Airway driving pressure and lung stress in ARDS patients

Different ventilation intensities among various categories of patients ventilated for reasons other than ARDS--A pooled analysis of 4 observational studies

PURPOSE

We investigated driving pressure (ΔP) and mechanical power (MP) and associations with clinical outcomes in critically ill patients ventilated for reasons other than ARDS.

MATERIALS AND METHODS

Individual patient data analysis of a pooled database that included patients from four observational studies of ventilation. ΔP and MP were compared among invasively ventilated non-ARDS patients with sepsis, with pneumonia, and not having sepsis or pneumonia. The primary endpoint was ΔP; secondary endpoints included MP, ICU mortality and length of stay, and duration of ventilation.

RESULTS

This analysis included 372 (11%) sepsis patients, 944 (28%) pneumonia patients, and 2040 (61%) patients ventilated for any other reason. On day 1, median ΔP was higher in sepsis (14 [11-18] cmH2O) and pneumonia patients (14 [11-18]cmH2O), as compared to patients not having sepsis or pneumonia (13 [10-16] cmH2O) (P < 0.001). Median MP was also higher in sepsis and pneumonia patients. ΔP, as opposed to MP, was associated with ICU mortality in sepsis and pneumonia patients.

CONCLUSIONS

The intensity of ventilation differed between patients with sepsis or pneumonia and patients receiving ventilation for any other reason; ΔP was associated with higher mortality in sepsis and pneumonia patients.

REGISTRATION

This post hoc analysis was not registered; the individual studies that were merged into the used database were registered at clinicaltrials.gov: NCT01268410 (ERICC), NCT02010073 (LUNG SAFE), NCT01868321 (PRoVENT), and NCT03188770 (PRoVENT-iMiC).

Differential Effects of Intra-Abdominal Hypertension and ARDS on Respiratory Mechanics in a Porcine Model

Background and Objectives: Intra-abdominal hypertension (IAH) and acute respiratory distress syndrome (ARDS) are common concerns in intensive care unit patients with acute respiratory failure (ARF). Although both conditions lead to impairment of global respiratory parameters, their underlying mechanisms differ substantially. Therefore, a separate assessment of the different respiratory compartments should reveal differences in respiratory mechanics. Materials and Methods: We prospectively investigated alterations in lung and chest wall mechanics in 18 mechanically ventilated pigs exposed to varying levels of intra-abdominal pressures (IAP) and ARDS. The animals were divided into three groups: group A (IAP 10 mmHg, no ARDS), B (IAP 20 mmHg, no ARDS), and C (IAP 10 mmHg, with ARDS). Following induction of IAP (by inflating an intra-abdominal balloon) and ARDS (by saline lung lavage and injurious ventilation), respiratory mechanics were monitored for six hours. Statistical analysis was performed using one-way ANOVA to compare the alterations within each group. Results: After six hours of ventilation, end-expiratory lung volume (EELV) decreased across all groups, while airway and thoracic pressures increased. Significant differences were noted between group (B) and (C) regarding alterations in transpulmonary pressure (TPP) (2.7 ± 0.6 vs. 11.3 ± 2.1 cmH2O, p < 0.001), elastance of the lung (EL) (8.9 ± 1.9 vs. 29.9 ± 5.9 cmH2O/mL, p = 0.003), and elastance of the chest wall (ECW) (32.8 ± 3.2 vs. 4.4 ± 1.8 cmH2O/mL, p < 0.001). However, global respiratory parameters such as EELV/kg bodyweight (-6.1 ± 1.3 vs. -11.0 ± 2.5 mL/kg), driving pressure (12.5 ± 0.9 vs. 13.2 ± 2.3 cmH2O), and compliance of the respiratory system (-21.7 ± 2.8 vs. -19.5 ± 3.4 mL/cmH2O) did not show significant differences among the groups. Conclusions: Separate measurements of lung and chest wall mechanics in pigs with IAH or ARDS reveals significant differences in TPP, EL, and ECW, whereas global respiratory parameters do not differ significantly. Therefore, assessing the compartments of the respiratory system separately could aid in identifying the underlying cause of ARF.

Prospective, randomized, controlled trial assessing the effects of a driving pressure-limiting strategy for patients with acute respiratory distress syndrome due to community-acquired pneumonia (STAMINA trial): protocol and statistical analysis plan

BACKGROUND

Driving pressure has been suggested to be the main driver of ventilator-induced lung injury and mortality in observational studies of acute respiratory distress syndrome. Whether a driving pressure-limiting strategy can improve clinical outcomes is unclear.

OBJECTIVE

To describe the protocol and statistical analysis plan that will be used to test whether a driving pressure-limiting strategy including positive end-expiratory pressure titration according to the best respiratory compliance and reduction in tidal volume is superior to a standard strategy involving the use of the ARDSNet low-positive end-expiratory pressure table in terms of increasing the number of ventilator-free days in patients with acute respiratory distress syndrome due to community-acquired pneumonia.

METHODS

The ventilator STrAtegy for coMmunIty acquired pNeumoniA (STAMINA) study is a randomized, multicenter, open-label trial that compares a driving pressure-limiting strategy to the ARDSnet low-positive end-expiratory pressure table in patients with moderate-to-severe acute respiratory distress syndrome due to community-acquired pneumonia admitted to intensive care units. We expect to recruit 500 patients from 20 Brazilian and 2 Colombian intensive care units. They will be randomized to a driving pressure-limiting strategy group or to a standard strategy using the ARDSNet low-positive end-expiratory pressure table. In the driving pressure-limiting strategy group, positive end-expiratory pressure will be titrated according to the best respiratory system compliance.

OUTCOMES

The primary outcome is the number of ventilator-free days within 28 days. The secondary outcomes are in-hospital and intensive care unit mortality and the need for rescue therapies such as extracorporeal life support, recruitment maneuvers and inhaled nitric oxide.

CONCLUSION

STAMINA is designed to provide evidence on whether a driving pressure-limiting strategy is superior to the ARDSNet low-positive end-expiratory pressure table strategy for increasing the number of ventilator-free days within 28 days in patients with moderate-to-severe acute respiratory distress syndrome. Here, we describe the rationale, design and status of the trial.

Flow-Limited and Reverse-Triggered Ventilator Dyssynchrony Are Associated With Increased Tidal and Dynamic Transpulmonary Pressure

OBJECTIVES

Ventilator dyssynchrony may be associated with increased delivered tidal volumes (V t s) and dynamic transpulmonary pressure (ΔP L,dyn ), surrogate markers of lung stress and strain, despite low V t ventilation. However, it is unknown which types of ventilator dyssynchrony are most likely to increase these metrics or if specific ventilation or sedation strategies can mitigate this potential.

DESIGN

A prospective cohort analysis to delineate the association between ten types of breaths and delivered V t , ΔP L,dyn , and transpulmonary mechanical energy.

SETTING

Patients admitted to the medical ICU.

PATIENTS

Over 580,000 breaths from 35 patients with acute respiratory distress syndrome (ARDS) or ARDS risk factors.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Patients received continuous esophageal manometry. Ventilator dyssynchrony was identified using a machine learning algorithm. Mixed-effect models predicted V t , ΔP L,dyn , and transpulmonary mechanical energy for each type of ventilator dyssynchrony while controlling for repeated measures. Finally, we described how V t , positive end-expiratory pressure (PEEP), and sedation (Richmond Agitation-Sedation Scale) strategies modify ventilator dyssynchrony's association with these surrogate markers of lung stress and strain. Double-triggered breaths were associated with the most significant increase in V t , ΔP L,dyn , and transpulmonary mechanical energy. However, flow-limited, early reverse-triggered, and early ventilator-terminated breaths were also associated with significant increases in V t , ΔP L,dyn , and energy. The potential of a ventilator dyssynchrony type to increase V t , ΔP L,dyn , or energy clustered similarly. Increasing set V t may be associated with a disproportionate increase in high-volume and high-energy ventilation from double-triggered breaths, but PEEP and sedation do not clinically modify the interaction between ventilator dyssynchrony and surrogate markers of lung stress and strain.

CONCLUSIONS

Double-triggered, flow-limited, early reverse-triggered, and early ventilator-terminated breaths are associated with increases in V t , ΔP L,dyn , and energy. As flow-limited breaths are more than twice as common as double-triggered breaths, further work is needed to determine the interaction of ventilator dyssynchrony frequency to cause clinically meaningful changes in patient outcomes.

Quantifiable identification of flow-limited ventilator dyssynchrony with the deformed lung ventilator model

BACKGROUND

Ventilator dyssynchrony (VD) can worsen lung injury and is challenging to detect and quantify due to the complex variability in the dyssynchronous breaths. While machine learning (ML) approaches are useful for automating VD detection from the ventilator waveform data, scalable severity quantification and its association with pathogenesis and ventilator mechanics remain challenging.

OBJECTIVE

We develop a systematic framework to quantify pathophysiological features observed in ventilator waveform signals such that they can be used to create feature-based severity stratification of VD breaths.

METHODS

A mathematical model was developed to represent the pressure and volume waveforms of individual breaths in a feature-based parametric form. Model estimates of respiratory effort strength were used to assess the severity of flow-limited (FL)-VD breaths compared to normal breaths. A total of 93,007 breath waveforms from 13 patients were analyzed.

RESULTS

A novel model-defined continuous severity marker was developed and used to estimate breath phenotypes of FL-VD breaths. The phenotypes had a predictive accuracy of over 97% with respect to the previously developed ML-VD identification algorithm. To understand the incidence of FL-VD breaths and their association with the patient state, these phenotypes were further successfully correlated with ventilator-measured parameters and electronic health records.

CONCLUSION

This work provides a computational pipeline to identify and quantify the severity of FL-VD breaths and paves the way for a large-scale study of VD causes and effects. This approach has direct application to clinical practice and in meaningful knowledge extraction from the ventilator waveform data.

Driving pressure in mechanical ventilation: A review

Driving pressure (∆P) is a core therapeutic component of mechanical ventilation (MV). Varying levels of ∆P have been employed during MV depending on the type of underlying pathology and severity of injury. However, ∆P levels have also been shown to closely impact hard endpoints such as mortality. Considering this, conducting an in-depth review of ∆P as a unique, outcome-impacting therapeutic modality is extremely important. There is a need to understand the subtleties involved in making sure ∆P levels are optimized to enhance outcomes and minimize harm. We performed this narrative review to further explore the various uses of ∆P, the different parameters that can affect its use, and how outcomes vary in different patient populations at different pressure levels. To better utilize ∆P in MV-requiring patients, additional large-scale clinical studies are needed.

Positive end-expiratory pressure in the pediatric intensive care unit

Application of positive end-expiratory pressure (PEEP) targeted towards improving oxygenation is one of the components of the ventilatory management of pediatric acute respiratory distress syndrome (PARDS). Low end-expiratory airway pressures cause repetitive opening and closure of unstable alveoli, leading to surfactant dysfunction and parenchymal shear injury. Consequently, there is less lung volume available for tidal ventilation when there are atelectatic lung regions. This will increase lung strain in aerated lung areas to which the tidal volume is preferentially distributed. Pediatric critical care practitioners tend to use low levels of PEEP and inherently accept higher FiO2, but these practices may negatively affect patient outcome. The Pediatric Acute Lung Injury Consensus Conference (PALICC) suggests that PEEP should be titrated to oxygenation/oxygen delivery, hemodynamics, and compliance measured under static conditions as compared to other clinical parameters or any of these parameters in isolation in patients with PARDS, while limiting plateau pressure and/or driving pressure limits.

Effects of driving pressure-guided ventilation on postoperative pulmonary complications in patients with COVID-19 undergoing abdominal surgery: A post-hoc propensity score-matched analysis

Background

Application of individualized positive end-expiratory pressure (PEEP) based on minimum driving pressure facilitates to prevent from postoperative pulmonary complications (PPCs). Whether lung protective ventilation strategy can reduce the risk of PPCs in COVID-19 patients remains unclear. In this study, we compared the effects of driving pressure-guided ventilation with conventional mechanical ventilation on PPCs in patients with COVID-19.

Methods

Patients infected COVID-19 within 30-day before surgery were retrospectively enrolled consecutively. Patients were divided into two group: driving pressure-guided lung protective ventilation strategy group (LPVS group) and conventional mechanical ventilation group (Control group). Propensity score matching for variables selected was used by logistic regression with the nearest-neighbor method. The outcomes were the incidence of PPCs and hypoxemia in post-anesthesia care unit.

Results

There was no significant difference in the baseline data between both groups (P > 0.05). The incidence of PPCs (12.73 % vs 36.36 %, χ2 = 7.068, P = 0.008) and hypoxemia [18.18 % vs 38.18 %, χ2 = 4.492, P = 0.034], and lung ultrasound scores [4.68 ± 1.60 vs 8.39 ± 1.87, t = 8.383, P < 0.001] in LPVS group were lower than control group. The PEEP, airway pressure and plateau pressure in LPVS group were higher than control group, but driving pressure and tidal volume was lower than control group, the difference was statistically significant (P < 0.05).

Conclusion

Individualized PEEP ventilation strategy guided by minimum driving pressure could improve oxygenation and reduce the incidence of PPCs in surgical patients with COVID-19.

Association between mechanical power and intensive care unit mortality in Korean patients under pressure-controlled ventilation

BACKGROUND

Mechanical power (MP) has been reported to be associated with clinical outcomes. Because the original MP equation is derived from paralyzed patients under volume-controlled ventilation, its application in practice could be limited in patients receiving pressure-controlled ventilation (PCV). Recently, a simplified equation for patients under PCV was developed. We investigated the association between MP and intensive care unit (ICU) mortality.

METHODS

We conducted a retrospective analysis of Korean data from the Fourth International Study of Mechanical Ventilation. We extracted data of patients under PCV on day 1 and calculated MP using the following simplified equation: MPPCV = 0.098 ∙ respiratory rate ∙ tidal volume ∙ (ΔPinsp + positive end-expiratory pressure), where ΔPinsp is the change in airway pressure during inspiration. Patients were divided into survivors and non-survivors and then compared. Multivariable logistic regression was performed to determine association between MPPCV and ICU mortality. The interaction of MPPCV and use of neuromuscular blocking agent (NMBA) was also analyzed.

RESULTS

A total of 125 patients was eligible for final analysis, of whom 38 died in the ICU. MPPCV was higher in non-survivors (17.6 vs. 26.3 J/min, P<0.001). In logistic regression analysis, only MPPCV was significantly associated with ICU mortality (odds ratio, 1.090; 95% confidence interval, 1.029-1.155; P=0.003). There was no significant effect of the interaction between MPPCV and use of NMBA on ICU mortality (P=0.579).

CONCLUSIONS

MPPCV is associated with ICU mortality in patients mechanically ventilated with PCV mode, regardless of NMBA use.

Driving pressure of respiratory system and lung stress in mechanically ventilated patients with active breathing

BACKGROUND

During control mechanical ventilation (CMV), the driving pressure of the respiratory system (ΔPrs) serves as a surrogate of transpulmonary driving pressure (ΔPlung). Expiratory muscle activity that decreases end-expiratory lung volume may impair the validity of ΔPrs to reflect ΔPlung. This prospective observational study in patients with acute respiratory distress syndrome (ARDS) ventilated with proportional assist ventilation (PAV+), aimed to investigate: (1) the prevalence of elevated ΔPlung, (2) the ΔPrs-ΔPlung relationship, and (3) whether dynamic transpulmonary pressure (Plungsw) and effort indices (transdiaphragmatic and respiratory muscle pressure swings) remain within safe limits.

METHODS

Thirty-one patients instrumented with esophageal and gastric catheters (n = 22) were switched from CMV to PAV+ and respiratory variables were recorded, over a maximum of 24 h. To decrease the contribution of random breaths with irregular characteristics, a 7-breath moving average technique was applied. In each patient, measurements were also analyzed per deciles of increasing lung elastance (Elung). Patients were divided into Group A, if end-inspiratory transpulmonary pressure (PLEI) increased as Elung increased, and Group B, which showed a decrease or no change in PLEI with Elung increase.

RESULTS

In 44,836 occluded breaths, ΔPlung ≥ 12 cmH2O was infrequently observed [0.0% (0.0-16.9%) of measurements]. End-expiratory lung volume decrease, due to active expiration, was associated with underestimation of ΔPlung by ΔPrs, as suggested by a negative linear relationship between transpulmonary pressure at end-expiration (PLEE) and ΔPlung/ΔPrs. Group A included 17 and Group B 14 patients. As Elung increased, ΔPlung increased mainly due to PLEI increase in Group A, and PLEE decrease in Group B. Although ΔPrs had an area receiver operating characteristic curve (AUC) of 0.87 (95% confidence intervals 0.82-0.92, P < 0.001) for ΔPlung ≥ 12 cmH2O, this was due exclusively to Group A [0.91 (0.86-0.95), P < 0.001]. In Group B, ΔPrs showed no predictive capacity for detecting ΔPlung ≥ 12 cmH2O [0.65 (0.52-0.78), P > 0.05]. Most of the time Plungsw and effort indices remained within safe range.

CONCLUSION

In patients with ARDS ventilated with PAV+, injurious tidal lung stress and effort were infrequent. In the presence of expiratory muscle activity, ΔPrs underestimated ΔPlung. This phenomenon limits the usefulness of ΔPrs as a surrogate of tidal lung stress, regardless of the mode of support.

Three subtypes of postoperative ARDS that showing different outcomes and responses to mechanical ventilation and fluid management: A machine learning and latent profile analysis

BACKGROUND

ARDS is a heterogeneous clinical syndrome, and operation and trauma are common indirect etiologies. The identification of postoperative ARDS subtypes may optimize individualized clinical management.

OBJECTIVES

To identify the subtypes of postoperative ARDS and explore the impact of therapy on outcomes.

METHODS

This retrospective study used data obtained from a database. Patients diagnosed with ARDS who underwent surgical procedures within 7 days were included in the study. Laboratory and clinical variables were used for latent profile analysis (LPA). XGBoost and multivariable logistic regression models were used to explore the association between therapy and outcomes.

RESULTS

A total of 1065 patients were included. The LPA identified three subtypes of postoperative ARDS: Patients in profile 1 were mainly accepted neurosurgery, while those in profile 2 and 3 were treated with orthopedic and vascular or thoracic surgery, respectively. The XGBoost model effectively predicted mortality with an AUC of 0.935, which was higher than SOFA (0.622), APACHE 2 (0.629), SLIP (0.579), and SLIP-2 (0.550).

CONCLUSIONS

This study identified three subtypes of postoperative ARDS with different clinical characteristics, mechanical support, and fluid resuscitation responses.

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

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.

[Driving pressure-guided lung protective ventilation strategy reduces postoperative pulmonary complications in patients recovered from COVID-19]

OBJECTIVE

To investigate the value of lung protective ventilation strategy (LPVS) guided by driving pressure for preventing postoperative pulmonary complications (PPCs) in patients recovered from COVID-19 and optimize intraoperative respiratory management.

METHODS

From December, 2022 to February, 2023, a total of 118 patients recovered from COVID-19 within a month (ASA Ⅰ~Ⅲ, aged ≥18 years) undergoing elective non-cardiac surgeries under general anesthesia in our hospital were randomized equally into LPVS group and control group.The patients in LPVS group received a tidal volume of 6 mL/kg with an individualized PEEP guided by minimum driving pressure and lung re-expansion every 30 min, and those in the control group received conventional mechanical ventilation.The incidence of PPCs and hypoxemia and pulmonary ultrasound score of the patients were compared between the two groups.

RESULTS

There was no significant difference in the baseline data between LPVS group and the control group (P>0.05).Compared with the control group, LPVS group showed significantly lower incidences of PPCs (16.95%vs 35.59%, χ2=5.294, P=0.021) and hypoxemia (15.25%vs 30.51%, χ2=3.890, P=0.049) with also lower pulmonary ultrasound scores (5.31±1.07 vs 8.32±2.34, t=8.986, P<0.001).The PEEP value, airway pressure and plateau pressure in LPVS group were significantly higher, but the driving pressure and the tidal volume were lower than those in the control group (P<0.05).

CONCLUSION

LPVS guided by driving pressure can improve oxygenation and reduce the risk of PPCs in patients recently recovered from COVID-19.

Mechanical ventilation during pediatric extracorporeal life support

PURPOSE OF REVIEW

To discuss the role of ventilator induced lung injury (VILI) and patient self-inflicted lung injury in ventilated children supported on extracorporeal membrane oxygenation (ECMO).

RECENT FINDINGS

While extracorporeal life support is used routinely used every day around the globe to support neonatal, pediatric, and adult patients with refractory cardiac and/or respiratory failure, the optimal approach to mechanical ventilation, especially for those with acute respiratory distress syndrome (ARDS), remains unknown and controversial. Given the lack of definitive data in this population, one must rely on available evidence in those with ARDS not supported with ECMO and extrapolate adult observations. Ventilatory management should include, as a minimum standard, limiting inspiratory and driving pressures, providing a sufficient level of positive end-expiratory pressure, and setting a low rate to reduce mechanical power. Allowing for spontaneous breathing and use of pulmonary specific ancillary treatment modalities must be individualized, while balancing the risk and benefits. Future studies delineating the best strategies for optimizing MV during pediatric extracorporeal life support are much needed.

SUMMARY

Future investigations will hopefully provide the needed evidence and better understanding of the overall goal of reducing mechanical ventilation intensity to decrease risk for VILI and promote lung recovery for those supported with ECMO.

Comparison of hemodynamic and respiratory outcomes between two surgical positions for percutaneous nephrolithotomy: a prospective, randomized clinical trial

INTRODUCTION

Percutaneous nephrolithotomy (PCNL) has become the gold standard for the treatment of large and complex kidney stones.

OBJECTIVES

The objective of this study is to evaluate the efficacy and safety of percutaneous nephrolithotomy (PCNL) for patients in the flank position versus prone position.

METHODS

In our prospective randomized trial, 60 patients who would undergo fluoroscopy and ultrasound-guided PCNL in prone or flank position were divided into two groups. Demographic features, hemodynamics, respiratory and metabolic parameters, postoperative pain scores, analgesic requirements, amount of fluid given, blood loss and transfusion, duration of operation and hospital stay, and perioperative complications were compared.

RESULTS

PaO2, SaO2, SpO2 and Oxygen Reserve İndex (ORi) at the 60th minute of the operation and in the postoperative period, Pleth Variability index (PVi) at the 60th minute of the operation, driving pressure in all time periods and the amount of bleeding during the operation were determined to be statistically significantly higher in the prone group. There was no difference between the groups in terms of other parameters. Was found to be statistically significantly higher in the prone group.

CONCLUSIONS

Due to our results the flank position can be preferred in PCNL operations, considering that the position should be chosen according to the surgeon's experience, the patient's anatomical and physiological data, positive effects on respiratory parameters and bleeding, and the operation time can be shortened as the experience increases.

Advanced respiratory mechanics assessment in mechanically ventilated obese and non-obese patients with or without acute respiratory distress syndrome

BACKGROUND

Respiratory mechanics is a key element to monitor mechanically ventilated patients and guide ventilator settings. Besides the usual basic assessments, some more complex explorations may allow to better characterize patients' respiratory mechanics and individualize ventilation strategies. These advanced respiratory mechanics assessments including esophageal pressure measurements and complete airway closure detection may be particularly relevant in critically ill obese patients. This study aimed to comprehensively assess respiratory mechanics in obese and non-obese ICU patients with or without ARDS and evaluate the contribution of advanced respiratory mechanics assessments compared to basic assessments in these patients.

METHODS

All intubated patients admitted in two ICUs for any cause were prospectively included. Gas exchange and respiratory mechanics including esophageal pressure and end-expiratory lung volume (EELV) measurements and low-flow insufflation to detect complete airway closure were assessed in standardized conditions (tidal volume of 6 mL kg-1 predicted body weight (PBW), positive end-expiratory pressure (PEEP) of 5 cmH2O) within 24 h after intubation.

RESULTS

Among the 149 analyzed patients, 52 (34.9%) were obese and 90 (60.4%) had ARDS (65.4% and 57.8% of obese and non-obese patients, respectively, p = 0.385). A complete airway closure was found in 23.5% of the patients. It was more frequent in obese than in non-obese patients (40.4% vs 14.4%, p < 0.001) and in ARDS than in non-ARDS patients (30% vs. 13.6%, p = 0.029). Respiratory system and lung compliances and EELV/PBW were similarly decreased in obese patients without ARDS and obese or non-obese patients with ARDS. Chest wall compliance was not impacted by obesity or ARDS, but end-expiratory esophageal pressure was higher in obese than in non-obese patients. Chest wall contribution to respiratory system compliance differed widely between patients but was not predictable by their general characteristics.

CONCLUSIONS

Most respiratory mechanics features are similar in obese non-ARDS and non-obese ARDS patients, but end-expiratory esophageal pressure is higher in obese patients. A complete airway closure can be found in around 25% of critically ill patients ventilated with a PEEP of 5 cmH2O. Advanced explorations may allow to better characterize individual respiratory mechanics and adjust ventilation strategies in some patients. Trial registration NCT03420417 ClinicalTrials.gov (February 5, 2018).

Conducting Prospective Research as a Trainee: Experiences with the DRIVE-SAFE Study

Conducting clinical research during a 2-year critical care fellowship is a challenging endeavor. Fellows are often met with multiple barriers when considering clinical research projects during fellowship, including time, mentorship, resources, and clinical support. This paper presents the perspective and experiences of a group of critical care fellows who conducted the DRIVE-SAFE (Driving Pressure in Assisted Ventilation as a Predictor for Successful Liberation from Invasive Mechanical Ventilation) feasibility study, which aimed to determine measurable physiological variables that could be associated with lung injury and affect duration of mechanical ventilation. This paper provides a guide for trainees on how to conduct prospective clinical research at the bedside. We describe three key steps, including formulating a research question, developing appropriate methodology, and establishing outcomes. We also present the challenges that trainees may encounter when conducting prospective studies and how to overcome these challenges with proper mentorship, training, and collaboration with key stakeholders. These perspectives may provide useful guidance for current and future trainees interested in conducting prospective clinical research at the bedside.

Setting the optimal positive end-expiratory pressure: a narrative review

The primary goals of positive end-expiratory pressure (PEEP) are to restore functional residual capacity through recruitment and prevention of alveolar collapse. Through these mechanisms, PEEP improves arterial oxygenation and may reduce the risk of ventilator-induced lung injury (VILI). Because of the many potential negative effects associated with the use of PEEP, much research has concentrated on determining the optimal PEEP setting. Arterial oxygenation targets and pressure-volume loops have been utilized to set the optimal PEEP for decades. Several other techniques have been suggested, including the use of PEEP tables, compliance, driving pressure (DP), stress index (SI), transpulmonary pressures, imaging, and electrical impedance tomography. Each of these techniques has its own benefits and limitations and there is currently not one technique that is recommended above all others.

A closed-loop ventilation mode that targets the lowest work and force of breathing reduces the transpulmonary driving pressure in patients with moderate-to-severe ARDS

INTRODUCTION

The driving pressure (ΔP) has an independent association with outcome in patients with acute respiratory distress syndrome (ARDS). INTELLiVENT-Adaptive Support Ventilation (ASV) is a closed-loop mode of ventilation that targets the lowest work and force of breathing.

AIM

To compare transpulmonary and respiratory system ΔP between closed-loop ventilation and conventional pressure controlled ventilation in patients with moderate-to-severe ARDS.

METHODS

Single-center randomized cross-over clinical trial in patients in the early phase of ARDS. Patients were randomly assigned to start with a 4-h period of closed-loop ventilation or conventional ventilation, after which the alternate ventilation mode was selected. The primary outcome was the transpulmonary ΔP; secondary outcomes included respiratory system ΔP, and other key parameters of ventilation.

RESULTS

Thirteen patients were included, and all had fully analyzable data sets. Compared to conventional ventilation, with closed-loop ventilation the median transpulmonary ΔP with was lower (7.0 [5.0-10.0] vs. 10.0 [8.0-11.0] cmH₂O, mean difference - 2.5 [95% CI - 2.6 to - 2.1] cmH₂O; P = 0.0001). Inspiratory transpulmonary pressure and the respiratory rate were also lower. Tidal volume, however, was higher with closed-loop ventilation, but stayed below generally accepted safety cutoffs in the majority of patients.

CONCLUSIONS

In this small physiological study, when compared to conventional pressure controlled ventilation INTELLiVENT-ASV reduced the transpulmonary ΔP in patients in the early phase of moderate-to-severe ARDS. This closed-loop ventilation mode also led to a lower inspiratory transpulmonary pressure and a lower respiratory rate, thereby reducing the intensity of ventilation. Trial registration Clinicaltrials.gov, NCT03211494, July 7, 2017. https://clinicaltrials.gov/ct2/show/NCT03211494?term=airdrop&draw=2&rank=1 .

Development and Internal Validation of a Novel Prognostic Score to Predict Mortality in Acute Respiratory Distress Syndrome - Driving Pressure, Oxygenation and Nutritional Evaluation - "DRONE Score"

Introduction

There are few scores for mortality prediction in acute respiratory distress syndrome (ARDS) incorporating comprehensive ventilatory, acute physiological, organ dysfunction, oxygenation, and nutritional parameters. This study aims to determine the risk factors of ARDS mortality from the above-mentioned parameters at 48 h of invasive mechanical ventilation (IMV), which are feasible across most intensive care unit settings.

Methods

Prospective, observational, single-center study with 150 patients with ARDS defined by Berlin definition, receiving IMV with lung protective strategy.

Results

Our study had a mortality of 41.3% (62/150). We developed a 9-point novel prediction score, the driving pressure oxygenation and nutritional evaluation (DRONE) score comprising of driving pressure (DP), oxygenation accessed by the ratio of partial pressure of arterial oxygen to the fraction of inspired oxygen (PaO2/FiO2) ratio and nutritional evaluation using the modified nutrition risk in the critically ill (mNUTRIC) score. Each component of the DRONE score with the cutoff value to predict mortality was assigned a particular score (the lowest DP within 48 h in a patient being always ≥15 cmH2O a score of 2, the highest achievable PaO2/FiO2 <208 was assigned a score of 4 and the mNUTRIC score ≥4 was assigned a score of (3). We obtained the DRONE score ≥4, area under the curve 0.860 to predict mortality. Cox regression for the DRONE score >4 was highly associated with mortality (P < 0.001, hazard ratio 5.43, 95% confidence interval [2.94-10.047]). Internal validation was done by bootstrap analysis. The clinical utility of the DRONE score ≥4 was assessed by Kaplan-Meier curve which showed significance.

Conclusions

The DRONE score ≥4 could be a reliable predictor of mortality at 48 h in ARDS patients receiving IMV.

Mechanical ventilation in patients with acute respiratory distress syndrome: current status and future perspectives

INTRODUCTION

Although there has been extensive research on mechanical ventilation for acute respiratory distress syndrome (ARDS), treatment remains mainly supportive. Recent studies and new ventilatory modes have been proposed to manage patients with ARDS; however, the clinical impact of these strategies remains uncertain and not clearly supported by guidelines. The aim of this narrative review is to provide an overview and update on ventilatory management for patients with ARDS.

AREAS COVERED

This article reviews the literature regarding mechanical ventilation in ARDS. A comprehensive overview of the principal settings for the ventilator parameters involved is provided as well as a report on the differences between controlled and assisted ventilation. Additionally, new modes of assisted ventilation are presented and discussed. The evidence concerning rescue strategies, including recruitment maneuvers and extracorporeal membrane oxygenation support, is analyzed. PubMed, EBSCO, and the Cochrane Library were searched up until June 2023, for relevant literature.

EXPERT OPINION

Available evidence for mechanical ventilation in cases of ARDS suggests the use of a personalized mechanical ventilation strategy. Although promising, new modes of assisted mechanical ventilation are still under investigation and guidelines do not recommend rescue strategies as the standard of care. Further research on this topic is required.

Colonic oxygen microbubbles augment systemic oxygenation and CO2 removal in a porcine smoke inhalation model of severe hypoxia

Inhalation injury can lead to pulmonary complications resulting in the development of respiratory distress and severe hypoxia. Respiratory distress is one of the major causes of death in critically ill patients with a reported mortality rate of up to 45%. The present study focuses on the effect of oxygen microbubble (OMB) infusion via the colon in a porcine model of smoke inhalation-induced lung injury. Juvenile female Duroc pigs (n = 6 colonic OMB, n = 6 no treatment) ranging from 39 to 51 kg in weight were exposed to smoke under general anesthesia for 2 h. Animals developed severe hypoxia 48 h after smoke inhalation as reflected by reduction in SpO₂ to 66.3 ± 13.1% and PaO₂ to 45.3 ± 7.6 mmHg, as well as bilateral diffuse infiltrates demonstrated on chest X-ray. Colonic OMB infusion (75-100 mL/kg dose) resulted in significant improvements in systemic oxygenation as demonstrated by an increase in PaO₂ of 13.2 ± 4.7 mmHg and SpO₂ of 15.2 ± 10.0% out to 2.5 h, compared to no-treatment control animals that experienced a decline in PaO₂ of 8.2 ± 7.9 mmHg and SpO₂ of 12.9 ± 18.7% over the same timeframe. Likewise, colonic OMB decreased PaCO₂ and PmvCO₂ by 19.7 ± 7.6 mmHg and 7.6 ± 6.7 mmHg, respectively, compared to controls that experienced increases in PaCO₂ and PmvCO₂ of 17.9 ± 11.7 mmHg and 18.3 ± 11.2 mmHg. We conclude that colonic delivery of OMB therapy has potential to treat patients experiencing severe hypoxemic respiratory failure.

Challenges in ARDS Definition, Management, and Identification of Effective Personalized Therapies

Over the last decade, the management of acute respiratory distress syndrome (ARDS) has made considerable progress both regarding supportive and pharmacologic therapies. Lung protective mechanical ventilation is the cornerstone of ARDS management. Current recommendations on mechanical ventilation in ARDS include the use of low tidal volume (V_T) 4-6 mL/kg of predicted body weight, plateau pressure (P_PLAT) < 30 cmH₂O, and driving pressure (∆P) < 14 cmH₂O. Moreover, positive end-expiratory pressure should be individualized. Recently, variables such as mechanical power and transpulmonary pressure seem promising for limiting ventilator-induced lung injury and optimizing ventilator settings. Rescue therapies such as recruitment maneuvers, vasodilators, prone positioning, extracorporeal membrane oxygenation, and extracorporeal carbon dioxide removal have been considered for patients with severe ARDS. Regarding pharmacotherapies, despite more than 50 years of research, no effective treatment has yet been found. However, the identification of ARDS sub-phenotypes has revealed that some pharmacologic therapies that have failed to provide benefits when considering all patients with ARDS can show beneficial effects when these patients were stratified into specific sub-populations; for example, those with hyperinflammation/hypoinflammation. The aim of this narrative review is to provide an overview on current advances in the management of ARDS from mechanical ventilation to pharmacological treatments, including personalized therapy.

Understanding clinical and biological heterogeneity to advance precision medicine in paediatric acute respiratory distress syndrome

Paediatric acute respiratory distress syndrome (PARDS) is a heterogeneous clinical syndrome that is associated with high rates of mortality and long-term morbidity. Factors that distinguish PARDS from adult acute respiratory distress syndrome (ARDS) include changes in developmental stage and lung maturation with age, precipitating factors, and comorbidities. No specific treatment is available for PARDS and management is largely supportive, but methods to identify patients who would benefit from specific ventilation strategies or ancillary treatments, such as prone positioning, are needed. Understanding of the clinical and biological heterogeneity of PARDS, and of differences in clinical features and clinical course, pathobiology, response to treatment, and outcomes between PARDS and adult ARDS, will be key to the development of novel preventive and therapeutic strategies and a precision medicine approach to care. Studies in which clinical, biomarker, and transcriptomic data, as well as informatics, are used to unpack the biological and phenotypic heterogeneity of PARDS, and implementation of methods to better identify patients with PARDS, including methods to rapidly identify subphenotypes and endotypes at the point of care, will drive progress on the path to precision medicine.

Pleural and transpulmonary pressures to tailor protective ventilation in children

This review aims to: (1) describe the rationale of pleural (P_PL) and transpulmonary (P_L) pressure measurements in children during mechanical ventilation (MV); (2) discuss its usefulness and limitations as a guide for protective MV; (3) propose future directions for paediatric research. We conducted a scoping review on P_L in critically ill children using PubMed and Embase search engines. We included peer-reviewed studies using oesophageal (P_ES) and P_L measurements in the paediatric intensive care unit (PICU) published until September 2021, and excluded studies in neonates and patients treated with non-invasive ventilation. P_L corresponds to the difference between airway pressure and P_PL Oesophageal manometry allows measurement of P_ES, a good surrogate of P_PL, to estimate P_L directly at the bedside. Lung stress is the P_L, while strain corresponds to the lung deformation induced by the changing volume during insufflation. Lung stress and strain are the main determinants of MV-related injuries with P_L and P_PL being key components. P_L-targeted therapies allow tailoring of MV: (1) Positive end-expiratory pressure (PEEP) titration based on end-expiratory P_L (direct measurement) may be used to avoid lung collapse in the lung surrounding the oesophagus. The clinical benefit of such strategy has not been demonstrated yet. This approach should consider the degree of recruitable lung, and may be limited to patients in which PEEP is set to achieve an end-expiratory P_L value close to zero; (2) Protective ventilation based on end-inspiratory P_L (derived from the ratio of lung and respiratory system elastances), might be used to limit overdistention and volutrauma by targeting lung stress values < 20-25 cmH₂O; (3) P_PL may be set to target a physiological respiratory effort in order to avoid both self-induced lung injury and ventilator-induced diaphragm dysfunction; (4) P_PL or P_L measurements may contribute to a better understanding of cardiopulmonary interactions. The growing cardiorespiratory system makes children theoretically more susceptible to atelectrauma, myotrauma and right ventricle failure. In children with acute respiratory distress, P_PL and P_L measurements may help to characterise how changes in PEEP affect P_PL and potentially haemodynamics. In the PICU, P_PL measurement to estimate respiratory effort is useful during weaning and ventilator liberation. Finally, the use of P_PL tracings may improve the detection of patient ventilator asynchronies, which are frequent in children. Despite these numerous theoritcal benefits in children, P_ES measurement is rarely performed in routine paediatric practice. While the lack of robust clincal data partially explains this observation, important limitations of the existing methods to estimate P_PL in children, such as their invasiveness and technical limitations, associated with the lack of reference values for lung and chest wall elastances may also play a role. P_PL and P_L monitoring have numerous potential clinical applications in the PICU to tailor protective MV, but its usefulness is counterbalanced by technical limitations. Paediatric evidence seems currently too weak to consider oesophageal manometry as a routine respiratory monitoring. The development and validation of a noninvasive estimation of P_L and multimodal respiratory monitoring may be worth to be evaluated in the future.

Gas distribution by EIT during PEEP inflation: PEEP response and optimal PEEP with lowest trans-pulmonary driving pressure can be determined without esophageal pressure during a rapid PEEP trial in patients with acute respiratory failure

Objective. Protective ventilation should be based onlungmechanics and transpulmonary driving pressure (ΔPTP), as this 'hits' the lung directly.Approach. The change in end-expiratory lung volume (ΔEELV) is determined by the size of the PEEP step and the elastic properties of the lung (EL), ΔEELV/ΔPEEP. Consequently, EL can be determined as ΔPEEP/ΔEELV. By calibration of tidal inspiratory impedance change with ventilator inspiratory tidal volume, end-expiratory lung impedance changes were converted to volume changes and lung P/V curves were obtained during a PEEP trial in ten patients with acute respiratory failure. The PEEP level where ΔPTP was lowest (optimal PEEP) was determined as the steepest point of the lung P/V curve.Main results. Over-all EL ranged between 7.0-23.2 cmH₂O/L. Optimal PEEP was 12.9 cmH₂O (10-16) with ΔPTP of 4.1 cmH₂O (2.8-7.6). Patients with highest EL were PEEP non-responders, where EL increased in non-dependent and dependent lung at high PEEP, indicating over-distension in all lung. Patients with lower EL were PEEP responders with decreasing EL in dependent lung when increasing PEEP.Significance. PEEP non-responders could be identified by regional lung P/V curves derived from ventilator calibrated EIT. Optimal PEEP could be determined from the equation for the lung P/V curve.

In-line miniature 3D-printed pressure-cycled ventilator maintains respiratory homeostasis in swine with induced acute pulmonary injury

The COVID-19 pandemic demonstrated the need for inexpensive, easy-to-use, rapidly mass-produced resuscitation devices that could be quickly distributed in areas of critical need. In-line miniature ventilators based on principles of fluidics ventilate patients by automatically oscillating between forced inspiration and assisted expiration as airway pressure changes, requiring only a continuous supply of pressurized oxygen. Here, we designed three miniature ventilator models to operate in specific pressure ranges along a continuum of clinical lung injury (mild, moderate, and severe injury). Three-dimensional (3D)-printed prototype devices evaluated in a lung simulator generated airway pressures, tidal volumes, and minute ventilation within the targeted range for the state of lung disease each was designed to support. In testing in domestic swine before and after induction of pulmonary injury, the ventilators for mild and moderate injury met the design criteria when matched with the appropriate degree of lung injury. Although the ventilator for severe injury provided the specified design pressures, respiratory rate was elevated with reduced minute ventilation, a result of lung compliance below design parameters. Respiratory rate reflected how well each ventilator matched the injury state of the lungs and could guide selection of ventilator models in clinical use. This simple device could help mitigate shortages of conventional ventilators during pandemics and other disasters requiring rapid access to advanced airway management, or in transport applications for hands-free ventilation.

Acute respiratory distress syndrome in adults: diagnosis, outcomes, long-term sequelae, and management

Acute respiratory distress syndrome (ARDS) is characterised by acute hypoxaemic respiratory failure with bilateral infiltrates on chest imaging, which is not fully explained by cardiac failure or fluid overload. ARDS is defined by the Berlin criteria. In this Series paper the diagnosis, management, outcomes, and long-term sequelae of ARDS are reviewed. Potential limitations of the ARDS definition and evidence that could inform future revisions are considered. Guideline recommendations, evidence, and uncertainties in relation to ARDS management are discussed. The future of ARDS strives towards a precision medicine approach, and the framework of treatable traits in ARDS diagnosis and management is explored.

An Updated Review of Driving-Pressure Guided Ventilation Strategy and Its Clinical Application

Traditional lung-protective ventilation strategies (LPVS) are currently used to reduce the incidence of postoperative pulmonary complications (PPCs), including low tidal volume (VT), positive end-expiratory pressure (PEEP), low inspiratory plateau pressure (Pplat), permissive hypercapnia, and recruitment maneuver (RM). However, a meta-analysis showed that high driving pressure was closely associated with the incidence of PPCs, but not with PEEP or VT, which led to the driving pressure-guided ventilation strategy. Some studies have proved that the driving pressure-guided ventilation strategy is superior to the traditional LPVS in reducing the incidence of PPCs. The purpose of this review is to present the current research progress and application of driving pressure-guided ventilation strategy.

Association between intraoperative tidal volume and postoperative respiratory complications is dependent on respiratory elastance: a retrospective, multicentre cohort study

BACKGROUND

The impact of high vs low intraoperative tidal volumes on postoperative respiratory complications remains unclear. We hypothesised that the effect of intraoperative tidal volume on postoperative respiratory complications is dependent on respiratory system elastance.

METHODS

We retrospectively recorded tidal volume (Vt; ml kg^-1 ideal body weight [IBW]) in patients undergoing elective, non-cardiothoracic surgery from hospital registry data. The primary outcome was respiratory failure (requiring reintubation within 7 days of surgery, desaturation after extubation, or both). The primary exposure was defined as the interaction between Vt and standardised respiratory system elastance (driving pressure divided by Vt; cm H₂O/[ml kg^-1]). Multivariable logistic regression models, with and without interaction terms (which categorised Vt as low [Vt ≤8 ml kg^-1] or high [Vt >8 ml kg^-1]), were adjusted for potential confounders. Additional analyses included path mediation analysis and fractional polynomial modelling.

RESULTS

Overall, 10 821/197 474 (5.5%) patients sustained postoperative respiratory complications. Higher Vt was associated with greater risk of postoperative respiratory complications (adjusted odds ratio=1.42 per ml kg^-1; 95% confidence interval [CI], 1.35-1.50]; P<0.001). This association was modified by respiratory system elastance (P<0.001); in patients with low compliance (<42.4 ml cm H₂O^-1), higher Vt was associated with greater risk of postoperative respiratory complications (adjusted risk difference=0.3% [95% CI, 0.0-0.5] at 41.2 ml cm H₂O^-1 compliance, compared with 5.8% [95% CI, 3.8-7.8] at 14 ml cm H₂O^-1 compliance). This association was absent when compliance exceeded 41.2 ml cm H₂O^-1. Adverse effects associated with high Vt were entirely mediated by driving pressures (P<0.001).

CONCLUSIONS

The association of harm with higher tidal volumes during intraoperative mechanical ventilation is modified by respiratory system elastance. These data suggest that respiratory elastance should inform the design of perioperative trials testing intraoperative ventilatory strategies.

Impact of Time-Varying Intensity of Mechanical Ventilation on 28-Day Mortality Depends on Fluid Balance in Patients With Acute Respiratory Distress Syndrome: A Retrospective Cohort Study

Background

Recent studies have mainly focused on the association between baseline intensity of mechanical ventilation (driving pressure or mechanical power) and mortality in acute respiratory distress syndrome (ARDS). It is unclear whether the association between the time-varying intensity of mechanical ventilation and mortality is significant and varies according to the fluid balance trajectories.

Methods

We conducted a secondary analysis based on the NHLBI ARDS Network’s Fluid and Catheter Treatment Trial (FACTT). The primary outcome was 28-day mortality. The group-based trajectory modeling (GBTM) was employed to identify phenotypes based on fluid balance trajectories. Bayesian joint models were used to account for informative censoring due to death during follow-up.

Results

A total of 1,000 patients with ARDS were included in the analysis. Our study identified two phenotypes of ARDS, and compared patients with Early Negative Fluid Balance (Early NFB) and patients with Persistent-Positive Fluid Balance (Persistent-PFB) accompanied by higher tidal volume, higher static driving pressure, higher mechanical power, and lower PaO₂/FiO₂, over time during mechanical ventilation. The 28-day mortality was 14.8% in Early NFB and 49.6% in Persistent-PFB (p < 0.001). In the Bayesian joint models, the hazard ratio (HR) of 28-day death for time-varying static driving pressure [HR 1.03 (95% CI 1.01–1.05; p < 0.001)] and mechanical power [HR 1.01 (95% CI 1.002–1.02; p = 0.01)] was significant in patients with Early NFB, but not in patients with Persistent-PFB.

Conclusion

Time-varying intensity of mechanical ventilation was associated with a 28-day mortality of ARDS in a patient with Early NFB but not in patients with Persistent-PFB.

ARDS Clinical Practice Guideline 2021

Background

The joint committee of the Japanese Society of Intensive Care Medicine/Japanese Respiratory Society/Japanese Society of Respiratory Care Medicine on ARDS Clinical Practice Guideline has created and released the ARDS Clinical Practice Guideline 2021.

Methods

The 2016 edition of the Clinical Practice Guideline covered clinical questions (CQs) that targeted only adults, but the present guideline includes 15 CQs for children in addition to 46 CQs for adults. As with the previous edition, we used a systematic review method with the Grading of Recommendations Assessment Development and Evaluation (GRADE) system as well as a degree of recommendation determination method. We also conducted systematic reviews that used meta-analyses of diagnostic accuracy and network meta-analyses as a new method.

Results

Recommendations for adult patients with ARDS are described: we suggest against using serum C-reactive protein and procalcitonin levels to identify bacterial pneumonia as the underlying disease (GRADE 2D); we recommend limiting tidal volume to 4–8 mL/kg for mechanical ventilation (GRADE 1D); we recommend against managements targeting an excessively low SpO₂ (PaO₂) (GRADE 2D); we suggest against using transpulmonary pressure as a routine basis in positive end-expiratory pressure settings (GRADE 2B); we suggest implementing extracorporeal membrane oxygenation for those with severe ARDS (GRADE 2B); we suggest against using high-dose steroids (GRADE 2C); and we recommend using low-dose steroids (GRADE 1B). The recommendations for pediatric patients with ARDS are as follows: we suggest against using non-invasive respiratory support (non-invasive positive pressure ventilation/high-flow nasal cannula oxygen therapy) (GRADE 2D), we suggest placing pediatric patients with moderate ARDS in the prone position (GRADE 2D), we suggest against routinely implementing NO inhalation therapy (GRADE 2C), and we suggest against implementing daily sedation interruption for pediatric patients with respiratory failure (GRADE 2D).

Conclusions

This article is a translated summary of the full version of the ARDS Clinical Practice Guideline 2021 published in Japanese (URL: https://www.jsicm.org/publication/guideline.html). The original text, which was written for Japanese healthcare professionals, may include different perspectives from healthcare professionals of other countries.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40560-022-00615-6.

ARDS clinical practice guideline 2021

BACKGROUND

The joint committee of the Japanese Society of Intensive Care Medicine/Japanese Respiratory Society/Japanese Society of Respiratory Care Medicine on ARDS Clinical Practice Guideline has created and released the ARDS Clinical Practice Guideline 2021.

METHODS

The 2016 edition of the Clinical Practice Guideline covered clinical questions (CQs) that targeted only adults, but the present guideline includes 15 CQs for children in addition to 46 CQs for adults. As with the previous edition, we used a systematic review method with the Grading of Recommendations Assessment Development and Evaluation (GRADE) system as well as a degree of recommendation determination method. We also conducted systematic reviews that used meta-analyses of diagnostic accuracy and network meta-analyses as a new method.

RESULTS

Recommendations for adult patients with ARDS are described: we suggest against using serum C-reactive protein and procalcitonin levels to identify bacterial pneumonia as the underlying disease (GRADE 2D); we recommend limiting tidal volume to 4-8 mL/kg for mechanical ventilation (GRADE 1D); we recommend against managements targeting an excessively low SpO₂ (PaO₂) (GRADE 2D); we suggest against using transpulmonary pressure as a routine basis in positive end-expiratory pressure settings (GRADE 2B); we suggest implementing extracorporeal membrane oxygenation for those with severe ARDS (GRADE 2B); we suggest against using high-dose steroids (GRADE 2C); and we recommend using low-dose steroids (GRADE 1B). The recommendations for pediatric patients with ARDS are as follows: we suggest against using non-invasive respiratory support (non-invasive positive pressure ventilation/high-flow nasal cannula oxygen therapy) (GRADE 2D); we suggest placing pediatric patients with moderate ARDS in the prone position (GRADE 2D); we suggest against routinely implementing NO inhalation therapy (GRADE 2C); and we suggest against implementing daily sedation interruption for pediatric patients with respiratory failure (GRADE 2D).

CONCLUSIONS

This article is a translated summary of the full version of the ARDS Clinical Practice Guideline 2021 published in Japanese (URL: https://www.jrs.or.jp/publication/jrs_guidelines/). The original text, which was written for Japanese healthcare professionals, may include different perspectives from healthcare professionals of other countries.

Monitoring Lung Injury Severity and Ventilation Intensity during Mechanical Ventilation

Acute respiratory distress syndrome (ARDS) is a severe form of respiratory failure burden by high hospital mortality. No specific pharmacologic treatment is currently available and its ventilatory management is a key strategy to allow reparative and regenerative lung tissue processes. Unfortunately, a poor management of mechanical ventilation can induce ventilation induced lung injury (VILI) caused by physical and biological forces which are at play. Different parameters have been described over the years to assess lung injury severity and facilitate optimization of mechanical ventilation. Indices of lung injury severity include variables related to gas exchange abnormalities, ventilatory setting and respiratory mechanics, ventilation intensity, and the presence of lung hyperinflation versus derecruitment. Recently, specific indexes have been proposed to quantify the stress and the strain released over time using more comprehensive algorithms of calculation such as the mechanical power, and the interaction between driving pressure (DP) and respiratory rate (RR) in the novel DP multiplied by four plus RR [(4 × DP) + RR] index. These new parameters introduce the concept of ventilation intensity as contributing factor of VILI. Ventilation intensity should be taken into account to optimize protective mechanical ventilation strategies, with the aim to reduce intensity to the lowest level required to maintain gas exchange to reduce the potential for VILI. This is further gaining relevance in the current era of phenotyping and enrichment strategies in ARDS.

Mechanical power measurement during mechanical ventilation of SARS-CoV-2 critically ill patients. A cohort study

Introduction: The ventilator-induced lung injury (VILI) depends on the amount of energy per minute transferred by the ventilator to the lung measured in Joules, which is called mechanical power. Mechanical power is a development variable probably associated with outcomes in ventilated patients. Objective: To describe the value of mechanical power in patients with SARS-CoV-2 infection and ventilated for other causes and its relationship between days of mechanical ventilation, length of stay in the intensive care unit (ICU), and mortality. Methods: A multicenter, analytical, observational cohort study was conducted in patients with SARS-CoV-2 infection who required invasive mechanical ventilation and patients ventilated for other causes for more than 24 hours. Results: The cohort included 91 patients on mechanical ventilation in three tertiary care centers in the city of Pereira, Colombia. The average value of the mechanical power found was 22.7 ± 1 Joules/min. In the subgroup of patients with SARS-CoV-2 infection, the value of mechanical power was higher 26.8 ± 9 than in the subgroup of patients without a diagnosis of SARS-CoV-2 infection 18.2 ± 1 (p <0.001). Conclusion: Mechanical power is an important variable to consider during the monitoring of mechanical ventilation. This study found an average value of mechanical power of 22.7 ± 1 Joules/min, being higher in patients with SARS-CoV-2 infection related to longer days of mechanical ventilation and a longer stay in the ICU.

The association of modifiable mechanical ventilation settings, blood gas changes and survival on extracorporeal membrane oxygenation for cardiac arrest

RESEARCH QUESTION

Given the relative independence of ventilator settings from gas exchange and plasticity of blood gas values during extracorporeal cardiopulmonary resuscitation (ECPR), do mechanical ventilation parameters and blood gas values influence survival?

METHODS

Observational cohort study of 7488 adult patients with ECPR from the Extracorporeal Life Support Organization (ELSO) Registry. We performed case-mix adjustment for severity of illness and patient type using generalized estimating equation logistic regression to determine factors associated with hospital survival accounting for clustering by center, standardizing variables by 1 standard deviation (SD) of their values. We examined non-linear relationships between ventilatory and blood gas values with hospital survival.

RESULTS

Hospital survival was decreased with higher PaO2 on ECMO (OR 0.69, per 1SD increase [95% CI 0.64, 0.74]; p < 0.001) and with any relative changes in PaCO2 (pre-arrest to on-ECMO) in a non-linear fashion. Survival was worsened with any peak inspiratory pressure >20 cmH20 (OR 0.69, per 1SD [0.64, 0.75]; p < 0.001) and above 40% fraction of inspired oxygen (OR 0.75, per 1SD [0.69, 0.82]; p < 0.001), and with higher dynamic driving pressure (OR 0.72, per 1 SD increase [0.65, 0.79]; <0.001). Ventilation settings and blood gas values varied widely across hospitals, but were not associated with annual hospital ECPR case volume.

CONCLUSION

Lower ventilatory pressures, avoidance of hyperoxia, and relatively unchanged CO2 (pre- to on-ECMO) were all associated with survival in patients after ECPR, yet varied across hospitals. Our findings represent potential targets for prospective trials for this rapidly growing therapy to test if these associations have causality.

Driving pressure is not predictive of ARDS outcome in chest trauma patients under mechanical ventilation

BACKGROUND

The relationship between the driving pressure of the respiratory system (ΔPrs) under mechanical ventilation and worse outcome has never been studied specifically in chest trauma patients. The objective of the present study was to assess in cases of chest trauma the relationship between ΔPrs and severity of acute respiratory distress syndrome (ARDS) or death and length of stay.

METHODS

A retrospective analysis of severe trauma patients (ISS > 15) with chest injuries admitted to the Trauma Centre from January 2010 to December 2018 was performed. Patients who received mechanical ventilation were included in our analysis. Mechanical ventilation parameters and ΔPrs were recorded during the stay in the intensive care unit. Association of ΔPrs with mortality and outcomes was specifically studied at the onset of ARDS (ΔPrs_-ARDS) by receiver operator characteristic curve analysis, Kaplan-Meier curves, and multivariate analysis.

RESULTS

Among the 266 chest trauma patients studied, 194 (73%) developed ARDS. ΔPrs was significantly higher in the ARDS group versus in the no ARDS group (11.6 ± 2.4 cm H₂O vs. 10.9 ± 1.9 cm H₂O, p = 0.04). Among the patients with ARDS, no difference according to the duration of mechanical ventilation was found between the high ΔPrs group (ΔPrs_-ARDS > 14 cm H₂O) and the low ΔPrs group (ΔPrs_-ARDS ≤ 14 cm H₂O), (p = 0.75). ΔPrs_-ARDS was not independently associated with the duration of mechanical ventilation (hazard ratio [HR], 1.006; 95% CI, 0.95-1.07; p = 0.8) or mortality (HR, 1.07; 95% CI, 0.9-1.28; p = 0.45). High mechanical power (≥ 12 J/min) was associated with a lower time for weaning of mechanical ventilation in Kaplan-Meier curves but not in multivariate analysis (HR, 0.98; 95% CI, 0.94-1.02; p = 0.22).

CONCLUSION

A high ΔPrs_-ARDS was not significantly associated with an increase in mechanical ventilation duration or mortality risk in ARDS patients with chest trauma in contrast with medical patients.

Differential Prognostic Analysis of Higher and Lower PEEP in ARDS Patients: Systematic Review and Meta-Analysis

Background

Positive end-expiratory pressure (PEEP) refers to the positive pressure in the respiratory tract at the end of the exhalation when we use a ventilator. The differences of higher PEEP and lower PEEP on clinical outcomes in acute respiratory distress syndrome (ARDS) patients are less well known.

Methods

A comprehensive literature search of all randomized control trials (RCTs) was conducted using PubMed, Embase, World Health Organization (WHO) Global Index Medicus, WHO clinical trial registry, and Clinicaltrials.gov. Inclusion criteria included RCTs comparing the clinical outcomes of higher and lower PEEP in ARDS patients.

Results

Eleven studies were included in the final analysis. In the higher PEEP group, the hospital mortality, 28-day mortality, and ICU mortality showed no significantly lower risk compared to the lower PEEP group (RR = 0.92, 95% CI 0.80-1.05, p = 0.22; RR = 0.88, 95% CI 0.73-1.05, p = 0.15; RR = 0.84, 95% CI 0.67-1.05, p = 0.12; respectively). High certainty could be obtained that there is no significant difference between the clinical outcomes of higher PEEP and lower PEEP in ARDS patients.

Conclusions

There is no significant difference of the hospital mortality, 28-day mortality, and ICU mortality between higher and lower PEEP in ARDS patients.

Driving Pressure Is Associated With Outcome in Pediatric Acute Respiratory Failure

OBJECTIVES

Driving pressure (ratio of tidal volume over respiratory system compliance) is associated with mortality in acute respiratory distress syndrome. We sought to evaluate if such association could be identified in critically ill children.

DESIGN

We studied the association between driving pressure on day 1 of mechanical ventilation and ventilator-free days at day 28 through secondary analyses of prospectively collected physiology data.

SETTING

Medical-surgical university hospital PICU.

PATIENTS

Children younger than 18 years (stratified by Pediatric Mechanical Ventilation Consensus Conference clinical phenotype definitions) without evidence of spontaneous respiration.

INTERVENTIONS

Inspiratory hold maneuvers.

MEASUREMENTS AND MAIN RESULTS

Data of 222 patients with median age 11 months (2-51 mo) were analyzed. Sixty-five patients (29.3%) met Pediatric Mechanical Ventilation Consensus Conference criteria for restrictive and 78 patients (35.1%) for mixed lung disease, and 10.4% of all patients had acute respiratory distress syndrome. Driving pressure calculated by the ratio of tidal volume over respiratory system compliance for the whole cohort was 16 cm H2O (12-21 cm H2O) and correlated with the static airway pressure gradient (plateau pressure minus positive end-expiratory pressure) (Spearman correlation coefficient = 0.797; p < 0.001). Bland-Altman analysis showed that the dynamic pressure gradient (peak inspiratory pressure minus positive end-expiratory pressure) overestimated driving pressure (levels of agreement -2.295 to 7.268). Rematching the cohort through a double stratification procedure (obtaining subgroups of patients with matched mean levels for one variable but different mean levels for another ranking variable) showed a reduction in ventilator-free days at day 28 with increasing driving pressure in patients ventilated for a direct pulmonary indication. Competing risk regression analysis showed that increasing driving pressure remained independently associated with increased time to extubation (p < 0.001) after adjusting for Pediatric Risk of Mortality III 24-hour score, presence of direct pulmonary indication jury, and oxygenation index.

CONCLUSIONS

Higher driving pressure was independently associated with increased time to extubation in mechanically ventilated children. Dynamic assessments of driving pressure should be cautiously interpreted.

Intra-operative ventilator mechanical power as a predictor of postoperative pulmonary complications in surgical patients: A secondary analysis of a randomised clinical trial

BACKGROUND

Studies in critically ill patients suggest a relationship between mechanical power (an index of the energy delivered by the ventilator, which includes driving pressure, respiratory rate, tidal volume and inspiratory pressure) and complications.

OBJECTIVE

We aimed to assess the association between intra-operative mechanical power and postoperative pulmonary complications (PPCs).

DESIGN

Post hoc analysis of a large randomised clinical trial.

SETTING

University-affiliated academic tertiary hospital in Melbourne, Australia, from February 2015 to February 2019.

PATIENTS

Adult patients undergoing major noncardiothoracic, nonintracranial surgery.

INTERVENTION

Dynamic mechanical power was calculated using the power equation adjusted by the respiratory system compliance (CRS). Multivariable models were used to assess the independent association between mechanical power and outcomes.

MAIN OUTCOME MEASURES

The primary outcome was the incidence of PPCs within the first seven postoperative days. The secondary outcome was the incidence of acute respiratory failure.

RESULTS

We studied 1156 patients (median age [IQR]: 64 [55 to 72] years, 59.5% men). Median mechanical power adjusted by CRS was 0.32 [0.22 to 0.51] (J min-1)/(ml cmH2O-1). A higher mechanical power was also independently associated with increased risk of PPCs [odds ratio (OR 1.34, 95% CI, 1.17 to 1.52); P < 0.001) and acute respiratory failure (OR 1.40, 95% CI, 1.21 to 1.61; P < 0.001).

CONCLUSION

In patients receiving ventilation during major noncardiothoracic, nonintracranial surgery, exposure to a higher mechanical power was independently associated with an increased risk of PPCs and acute respiratory failure.

TRIAL REGISTRATION

Australia and New Zealand Clinical Trials Registry no: 12614000790640.

Effects of end-expiratory lung volume versus PaO2 guided PEEP determination on respiratory mechanics and oxygenation in moderate to severe ARDS

There is no ideal method for determination of positive end-expiratory pressure (PEEP) in acute respiratory distress syndrome (ARDS) patients. We compared the effects of end-expiratory lung volume (EELV)-guided versus PaO₂-guided PEEP determination on respiratory mechanics and oxygenation during the first 48 hours in moderate to severe ARDS.

Twenty-two patients with moderate to severe ARDS admitted to an academic medical ICU were assigned to PaO₂-guided (n = 11) or to EELV-guided PEEP determination (n = 11) group. First, an incremental PEEP trial was performed by increasing PEEP by 3 cmH₂O steps from 8 to 20 cmH₂O and in each step EELV and lung mechanics were measured in both groups. Then, oxygenation and respiratory mechanics were measured under the determined PEEP at 4, 12, 24, and 48th hours.

After the incremental PEEP trial, over the 48 hours of the study period, in the EELV-guided group PaO₂ and PaO₂/FiO₂ increased (p = 0.04 and p = 0.02; respectively), whereas they did not change in PaO₂-guided group (p = 0.09 and p = 0.27; respectively). In all patients, the median value of EELV change (ΔEELV) during incremental PEEP trial was 25%. In patients with ΔEELV > 25% (n = 11) PaO₂, PaO₂/FiO₂ and Cs increased over time in 48 hours (p = 0.03, p < 0.01, and p = 0.04; respectively), whereas they did not change in those with ΔEELV ≤ 25% (n = 11) (p = 0.73, p = 0.51, and p = 0.73; respectively).

Compared to PaO₂-guided PEEP determination, EELV-guided PEEP determination resulted in greater improvement in oxygenation over time. Patients who had > 25% improvement in EELV during a PEEP trial had greater improvement in oxygenation and compliance over 48 hours.

Supplemental data for this article is available online at.

Maintenance of low driving pressure in patients with early acute respiratory distress syndrome significantly affects outcomes

Background

Driving pressure (∆P) is an important factor that predicts mortality in acute respiratory distress syndrome (ARDS). We test the hypothesis that serial changes in daily ΔP rather than Day 1 ΔP would better predict outcomes of patients with ARDS.

Methods

This retrospective cohort study enrolled patients admitted to five intensive care units (ICUs) at a medical center in Taiwan between March 2009 and January 2018 who met the criteria for ARDS and received the lung-protective ventilation strategy. ∆P was recorded daily for 3 consecutive days after the diagnosis of ARDS, and its correlation with 60-day survival was analyzed.

Results

A total of 224 patients were enrolled in the final analysis. The overall ICU and 60-day survival rates were 52.7% and 47.3%, respectively. ∆P on Days 1, 2, and 3 was significantly lower in the survival group than in the nonsurvival group (13.8 ± 3.4 vs. 14.8 ± 3.7, p = 0.0322, 14 ± 3.2 vs. 15 ± 3.5, p = 0.0194, 13.6 ± 3.2 vs. 15.1 ± 3.4, p = 0.0014, respectively). The patients were divided into four groups according to the daily changes in ∆P, namely, the low ∆P group (Day 1 ∆P < 14 cmH₂O and Day 3 ∆P < 14 cmH₂O), decrement group (Day 1 ∆P ≥ 14 cmH₂O and Day 3 ∆P < 14 cmH₂O), high ∆P group (Day 1 ∆P ≥ 14 cmH₂O and Day 3 ∆P ≥ 14 cmH₂O), and increment group (Day 1 ∆P < 14 cmH₂O and Day 3 ∆P ≥ 14 cmH₂O). The 60-day survival significantly differed among the four groups (log-rank test, p = 0.0271). Compared with the low ΔP group, patients in the decrement group did not have lower 60-day survival (adjusted hazard ratio 0.72; 95% confidence interval [CI] 0.31–1.68; p = 0.4448), while patients in the increment group had significantly lower 60-day survival (adjusted hazard ratio 1.96; 95% CI 1.11–3.44; p = 0.0198).

Conclusions

Daily ∆P remains an important predicting factor for survival in patients with ARDS. Serial changes in daily ΔP might be more informative than a single Day 1 ΔP value in predicting survival of patients with ARDS.

Relationship between Driving Pressure and Mortality in Ventilated Patients with Heart Failure: A Cohort Study

Background

Heart failure (HF) is a leading cause of mortality and morbidity worldwide, with an increasing incidence. Invasive ventilation is considered to be essential for patients with HF. Previous studies have shown that driving pressure is associated with mortality in acute respiratory distress syndrome (ARDS). However, the relationship between driving pressure and mortality has not yet been examined in ventilated patients with HF. We assessed the association of driving pressure and mortality in patients with HF.

Methods

We conducted a retrospective cohort study of invasive ventilated adult patients with HF from the Medical Information Mart for Intensive Care-III database. We used multivariable logistic regression models, a generalized additive model, and a two-piecewise linear regression model to show the effect of the average driving pressure within 24 h of intensive care unit admission on in-hospital mortality.

Results

Six hundred and thirty-two invasive ventilated patients with HF were enrolled. Driving pressure was independently associated with in-hospital mortality (odds ratio [OR], 1.12; 95% confidence interval [CI], 1.06–1.18; P < 0.001) after adjusted potential confounders. A nonlinear relationship was found between driving pressure and in-hospital mortality, which had a threshold around 14.27 cmH₂O. The effect sizes and CIs below and above the threshold were 0.89 (0.75 to 1.05) and 1.17 (1.07 to 1.30), respectively.

Conclusions

There was a nonlinear relationship between driving pressure and mortality in patients with HF who were ventilated for more than 48 h, and this relationship was associated with increased in-hospital mortality when the driving pressure was more than 14.27 cmH₂O.

A Damaged-Informed Lung Ventilator Model for Ventilator Waveforms

Motivated by a desire to understand pulmonary physiology, scientists have developed physiological lung models of varying complexity. However, pathophysiology and interactions between human lungs and ventilators, e.g., ventilator-induced lung injury (VILI), present challenges for modeling efforts. This is because the real-world pressure and volume signals may be too complex for simple models to capture, and while complex models tend not to be estimable with clinical data, limiting clinical utility. To address this gap, in this manuscript we developed a new damaged-informed lung ventilator (DILV) model. This approach relies on mathematizing ventilator pressure and volume waveforms, including lung physiology, mechanical ventilation, and their interaction. The model begins with nominal waveforms and adds limited, clinically relevant, hypothesis-driven features to the waveform corresponding to pulmonary pathophysiology, patient-ventilator interaction, and ventilator settings. The DILV model parameters uniquely and reliably recapitulate these features while having enough flexibility to reproduce commonly observed variability in clinical (human) and laboratory (mouse) waveform data. We evaluate the proof-in-principle capabilities of our modeling approach by estimating 399 breaths collected for differently damaged lungs for tightly controlled measurements in mice and uncontrolled human intensive care unit data in the absence and presence of ventilator dyssynchrony. The cumulative value of mean squares error for the DILV model is, on average, ≈12 times less than the single compartment lung model for all the waveforms considered. Moreover, changes in the estimated parameters correctly correlate with known measures of lung physiology, including lung compliance as a baseline evaluation. Our long-term goal is to use the DILV model for clinical monitoring and research studies by providing high fidelity estimates of lung state and sources of VILI with an end goal of improving management of VILI and acute respiratory distress syndrome.

Do ventilatory parameters influence outcome in patients with severe acute respiratory infection? Secondary analysis of an international, multicentre14-day inception cohort study

Purpose

To investigate the possible association between ventilatory settings on the first day of invasive mechanical ventilation (IMV) and mortality in patients admitted to the intensive care unit (ICU) with severe acute respiratory infection (SARI).

Materials and methods

In this pre-planned sub-study of a prospective, multicentre observational study, 441 patients with SARI who received controlled IMV during the ICU stay were included in the analysis.

Results

ICU and hospital mortality rates were 23.1 and 28.1%, respectively. In multivariable analysis, tidal volume and respiratory rate on the first day of IMV were not associated with an increased risk of death; however, higher driving pressure (DP: odds ratio (OR) 1.05; 95% confidence interval (CI): 1.01–1.1, p = 0.011), plateau pressure (Pplat) (OR 1.08; 95% CI: 1.04–1.13, p < 0.001) and positive end-expiratory pressure (PEEP) (OR 1.13; 95% CI: 1.03–1.24, p = 0.006) were independently associated with in-hospital mortality. In subgroup analysis, in hypoxemic patients and in patients with acute respiratory distress syndrome (ARDS), higher DP, Pplat, and PEEP were associated with increased risk of in-hospital death.

Conclusions

In patients with SARI receiving IMV, higher DP, Pplat and PEEP, and not tidal volume, were associated with a higher risk of in-hospital death, especially in those with hypoxemia or ARDS.