucus movement. Expiratory flow bias associated with intrinsic positive end-expiratory pressure generated by elevated minute ventilation moved mucus toward the airway opening, whereas intrinsic positive end-expiratory pressure generated by increased airway resistance moved the mucus toward the lungs. Inter-lung transfer of mucus simulant occurred rapidly across the 'carina! divider' between interconnected test lungs set to radically different compliances; the mucus moved out of the low-compliance lung and into the high-compliance lung. CONCLUSIONS: The movement of mucus simulant was influenced by the ventilation pattern and lung impedance. Flow bias obtained with ventilator settings may clear or embed mucus during mechanical ventilation. [ABSTRACT FROM AUTHOR]

Rationale: The hypothesis that lung collapse is detrimental during the acute respiratory distress syndrome is still debatable. One of the difficulties is the lack of an efficient maneuver to minimize it. Objectives: To test if a bedside recruitment strategy, capable of reversing hypoxemia and collapse in > 95% of lung units, is clinically applicable in early acute respiratory distress syndrome. Methods: Prospective assessment of a stepwise maximum-recruitment strategy using multislice computed tomography and continuous blood-gas hemodynamic monitoring. Measurements and Main Results: Twenty-six patients received sequential increments in inspiratory airway pressures, in 5 cm H(2)O steps, until the detection of Pa(O(2)) + Pa(CO(2)) >or= 400 mm Hg. Whenever this primary target was not met, despite inspiratory pressures reaching 60 cm H(2)O, the maneuver was considered incomplete. If there was hemodynamic deterioration or barotrauma, the maneuver was to be interrupted. Late assessment of recruitment efficacy was performed by computed tomography (9 patients) or by online continuous monitoring in the intensive care unit (15 patients) up to 6 h. It was possible to open the lung and to keep the lung open in the majority (24/26) of patients, at the expense of transient hemodynamic effects and hypercapnia but without major clinical consequences. No barotrauma directly associated with the maneuver was detected. There was a strong and inverse relationship between arterial oxygenation and percentage of collapsed lung mass (R = - 0.91; p < 0.0001). Conclusions: It is often possible to reverse hypoxemia and fully recruit the lung in early acute respiratory distress syndrome. Due to transient side effects, the required maneuver still awaits further evaluation before routine clinical application. [ABSTRACT FROM AUTHOR]

Imbalances in regional lung ventilation, with gravity-dependent collapse and overdistention of nondependent zones, are likely associated to ventilator-induced lung injury. Electric impedance tomography is a new imaging technique that is potentially capable of monitoring those imbalances. The aim of this study was to validate electrical impedance tomography measurements of ventilation distribution, by comparison with dynamic computerized tomography in a heterogeneous population of critically ill patients under mechanical ventilation. Multiple scans with both devices were collected during slow-inflation breaths. Six repeated breaths were monitored by impedance tomography, showing acceptable reproducibility. We observed acceptable agreement between both technologies in detecting right-left ventilation imbalances (bias = 0% and limits of agreement = -10 to +10%). Relative distribution of ventilation into regions or layers representing one-fourth of the thoracic section could also be assessed with good precision. Depending on electrode positioning, impedance tomography slightly overestimated ventilation imbalances along gravitational axis. Ventilation was gravitationally dependent in all patients, with some transient blockages in dependent regions synchronously detected by both scanning techniques. Among variables derived from computerized tomography, changes in absolute air content best explained the integral of impedance changes inside regions of interest (r(2) > or = 0.92). Impedance tomography can reliably assess ventilation distribution during mechanical ventilation. [ABSTRACT FROM AUTHOR]

Background: Double cycling with breath-stacking (DC/BS) during controlled mechanical ventilation is considered potentially injurious, reflecting a high respiratory drive. During partial ventilatory support, its occurrence might be attributable to physiological variability of breathing patterns, reflecting the response of the mode without carrying specific risks., Methods: This secondary analysis of a crossover study evaluated DC/BS events in hypoxemic patients resuming spontaneous breathing in cross-over under neurally adjusted ventilatory assist (NAVA), proportional assist ventilation (PAV +), and pressure support ventilation (PSV). DC/BS was defined as two inspiratory cycles with incomplete exhalation. Measurements included electrical impedance signal, airway pressure, esophageal and gastric pressures, and flow. Breathing variability, dynamic compliance (C L dyn), and end-expiratory lung impedance (EELI) were analyzed., Results: Twenty patients under assisted breathing, with a median of 9 [5-14] days on mechanical ventilation, were included. DC/BS was attributed to either a single (42%) or two apparent consecutive inspiratory efforts (58%). The median [IQR] incidence of DC/BS was low: 0.6 [0.1-2.6] % in NAVA, 0.0 [0.0-0.4] % in PAV + , and 0.1 [0.0-0.4] % in PSV (p = 0.06). DC/BS events were associated with patient's coefficient of variability for tidal volume (p = 0.014) and respiratory rate (p = 0.011). DC/BS breaths exhibited higher tidal volume, muscular pressure and regional stretch compared to regular breaths. Post-DC/BS cycles frequently exhibited improved EELI and C L dyn, with no evidence of expiratory muscle activation in 63% of cases., Conclusions: DC/BS events during partial ventilatory support were infrequent and linked to breathing variability. Their frequency and physiological effects on lung compliance and EELI resemble spontaneous sighs and may not be considered a priori as harmful., Competing Interests: Declarations. Ethics approval and consent to participate: The Institutional Review Board reviewed and approved the study (approval number N.027/2016, Comité Ético Científico Hospital Clínico Universidad de Chile). Informed consent was obtained from the patient’s next of kin. Competing interests: The authors declare that they have no competing interests., (© 2025. The Author(s).)

Electrical Impedance Tomography (EIT) is a groundbreaking, non-invasive, and radiation-free imaging technique for continuous, real-time ventilation monitoring. It also has an application in pulmonary perfusion monitoring. EIT quantifies ventilation and perfusion patterns across the lung from the measurement and processing of impedance changes in the thorax. It is a powerful tool for clinicians to visualize breath-by-breath changes in pulmonary function. An innovative application of EIT is its ability to assess pulmonary perfusion using the kinetic analysis of a hypertonic solution injection during a breath-hold. The solution generates an impedance change in the thorax as it circulates through the pulmonary vasculature. This indirect method allows for the estimation of perfusion patterns, contributing significantly to our understanding of pulmonary blood flow dynamics at the bedside. EIT is not just a tool for monitoring but also can be critical for the diagnosis of respiratory pathologies such as pneumothorax and bronchial intubation. It can help identify the etiology of ventilation/perfusion (V/Q) mismatch in patients receiving invasive mechanical ventilation, which is not possible with other diagnostic tools. Moreover, EIT can assist in the individual optimization of ventilator settings, such as Positive End-Expiratory Pressure (PEEP) titration and tidal volume improving oxygenation and lung health in critical care. In summary, EIT represents a paradigm shift in bedside pulmonary monitoring and diagnostics. Its non-invasive nature and immediacy of data make EIT an indispensable tool in modern respiratory medicine. With its growing applications, EIT will be pivotal in advancing our understanding of and approach to respiratory care, particularly in intensive care settings.

Background: Bronchoscopic lung volume reduction (BLVR) with one-way endobronchial valves (EBV) has better outcomes when the target lobe has poor collateral ventilation, resulting in complete lobe atelectasis. High-inspired oxygen fraction (F I O 2 ) promotes atelectasis through faster gas absorption after airway occlusion, but its application during BLVR with EBV has been poorly understood. We aimed to investigate the real-time effects of F I O 2 on regional lung volumes and regional ventilation/perfusion by electrical impedance tomography (EIT) during BLVR with EBV., Methods: Six piglets were submitted to left lower lobe occlusion by a balloon-catheter and EBV valves with F I O 2 0.5 and 1.0. Regional end-expiratory lung impedances (EELI) and regional ventilation/perfusion were monitored. Local pocket pressure measurements were obtained (balloon occlusion method). One animal underwent simultaneous acquisitions of computed tomography (CT) and EIT. Regions-of-interest (ROIs) were right and left hemithoraces., Results: Following balloon occlusion, a steep decrease in left ROI-EELI with F I O 2 1.0 occurred, 3-fold greater than with 0.5 (p < 0.001). Higher F I O 2 also enhanced the final volume reduction (ROI-EELI) achieved by each valve (p < 0.01). CT analysis confirmed the denser atelectasis and greater volume reduction achieved by higher F I O 2 (1.0) during balloon occlusion or during valve placement. CT and pocket pressure data agreed well with EIT findings, indicating greater strain redistribution with higher F I O 2 ., Conclusions: EIT demonstrated in real-time a faster and more complete volume reduction in the occluded lung regions under high F I O 2 (1.0), as compared to 0.5. Immediate changes in the ventilation and perfusion of ipsilateral non-target lung regions were also detected, providing better estimates of the full impact of each valve in place., Trial Registration: Not applicable., (© 2024. The Author(s).)

Rationale: It is unknown whether preventing overdistention or collapse is more important when titrating positive end-expiratory pressure (PEEP) in acute respiratory distress syndrome (ARDS). Objectives: To compare PEEP targeting minimal overdistention or minimal collapse or using a compromise between collapse and overdistention in a randomized trial and to assess the impact on respiratory mechanics, gas exchange, inflammation, and hemodynamics. Methods: In a porcine model of ARDS, lung collapse and overdistention were estimated using electrical impedance tomography during a decremental PEEP titration. Pigs were randomized to three groups and ventilated for 12 hours: PEEP set at ⩽3% of overdistention (low overdistention), ⩽3% of collapse (low collapse), and the crossing point of collapse and overdistention. Measurements and Main Results: Thirty-six pigs (12 per group) were included. Median (interquartile range) values of PEEP were 7 (6-8), 11 (10-11), and 15 (12-16) cm H 2 O in the three groups ( P  < 0.001). With low overdistension, 6 (50%) pigs died, whereas survival was 100% in both other groups. Cause of death was hemodynamic in nature, with high transpulmonary vascular gradient and high epinephrine requirements. Compared with the other groups, pigs surviving with low overdistension had worse respiratory mechanics and gas exchange during the entire protocol. Minimal differences existed between crossing-point and low-collapse animals in physiological parameters, but postmortem alveolar density was more homogeneous in the crossing-point group. Inflammatory markers were not significantly different. Conclusions: PEEP to minimize overdistention resulted in high mortality in an animal model of ARDS. Minimizing collapse or choosing a compromise between collapse and overdistention may result in less lung injury, with potential benefits of the compromise approach.

Background: Protective ventilation seems crucial during early Acute Respiratory Distress Syndrome (ARDS), but the optimal duration of lung protection remains undefined. High driving pressures (ΔP) and excessive patient ventilatory drive may hinder lung recovery, resulting in self-inflicted lung injury. The hidden nature of the ΔP generated by patient effort complicates the situation further. Our study aimed to assess the feasibility of an extended lung protection strategy that includes a stepwise protocol to control the patient ventilatory drive, assessing its impact on lung recovery., Methods: We conducted a single-center randomized study on patients with moderate/severe COVID-19-ARDS with low respiratory system compliance (C RS  < 0.6 (mL/Kg)/cmH 2 O). The intervention group received a ventilation strategy guided by Electrical Impedance Tomography aimed at minimizing ΔP and patient ventilatory drive. The control group received the ARDSNet low-PEEP strategy. The primary outcome was the modified lung injury score ( m LIS), a composite measure that integrated daily measurements of C RS , along with oxygen requirements, oxygenation, and X-rays up to day 28. The m LIS score was also hierarchically adjusted for survival and extubation rates., Results: The study ended prematurely after three consecutive months without patient enrollment, attributed to the pandemic subsiding. The intention-to-treat analysis included 76 patients, with 37 randomized to the intervention group. The average m LIS score up to 28 days was not different between groups (P = 0.95, primary outcome). However, the intervention group showed a faster improvement in the m LIS (1.4 vs. 7.2 days to reach 63% of maximum improvement; P < 0.001), driven by oxygenation and sustained improvement of X-ray (P = 0.001). The intervention group demonstrated a sustained increase in C RS up to day 28 (P = 0.009) and also experienced a shorter time from randomization to room-air breathing (P = 0.02). Survival at 28 days and time until liberation from the ventilator were not different between groups., Conclusions: The implementation of an individualized PEEP strategy alongside extended lung protection appears viable. Promising secondary outcomes suggested a faster lung recovery, endorsing further examination of this strategy in a larger trial. Clinical trial registration This trial was registered with ClinicalTrials.gov (number NCT04497454) on August 04, 2020., (© 2024. The Author(s).)

Objective: To examine the physical function and respiratory muscle strength of patients - who recovered from critical COVID-19 - after intensive care unit discharge to the ward on Days one (D1) and seven (D7), and to investigate variables associated with functional impairment., Methods: This was a prospective cohort study of adult patients with COVID-19 who needed invasive mechanical ventilation, non-invasive ventilation or high-flow nasal cannula and were discharged from the intensive care unit to the ward. Participants were submitted to Medical Research Council sum-score, handgrip strength, maximal inspiratory pressure, maximal expiratory pressure, and short physical performance battery tests. Participants were grouped into two groups according to their need for invasive ventilation: the Invasive Mechanical Ventilation Group (IMV Group) and the Non-Invasive Mechanical Ventilation Group (Non-IMV Group)., Results: Patients in the IMV Group (n = 31) were younger and had higher Sequential Organ Failure Assessment scores than those in the Non-IMV Group (n = 33). The short physical performance battery scores (range 0 - 12) on D1 and D7 were 6.1 ± 4.3 and 7.3 ± 3.8, respectively for the Non-Invasive Mechanical Ventilation Group, and 1.3 ± 2.5 and 2.6 ± 3.7, respectively for the IMV Group. The prevalence of intensive care unit-acquired weakness on D7 was 13% for the Non-IMV Group and 72% for the IMV Group. The maximal inspiratory pressure, maximal expiratory pressure, and handgrip strength increased on D7 in both groups, but the maximal expiratory pressure and handgrip strength were still weak. Only maximal inspiratory pressure was recovered (i.e., > 80% of the predicted value) in the Non-IMV Group. Female sex, and the need and duration of invasive mechanical were independently and negatively associated with the short physical performance battery score and handgrip strength., Conclusion: Patients who recovered from critical COVID-19 and who received invasive mechanical ventilation presented greater disability than those who were not invasively ventilated. However, they both showed marginal functional improvement during early recovery, regardless of the need for invasive mechanical ventilation. This might highlight the severity of disability caused by SARS-CoV-2.

Background: Lower fractional inspired oxygen tension (Fio2) during general anesthesia can reduce lung atelectasis. The objectives are to evaluate the effect of two Fio2 (0.4 and 1) during low positive end-expiratory pressure (PEEP) ventilation over lung perfusion distribution, volume, and regional ventilation. These variables were evaluated at two PEEP levels and unilateral lung atelectasis., Methods: In this exploratory study, 10 healthy female piglets (32.3 ± 3.4 kg) underwent mechanical ventilation in two atelectasis models: (1) bilateral gravitational atelectasis (n = 6), induced by changes in PEEP and Fio2 in three combinations: high PEEP with low Fio2 (Fio2 = 0.4), zero PEEP (PEEP0) with low Fio2 (Fio2 = 0.4), and PEEP0 with high Fio2 (Fio2 = 1); and (2) unilateral atelectasis (n = 6), induced by left bronchial occlusion, with the left lung aerated (Fio2 = 0.21) and low aerated (Fio2 = 1; n = 5 for this step). Measurements were conducted after 10 min in each step, encompassing assessment of respiratory mechanics, oxygenation, and hemodynamics; lung ventilation and perfusion by electrical impedance tomography; and lung aeration and perfusion by computed tomography., Results: During bilateral gravitational atelectasis, PEEP reduction increased atelectasis in dorsal regions, decreased respiratory compliance, and distributed lung ventilation to ventral regions with a parallel shift of perfusion to the same areas. With PEEP0, there were no differences between low and high Fio2 in respiratory compliance (23.9 ± 6.5 ml/cm H2O vs. 21.9 ± 5.0; P = 0.441), regional ventilation, and regional perfusion, despite higher lung collapse (18.6 ± 7.6% vs. 32.7 ± 14.5%; P = 0.045) with high Fio2. During unilateral lung atelectasis, the deaerated lung had a lower shunt (19.3 ± 3.6% vs. 25.3 ± 5.5%; P = 0.045) and lower computed tomography perfusion to the left lung (8.8 ± 1.8% vs. 23.8 ± 7.1%; P = 0.007)., Conclusions: PEEP0 with low Fio2, compared with high Fio2, did not produce significant changes in respiratory system compliance, regional lung ventilation, and perfusion despite significantly lower lung collapse. After left bronchial occlusion, the shrinkage of the parenchyma with Fio2 = 1 enhanced hypoxic pulmonary vasoconstriction, reducing intrapulmonary shunt and perfusion of the nonventilated areas., (Copyright © 2024 American Society of Anesthesiologists. All Rights Reserved.)

Rationale: Hypoxemia during mechanical ventilation might be worsened by expiratory muscle activity, which reduces end-expiratory lung volume through lung collapse. A proposed mechanism of benefit of neuromuscular blockade in acute respiratory distress syndrome (ARDS) is the abolition of expiratory efforts. This may contribute to the restoration of lung volumes. The prevalence of this phenomenon, however, is unknown. Objectives: To investigate the incidence and amount of end-expiratory lung impedance (EELI) increase after the administration of neuromuscular blocking agents (NMBAs), clinical factors associated with this phenomenon, its impact on regional lung ventilation, and any association with changes in pleural pressure. Methods: We included mechanically ventilated patients with ARDS monitored with electrical impedance tomography (EIT) who received NMBAs in one of two centers. We measured changes in EELI, a surrogate for end-expiratory lung volume, before and after NMBA administration. In an additional 10 patients, we investigated the characteristic signatures of expiratory muscle activity depicted by EIT and esophageal catheters simultaneously. Clinical factors associated with EELI changes were assessed. Measurements and Main Results: We included 46 patients, half of whom showed an increase in EELI of >10% of the corresponding Vt (46.2%; IQR, 23.9-60.9%). The degree of EELI increase correlated positively with fentanyl dosage and negatively with changes in end-expiratory pleural pressures. This suggests that expiratory muscle activity might exert strong counter-effects against positive end-expiratory pressure that are possibly aggravated by fentanyl. Conclusions: Administration of NMBAs during EIT monitoring revealed activity of expiratory muscles in half of patients with ARDS. The resultant increase in EELI had a dose-response relationship with fentanyl dosage. This suggests a potential side effect of fentanyl during protective ventilation.

Objective . Understanding a patient's respiratory effort and mechanics is essential for the provision of individualized care during mechanical ventilation. However, measurement of transpulmonary pressure (the difference between airway and pleural pressures) is not easily performed in practice. While airway pressures are available on most mechanical ventilators, pleural pressures are measured indirectly by an esophageal balloon catheter. In many cases, esophageal pressure readings take other phenomena into account and are not a reliable measure of pleural pressure. Approach. A system identification approach was applied to provide accurate pleural measures from esophageal pressure readings. First, we used a closed pressurized chamber to stimulate an esophageal balloon and model its dynamics. Second, we created a simplified version of an artificial lung and tried the model with different ventilation configurations. For validation, data from 11 patients (five male and six female) were used to estimate respiratory effort profile and patient mechanics. Main results. After correcting the dynamic response of the balloon catheter, the estimates of resistance and compliance and the corresponding respiratory effort waveform were improved when compared with the adjusted quantities in the test bench. The performance of the estimated model was evaluated using the respiratory pause/occlusion maneuver, demonstrating improved agreement between the airway and esophageal pressure waveforms when using the normalized mean squared error metric. Using the corrected muscle pressure waveform, we detected start and peak times 130 ± 50 ms earlier and a peak amplitude 2.04 ± 1.46 cmH 2 O higher than the corresponding estimates from esophageal catheter readings. Significance. Compensating the acquired measurements with system identification techniques makes the readings more accurate, possibly better portraying the patient's situation for individualization of ventilation therapy., (© 2024 Institute of Physics and Engineering in Medicine.)

Objectives: High mechanical power and driving pressure (ΔP) have been associated with postoperative respiratory failure (PRF) and may be important parameters guiding mechanical ventilation. However, it remains unclear whether high mechanical power and ΔP merely reflect patients with poor respiratory system mechanics at risk of PRF. We investigated the effect of mechanical power and ΔP on PRF in cohorts after exact matching by patients' baseline respiratory system compliance., Design: Hospital registry study., Setting: Academic hospital in New England., Patients: Adult patients undergoing general anesthesia between 2008 and 2020., Intervention: None., Measurements and Main Results: The primary exposure was high (≥ 6.7 J/min, cohort median) versus low mechanical power and the key-secondary exposure was high (≥ 15.0 cm H 2 O) versus low ΔP. The primary endpoint was PRF (reintubation or unplanned noninvasive ventilation within seven days). Among 97,555 included patients, 4,030 (4.1%) developed PRF. In adjusted analyses, high intraoperative mechanical power and ΔP were associated with higher odds of PRF (adjusted odds ratio [aOR] 1.37 [95% CI, 1.25-1.50]; p < 0.001 and aOR 1.45 [95% CI, 1.31-1.60]; p < 0.001, respectively). There was large variability in applied ventilatory parameters, dependent on the anesthesia provider. This facilitated matching of 63,612 (mechanical power cohort) and 53,260 (ΔP cohort) patients, yielding identical baseline standardized respiratory system compliance (standardized difference [SDiff] = 0.00) with distinctly different mechanical power (9.4 [2.4] vs 4.9 [1.3] J/min; SDiff = -2.33) and ΔP (19.3 [4.1] vs 11.9 [2.1] cm H 2 O; SDiff = -2.27). After matching, high mechanical power and ΔP remained associated with higher risk of PRF (aOR 1.30 [95% CI, 1.17-1.45]; p < 0.001 and aOR 1.28 [95% CI, 1.12-1.46]; p < 0.001, respectively)., Conclusions: High mechanical power and ΔP are associated with PRF independent of patient's baseline respiratory system compliance. Our findings support utilization of these parameters for titrating mechanical ventilation in the operating room and ICU., Competing Interests: Drs. Talmor and Baedorf-Kassis received funding from Hamilton Medical. Drs. Talmor and Schaefer received funding from Mindray Medical. Dr. Amato’s institution received funding from Covidien/Mdtronics, Orange Med/Nihon Kohden, and Timpel; he disclosed that he is a minority shareholder in Timpel. Dr. Schaefer received funding from Jeffrey and Judy Buzen, Merck & Co., and Fisher and Paykel Healthcare; he disclosed that he is an Associate Editor for BMC Anesthesiology. The remaining authors have disclosed that they do not have any potential conflicts of interest., (Copyright © 2023 by the Society of Critical Care Medicine and Wolters Kluwer Health, Inc. All Rights Reserved.)

Background: Internal redistribution of gas, referred to as pendelluft, is a new potential mechanism of effort-dependent lung injury. Neurally-adjusted ventilatory assist (NAVA) and proportional assist ventilation (PAV +) follow the patient's respiratory effort and improve synchrony compared with pressure support ventilation (PSV). Whether these modes could prevent the development of pendelluft compared with PSV is unknown. We aimed to compare pendelluft magnitude during PAV + and NAVA versus PSV in patients with resolving acute respiratory distress syndrome (ARDS)., Methods: Patients received either NAVA, PAV + , or PSV in a crossover trial for 20-min using comparable assistance levels after controlled ventilation (> 72 h). We assessed pendelluft (the percentage of lost volume from the non-dependent lung region displaced to the dependent region during inspiration), drive (as the delta esophageal swing of the first 100 ms [ΔP es 100 ms ]) and inspiratory effort (as the esophageal pressure-time product per minute [PTP min ]). We performed repeated measures analysis with post-hoc tests and mixed-effects models., Results: Twenty patients mechanically ventilated for 9 [5-14] days were monitored. Despite matching for a similar tidal volume, respiratory drive and inspiratory effort were slightly higher with NAVA and PAV + compared with PSV (ΔP es 100 ms of -2.8 [-3.8--1.9] cm H 2 O, -3.6 [-3.9--2.4] cm H 2 O and -2.1 [-2.5--1.1] cm H 2 O, respectively, p < 0.001 for both comparisons; PTP min of 155 [118-209] cm H 2 O s/min, 197 [145-269] cm H 2 O s/min, and 134 [93-169] cm H 2 O s/min, respectively, p < 0.001 for both comparisons). Pendelluft magnitude was higher in NAVA (12 ± 7%) and PAV + (13 ± 7%) compared with PSV (8 ± 6%), p < 0.001. Pendelluft magnitude was strongly associated with respiratory drive (β = -2.771, p-value < 0.001) and inspiratory effort (β = 0.026, p  < 0.001), independent of the ventilatory mode. A higher magnitude of pendelluft in proportional modes compared with PSV existed after adjusting for PTP min (β = 2.606, p = 0.010 for NAVA, and β = 3.360, p = 0.004 for PAV +), and only for PAV + when adjusted for respiratory drive (β = 2.643, p = 0.009 for PAV +)., Conclusions: Pendelluft magnitude is associated with respiratory drive and inspiratory effort. Proportional modes do not prevent its occurrence in resolving ARDS compared with PSV., (© 2023. The Author(s).)

Background: In the acute distress respiratory syndrome (ARDS), specific lung regions can be exposed to excessive strain due to heterogeneous disease, gravity-dependent lung collapse and injurious mechanical ventilation. Computed tomography (CT) is the gold standard for regional strain assessment. An alternative tool could be the electrical impedance tomography (EIT). We aimed to determine whether EIT-based methods can predict the dynamic relative regional strain (DRRS) between two levels of end-expiratory pressure (PEEP) in gravity-non-dependent and dependent lung regions., Methods: Fourteen ARDS patients underwent CT and EIT acquisitions (at end-inspiratory and end-expiratory) at two levels of PEEP: a low-PEEP based on ARDS-net strategy and a high-PEEP titrated according to EIT. Three EIT-based methods for DRRS were compared to relative CT-based strain: (1) the change of the ratio between EIT ventilation and end-expiratory lung impedance in arbitrary units ([ΔZ AU low-PEEP /EELI AU low-PEEP ]/[ΔZ AU high-PEEP /EELI AU high-PEEP ]), (2) the change of ΔZ/EELI ratio calibrated to mL ([ΔZ ml low-PEEP /EELI ml low-PEEP ]/[ΔZ ml high-PEEP /EELI ml high-PEEP ]) using CT data, and (3) the relative change of ∆Z AU (∆Z AU low-PEEP /∆Z AU high-PEEP ). We performed linear regressions analysis and calculated bias and limits of agreement to assess the performance of DRRS by EIT in comparison with CT., Results: The DRRS assessed by (ΔZ ml low-PEEP /EELI ml low-PEEP )/(ΔZ ml high-PEEP /EELI ml high-PEEP ) and ∆Z AU low-PEEP /∆Z AU high-PEEP showed good relationship and agreement with the CT method (R 2 of 0.9050 and 0.8679, respectively, in non-dependent region; R 2 of 0.8373 and 0.6588, respectively, in dependent region; biases ranging from - 0.11 to 0.51 and limits of agreement ranging from - 0.73 to 1.16 for both methods and lung regions). Conversely, DRRS based on EELI AU ([ΔZ AU low-PEEP /EELI AU low-PEEP ]/[ΔZ AU high-PEEP /EELI AU high-PEEP ]) exhibited a weak negative relationship and poor agreement with the CT method for both non-dependent and dependent regions (R 2  ~ 0.3; bias of 3.11 and 2.08, and limits of agreement of - 2.13 to 8.34 and from - 1.49 to 5.64, respectively)., Conclusion: Changes in DRRS during a PEEP trial in ARDS patients could be monitored using EIT, based on changes in ΔZ mL /EELI ml and ∆Z AU . The relative change ∆Z AU offers the advantage of not requiring CT data for calibration., (© 2023. The Author(s).)

Objectives: Experimental models suggest that prone position and positive end-expiratory pressure (PEEP) homogenize ventral-dorsal ventilation distribution and regional respiratory compliance. However, this response still needs confirmation on humans. Therefore, this study aimed to assess the changes in global and regional respiratory mechanics in supine and prone positions over a range of PEEP levels in acute respiratory distress syndrome (ARDS) patients., Design: A prospective cohort study., Patients: Twenty-two intubated patients with ARDS caused by COVID-19 pneumonia., Interventions: Electrical impedance tomography and esophageal manometry were applied during PEEP titrations from 20 cm H 2 O to 6 cm H 2 O in supine and prone positions., Measurements: Global respiratory system compliance (Crs), chest wall compliance, regional lung compliance, ventilation distribution in supine and prone positions., Main Results: Compared with supine position, the maximum level of Crs changed after prone position in 59% of ARDS patients ( n = 13), of which the Crs decreased in 32% ( n = 7) and increased in 27% ( n = 6). To reach maximum Crs after pronation, PEEP was changed in 45% of the patients by at least 4 cm H 2 O. After pronation, the ventilation and compliance of the dorsal region did not consistently change in the entire sample of patients, increasing specifically in a subgroup of patients who showed a positive change in Crs when transitioning from supine to prone position. These combined changes in ventilation and compliance suggest dorsal recruitment postpronation. In addition, the subgroup with increased Crs postpronation demonstrated the most pronounced difference between dorsal and ventral ventilation distribution from supine to prone position ( p = 0.01), indicating heterogeneous ventilation distribution in prone position., Conclusions: Prone position modifies global respiratory compliance in most patients with ARDS. Only a subgroup of patients with a positive change in Crs postpronation presented a consistent improvement in dorsal ventilation and compliance. These data suggest that the response to pronation on global and regional mechanics can vary among ARDS patients, with some patients presenting more dorsal lung recruitment than others., (Copyright © 2023 The Authors. Published by Wolters Kluwer Health, Inc. on behalf of the Society of Critical Care Medicine.)

The aim of these guidelines is to update the 2017 clinical practice guideline (CPG) of the European Society of Intensive Care Medicine (ESICM). The scope of this CPG is limited to adult patients and to non-pharmacological respiratory support strategies across different aspects of acute respiratory distress syndrome (ARDS), including ARDS due to coronavirus disease 2019 (COVID-19). These guidelines were formulated by an international panel of clinical experts, one methodologist and patients' representatives on behalf of the ESICM. The review was conducted in compliance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement recommendations. We followed the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach to assess the certainty of evidence and grade recommendations and the quality of reporting of each study based on the EQUATOR (Enhancing the QUAlity and Transparency Of health Research) network guidelines. The CPG addressed 21 questions and formulates 21 recommendations on the following domains: (1) definition; (2) phenotyping, and respiratory support strategies including (3) high-flow nasal cannula oxygen (HFNO); (4) non-invasive ventilation (NIV); (5) tidal volume setting; (6) positive end-expiratory pressure (PEEP) and recruitment maneuvers (RM); (7) prone positioning; (8) neuromuscular blockade, and (9) extracorporeal life support (ECLS). In addition, the CPG includes expert opinion on clinical practice and identifies the areas of future research., (© 2023. The Author(s).)

ICU clinicians rely on bedside physiological measurements to inform many routine clinical decisions. Because deranged physiology is usually associated with poor clinical outcomes, it is tempting to hypothesize that manipulating and intervening on physiological parameters might improve outcomes for patients. However, testing these hypotheses through mathematical models of the relationship between physiology and outcomes presents a number of important methodological challenges. These models reflect the theories of the researcher and can therefore be heavily influenced by one's assumptions and background beliefs. Model building must therefore be approached with great care and forethought, because failure to consider relevant sources of measurement error, confounding, coupling, and time dependency or failure to assess the direction of causality for associations of interest before modeling may give rise to spurious results. This paper outlines the main challenges in analyzing and interpreting these models and offers potential solutions to address these challenges.

The study aimed to evaluate a quantification method of pulmonary perfusion with Dual-Energy CT Angiography (DE-CTA) normalized by lung density in the prediction of outcome in acute pulmonary embolism (PE). In this prospective study with CTA scans acquired with different breathing protocols, two perfusion parameters were calculated: %PBV (relative value of PBV, expressed per unit volume) and PBVm (PBV normalized by lung density, expressed per unit mass). DE-CTA parameters were correlated with simplified pulmonary embolism severity index (sPESI) and with outcome groups, alone and in combinationwith tomographic right-to-left ventricular ratios (RV/LV). PBVm showed significant correlation with sPESI. PBVm presented higher accuracy than %PBV In the prediction of ICU admission or death in patients with PE, with the best performance when combined with RV/LV volumetric ratio., (© 2022. The Author(s), under exclusive licence to Springer Nature B.V.)

Introduction: General anesthesia is associated with the development of atelectasis, which may affect lung ventilation. Electrical impedance tomography (EIT) is a noninvasive imaging tool that allows monitoring in real time the topographical changes in aeration and ventilation., Objective: To evaluate the pattern of distribution of pulmonary ventilation through EIT before and after anesthesia induction in pediatric patients without lung disease undergoing nonthoracic surgery., Methods: This was a prospective observational study including healthy children younger than 5 years who underwent nonthoracic surgery. Monitoring was performed continuously before and throughout the surgical period. Data analysis was divided into 5 periods: induction (spontaneous breathing, SB), ventilation-5min, ventilation-30min, ventilation-late and recovery-SB. In addition to demographic data, mechanical ventilation parameters were also collected. Ventilation impedance (Delta Z) and pulmonary ventilation distribution were analyzed cycle by cycle at the 5 periods., Results: Twenty patients were included, and redistribution of ventilation from the posterior to the anterior region was observed with the beginning of mechanical ventilation: on average, the percentage ventilation distribution in the dorsal region decreased from 54%(IC95%:49-60%) to 49%(IC95%:44-54%). With the restoration of spontaneous breathing, ventilation in the posterior region was restored., Conclusion: There were significant pulmonary changes observed during anesthesia and controlled mechanical ventilation in children younger than 5 years, mirroring the findings previously described adults. Monitoring these changes may contribute to guiding the individualized settings of the mechanical ventilator with the goal to prevent postoperative complications., Competing Interests: Letícia C. Corrêa and Glasiele C. Alcala are employees of Timpel S.A.; Eduardo Leite and Felipe S. Rossi are Timpel S.A. consultants, Marcelo B. P. Amato is Timpel S.A. consultant and minority shareholder. The other authors declare no competing interests. This does not alter our adherence to PLOS ONE policies on sharing data and materials., (Copyright: © 2023 Nascimento et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

The transition from controlled to partial support ventilation is a challenge in acute respiratory distress syndrome (ARDS) patients due to the risks of patient-self-inflicted lung injury. The magnitude of tidal volume (V T ) and intrapulmonary dyssynchrony (pendelluft) are suggested mechanisms of lung injury. We conducted a prospective, observational, physiological study in a tertiary academic intensive care unit. ARDS patients transitioning from controlled to partial support ventilation were included. On these, we evaluated the association between changes in inflammatory biomarkers and esophageal pressure swing (ΔP es ), transpulmonary driving pressure (ΔP L ), V T , and pendelluft. Pendelluft was defined as the percentage of the tidal volume that moves from the non-dependent to the dependent lung region during inspiration, and its frequency at different thresholds (- 15, - 20 and - 25%) was also registered. Blood concentrations of inflammatory biomarkers (IL-6, IL-8, TNF-α, ANGPT2, RAGE, IL-18, Caspase-1) were measured before (T 0 ) and after 4-h (T 4 ) of partial support ventilation. Pendelluft, ΔP es , ΔP L and V T were recorded. Nine out of twenty-four patients (37.5%) showed a pendelluft mean ≥ 10%. The mean values of ΔP es , ΔP L , and V T were - 8.4 [- 6.7; - 10.2] cmH 2 O, 15.2 [12.3-16.5] cmH 2 O and 8.1 [7.3-8.9] m/kg PBW, respectively. Significant associations were observed between the frequency of high-magnitude pendelluft and IL-8, IL-18, and Caspase-1 changes (T 0 /T 4 ratio). These results suggest that the frequency of high magnitude pendelluft may be a potential determinant of inflammatory response related to inspiratory efforts in ARDS patients transitioning to partial support ventilation. Future studies are needed to confirm these results., (© 2022. The Author(s).)

Objectives: To evaluate the effects of four flow rates on the functional residual capacity (FRC) and pulmonary ventilation distribution while using a high-flow nasal cannula (HFNC)., Working Hypothesis: Our hypothesis is that flow rates below 1.5 L·kg -1 ·min -1 lead to FRC loss and respiratory distress., Study Design: A single-center, prospective clinical study., Patient Selection: Infants diagnosed with acute viral bronchiolitis were given HFNC., Methodology: Through a prospective clinical study, the effects of four different flow rates, 2.0, 1.5, 1.0, and 0.5 L·kg -1 ·min -1 , on FRC and the pulmonary ventilation pattern were evaluated using electrical impedance tomography. The impedance variation (delta Z), end-expiratory lung volume (EELZ), respiratory rate, heart rate, respiratory distress score, and saturation/fraction of inspired oxygen ratio (SpO 2 /F I O 2 ), were also evaluated at each flow rate., Results: Among the 11 infants included, There was a decrease in respiratory distress score at a flow rate of 1.5 L·kg -1 ·min -1 (*p = 0.021), and at a flow rate of 2.0 L·kg -1 ·min -1 (**p = 0.003) compared to 0.5 L·kg -1 ·min -1 . There was also a small but significant increase in SpO 2 /FiO 2 at flow rates of 1.5 (*p = 0.023), and 2.0 L·kg -1 ·min -1 (**p = 0.008) compared to 0.5 L·kg -1 ·min -1 . There were no other significant changes in the clinical parameters. In the global EELZ measurements, there was a significant increase under a flow rate of 2.0 L·kg -1 ·min -1 as compared to 0.5 L·kg -1 ·min -1 (p = 0.03). In delta Z values, there were no significant variations between the different flow rates., Conclusion: The ∆EELZ increases at the highest flow rates were accompanied by decreased distress scores and improved oxygenation., (© 2022 Wiley Periodicals LLC.)

Background: Insufficient or excessive respiratory effort during acute hypoxemic respiratory failure (AHRF) increases the risk of lung and diaphragm injury. We sought to establish whether respiratory effort can be optimized to achieve lung- and diaphragm-protective (LDP) targets (esophageal pressure swing - 3 to - 8 cm H 2 O; dynamic transpulmonary driving pressure ≤ 15 cm H 2 O) during AHRF., Methods: In patients with early AHRF, spontaneous breathing was initiated as soon as passive ventilation was not deemed mandatory. Inspiratory pressure, sedation, positive end-expiratory pressure (PEEP), and sweep gas flow (in patients receiving veno-venous extracorporeal membrane oxygenation (VV-ECMO)) were systematically titrated to achieve LDP targets. Additionally, partial neuromuscular blockade (pNMBA) was administered in patients with refractory excessive respiratory effort., Results: Of 30 patients enrolled, most had severe AHRF; 16 required VV-ECMO. Respiratory effort was absent in all at enrolment. After initiating spontaneous breathing, most exhibited high respiratory effort and only 6/30 met LDP targets. After titrating ventilation, sedation, and sweep gas flow, LDP targets were achieved in 20/30. LDP targets were more likely to be achieved in patients on VV-ECMO (median OR 10, 95% CrI 2, 81) and at the PEEP level associated with improved dynamic compliance (median OR 33, 95% CrI 5, 898). Administration of pNMBA to patients with refractory excessive effort was well-tolerated and effectively achieved LDP targets., Conclusion: Respiratory effort is frequently absent  under deep sedation but becomes excessive when spontaneous breathing is permitted in patients with moderate or severe AHRF. Systematically titrating ventilation and sedation can optimize respiratory effort for lung and diaphragm protection in most patients. VV-ECMO can greatly facilitate the delivery of a LDP strategy., Trial Registration: This trial was registered in Clinicaltrials.gov in August 2018 (NCT03612583)., (© 2022. The Author(s).)

Background: Electrical impedance tomography (EIT) is a nonionizing imaging technique for real-time imaging of ventilation of patients with respiratory distress. Cross-sectional dynamic images are formed by reconstructing the conductivity distribution from measured voltage data arising from applied alternating currents on electrodes placed circumferentially around the chest. Since the conductivity of lung tissue depends on air content, blood flow, and the presence of pathology, the dynamic images provide regional information about ventilation, pulsatile perfusion, and abnormalities. However, due to the ill-posedness of the inverse conductivity problem, EIT images have a coarse spatial resolution. One method of improving the resolution is to include prior information in the reconstruction., Purpose: In this work, we propose a technique in which a statistical prior built from an anatomical atlas is used to postprocess EIT reconstructions of human chest data. The effectiveness of the method is demonstrated on data from two patients with cystic fibrosis., Methods: A direct reconstruction algorithm known as the D-bar method was used to compute a two-dimensional reconstruction of the conductivity distribution in the plane of the electrodes. Reconstructions using one step in an iterative (regularized) Newton's method were also computed for comparison. An anatomical atlas consisting of 1589 synthetic EIT images computed from X-ray computed tomography (CT) scans of 74 adult male subjects was computed for use as a statistical prior. The resolution of the D-bar images was then improved by maximizing the conditional probability density function of an image that is consistent with the a priori information and the statistical model. A new method to evaluate the accuracy of the EIT images using CT scans of the imaged patient as ground truth is presented. The novel approach is tested on data from two patients with cystic fibrosis., Results and Conclusions: The D-bar images resulted in better structural similarity index measures (SSIM) and multiscale (MS) SSIM measures for both subjects using the mask or amplitude evaluation approach than the one-step (regularized) Newton's method. Further improvement was achieved using the Schur complement (SC) approach, with MS-SSIM values of 0.718 and 0.682 using SC evaluated with the mask and amplitude approach, respectively, for Patient 1, and MS-SSIM values of 0.726 and 0.692 using SC evaluated with the mask and amplitude approach, respectively, for Patient 2. The results from applying an anatomical atlas and statistical prior to EIT data from two patients with cystic fibrosis suggest that the spatial resolution of the EIT image can be improved to reveal pathology that may be difficult to discern in the original EIT image. The novel metric of evaluation is consistent with the appearance of improved spatial resolution and provides a new way to evaluate the accuracy of EIT reconstructions when a CT scan is available., (© 2022 The Authors. Medical Physics published by Wiley Periodicals LLC on behalf of American Association of Physicists in Medicine.)