Positive End-expiratory Pressure Set Research Articles

Mechanical ventilation strategies for the surgical patient.

To summarize clinical evidence for intraoperative ventilation settings, which could protect against postoperative pulmonary complications (PPCs) in surgical patients with uninjured lungs. There is convincing evidence for protection against PPCs by low tidal volumes: benefit was found in several randomized controlled trials, and was recently confirmed in meta-analyses. Evidence for protection against PPCs by high levels of positive end-expiratory pressure (PEEP) is less definite. Although benefit was found in several randomized controlled trials, most of them compared a bundle of low tidal volume and high level of PEEP with conventional ventilation; one recent large randomized controlled trial that compared high with low levels of PEEP showed that ventilation with high level of PEEP did not protect against PPCs but caused intraoperative complications instead. A recent individual patient data meta-analysis of trials comparing bundles of low tidal volume and high levels of PEEP to conventional intraoperative ventilation suggested that protection against PPCs comes from tidal volume reductions, and not from increasing levels of PEEP. The understanding on the protective roles of tidal volume and PEEP settings against PPCs has rapidly expanded. During intraoperative ventilation, low tidal volumes are protective, the protective role of high levels of PEEP is uncertain.

Influence of tidal volume on ventilation inhomogeneity assessed by electrical impedance tomography during controlled mechanical ventilation

The global inhomogeneity (GI) index is a parameter of ventilation inhomogeneity that can be calculated from images of tidal ventilation distribution obtained by electrical impedance tomography (EIT). It has been suggested that the GI index may be useful for individual adjustment of positive end-expiratory pressure (PEEP) and for guidance of ventilator therapy. The aim of the present work was to assess the influence of tidal volume (VT) on the GI index values. EIT data from 9 patients with acute respiratory distress syndrome ventilated with a low and a high VT of 5 ± 1 (mean ± SD) and 9 ± 1 ml kg−1 predicted body weight at a high and a low level of PEEP (PEEPhigh, PEEPlow) were analyzed. PEEPhigh and PEEPlow were set 2 cmH2O above and 5 cmH2O below the lower inflection point of a quasi-static pressure volume loop, respectively. The lower inflection point was identified at 8.1 ± 1.4 (mean ± SD) cmH2O, resulting in a PEEPhigh of 10.1 ± 1.4 and a PEEPlow of 3.1 ± 1.4 cmH2O. At PEEPhigh, we found no significant trend in GI index with low VT when compared to high VT (0.49 ± 0.15 versus 0.44 ± 0.09, p = 0.13). At PEEPlow, we found a significantly higher GI index with low VT compared to high VT (0.66 ± 0.19 versus 0.59 ± 0.17, p = 0.01). When comparing the PEEP levels, we found a significantly lower GI index at PEEPhigh both for high and low VT. We conclude that high VT may lead to a lower GI index, especially at low PEEP settings. This should be taken into account when using the GI index for individual adjustment of ventilator settings.

Positive end-expiratory pressure titration at bedside using electrical impedance tomography in post-operative cardiac surgery patients.

Post-operative positive end-expiratory pressure (PEEP) setting to minimize the risk of ventilator-associated lung injury is still controversial. Assessment of regional ventilation distribution by electrical impedance tomography (EIT) might be superior as compared with global parameters. The aim of this prospective observational study was to compare global dynamic compliance (CRS ) with different EIT indices during a short clinical applicable descending PEEP trial. Twenty mechanically ventilated patients after elective cardiac surgery received a standard recruitment manoeuvre (RM) following descending PEEP trial in steps of 2 cmH2 O from PEEP 14 cmH2 O to 6 cmH2 O. During baseline and all PEEP steps, CRS was assessed and regional ventilation distribution was measured by means of EIT. The individual 'best' PEEP values for the derived EIT indices and CRS were calculated and compared. The descending PEEP trial lasted less than 10min. CRS increased after the RM and showed a maximum value at PEEP 8 cmH2 O. Ventilation distribution shifted more to dependent lung regions after RM and back to more non-dependent regions during the PEEP trial. Individual 'best' PEEP by CRS showed significantly lower values than 'best' PEEP by ventilation distribution measured with EIT indices. During a short descending PEEP trial at bedside, EIT is capable of following the status of regional ventilation distribution in ventilated patients. The 'best' PEEP value identified by individual maximum CRS was lower than optimal PEEP levels as determined by means of EIT indices. EIT could help setting PEEP in post-operative ventilated patients.

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.

Mechanical ventilation for ARDS patients--for a better understanding of the 2012 Surviving Sepsis Campaign Guidelines.

The mortality rate among patients suffering acute respiratory distress syndrome (ARDS) remains high despite implementation at clinical centers of the lung protective ventilatory strategies recommended by the International Guidelines for Management of Severe Sepsis and Septic Shock, 2012. This suggests that such strategies are still sub-optimal for some ARDS patients. For these patients, tailored use of ventilator settings should be considered, including: further reduction of tidal volumes, administration of neuromuscular blocking agents if the patient’s spontaneous breathing is incompatible with mechanical ventilation, and adjusting positive end-expiratory pressure (PEEP) settings based on transpulmonary pressure levels.

Lung-Protective Ventilation Strategy in Surgical Patients: Optimal Setting of Positive End-Expiratory Pressure?

More than 230 million of patients undergoing general anesthesia for major surgery require mechanical ventilation annually worldwide (1). It has been reported that 5-10% of all surgical patients and about 30-40% of those undergoing thoracic or abdominal surgery develop postoperative pulmonary complications (PPCs), such as atelectasis, pneumonia, respiratory failure, acute respiratory distress syndrome, pleural effsion, etc (2). The improved perioperative management in the past decade has significantly decreased case-fatality rate of surgical patients, but the frequency of PPCs has still remained relatively constant due to the increased number and complexity of the operations performed and the increased acuity and age of patients. It has been shown that PPCs are major causes of postoperative morbidity and mortality, and are associated with considerable costs in hospital cares (3). Thus, PPCs are important clinical problems in modern practice and the prevention of PPCs has become a measure of quality of care (4). Citation: Fu-Shan Xue, Xu Liao, Rui-Ping Li, Xin-Long Cui. Lung-protective ventilation strategy in surgical patients: optimal setting of positive end-expiratory pressure? J Anesth Perioper Med 2015; 2: 45-7. doi: 10.24015/JAPM.2015.0007This is an open-access article, published by Evidence Based Communications (EBC). This work is licensed under the Creative Commons Attribution 4.0 International License, which permits unrestricted use, distribution, and reproduction in any medium or format for any lawful purpose. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

Lung Ultrasonography for the Detection of Anesthesia-induced Lung Atelectasis

We have read with great interest the article by Acosta et al.1 exploring the use of lung ultrasound as a mean to detect intraoperative atelectasis. However, despite their statement to the contrary, the occurrence of B lines in the setting of atelectasis has already been described by others. Although B lines were initially thought to originate from the interaction of the ultrasound beam with thickened subpleural interlobular septa found in alveolar-interstitial pathologies,2 recent work has challenged this hypothesis. In an elegant series of experiments, Soldati et al.3–5 have shown that B lines are observed when the ultrasound beam interacts at the pleural surface with lung tissue of a specific density. Although this can occur with the replacement of subpleural air by an ultrasound-conductive substance (e.g., water, pus, blood, and fibrous tissue), the withdrawal of air (e.g., resorption atelectasis) will also lead to the genesis of B lines. Demonstrating this last point, in an ex vivo animal model of graded atelectasis, B lines were observed in increasing numbers with increasing atelectasis. Pathologic examination of the excised lungs showed diffusely compressed alveoli mixed with sporadic areas of normally expanded distal air spaces.5The study by Acosta et al. comes at an interesting moment. The recent publication of two randomized controlled trials6,7 exploring the impact of intraoperative mechanical ventilation parameters on postoperative pulmonary complications has generated much interest.8 Although some have linked the negative results of the PROVHILO (PROtective Ventilation using HIgh versus LOw positive end-expiratory pressure) trial to a lack of regular recruitment maneuvers and a positive end-expiratory pressure set too high,9 others blame the use of inappropriately high tidal volumes in the control group for the positive results in the IMPROVE (Intraoperative PROtective VEntilation) trial.10 In the absence of imagery supporting claims of atelectasis or overdistention, the culprits usually blamed for the development of postoperative pulmonary complications, it is unlikely this question will be resolved before more data becomes available. Interestingly, recent anesthesiology literature has demonstrated the advantage of hemodynamic optimization11 championing the concept that individualization is preferable to a “one size fits all” approach. Likewise, individualization of mechanical ventilation parameters might be an interesting avenue to explore if we wish to decrease the occurrence of postoperative respiratory complications. This hypothesis is supported by spiral computed tomography studies reporting significant interpatient variability in the amount of atelectasis induced by general anesthesia.12,13 Therefore, we believe that bedside monitoring to detect lung atelectasis or overdistention is needed. Although magnetic resonance imaging and computed tomography fulfill this requirement, they cannot be used in an intraoperative setting except in specially designed operating rooms and could not realistically be repeated throughout a procedure. Because lung ultrasonography can be performed at the bedside and is devoid of any ionizing radiation, the present study by Acosta et al., although interesting in and of itself, is an important milestone toward establishing lung ultrasonography as a tool to optimize intraoperative mechanical ventilation parameters. Other investigators have described loss of aeration scales that have allowed the study of the therapeutic effects of antibiotics in ventilator-associated pneumonia,14 the effect of different levels of positive end-expiratory pressure in patients with acute respiratory distress syndrome on lung reexpansion15 and the detection of patients likely to fail extubation after a successful spontaneous breathing trial.16 Although not developed specifically for the diagnosis and monitoring of anesthesia-induced atelectasis, the use of these scales would have been an interesting addition to the study by Acosta et al. Whether to optimize intraoperative mechanical ventilation parameters or to assist anesthesiologists in the care of hypoxemic patients, lung ultrasonography is likely to have a bright future in our operating rooms.Supported by Grant of the Fondation 2013, Fondation d’anesthésiologie et réanimation du Québec; Grant of the Fonds de développement 2014, Département d’anesthésiologie, Université de Montréal.The authors declare no competing interests.

Effects of positive end-expiratory pressure on lung ventilation/ perfusion matching: a clinical study

Positive end-expiratory pressure (PEEP) exerts multiple protective effects in hypoxemic critically ill patients: PEEP can increase end-expiratory lung volume (EELV) and induce recruitment, thus reducing lung strain and opening and closing of alveoli and potentially improving the ventilation/perfusion matching. In particular, estimation of PEEP-induced ventilation/perfusion matching might help identify the optimal PEEP setting, but bedside non-invasive methods are few and complex to be applied in daily clinical practice. Electrical impedance tomography (EIT) is a non-invasive bedside technique that claims to track global and regional changes in perfusion and ventilation over time. In the present study we aimed at verifying the effects of PEEP on ventilation/perfusion matching, as assessed by EIT, in acute respiratory failure patients.

Ventilatory strategies in severe acute respiratory failure.

Lung-protective ventilator strategies are considered standard practice in the care of patients with the acute respiratory distress syndrome (ARDS). To minimize ventilator-induced lung injury, attention is directed at avoidance of alveolar overdistention and cyclical opening and closing. The lowest possible plateau pressure and tidal volume (V(T)) should be selected. A reasonable target V(T) in all mechanically ventilated patients is 6 mL/kg. A topic of much controversy is the optimal setting of positive end-expiratory pressure (PEEP). Results of a meta-analysis using individual patient data from three randomized controlled trials suggest that higher PEEP should be used for moderate and severe ARDS, whereas lower PEEP may be more appropriate in patients with mild ARDS. PEEP should be set to maximize alveolar recruitment while avoiding overdistention. Volume and pressure limitation during mechanical ventilation can be described in terms of stress and strain. Fraction of inspired oxygen (Fio(2)) and PEEP are typically titrated to maintain arterial oxygen saturation (Spo(2)) of 88 to 95% (Pao(2) 55-80 mm Hg). There is currently no clear proven benefit for advanced modes.

Monitoring of oesophageal pressure.

Studies in patients with acute respiratory distress syndrome (ARDS) have been unable to demonstrate a survival advantage with higher levels of positive end-expiratory pressure (PEEP) to open atelectatic lung regions or prevent their cyclic collapse. This review will discuss the challenges of accurately measuring pleural pressure with balloon-tipped catheters in the oesophagus, and the utility of such pressure monitoring to set PEEP and assess lung mechanics, focusing on patients with ARDS. Recent investigations have suggested that the monitoring of oesophageal pressure in ARDS patients may help individualize PEEP settings to optimize lung recruitment based on transpulmonary pressure. Changes in oesophageal pressure likely accurately reflect global changes in pleural pressure in supine patients with ARDS. However, absolute oesophageal pressure values in such patients may be subject to local artefacts and may substantially overestimate pleural pressure in other lung regions. Setting PEEP high enough to achieve a targeted end-expiratory transpulmonary pressure in the region of the oesophageal balloon catheter could overdistend other lung regions. Measurement of oesophageal pressure is feasible, but its clinical utility to titrate PEEP, compared with routine assessment, awaits experimental confirmation.

Influence of ventilatory strategy on the PRESERVE mortality risk score: response to Camporota et al.

Dear Editor, We thank Dr. Camporota et al. [1] for their interest in our study [2]. We fully agree that the ventilation strategy, especially positive end expiratory pressure (PEEP) setting, is relevant to the validity and applicability of the PRESERVE score. PEEP was adjusted before extracorporeal membrane oxygenation (ECMO) initiation according to the high recruitment arm of the Express trial [3] in our study, targeting plateau pressure (Pplat) of less than 30 cmH2O. This is the reason why PEEP was only 8 cmH2O on average while FiO2 was 1.0 and tidal volume (Vt) 6 ml/kg for non-survivors who had the lowest lung compliance (16 ml/cmH2O on average before ECMO initiation). Using these mechanical ventilation settings and with a mean respiratory rate of 30/min, mean values for Pplat, pH and PCO2 were 34 cmH2O, 7.22 and 70 mmHg, respectively. Although ARDSNet protocols recommended PEEP up to 20–24 cmH2O for FiO2 = 1.0, they also recommended to keep Pplat no greater than 30 cmH2O. Therefore, considering the extreme severity of these patients, it appears unlikely that applying the ARDSNet strategy might have resulted in significantly higher PEEP, unless Pplat greater than 40–45 cmH2O had been tolerated. We concur with Dr. Camporota et al. that obese patients have lower transpulmonary pressure for the same Pplat, which might be associated with lower effective PEEP. In our multivariate analysis, BMI greater than 30 kg/m was associated with better outcomes, independently of preECMO plateau pressure and PEEP. Whether this ‘‘protective’’ effect of higher BMI was related to lower transpulmonary pressures or to an intrinsic survival benefit for obese patients as previously reported will remain speculative. Our cohort does not permit a reliable sensitivity analysis according to H1N1 status because only 26 % of our patients had flu-associated ARDS. In a previous report by the REVA Research Network in France [4], multivariable analysis retained higher age, lactate and plateau pressure under ECMO as significantly associated with ICU death. Validation of the PRESERVE score on specific ARDS populations should be the focus of future studies. Lastly, both SAPS II and SOFA scores were significantly associated with mortality. Since these two variables were collinear, only SAPS II was entered in the first multivariable model. However, SOFA score was preferred over SAPS II for simpler construction of the score at the bedside. Interestingly, the same threshold (SOFA [ 12) was recently used by Roch et al. [5] to evaluate the risk of death in ARDS patients considered for retrieval under ECMO from distant hospitals.

2014 Annual Journal Symposium

2014 Annual Journal Symposium

2014 Annual Journal Symposium

2014 Annual Journal Symposium

Open lung approach with low tidal volume mechanical ventilation attenuates lung injury in rats with massive brain damage

IntroductionThe ideal ventilation strategy for patients with massive brain damage requires better elucidation. We hypothesized that in the presence of massive brain injury, a ventilation strategy using low (6 milliliters per kilogram ideal body weight) tidal volume (VT) ventilation with open lung positive end-expiratory pressure (LVT/OLPEEP) set according to the minimal static elastance of the respiratory system, attenuates the impact of massive brain damage on gas-exchange, respiratory mechanics, lung histology and whole genome alterations compared with high (12 milliliters per kilogram ideal body weight) VT and low positive end-expiratory pressure ventilation (HVT/LPEEP).MethodsIn total, 28 adult male Wistar rats were randomly assigned to one of four groups: 1) no brain damage (NBD) with LVT/OLPEEP; 2) NBD with HVT/LPEEP; 3) brain damage (BD) with LVT/OLPEEP; and 4) BD with HVT/LPEEP. All animals were mechanically ventilated for six hours. Brain damage was induced by an inflated balloon catheter into the epidural space. Hemodynamics was recorded and blood gas analysis was performed hourly. At the end of the experiment, respiratory system mechanics and lung histology were analyzed. Genome wide gene expression profiling and subsequent confirmatory quantitative polymerase chain reaction (qPCR) for selected genes were performed.ResultsIn NBD, both LVT/OLPEEP and HVT/LPEEP did not affect arterial blood gases, as well as whole genome expression changes and real-time qPCR. In BD, LVT/OLPEEP, compared to HVT/LPEEP, improved oxygenation, reduced lung damage according to histology, genome analysis and real-time qPCR with decreased interleukin 6 (IL-6), cytokine-induced neutrophil chemoattractant 1 (CINC)-1 and angiopoietin-4 expressions. LVT/OLPEEP compared to HVT/LPEEP improved overall survival.ConclusionsIn BD, LVT/OLPEEP minimizes lung morpho-functional changes and inflammation compared to HVT/LPEEP.

2014 Annual Journal Symposium

2014 Annual Journal Symposium

Optimization of Positive End-Expiratory Pressure by Volumetric Capnography Variables in Lavage-Induced Acute Lung Injury

Background: In the acute respiratory distress syndrome (ARDS), lung-protective ventilation strategies combine the delivery of small tidal volumes (V<smlcap>T</smlcap>) with sufficient positive end-expiratory pressure (PEEP). However, an optimal approach guiding the setting of PEEP has not been defined. Monitoring volumetric capnography is useful to detect changes in lung aeration. Objectives: The aim of this study was to determine whether volumetric capnography may be a useful method to determine the optimal PEEP in ARDS. Methods: In 8 lung-lavaged piglets, PEEP was reduced from 20 to 4 cm H₂O in steps of 4 cm H₂O every 10 min followed by full lung recruitment. Volumetric capnography, respiratory mechanics, blood gas analysis, hemodynamic data and whole-lung computed tomography scans were obtained at each PEEP level. Results: After lung recruitment, end-expiratory lung volume progressively decreased from 1,160 ± 273 ml at PEEP 20 cm H₂O to 314 ± 86 ml at PEEP 4 cm H₂O. The ratio of alveolar dead space (V<smlcap>D</smlcap>_alv) to alveolar V<smlcap>T</smlcap> (V<smlcap>T</smlcap>_alv) and the phase III slope of volumetric capnography (S_III) reached a minimum at PEEP 16 cm H₂O. At this PEEP level, overaerated lung regions were significantly reduced, nonaerated lung regions did not increase, and partial pressure of oxygen in arterial blood/fraction of inspired oxygen (P/F) and static respiratory system compliance (Crs) reached a maximum. At PEEP levels <16 cm H₂O, nonaerated lung regions significantly increased, P/F and Crs deteriorated, and V<smlcap>D</smlcap>_alv/V<smlcap>T</smlcap>_alv and S_III began to increase. Conclusions: In this surfactant-depleted model, PEEP at the lowest V<smlcap>D</smlcap>_alv/V<smlcap>T</smlcap>_alv and S_III allows an optimal balance between lung overinflation and collapse. Hence, volumetric capnography is a useful bedside approach to identify the optimal PEEP.

Airway Pressure Release Ventilation Prevents Ventilator-Induced Lung Injury in Normal Lungs

Up to 25% of patients with normal lungs develop acute lung injury (ALI) secondary to mechanical ventilation, with 60% to 80% progressing to acute respiratory distress syndrome (ARDS). Once established, ARDS is treated with mechanical ventilation that can paradoxically elevate mortality. A ventilation strategy that reduces the incidence of ARDS could change the clinical paradigm from treatment to prevention. To demonstrate that (1) mechanical ventilation with tidal volume (VT) and positive end-expiratory pressure (PEEP) settings used routinely on surgery patients causes ALI/ARDS in normal rats and (2) preemptive application of airway pressure release ventilation (APRV) blocks drivers of lung injury (ie, surfactant deactivation and alveolar edema) and prevents ARDS. Rats were anesthetized and tracheostomy was performed at State University of New York Upstate Medical University. Arterial and venous lines, a peritoneal catheter, and a rectal temperature probe were inserted. Animals were randomized into 3 groups and followed up for 6 hours: spontaneous breathing ventilation (SBV, n = 5), continuous mandatory ventilation (CMV, n = 6), and APRV (n = 5). Rats in the CMV group were ventilated with Vt of 10 cc/kg and PEEP of 0.5 cm H2O. Airway pressure release ventilation was set with a P(High) of 15 to 20 cm H2O; P(Low) was set at 0 cm H2O. Time at P(High) (T(High)) was 1.3 to 1.5 seconds and a T(Low) was set to terminate at 75% of the peak expiratory flow rate (0.11-0.14 seconds), creating a minimum 90% cycle time spent at P(High). Bronchoalveolar lavage fluid and lungs were harvested for histopathologic analysis at necropsy. Acute lung injury/ARDS developed in the CMV group (mean [SE] PaO2/FiO2 ratio, 242.96 [24.82]) and was prevented with preemptive APRV (mean [SE] PaO2/FIO2 ratio, 478.00 [41.38]; P < .05). Airway pressure release ventilation also significantly reduced histopathologic changes and bronchoalveolar lavage fluid total protein (endothelial permeability) and preserved surfactant proteins A and B concentrations as compared with the CMV group. Continuous mandatory ventilation in normal rats for 6 hours with Vt and PEEP settings similar to those of surgery patients caused ALI. Preemptive application of APRV blocked early drivers of lung injury, preventing ARDS. Our data suggest that APRV applied early could reduce the incidence of ARDS in patients at risk.

Effects of Sitting Position and Applied Positive End-Expiratory Pressure on Respiratory Mechanics of Critically Ill Obese Patients Receiving Mechanical Ventilation*

To evaluate the extent to which sitting position and applied positive end-expiratory pressure improve respiratory mechanics of severely obese patients under mechanical ventilation. Prospective cohort study. A 15-bed ICU of a tertiary hospital. Fifteen consecutive critically ill patients with a body mass index (the weight in kilograms divided by the square of the height in meters) above 35 were compared to 15 controls with body mass index less than 30. Respiratory mechanics was first assessed in the supine position, at zero end-expiratory pressure, and then at positive end-expiratory pressure set at the level of auto-positive endexpiratory pressure. Second, all measures were repeated in the sitting position. Assessment of respiratory mechanics included plateau pressure, auto-positive end-expiratory pressure, and flow-limited volume during manual compression of the abdomen, expressed as percentage of tidal volume to evaluate expiratory flow limitation. In supine position at zero end-expiratory pressure, all critically ill obese patients demonstrated expiratory flow limitation (flow-limited volume, 59.4% [51.3-81.4%] vs 0% [0-0%] in controls; p < 0.0001) and greater auto-positive end-expiratory pressure (10 [5-12.5] vs 0.7 [0.4-1.25] cm H2O in controls; p < 0.0001). Applied positive end-expiratory pressure reverses expiratory flow limitation (flow-limited volume, 0% [0-21%] vs 59.4% [51-81.4%] at zero end-expiratory pressure; p < 0.001) in almost all the obese patients, without increasing plateau pressure (24 [19-25] vs 22 [18-24] cm H2O at zero end-expiratory pressure; p = 0.94). Sitting position not only reverses partially or completely expiratory flow limitation at zero end-expiratory pressure (flow-limited volume, 0% [0-58%] vs 59.4% [51-81.4%] in supine obese patients; p < 0.001) but also results in a significant drop in auto-positive end-expiratory pressure (1.2 [0.6-4] vs 10 [5-12.5] cm H2O in supine obese patients; p < 0.001) and plateau pressure (15.6 [14-17] vs 22 [18-24] cm H2O in supine obese patients; p < 0.001). In critically ill obese patients under mechanical ventilation, sitting position constantly and significantly relieved expiratory flow limitation and auto-positive end-expiratory pressure resulting in a dramatic drop in alveolar pressures. Combining sitting position and applied positive end-expiratory pressure provides the best strategy.

Oxygenation advisor recommends appropriate positive end expiratory pressure and FIO2 settings: retrospective validation study

A decision support, rule-based oxygenation advisor that provides guidance for setting positive end expiratory pressure (PEEP) and fractional inhaled oxygen concentration (FIO2) for patients with respiratory failure is described. The target oxygenation goal is to achieve and maintain pulse oximeter oxygen saturation (SpO2) ≥ 88 and ≤ 95%, as posited by the Acute Respiratory Distress Syndrome Network, by recommending appropriate combinations of PEEP and FIO2. For patient safety, the oxygenation advisor monitors mean arterial blood pressure (MAP) to ensure it is ≥ 65 mmHg for hemodynamic stability and inspiratory plateau pressure (Pplt) so it is ≤ 30 cm H2O for lung protection. The purpose of this validation study was to compare attending physicians' recommendations to those recommendations of the oxygenation advisor for setting PEEP and FIO2. Adults with respiratory failure (n = 117) receiving ventilatory support were studied. PEEP, FIO2, SpO2, MAP, and Pplt are input variables into the advisor. Recommendations to increase, maintain, or decrease PEEP and FIO2 are the oxygenation advisor's output variables. Physicians' recommendations for setting PEEP and FIO2 were recorded; the oxygenation advisor's recommendations were also recorded for comparison. At all times, ventilator settings were based on recommendations from attending physicians. PEEP ranged from 2 to 22 cm H2O and FIO2 ranged from 0.30 to 0.65. A total of 326 recommendations by the oxygenation advisor and attending physicians were made to increase, maintain, or decrease PEEP and FIO2. There was a very significant relationship (p < 0.0001) between recommendations of the oxygenation advisor and attending physicians for setting PEEP and FIO2. The agreement rate for recommendations by the oxygenation advisor and attending physicians was 92%. The K statistic, a test of the strength of agreement of recommendations between the oxygenation advisor and attending physicians, was 0.82 (p < 0.0001), indicating "almost perfect agreement". Relationships for recommendations made by the oxygenation advisor and attending physicians for setting PEEP and FIO2 were excellent, PEEP: r = 0.98 (p < 0.01), r(2) = 0.96; FIO2: r = 0.91 (p < 0.01), r(2) = 0.83, bias and precision values were negligible. A novel oxygenation advisor provided continuous and automatic recommendations for setting PEEP and FIO2 that were shown to be as good as the clinical judgment of experienced attending physicians. For all patients, the target oxygenation goal was achieved. Concerning patient safety, the oxygenation advisor detected those occasions when MAP and Pplt were in potentially unsafe ranges.

Pleural Pressure and Optimal Positive End-Expiratory Pressure Based on Esophageal Pressure Versus Chest Wall Elastance

1) To compare two published methods for estimating pleural pressure, one based on directly measured esophageal pressure and the other based on chest wall elastance. 2) To evaluate the agreement between two published positive end-expiratory pressure optimization strategies based on these methods, one targeting an end-expiratory esophageal pressure-based transpulmonary pressure of 0 cm H2O and the other targeting an end-inspiratory elastance-based transpulmonary pressure of 26 cm H2O.Retrospective study using clinical data.Medical and surgical ICUs.Sixty-four patients mechanically ventilated for acute respiratory failure with esophageal balloons placed for clinical management.Esophageal pressure and chest wall elastance-based methods for estimating pleural pressure and setting positive end-expiratory pressure were retrospectively applied to each of the 64 patients. In patients who were ventilated at two positive end-expiratory pressure levels, chest wall and respiratory system elastances were calculated at each positive end-expiratory pressure level.The pleural pressure estimates using both methods were discordant and differed by as much as 10 cm H2O for a given patient. The two positive end-expiratory pressure optimization strategies recommended positive end-expiratory pressure changes in opposite directions in 33% of patients. The ideal positive end-expiratory pressure levels recommended by the two methods for each patient were discordant and uncorrelated (R = 0.05). Chest wall and respiratory system elastances grew with increases in positive end-expiratory pressure in patients with positive end-expiratory esophageal pressure-based transpulmonary pressures (p < 0.05).Esophageal pressure and chest wall elastance-based methods for estimating pleural pressure do not yield similar results. The strategies of targeting an end-expiratory esophageal pressure-based transpulmonary pressure of 0 cm H2O and targeting an end-inspiratory elastance-based transpulmonary pressure of 26 cm H2O cannot be considered interchangeable. Finally, chest wall and respiratory system elastances may vary unpredictably with changes in positive end-expiratory pressure.