Positive End-expiratory Pressure Selection Research Articles

Recruitment-to-inflation ratio for bedside PEEP selection in acute respiratory distress syndrome.

In acute respiratory distress syndrome, the role of positive end-expiratory pressure (PEEP) to prevent ventilator-induced lung injury is controversial. Randomized trials comparing higher versus lower PEEP strategies failed to demonstrate a clinical benefit. This may depend on the inter-individually variable potential for lung recruitment (i.e. recruitability), which would warrant PEEP individualization to balance alveolar recruitment and the unavoidable baby lung overinflation produced by high pressure. Many techniques have been used to assess recruitability, including lung imaging, multiple pressure-volume curves and lung volume measurement. The Recruitment-to-Inflation ratio (R/I) has been recently proposed to bedside assess recruitability without additional equipment. R/I assessment is a simplified technique based on the multiple pressure-volume curve concept: it is measured by monitoring respiratory mechanics and exhaled tidal volume during a 10-cmH<inf>2</inf>O one-breath derecruitment maneuver after a short high-PEEP test. R/I scales recruited volume to respiratory system compliance, and normalizes recruitment to a proxy of actual lung size. With modest R/I (<0.3-0.4), setting low PEEP (5-8 cmH<inf>2</inf>O) may be advisable; with R/I>0.6-0.7, high PEEP (≥15 cmH<inf>2</inf>O) can be considered, provided that airway and/or transpulmonary plateau pressure do not exceed safety limits. In case of intermediate R/I (≈0.5), a more granular assessment of recruitability may be needed. This could be accomplished with advanced monitoring tools, like sequential lung volume measurement with granular R/I assessment or electrical impedance tomography monitoring during a decremental PEEP trial. In this review, we discuss R/I rationale, applications and limits, providing insights on its clinical use for PEEP selection in moderate-to-severe acute respiratory distress syndrome.

Recruitment-to-inflation ratio assessed through sequential end-expiratory lung volume measurement in acute respiratory distress syndrome.

Positive end-expiratory pressure (PEEP) benefits in acute respiratory distress syndrome (ARDS) are driven by lung dynamic strain reduction: this depends on the variable extent of alveolar recruitment. The recruitment-to-inflation (R/I) ratio estimates recruitability across a 10-cmH2O PEEP range through a simplified maneuver. Whether recruitability is uniform or not across this range is unknown. The hypotheses of this study are that R/I represents an accurate estimate of PEEP-induced changes in dynamic strain, but may show a non-uniform behaviour across the conventionally tested PEEP range (15-5 cmH2O). Twenty patients with moderate-to-severe COVID-19 ARDS underwent a decremental PEEP trial (PEEP 15-13-10-8-5 cmH2O). Respiratory mechanics and end-expiratory lung volume by nitrogen dilution were measured the end of each step. Gas exchange, recruited volume, R/I, changes in dynamic, static and total strain were computed between 15 and 5 cmH2O (global R/I) and within narrower PEEP ranges (granular R/I). Between 15 and 5 cmH2O, median [Interquartile range] global R/I was 1.27 [0.40-1.69] and displayed a linear correlation with PEEP-induced dynamic strain reduction (r=-0.94, p<0.001). Intra-individual R/I variability within the narrower ranges was high (85% [70-109]). The relationship between granular R/I and PEEP was mathematically described by a non-linear, quadratic equation (r 2=0.96). Granular R/I across the narrower PEEP ranges had itself a linear correlation with PEEP-induced reduction in dynamic strain (r=-0.89, p<0.001). Both global and granular R/I well estimate PEEP-induced changes in lung dynamic strain. However, the effect of 10-cmH2O of PEEP on lung strain may be non-uniform. Granular R/I assessment within narrower PEEP ranges guided by end-expiratory lung volume measurement may aid more precise PEEP selection, especially when R/I obtained with the simplified maneuver between PEEP 15 and 5 cmH2O yields intermediate values, that are difficult to interpret for a proper choice between a high vs. low PEEP strategy.

Effect of EIT-guided PEEP titration on prognosis of patients with moderate to severe ARDS: study protocol for a multicenter randomized controlled trial

BackgroundAcute respiratory syndrome distress (ARDS) is a clinical common syndrome with high mortality. Electrical impedance tomography (EIT)-guided positive end-expiratory pressure (PEEP) titration can achieve the compromise between lung overdistension and collapse which may minimize ventilator-induced lung injury in these patients. However, the effect of EIT-guided PEEP titration on the clinical outcomes remains unknown. The objective of this trial is to investigate the effects of EIT-guided PEEP titration on the clinical outcomes for moderate or severe ARDS, compared to the low fraction of inspired oxygen (FiO2)-PEEP table.MethodsThis is a prospective, multicenter, single-blind, parallel-group, adaptive designed, randomized controlled trial (RCT) with intention-to-treat analysis. Adult patients with moderate to severe ARDS less than 72 h after diagnosis will be included in this study. Participants in the intervention group will receive PEEP titrated by EIT with a stepwise decrease PEEP trial, whereas participants in the control group will select PEEP based on the low FiO2-PEEP table. Other ventilator parameters will be set according to the ARDSNet strategy. Participants will be followed up until 28 days after enrollment. Three hundred seventy-six participants will be recruited based on a 15% decrease of 28-day mortality in the intervention group, with an interim analysis for sample size re-estimation and futility assessment being undertaken once 188 participants have been recruited. The primary outcome is 28-day mortality. The secondary outcomes include ventilator-free days and shock-free days at day 28, length of ICU and hospital stay, the rate of successful weaning, proportion requiring rescue therapies, compilations, respiratory variables, and Sequential Organ Failure Assessment (SOFA).DiscussionAs a heterogeneous syndrome, ARDS has different responses to treatment and further results in different clinical outcomes. PEEP selection will depend on the properties of patients and can be individually achieved by EIT. This study will be the largest randomized trial to investigate thoroughly the effect of individual PEEP titrated by EIT in moderate to severe ARDS patients to date.Trial registrationClinicalTrial.gov NCT05207202. First published on January 26, 2022.

Electric impedance tomography-guided PEEP titration reduces mechanical power in ARDS: a randomized crossover pilot trial

BackgroundIn patients with acute respiratory distress syndrome undergoing mechanical ventilation, positive end-expiratory pressure (PEEP) can lead to recruitment or overdistension. Current strategies utilized for PEEP titration do not permit the distinction. Electric impedance tomography (EIT) detects and quantifies the presence of both collapse and overdistension. We investigated whether using EIT-guided PEEP titration leads to decreased mechanical power compared to high-PEEP/FiO2 tables.MethodsA single-center, randomized crossover pilot trial comparing EIT-guided PEEP selection versus PEEP selection using the High-PEEP/FiO2 table in patients with moderate–severe acute respiratory distress syndrome. The primary outcome was the change in mechanical power after each PEEP selection strategy. Secondary outcomes included changes in the 4 × driving pressure + respiratory rate (4 ΔP, + RR index) index, driving pressure, plateau pressure, PaO2/FiO2 ratio, and static compliance.ResultsEIT was consistently associated with a decrease in mechanical power compared to PEEP/FiO2 tables (mean difference − 4.36 J/min, 95% CI − 6.7, − 1.95, p = 0.002) and led to lower values in the 4ΔP + RR index (− 11.42 J/min, 95% CI − 19.01, − 3.82, p = 0.007) mainly driven by a decrease in the elastic–dynamic power (− 1.61 J/min, − 2.99, − 0.22, p = 0.027). The elastic–static and resistive powers were unchanged. Similarly, EIT led to a statistically significant change in set PEEP (− 2 cmH2O, p = 0.046), driving pressure, (− 2.92 cmH2O, p = 0.003), peak pressure (− 6.25 cmH2O, p = 0.003), plateau pressure (− 4.53 cmH2O, p = 0.006), and static respiratory system compliance (+ 7.93 ml/cmH2O, p = 0.008).ConclusionsIn patients with moderate–severe acute respiratory distress syndrome, EIT-guided PEEP titration reduces mechanical power mainly through a reduction in elastic–dynamic power.Trial registration This trial was prospectively registered on Clinicaltrials.gov (NCT 03793842) on January 4th, 2019.

Association of Positive End-Expiratory Pressure and Lung Recruitment Selection Strategies with Mortality in Acute Respiratory Distress Syndrome: A Systematic Review and Network Meta-analysis.

Rationale: The most beneficial positive end-expiratory pressure (PEEP) selection strategy in patients with acute respiratory distress syndrome (ARDS) is unknown, and current practice is variable. Objectives: To compare the relative effects of different PEEP selection strategies on mortality in adults with moderate to severe ARDS. Methods: We conducted a network meta-analysis using a Bayesian framework. Certainty of evidence was evaluated using grading of recommendations assessment, development and evaluation methodology. Measurements and Main Results: We included 18 randomized trials (4,646 participants). Compared with a lower PEEP strategy, the posterior probability of mortality benefit from a higher PEEP without lung recruitment maneuver (LRM) strategy was 99% (risk ratio [RR], 0.77; 95% credible interval [CrI], 0.60-0.96, high certainty), the posterior probability of benefit of the esophageal pressure-guided strategy was 87% (RR, 0.77; 95% CrI, 0.48-1.22, moderate certainty), the posterior probability of benefit of a higher PEEP with brief LRM strategy was 96% (RR, 0.83; 95% CrI, 0.67-1.02, moderate certainty), and the posterior probability of increased mortality from a higher PEEP with prolonged LRM strategy was 77% (RR, 1.06; 95% CrI, 0.89-1.22, low certainty). Compared with a higher PEEP without LRM strategy, the posterior probability of increased mortality from a higher PEEP with prolonged LRM strategy was 99% (RR, 1.37; 95% CrI, 1.04-1.81, moderate certainty). Conclusions: In patients with moderate to severe ARDS, higher PEEP without LRM is associated with a lower risk of death than lower PEEP. A higher PEEP with prolonged LRM strategy is associated with increased risk of death when compared with higher PEEP without LRM.

Electrical Impedance Tomography to Set Positive End Expiratory Pressure During Pediatric Extracorporeal Membrane Oxygenation for Respiratory Failure... Is it Feasible?

Electrical Impedance Tomography to Set Positive End Expiratory Pressure During Pediatric Extracorporeal Membrane Oxygenation for Respiratory Failure... Is it Feasible?

Progress in Clinical Application of Positive End-Expiratory Pressure

In the surgery patient under general anesthesia doesn’t breathe spontaneously, and lung movement is completely dependent on the mechanical ventilation of the anesthesia machine. In order to achieve effective and safe mechanical ventilation of the patient’s lungs during the operation, the concept of lung protective ventilation strategy (LPVS) was proposed, that is, the use of a low tidal volume and an appropriate level of positive end expiratory pressure (PEEP) to reduce alveolar overexpansion and prevent alveolar collapse. In the past, PEEP was an important measure to treat acute lung injury(ALI) or acute respiratory distress syndrome(ARDS) by improving oxygenation and reducing pulmonary edema. Subsequent studies found that PEEP not only be used to treat patients with ALI or ARDS, but also can reduce the incidence of postoperative pulmonary complications(PPCs) in some thoracoabdominal operations. Moreover, PEEP can prevent atelectasis during and after surgery in patients undergoing thoracic and abdominal surgery under general anesthesia, and decrease the incidence of postoperative infection. However, PEEP can affect venous return by increasing intrathoracic pressure, thereby causing changes in heart function and hemodynamics, and indirectly affecting intracranial pressure and renal function. Therefore, with the widespread clinical application of PEEP, more and more people are starting to focus on how to choose the appropriate PEEP. This article reviews the research progress of PEEP selection method, the influence of PEEP on physiological function and the clinical application of PEEP during mechanical ventilation.

Use of Lung Ultrasound for Assessment of Lung Recruitment Maneuvers in Patients with ARDS

BACKGROUND: Positive pressure mechanical ventilation is a non-physiological intervention that saves lives but is not free of important side effects. It invariably results in different degrees of collapse of small airways. Recruitment maneuver (RM) aims to resolve lung collapse by a brief and controlled increment in airway pressure while positive end-expiratory pressure (PEEP) afterward keeps the lungs open. Therefore, ideally RM and PEEP selection must be individualized and this can only be done when guided by specific monitoring tools since lung’s opening and closing pressures vary among patients with different lung conditions. AIM: The aim of this study was to explore the clinical value of ultrasonic monitoring in the assessment of pulmonary recruitment and the best PEEP. PATIENTS AND METHODS: This study was conducted on 120 patients, 30 were excluded as in whom lung collapse cannot be confirmed then the rest were 90 patients from whom another 25 patients excluded as they were hemodynamically unstable the rest 65 patients were divided into two groups: Group A: Included 50 mechanically ventilated patients with ARDS, underwent lung recruitment using lung ultrasound and Group B: Included 15 mechanically ventilated patients with ARDS, underwent lung recruitment using oxygenation index. This prospective study was held at many critical care departments around Egypt. RESULTS: We noticed that lung recruitment in both groups significantly increased Pao2/Fio2 ratio immediately after recruitment compared with basal state and also significantly increase dynamic compliance compared with basal state. The increase in PF ratio immediately was significantly more in ultrasound group than in oxygenation group. Furthermore, we noticed that that P/F ratio 12 h after recruitment decreased compared with P/F ratio immediately after recruitment but significantly increased compared with basal state before recruitment and also we found that the increase in P/F ratio 12 h after recruitment was more significantly in lung ultrasound group than in oxygenation group. Furthermore, we noticed that lung recruitment (both lung ultrasound and oxygenation group) significantly increase RV function using TAPSE compared with basal state. Both opening pressure and optimal PEEP were significantly higher in lung ultrasound group than in oxygenation group. In our study, opening pressure was 37.28 ± 1.25 in lung ultrasound group and was 36.67±0.98 in oxygenation group and optimal PEEP was 14.64 ± 1.08 in lung ultrasound group and was 13.13 ± 0.74 in oxygenation group. CONCLUSION: Lung US is an effective mean of evaluating and guiding alveolar recruitment in ARDS. Compared with the maximal oxygenation–guided method, the protocol for reaeration in US-guided lung recruitment achieved a higher opening pressure, resulted in greater improvements in lung aeration, and substantially reduced lung heterogeneity in ARDS.

Association of different positive end-expiratory pressure selection strategies with all-cause mortality in adult patients with acute respiratory distress syndrome

BackgroundThe acute respiratory distress syndrome (ARDS) has high morbidity and mortality. Positive end-expiratory pressure (PEEP) is commonly used in patients with ARDS but the best method to select the optimal PEEP level and reduce all-cause mortality is unclear. The primary objective of this network meta-analysis is to summarize the available evidence and to compare the effect of different PEEP selection strategies on all-cause mortality in adult patients with ARDS.MethodsWe will search MEDLINE, Cochrane Central Register of Controlled Trials, PubMed, EMBASE, and LILACS from inception onwards for randomized controlled trials assessing the effect of PEEP selection strategies in adult patients with moderate to severe ARDS. We will exclude studies that did not use a lung-protective ventilation approach as part of the comparator or intervention strategy. The primary outcome will be all-cause mortality (at the longest available follow-up and up to 90 days). Secondary outcomes will include barotrauma, ventilator-free days, intensive care unit and hospital length of stay, and changes in oxygenation. Two reviewers will independently screen all citations, full-text articles, and extract study-data. We will assess the risk of bias for each of the outcomes using version 2 of the Cochrane risk of bias tool for randomized controlled trials. If feasible, Bayesian network meta-analyses will be conducted to obtain pooled estimates of all potential head-to-head comparisons. We will report pairwise and network meta-analysis treatment effect estimates as risk ratios and risk differences, together with the associated 95% credible intervals. We will assess certainty in effect estimates using GRADE methodology.DiscussionThe present study will inform clinical decision-making for adult patients with ARDS and will improve our understanding of the limitations of the available literature assessing PEEP selection strategies. Finally, this information may also inform the design of future randomized trials, including the selection of interventions, comparators, and predictive enrichment strategies.Trial registrationPROSPERO 2020 CRD42020193302.

A clinical study on mechanical ventilation PEEP setting for traumatic ARDS patients guided by esophageal pressure.

This study aims to explore whether positive end-expiratory pressure (PEEP) guided by esophageal pressure is better than the acute respiratory distress syndrome network (ARDSNet) during the treatment of traumatic acute respiratory distress syndrome (ARDS) patients. The use of the oxygenation method of inhaled oxygen concentration titration PEEP is suggested. This study takes traumatic ARDS patients as the research object. The data of 23 patients were included in this study. The patients were randomly divided into two groups: the esophageal pressure titration PEEP group (n= 12), and the ARDSNet (PEEP-FiO2 table) titration PEEP group (n= 11). All patients were given mechanical ventilation, and changes in oxygenation index, respiratory mechanics, hemodynamics and inflammatory reaction index were recorded when titrating the best PEEP with the two methods on the current day of grouping and after grouping for 24, 48 and 72 hours. The PEEP titration value in the esophageal pressure group was 12 ± 4 cm H2O, and this value was significantly higher than the PEEP titration value in the ARDSNet group (8 ± 3 cm H2O) (P< 0.05). The end-expiratory transpulmonary pressure of titrating the best PEEP with the esophageal pressure method and ARDSNet method is 0.5 ± 0.7 cm H2O vs.-1.1 ± 3.3 cm H2O (P< 0.05). When titrating the best PEEP with the esophageal pressure method, lung tissue compliance, end-expiratory transpulmonary pressure and the oxygenation index are higher than those obtained through the ARDSNet method (P< 0.05). (2) In the esophageal pressure group, with the extension of treatment time, high-sensitivity C reactive protein (hs-CRP) and procalcitonin (PCT) exhibited a trend of significant decrease (P< 0.05). In the ARDSNet group, with the extension of treatment time, PCT also exhibited a significant decrease (P< 0.05), while the decrease in hs-CRP was not significant (P> 0.05). After comparing these two treatment groups at each monitoring time point, we found that the difference in hs-CRP and PCT was not statistically significant (P> 0.05). During the 72-hour treatment of interleukin-6 (IL-6) and interleukin-8 (IL-8), we found that these two were significantly lower in the esophageal pressure group than in the ARDSNet group (P< 0.05). The PEEP selection of mechanical ventilation of patients with traumatic ARDS guided by transpulmonary pressure and calculated by measuring intrapleural pressure can realize the individual adjustment of PEEP, identify ARDS patients benefiting from high PEEP, and provide a PEEP setting that can better meet the needs of traumatic patients.

Intraoperative Ventilation Patterns in Morbidly Obese Patients Undergoing Laparoscopic Bariatric Surgery

Background: The purpose of this study was to examine ventilation patterns, including tidal volume (TV) and positive end-expiratory pressure (PEEP) selection in morbidly obese patients undergoing laparoscopic Roux-en-Y gastric bypass or laparoscopic sleeve gastrectomy. Methods: Intraoperative ventilation data, including TV and PEEP, were abstracted from the electronic anesthesia record (Metavision) at Brigham and Women's Hospital. Ideal body weight (IBW) was calculated using the Devine formula, and TV per kg IBW was calculated for each patient. Results: The mean TV delivered per kg IBW was 7.35 ± 1.07 mL/kg, and 24% (281/1186) of patients received TVs of >8 mL/kg IBW. The median PEEP applied was 5.5 ± 0.6 cmH2O, and 87% (1035/1186) of patients received PEEP >0 cmH2O. There was significant variation in both TV and PEEP selection. Conclusions: The significant variation in TV per kg IBW as well as in PEEP values at our institution may reflect the lack of well-established guidelines for intraoperative ventilation. Many patients in this study received inappropriately large TVs (>8 mL/kg IBW), which may be due to calculation of TVs based on total body weight rather than IBW. Patients of shorter stature and higher body mass index appear to be at higher risk for ventilation with inappropriately large TVs.

Validation of a Model-based Method for Estimating Functional Volume Gains during Recruitment Manoeuvres in Mechanical Ventilation

Abstract Mechanical ventilation is a core therapy for patients suffering from respiratory failure in an intensive care unit. However, incorrect ventilator settings can cause further lung damage due to the heterogeneity of lung diseases. A common lung protective strategy is titrating Positive end-expiratory pressure (PEEP) to minimum elastance during a staircase recruitment manoeuvre. Increases in applied PEEP can result in additional lung volume due to alveolar recruitment. However, excessive increases in pressure risks ventilator induced lung injury (VILI). Thus, a trade-off must be made between maximising recruitment and minimising risk. In this study, a non-invasive and clinically relevant model-based method to predict the quantity of this additional volume is developed and the accuracy assessed against measured volume changes. Initial results show reasonable accuracy in estimating gained volume with median [IQR] error of 40 [20 – 60] mL in PEEP changes of up to 9 cmH2O. Use of this parameter to predict lung mechanics at a higher PEEP level was also assessed and had an absolute median [IQR] error of 1.0 [0.5 – 1.8] cmH2O in predicting peak inspiratory pressure. These results offer an opportunity for clinicians to better optimise PEEP selection as patient condition evolves.

Bedside selection of positive end-expiratory pressure by electrical impedance tomography in hypoxemic patients: a feasibility study

BackgroundPositive end-expiratory pressure (PEEP) is a key element of mechanical ventilation. It should optimize recruitment, without causing excessive overdistension, but controversy exists on the best method to set it. The purpose of the study was to test the feasibility of setting PEEP with electrical impedance tomography in order to prevent lung de-recruitment following a recruitment maneuver. We enrolled 16 patients undergoing mechanical ventilation with PaO2/FiO2 <300 mmHg. In all patients, under constant tidal volume (6–8 ml/kg) PEEP was set based on the PEEP/FiO2 table proposed by the ARDS network (PEEPARDSnet). We performed a recruitment maneuver and monitored the end-expiratory lung impedance (EELI) over 10 min. If the EELI signal decreased during this period, the recruitment maneuver was repeated and PEEP increased by 2 cmH2O. This procedure was repeated until the EELI maintained a stability over time (PEEPEIT).ResultsThe procedure was feasible in 87% patients. PEEPEIT was higher than PEEPARDSnet (13 ± 3 vs. 9 ± 2 cmH2O, p < 0.001). PaO2/FiO2 improved during PEEPEIT and driving pressure decreased. Recruited volume correlated with the decrease in driving pressure but not with oxygenation improvement. Finally, regional alveolar hyperdistention and collapse was reduced in dependent lung layers and increased in non-dependent lung layers.ConclusionsIn hypoxemic patients, a PEEP selection strategy aimed at stabilizing alveolar recruitment guided by EIT at the bedside was feasible and safe. This strategy led, in comparison with the ARDSnet table, to higher PEEP, improved oxygenation and reduced driving pressure, allowing to estimate the relative weight of overdistension and recruitment.

Positive end-expiratory pressure: how to set it at the individual level.

The positive end-expiratory pressure (PEEP), since its introduction in the treatment of acute respiratory failure, up to the 1980s was uniquely aimed to provide a viable oxygenation. Since the first application, a large debate about the criteria for selecting the PEEP levels arose within the scientific community. Lung mechanics, oxygen transport, venous admixture thresholds were all proposed, leading to PEEP recommendations from 5 up to 25 cmH2O. Throughout this period, the main concern was the hemodynamics. This paradigm changed during the 1980s after the wide acceptance of atelectrauma as one of the leading causes of ventilator induced lung injury. Accordingly, the PEEP aim shifted from oxygenation to lung protection. In this framework, the prevention of lung opening and closing became an almost unquestioned dogma. Consequently, as PEEP keeps open the pulmonary units opened during the previous inspiratory phase, new methods were designed to identify the 'optimal' PEEP during the expiratory phase. The open lung approach requires that every collapsed unit potentially openable is opened and maintained open. The methods to assess the recruitment are based on imaging (computed tomography, electric impedance tomography, ultrasound) or mechanically-driven gas exchange modifications. All the latest assume that whatever change in respiratory system compliance is due to changes in lung compliance, which in turn is uniquely function of the recruitment. Comparative studies, however, showed that the only possible approach to measure the amount of collapsed tissue regaining inflation is the CT scan. In fact, all the other methods estimate as recruitment the gas entry in pulmonary units already open at lower PEEP, but increasing their compliance at higher PEEP. Since higher PEEP is usually more indicated (also for oxygenation) when the recruitability is higher, as occurs with increasing severity, a meaningful PEEP selection requires the assessment of recruitment. The Berlin definition may help in this assessment.

Compliance-guided versus FiO2-driven positive-end expiratory pressure in patients with moderate or severe acute respiratory distress syndrome according to the Berlin definition

ObjectiveTo study the effect of setting positive end-expiratory pressure (PEEP) in an individualized manner (based on highest static compliance) compared to setting PEEP according to FiO2 upon mortality at 28 and 90 days, in patients with different severity acute respiratory distress syndrome (ARDS). SettingA Spanish medical–surgical ICU. DesignA post hoc analysis of a randomized controlled pilot study. PatientsPatients with ARDS. InterventionsVentilation with low tidal volumes and pressure limitation at 30cmH2O, randomized in two groups according to the method used to set PEEP: FiO2-guided PEEP group according to FiO2 applied and compliance-guided group according to the highest compliance. Primary variables of interestDemographic data, risk factors and severity of ARDS, APACHE II and SOFA scores, daily Lung Injury Score, ventilatory measurements, ICU and hospital stay, organ failure and mortality at day 28 and 90 after inclusion. ResultsA total of 159 patients with ARDS were evaluated, but just 70 patients were included. Severe ARDS patients showed more organ dysfunction-free days at 28 days (12.83±10.70 versus 3.09±7.23; p=0.04) and at 90 days (6.73±22.31 vs. 54.17±42.14, p=0.03), and a trend toward lower 90-days mortality (33.3% vs. 90.9%, p=0.02), when PEEP was applied according to the best static compliance. Patients with moderate ARDS did not show these effects. ConclusionsIn patients with severe ARDS, individualized PEEP selection based on the best static compliance was associated to lower mortality at 90 days, with an increase in organ dysfunction-free days at 28 and 90 days.

Compliance-guided versus FiO2-driven positive-end expiratory pressure in patients with moderate or severe acute respiratory distress syndrome according to the Berlin definition

ObjectiveTo study the effect of setting positive end-expiratory pressure (PEEP) in an individualized manner (based on highest static compliance) compared to setting PEEP according to FiO2 upon mortality at 28 and 90 days, in patients with different severity acute respiratory distress syndrome (ARDS). SettingA Spanish medical–surgical ICU. DesignA post hoc analysis of a randomized controlled pilot study. PatientsPatients with ARDS. InterventionsVentilation with low tidal volumes and pressure limitation at 30cmH2O, randomized in two groups according to the method used to set PEEP: FiO2-guided PEEP group according to FiO2 applied and compliance-guided group according to the highest compliance. Primary variables of interestDemographic data, risk factors and severity of ARDS, APACHE II and SOFA scores, daily Lung Injury Score, ventilatory measurements, ICU and hospital stay, organ failure and mortality at day 28 and 90 after inclusion. ResultsA total of 159 patients with ARDS were evaluated, but just 70 patients were included. Severe ARDS patients showed more organ dysfunction-free days at 28 days (12.83±10.70 versus 3.09±7.23; p=0.04) and at 90 days (6.73±22.31 vs. 54.17±42.14, p=0.03), and a trend toward lower 90-days mortality (33.3% vs. 90.9%, p=0.02), when PEEP was applied according to the best static compliance. Patients with moderate ARDS did not show these effects. ConclusionsIn patients with severe ARDS, individualized PEEP selection based on the best static compliance was associated to lower mortality at 90 days, with an increase in organ dysfunction-free days at 28 and 90 days.

Feasibility of titrating PEEP to minimum elastance for mechanically ventilated patients.

BackgroundSelecting positive end-expiratory pressure (PEEP) during mechanical ventilation is important, as it can influence disease progression and outcome of acute respiratory distress syndrome (ARDS) patients. However, there are no well-established methods for optimizing PEEP selection due to the heterogeneity of ARDS. This research investigates the viability of titrating PEEP to minimum elastance for mechanically ventilated ARDS patients.MethodsTen mechanically ventilated ARDS patients from the Christchurch Hospital Intensive Care Unit were included in this study. Each patient underwent a stepwise PEEP recruitment manoeuvre. Airway pressure and flow data were recorded using a pneumotachometer. Patient-specific respiratory elastance (Ers) and dynamic functional residual capacity (dFRC) at each PEEP level were calculated and compared. Optimal PEEP for each patient was identified by finding the minima of the PEEP-Ers profile.ResultsMedian Ers and dFRC over all patients and PEEP values were 32.2 cmH2O/l [interquartile range (IQR) 25.0–45.9] and 0.42 l [IQR 0.11–0.87]. These wide ranges reflect patient heterogeneity and variable response to PEEP. The level of PEEP associated with minimum Ers corresponds to a high change of functional residual capacity, representing the balance between recruitment and minimizing the risk of overdistension.ConclusionsMonitoring patient-specific Ers can provide clinical insight to patient-specific condition and response to PEEP settings. The level of PEEP associated with minimum-Ers can be identified for each patient using a stepwise PEEP recruitment manoeuvre. This ‘minimum elastance PEEP’ may represent a patient-specific optimal setting during mechanical ventilation.Trial registrationAustralian New Zealand Clinical Trials Registry: ACTRN12611001179921.Electronic supplementary materialThe online version of this article (doi:10.1186/s40814-015-0006-2) contains supplementary material, which is available to authorized users.

Gas exchange and lung mechanics in patients with acute respiratory distress syndrome: Comparison of three different strategies of positive end expiratory pressure selection

PurposeThe purpose of the study was to compare gas exchange and lung mechanics between different strategies to select positive end-expiratory pressure (PEEP) in acute respiratory distress syndrome (ARDS). MethodsIn 20 consecutive ARDS patients, 3 PEEP selection strategies were evaluated. One strategy was based on oxygenation using the ARDS network PEEP/fraction of inspired oxygen (Fio2) table; and two were based on lung mechanics, either PEEP titrated to reach a plateau pressure of 28 to 30 cm H2O as in the ExPress trial or best respiratory compliance method during a derecruitment maneuver. Gas exchange, airway pressures, stress index (SI), and end-expiratory transpulmonary pressure (Ptpe) and end-inspiratory transpulmonary pressure (Ptpi) values were assessed. Data are expressed as median (interquartile range [IQR]). ResultsLower total PEEP levels were observed with the use of the PEEP/Fio2 table (8.7 [6-10] cm H2O); intermediate PEEP levels, with the Best Compliance approach (13.0 [10.2-13.8] cm H2O); and higher PEEP levels, with the ExPress strategy (16.5 [15.0-18.5] cm H2O) (P < .01). Pao2/Fio2 ratio was lower with the PEEP/Fio2 table. Oxygenation with Best Compliance approach and ExPress strategy was not different with lower plateau pressure in the former (23 [20-25] vs 30 [29-30] cm H2O; P < .01). Paco2 was slightly higher with the ExPress method than the others 2 strategies. Negative Ptpe was observed in 35% of the patients with the PEEP/Fio2 table, in 15% applying the Best Compliance, and in only 1 case with the ExPress method. Higher SI and Ptpi, with lower lung compliance, were obtained with ExPress strategy. ConclusionsUsing a best respiratory compliance approach resulted in better oxygenation levels without risk of overdistension according to SI and Ptpi, achieving a mild risk of lung collapse according to Ptpe.

A minimal algorithm for a minimal recruitment model–model estimation of alveoli opening pressure of an acute respiratory distress syndrome (ARDS) lung

A minimal recruitment model can be used to guide mechanical ventilation PEEP selection for acute respiratory distress syndrome (ARDS) patients. However, implementation of this model requires a specific clinical protocol and is computationally expensive, and thus not suitable for bedside application. This work aims to improve the performance and bedside utility of the minimal recruitment model through simplifying the model, and improving the identification algorithm without compromising the model's physiological relevance to the disease. Identifying the model requires fitting of 8 unique parameters to pressure–volume data at multiple levels of positive end-expiratory pressure (PEEP). A minimal algorithm is proposed to improve the model's performance. The algorithm utilises a non-linear least-squares solver to estimate a global set of the parameters to a pressure–volume curve at one PEEP level. These global parameters were then subsequently used to estimate other parameters at different pressure–volume curves. The accuracy and computational performance of the minimal algorithm is compared to the grid search algorithm for 2 ARDS patient cohorts. The median [IQR] absolute percentage curve fitting error over all patients for grid search algorithm is 1.40% [0.55–3.75], and for the minimal algorithm is 2.43% [0.83–8.09] (p<0.005). The median [IQR] computational time for all patients for the grid search algorithm is 394.51s [284.79–630.45], and for the minimal algorithm is 0.72s [0.39–1.46], where a 600% of reduction of computational time was found for the minimal algorithm. The estimated parameters using the minimal algorithm are correlated with the grid search algorithm with median person's correlation of R2>0.9. The model fitting error for the minimal algorithm is higher than the grid search algorithm. However the model was able capture similar trends in physiologically relevant parameters without the loss of important clinical information. The minimal algorithm is less computationally intensive than the grid search algorithm, whilst still providing a means of selecting PEEP with only a small increase in model fitting error. The minimal algorithm is able to improve computational performance while maintaining the ability to capture physiological parameters as the grid search algorithm. The significant reduction in computational time encourages its clinical application at the bedside for decision making.

Bedside Selection of Positive End-Expiratory Pressure in Mild, Moderate, and Severe Acute Respiratory Distress Syndrome*

Positive end-expiratory pressure exerts its effects keeping open at end-expiration previously collapsed areas of the lung; consequently, higher positive end-expiratory pressure should be limited to patients with high recruitability. We aimed to determine which bedside method would provide positive end-expiratory pressure better related to lung recruitability. Prospective study performed between 2008 and 2011. Two university hospitals (Italy and Germany). Fifty-one patients with acute respiratory distress syndrome. Whole lung CT scans were taken in static conditions at 5 and 45 cm H2O during an end-expiratory/end-inspiratory pause to measure lung recruitability. To select individual positive end-expiratory pressure, we applied bedside methods based on lung mechanics (ExPress, stress index), esophageal pressure, and oxygenation (higher positive end-expiratory pressure table of lung open ventilation study). Patients were classified in mild, moderate and severe acute respiratory distress syndrome. Positive end-expiratory pressure levels selected by the ExPress, stress index, and absolute esophageal pressures methods were unrelated with lung recruitability, whereas positive end-expiratory pressure levels selected by the lung open ventilation method showed a weak relationship with lung recruitability (r = 0.29; p < 0.0001). When patients were classified according to the acute respiratory distress syndrome Berlin definition, the lung open ventilation method was the only one which gave lower positive end-expiratory pressure levels in mild and moderate acute respiratory distress syndrome compared with severe acute respiratory distress syndrome (8 ± 2 and 11 ± 3 cm H2O vs 15 ± 3 cm H2O; p < 0.05), whereas ExPress, stress index, and esophageal pressure methods gave similar positive end-expiratory pressure values in mild, moderate, and severe acute respiratory distress syndrome. The positive end-expiratory pressure selected by the different methods were unrelated to each other with the exception of the two methods based on lung mechanics (ExPress and stress index). Bedside positive end-expiratory pressure selection methods based on lung mechanics or absolute esophageal pressures provide positive end-expiratory pressure levels unrelated to lung recruitability and similar in mild, moderate, and severe acute respiratory distress syndrome, whereas the oxygenation-based method provided positive end-expiratory pressure levels related with lung recruitability progressively increasing from mild to moderate and severe acute respiratory distress syndrome.