Low Positive End-expiratory Pressure Research Articles

Safety and Feasibility of Intraoperative High PEEP Titrated to the Lowest Driving Pressure (ΔP)-Interim Analysis of DESIGNATION.

Uncertainty remains about the best level of intraoperative positive end-expiratory pressure (PEEP). An ongoing RCT ('DESIGNATION') compares an 'individualized high PEEP' strategy ('iPEEP')-titrated to the lowest driving pressure (ΔP) with recruitment maneuvers (RM), with a 'standard low PEEP' strategy ('low PEEP')-using 5 cm H2O without RMs with respect to the incidence of postoperative pulmonary complications. This report is an interim analysis of safety and feasibility. From September 2018 to July 2022, we enrolled 743 patients. Data of 698 patients were available for this analysis. Hypotension occurred more often in 'iPEEP' vs. 'low PEEP' (54.7 vs. 44.1%; RR, 1.24 (95% CI 1.07 to 1.44); p < 0.01). Investigators were compliant with the study protocol 285/344 patients (82.8%) in 'iPEEP', and 345/354 patients (97.5%) in 'low PEEP' (p < 0.01). Most frequent protocol violation was missing the final RM at the end of anesthesia before extubation; PEEP titration was performed in 99.4 vs. 0%; PEEP was set correctly in 89.8 vs. 98.9%. Compared to 'low PEEP', the 'iPEEP' group was ventilated with higher PEEP (10.0 (8.0-12.0) vs. 5.0 (5.0-5.0) cm H2O; p < 0.01). Thus, in patients undergoing general anesthesia for open abdominal surgery, an individualized high PEEP ventilation strategy is associated with hypotension. The protocol is feasible and results in clear contrast in PEEP. DESIGNATION is expected to finish in late 2023.

An Update on Management of Adult Patients with Acute Respiratory Distress Syndrome: An Official American Thoracic Society Clinical Practice Guideline.

Background: This document updates previously published Clinical Practice Guidelines for the management of patients with acute respiratory distress syndrome (ARDS), incorporating new evidence addressing the use of corticosteroids, venovenous extracorporeal membrane oxygenation, neuromuscular blocking agents, and positive end-expiratory pressure (PEEP). Methods: We summarized evidence addressing four "PICO questions" (patient, intervention, comparison, and outcome). A multidisciplinary panel with expertise in ARDS used the Grading of Recommendations, Assessment, Development, and Evaluation framework to develop clinical recommendations. Results: We suggest the use of: 1) corticosteroids for patients with ARDS (conditional recommendation, moderate certainty of evidence), 2) venovenous extracorporeal membrane oxygenation in selected patients with severe ARDS (conditional recommendation, low certainty of evidence), 3) neuromuscular blockers in patients with early severe ARDS (conditional recommendation, low certainty of evidence), and 4) higher PEEP without lung recruitment maneuvers as opposed to lower PEEP in patients with moderate to severe ARDS (conditional recommendation, low to moderate certainty), and 5) we recommend against using prolonged lung recruitment maneuvers in patients with moderate to severe ARDS (strong recommendation, moderate certainty). Conclusions: We provide updated evidence-based recommendations for the management of ARDS. Individual patient and illness characteristics should be factored into clinical decision making and implementation of these recommendations while additional evidence is generated from much-needed clinical trials.

Impact of a positive end-expiratory pressure strategy on oxygenation, respiratory compliance, and hemodynamics during laparoscopic surgery in non-obese patients: a systematic review and meta-analysis of randomized controlled trials

BackgroundHigher positive end-expiratory pressure (PEEP) during laparoscopic surgery may increase oxygenation and respiratory compliance. This meta-analysis aimed to compare the impact of different intraoperative PEEP strategies on arterial oxygenation, compliance, and hemodynamics during laparoscopic surgery in non-obese patients.MethodsWe searched RCTs in PubMed, Cochrane Library, Web of Science, and Google Scholar from January 2012 to April 2022 comparing the different intraoperative PEEP (Low PEEP (LPEEP): 0–4 mbar; Moderate PEEP (MPEEP): 5–8 mbar; high PEEP (HPEEP): >8 mbar; individualized PEEP - iPEEP) on arterial oxygenation, respiratory compliance (Cdyn), mean arterial pressure (MAP), and heart rate (HR). We calculated mean differences (MD) with 95% confidence intervals (CI), and predictive intervals (PI) using random-effects models. The Cochrane Bias Risk Assessment Tool was applied.Results21 RCTs (n = 1554) met the inclusion criteria. HPEEP vs. LPEEP increased PaO2 (+ 29.38 [16.20; 42.56] mmHg, p < 0.0001) or PaO2/FiO2 (+ 36.7 [+ 2.23; +71.70] mmHg, p = 0.04). HPEEP vs. MPEEP increased PaO2 (+ 22.00 [+ 1.11; +42.88] mmHg, p = 0.04) or PaO2/FiO2 (+ 42.7 [+ 2.74; +82.67] mmHg, p = 0.04). iPEEP vs. MPEEP increased PaO2/FiO2 (+ 115.2 [+ 87.21; +143.20] mmHg, p < 0.001). MPEEP vs. LPEP, and HPEEP vs. MPEEP increased PaO2 or PaO2/FiO2 significantly with different heterogeneity. HPEEP vs. LPEEP increased Cdyn (+ 7.87 [+ 1.49; +14.25] ml/mbar, p = 0.02). MPEEP vs. LPEEP, and HPEEP vs. MPEEP did not impact Cdyn (p = 0.14 and 0.38, respectively). iPEEP vs. LPEEP decreased driving pressure (-4.13 [-2.63; -5.63] mbar, p < 0.001). No significant differences in MAP or HR were found between any subgroups.ConclusionHPEEP and iPEEP during PNP in non-obese patients could promote oxygenation and increase Cdyn without clinically significant changes in MAP and HR. MPEEP could be insufficient to increase respiratory compliance and improve oxygenation. LPEEP may lead to decreased respiratory compliance and worsened oxygenation.Prospero registrationCRD42022362379; registered October 09, 2022.

Meta-Analysis of Higher PEEP Strategies' Effects on Mortality Rates and Inflammatory Mediators in Patients with ARDS: A Perspective Review on Patients with Severe COVID-19-Associated ARDS

&lt;strong&gt;Background: &lt;/strong&gt;Different strategies of positive end-expiratory pressure (PEEP) in mechanical ventilation are crucial for patients with coronavirus disease 2019 (COVID-19)-associated acute respiratory distress syndrome (ARDS). PEEP acts as a “double-edged sword” for ARDS patients. PEEP could recover pulmonary atelectasis but can induce alveolar hyperinflation.&lt;p&gt;&lt;strong&gt;Objective: &lt;/strong&gt;This review aimed to evaluate the effect of higher PEEP in patients with severe COVID-19-associated ARDS.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Method: &lt;/strong&gt;This meta-analysis included randomized controlled trial (RCT) studies to assess the mortality rates, barotrauma events, and inflammatory mediators modulation due to higher PEEP strategies. The pooled effect of the mortality rates and barotrauma events were presented as risk ratios (RR) with 95% confidence of interval (CI) using random-effects model (REM) or fixed-effects model (FEM).&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Results: &lt;/strong&gt;We identified twelve RCTs comparing higher versus lower PEEP in ARDS patients. There was unsignificant result in overall mortality rates group [RR=0.94,95%CI(85,1.03),p=0.21] but not in mortality after positive response of oxygenation group [RR=0.88,95%CI(0.81,0.95),p=0.002] in higher PEEP group. In terms of patients without positive response of oxygenation, higher PEEP group had significantly higher mortality rates [RR=1.07,95%CI(1.00,1.15),p=0.06]. Higher PEEP significantly reduced the mortality rates in ARDS patients with PaO&lt;sub&gt;2&lt;/sub&gt;/FiO&lt;sub&gt;2&lt;/sub&gt;&amp;lt;150 mmHg [RR=0.867,95%CI(0.74,1.00),p=0.04] instead of patients with moderate ARDS (PaO&lt;sub&gt;2&lt;/sub&gt;/FiO&lt;sub&gt;2 &lt;/sub&gt;≥150 mmHg) [RR=1.12, 95%CI(0.85,1.47), p=0.44]. There were no differences in overall barotrauma events [RR=1.03,95%CI(0.78,1.36),p=0.85] between higher and lower PEEP group. The use of higher and lower PEEP also contribute to the modulation of inflammatory mediators including TNF-α, IL-6, IL-1RA, and IL-8.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Conclusion: &lt;/strong&gt;Higher PEEP could reduce the mortality of patients with ARDS who responded to the oxygenation. Higher PEEP does not increase the risk of overall barotrauma events. Higher PEEP can modulate the inflammatory mediators.&lt;/p&gt;

Respiratory mechanics and mechanical power during low vs. high positive end-expiratory pressure in obese surgical patients – A sub-study of the PROBESE randomized controlled trial

Study objectiveWe aimed to characterize intra-operative mechanical ventilation with low or high positive end-expiratory pressure (PEEP) and recruitment manoeuvres (RM) regarding intra-tidal recruitment/derecruitment and overdistension using non-linear respiratory mechanics, and mechanical power in obese surgical patients enrolled in the PROBESE trial. DesignProspective, two-centre substudy of the international, multicentre, two-arm, randomized-controlled PROBESE trial. SettingOperating rooms of two European University Hospitals. PatientsForty-eight adult obese patients undergoing abdominal surgery. InterventionsIntra-operative protective ventilation with either PEEP of 12 cmH2O and repeated RM (HighPEEP+RM) or 4 cmH2O without RM (LowPEEP). MeasurementsThe index of intra-tidal recruitment/de-recruitment and overdistension (%E2) as well as airway pressure, tidal volume (VT), respiratory rate (RR), resistance, elastance, and mechanical power (MP) were calculated from respiratory signals recorded after anesthesia induction, 1 h thereafter, and end of surgery (EOS). Main resultsTwenty-four patients were analyzed in each group. PEEP was higher (mean ± SD, 11.7 ± 0.4 vs. 3.7 ± 0.6 cmH2O, P < 0.001) and driving pressure lower (12.8 ± 3.5 vs. 21.7 ± 6.8 cmH2O, P < 0.001) during HighPEEP+RM than LowPEEP, while VT and RR did not differ significantly (7.3 ± 0.6 vs. 7.4 ± 0.8 ml∙kg−1, P = 0.835; and 14.6 ± 2.5 vs. 15.7 ± 2.0 min−1, P = 0.150, respectively). %E2 was higher in HighPEEP+RM than in LowPEEP following induction (−3.1 ± 7.2 vs. -12.4 ± 10.2%; P < 0.001) and subsequent timepoints. Total resistance and elastance (13.3 ± 3.8 vs. 17.7 ± 6.8 cmH2O∙l∙s−2, P = 0.009; and 15.7 ± 5.5 vs. 28.5 ± 8.4 cmH2O∙l, P < 0.001, respectively) were lower during HighPEEP+RM than LowPEEP. Additionally, MP was lower in HighPEEP+RM than LowPEEP group (5.0 ± 2.2 vs. 10.4 ± 4.7 J∙min−1, P < 0.001). ConclusionsIn this sub-cohort of PROBESE, intra-operative ventilation with high PEEP and RM reduced intra-tidal recruitment/de-recruitment as well as driving pressure, elastance, resistance, and mechanical power, as compared with low PEEP. Trial registrationThe PROBESE study was registered at www.clinicaltrials.gov, identifier: NCT02148692 (submission for registration on May 23, 2014).

High versus low positive end-expiratory pressure setting in patients receiving veno-venous extracorporeal membrane oxygenation support for severe acute respiratory distress syndrome: study protocol for the multicentre, randomised ExPress SAVER Trial

IntroductionWhile limiting the tidal volume to 6 mL/kg during veno-venous extracorporeal membrane oxygenation (V-V ECMO) to ameliorate lung injury in patients with acute respiratory distress syndrome (ARDS) is widely accepted,...

Cardiopulmonary Bypass and Perioperative Mechanical Ventilation Strategy: National Turkey Study

Objective: This study aims to describe anesthesiologists' perioperative mechanical ventilation strategies in cases where cardiopulmonary bypass (CPB) is performed in Turkey. Material and Methods: Survey questions were sent twice via e-mail to members of the two associations consisting of specialists in Anesthesiology and Reanimation. The questions were divided into three parts to determine anesthesia applications and mechanical ventilation strategies in the preoperative, intraoperative, and postoperative periods of CPB. Results: The questionnaire was provided with the participation of 269 anesthesiologists. 105 (40.2%) participants stated that the number of intensive care unit beds in their hospital was over 20. A 6 ml/kg (42.5%) coefficient is preferred in calculating tidal volume outside the CPB process. The number of participants who preferred low (0-5 cmH2O) positive end-expiratory pressure (PEEP) throughout the surgery was 41.1%. 40.8% of the participants prefer 5-10 cmH2O PEEP in “hemodynamically stable and obese patients”. During the CPB process, 38.3% of the participants turned off the mechanical ventilator, and 24.4 % preferred to wean the patient from the mechanical ventilator. While 35.8 % of anesthesia specialists preferred recruitment maneuvers, 38.9% did not. It was concluded that 51% of the participants preferred non-invasive ventilation in patients with hypoxemia/hypercapnia, and 55.1% applied pulmonary rehabilitation after extubation to all patients. Conclusion: Our study showed that the mechanical ventilation strategies followed by most anesthesiologists in CPB in Turkey are similar.

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.

Differences in Ventilation Management and Outcomes between the Two First Waves of the COVID-19 Pandemic—A Comparison between Two Nationwide Observational Studies in The Netherlands

The aim of this analysis was to compare ventilation management and outcomes in invasively ventilated patients with acute hypoxemic respiratory failure due to coronavirus disease 2019 (COVID-19) between the first and second wave in the Netherlands. This is a post hoc analysis of two nationwide observational COVID-19 studies conducted in quick succession. The primary endpoint was ventilation management. Secondary endpoints were tracheostomy use, duration of ventilation, intensive care unit (ICU) and hospital length of stay (LOS), and mortality. We used propensity score matching to control for observed confounding factors. This analysis included 1122 patients from the first and 568 patients from the second wave. Patients in the second wave were sicker, had more comorbidities, and had worse oxygenation parameters. They were ventilated with lower positive end-expiratory pressure and higher fraction inspired oxygen, had a lower oxygen saturation, received neuromuscular blockade more often, and were less often tracheostomized. Duration of ventilation was shorter, but mortality rates were similar. After matching, the fraction of inspired oxygen was lower in the second wave. In patients with acute hypoxemic respiratory failure due to COVID-19, aspects of respiratory care and outcomes rapidly changed over the successive waves.

Effect of intraoperative PEEP with recruitment maneuvers on the occurrence of postoperative pulmonary complications during general anesthesia––protocol for Bayesian analysis of three randomized clinical trials of intraoperative ventilation

Background: Using the frequentist approach, a recent meta–analysis of three randomized clinical trials in patients undergoing intraoperative ventilation during general anesthesia for major surgery failed to show the benefit of ventilation that uses high positive end–expiratory pressure with recruitment maneuvers when compared to ventilation that uses low positive end–expiratory pressure without recruitment maneuvers. Methods: We designed a protocol for a Bayesian analysis using the pooled dataset. The multilevel Bayesian logistic model will use the individual patient data. Prior distributions will be prespecified to represent a varying level of skepticism for the effect estimate. The primary endpoint will be a composite of postoperative pulmonary complications (PPC) within the first seven postoperative days, which reflects the primary endpoint of the original studies. We preset a range of practical equivalence to assess the futility of the intervention with an interval of odds ratio (OR) between 0.9 and 1.1 and assess how much of the 95% of highest density interval (HDI) falls between the region of practical equivalence. Ethics and dissemination: The used data derive from approved studies that were published in recent years. The findings of this current analysis will be reported in a new manuscript, drafted by the writing committee on behalf of the three research groups. All investigators listed in the original trials will serve as collaborative authors.

High positive end-expiratory pressure ventilation mitigates the progression from unilateral pulmonary contusion to ARDS: An animal study.

Pulmonary contusion (PC) is common in severely traumatized patients and can lead to respiratory failure requiring mechanical ventilation (MV). Ventilator-induced lung injury (VILI) might aggravate lung damage. Despite underrepresentation of trauma patients in trials on lung-protective MV, results are extrapolated to these patients, potentially disregarding important pathophysiological differences. Three MV protocols with different positive end-expiratory pressure (PEEP) levels: ARDSnetwork lower PEEP (ARDSnet-low), ARDSnetwork higher PEEP (ARDSnet-high), and open lung concept (OLC) were applied in swine for 24 hours following PC. Gas exchange, lung mechanics, quantitative computed tomography, and diffuse alveolar damage (DAD) score were analyzed. Results are given as median (interquartile range) at 24 hours. Statistical testing was performed using general linear models (group effect) over all measurement points and pairwise Mann-Whitney U tests for DAD. There were significant differences between groups: PEEP ( p < 0.0001) ARDSnet-low (8 [8-10] cmH 2 O), ARDSnet-high (12 [12-12] cmH 2 O), OLC (21 [20-22] cmH 2 O). The fraction of arterial partial pressure of oxygen and inspired oxygen fraction ( p = 0.0016) was lowest in ARDSnet-low (78 (73-111) mm Hg) compared with ARDSnet-high (375 (365-423) mm Hg) and OLC (499 (430-523) mm Hg). The end-expiratory lung volume (EELV) differed significantly ( p < 0.0001), with highest values in OLC (64% [60-70%]) and lowest in ARDSnet-low (34% [24-37%]). Costa's surrogate for mechanical power differed significantly ( p < 0.0001), with lowest values for ARDSnet-high (73 [58-76]) compared with OLC (105 [108-116]). Diffuse alveolar damage was lower in ARDSnet-high compared with ARDSnet-low (0.0007). Progression to ARDS, 24 hours after PC, was mitigated by OLC and ARDSnet-high. Both concepts restored EELV. ARDSnet-high had the lowest mechanical power surrogate and DAD. Our data suggest, that ARDSnet-high restored oxygenation and functional lung volume and reduced physiological and histological surrogates for VILI. ARDSnet-low generated unfavorable outcomes, such as loss of EELV, increased mechanical power and DAD after PC in swine. The high respiratory rate in the OLC may blunt favorable effects of lung recruitment.

Lung Ultrasound to Determine the Effect of Lower vs. Higher PEEP on Lung Aeration in Patients without ARDS—A Substudy of a Randomized Clinical Trial

Background: Ventilation with lower positive end–expiratory pressure (PEEP) may cause loss of lung aeration in critically ill invasively ventilated patients. This study investigated whether a systematic lung ultrasound (LUS) scoring system can detect such changes in lung aeration in a study comparing lower versus higher PEEP in invasively ventilated patients without acute respiratory distress syndrome (ARDS). Methods: Single center substudy of a national, multicenter, randomized clinical trial comparing lower versus higher PEEP ventilation strategy. Fifty–seven patients underwent a systematic 12–region LUS examination within 12 h and between 24 to 48 h after start of invasive ventilation, according to randomization. The primary endpoint was a change in the global LUS aeration score, where a higher value indicates a greater impairment in lung aeration. Results: Thirty–three and twenty–four patients received ventilation with lower PEEP (median PEEP 1 (0–5) cm H2O) or higher PEEP (median PEEP 8 (8–8) cm H2O), respectively. Median global LUS aeration scores within 12 h and between 24 and 48 h were 8 (4 to 14) and 9 (4 to 12) (difference 1 (–2 to 3)) in the lower PEEP group, and 7 (2–11) and 6 (1–12) (difference 0 (–2 to 3)) in the higher PEEP group. Neither differences in changes over time nor differences in absolute scores reached statistical significance. Conclusions: In this substudy of a randomized clinical trial comparing lower PEEP versus higher PEEP in patients without ARDS, LUS was unable to detect changes in lung aeration.

Inflating Pressure and Not Expiratory Pressure Initiates Lung Injury at Birth in Preterm Lambs.

Rationale: Inflation is essential for aeration at birth, but current inflating pressure settings are without an evidence base. Objectives: To determine the role of inflating pressure (ΔP), and relationship with positive end-expiratory pressure (PEEP), in initiating early lung injury pathways in the preterm lamb lung. Methods: 124-127d steroid exposed preterm lambs (n=45) were randomly allocated (8-10/gp) to 15 min of respiratory support with placental circulation and 20 or 30 cmH2O ΔP, with an initial high PEEP (maximum 20 cmH2O) recruitment manoeuvre known to facilitate aeration (dynamic PEEP), and compared to dynamic PEEP with no ΔP or 30 cmH2O ΔP and low (4 cmH2O) PEEP. Lung mechanics and aeration were measured throughout. after an additional 30 min of apnoeic placental support, lung tissue and bronchoalveolar fluid were analysed for regional lung injury, including proteomics. Results: 30 cmH2O ΔP and dynamic PEEP resulted in quicker aeration, better compliance, but higher tidal volumes (often >8 ml/kg, all p<0.0001; mixed effects) and injury. ΔP 20 cmH2O with dynamic PEEP resulted in the same lung mechanics and aeration, but less energy transmission (tidal mechanical power), as ΔP 30 cmH2O with low PEEP.. Dynamic PEEP without any tidal inflations resulted in the least lung injury. Use of any tidal inflating pressures altered metabolic, coagulation and complemented protein pathways within the lung. Conclusions: Inflating pressure is essential for the preterm lung at birth, but also the primary mediator of lung injury. Greater focus is needed on strategies that identify safest application of pressure in the delivery room.

Postoperative Pulmonary Complications and Perioperative Strategies: A Systematic Review.

The occurrence of postoperative pulmonary complications (PPCs) is frequently observed and has been linked to elevated levels of morbidity and mortality, which have adverse effects on both clinical and financial outcomes in healthcare settings. This systematic review aims to present the evidence that supports our comprehension of PPCs and emphasize the circumstances that necessitate the use of postoperative noninvasive ventilation (PNIV) or re-intubation with postoperative mechanical ventilation (POMV). A search was conducted on the National Library of Medicine's Pubmed database and Cochrane Library until November 29, 2020, to find published reports of randomized control trials (RCTs) that assessed postoperative pulmonary complications. Data related to the prevalence of PPCs and the use of PNIV, POMV, and length of hospital stay were extracted from all the studies. For the analysis, a total of 13 studies involving 6,609 patients were included, and out of these, four RCTsreported statistically significant results. The use of protective lung ventilation (PLV) with low tidal volume and positive end-expiratory pressure (PEEP) during intraoperative ventilation, along with pressure-controlled (PCV) ventilation, as well as the postoperative ventilation strategy of continuous positive airway pressure (CPAP) combined with standard oxygen therapy were the only techniques that demonstrated a clear reduction in the incidence of PPCs. Furthermore, the use of PLV with low tidal volume and PEEP and intraoperative mechanical ventilation with a vital capacity maneuver followed by 10 cm H2O of PEEP were found to decrease the requirement for postoperative noninvasive ventilation. CPAP with standard oxygen therapy was the only intervention that reduced the need for reintubation. Various ventilation strategies are available for both intraoperative and postoperative periods with the goal of decreasing the need for postoperative noninvasive ventilation (PNIV) or re-intubation with postoperative mechanical ventilation (POMV).

Personalized ventilatory strategy based on lung recruitablity in COVID-19-associated acute respiratory distress syndrome: a prospective clinical study

BackgroundHeterogeneity is an inherent nature of ARDS. Recruitment-to-inflation ratio has been developed to identify the patients who has lung recruitablity. This technique might be useful to identify the patients that match specific interventions, such as higher positive end-expiratory pressure (PEEP) or prone position or both. We aimed to evaluate the physiological effects of PEEP and body position on lung mechanics and regional lung inflation in COVID-19-associated ARDS and to propose the optimal ventilatory strategy based on recruitment-to-inflation ratio.MethodsPatients with COVID-19-associated ARDS were consecutively enrolled. Lung recruitablity (recruitment-to-inflation ratio) and regional lung inflation (electrical impedance tomography [EIT]) were measured with a combination of body position (supine or prone) and PEEP (low 5 cmH2O or high 15 cmH2O). The utility of recruitment-to-inflation ratio to predict responses to PEEP were examined with EIT.ResultsForty-three patients were included. Recruitment-to-inflation ratio was 0.68 (IQR 0.52–0.84), separating high recruiter versus low recruiter. Oxygenation was the same between two groups. In high recruiter, a combination of high PEEP with prone position achieved the highest oxygenation and less dependent silent spaces in EIT (vs. low PEEP in both positions) without increasing non-dependent silent spaces in EIT. In low recruiter, low PEEP in prone position resulted in better oxygenation (vs. both PEEPs in supine position), less dependent silent spaces (vs. low PEEP in supine position) and less non-dependent silent spaces (vs. high PEEP in both positions). Recruitment-to-inflation ratio was positively correlated with the improvement in oxygenation and respiratory system compliance, the decrease in dependent silent spaces, and was inversely correlated with the increase in non-dependent silent spaces, when applying high PEEP.ConclusionsRecruitment-to-inflation ratio may be useful to personalize PEEP in COVID-19-associated ARDS. Higher PEEP in prone position and lower PEEP in prone position decreased the amount of dependent silent spaces (suggesting lung collapse) without increasing the amount of non-dependent silent spaces (suggesting overinflation) in high recruiter and in low recruiter, respectively.

Flow-controlled expiration reduces positive end-expiratory pressure requirement in dorsally recumbent, anesthetized horses.

Equine peri-anesthetic mortality is higher than that for other commonly anesthetized veterinary species. Unique equine pulmonary pathophysiologic aspects are believed to contribute to this mortality due to impairment of gas exchange and subsequent hypoxemia. No consistently reliable solution for the treatment of peri-anesthetic gas exchange impairment is available. Flow-controlled expiration (FLEX) is a ventilatory mode that linearizes gas flow throughout the expiratory phase, reducing the rate of lung emptying and alveolar collapse. FLEX has been shown to improve gas exchange and pulmonary mechanics in anesthetized horses. This study further evaluated FLEX ventilation in anesthetized horses positioned in dorsal recumbency, hypothesizing that after alveolar recruitment, horses ventilated using FLEX would require a lower positive end-expiratory pressure (PEEP) to prevent alveolar closure than horses conventionally ventilated. Twelve adult horses were used in this prospective, randomized study. Horses were assigned either to conventional volume-controlled ventilation (VCV) or to FLEX. Following induction of general anesthesia, horses were placed in dorsal recumbency mechanically ventilated for a total of approximately 6.5 hours. Thirty-minutes after starting ventilation with VCV or FLEX, a PEEP-titration alveolar recruitment maneuver was performed at the end of which the PEEP was reduced in decrements of 3 cmH2O until the alveolar closure pressure was determined. The PEEP was then increased to the previous level and maintained for additional three hours. During this time, the mean arterial blood pressure, pulmonary arterial pressure, central venous blood pressure, cardiac output (CO), dynamic respiratory system compliance and arterial blood gas values were measured. The alveolar closure pressure was significantly lower (6.5 ± 1.2 vs 11.0 ± 1.5 cmH2O) and significantly less PEEP was required to prevent alveolar closure (9.5 ± 1.2 vs 14.0 ± 1.5 cmH2O) for horses ventilated using FLEX compared with VCV. The CO was significantly higher in the horses ventilated with FLEX (37.5 ± 4 vs 30 ± 6 l/min). We concluded that FLEX ventilation was associated with a lower PEEP requirement due to a more homogenous distribution of ventilation in the lungs during expiration. This lower PEEP requirement led to more stable and improved cardiovascular conditions in horses ventilated with FLEX.

Positive End-Expiratory Pressure Levels in Adult Patients With Acute Lung Injury and Acute Respiratory Distress Syndrome

Positive End-Expiratory Pressure Levels in Adult Patients With Acute Lung Injury and Acute Respiratory Distress Syndrome

Taking a Big Breath: Identifying and Preventing Pulmonary Complications After Liver Transplantation.

In this issue of Transplantation, Oh et al1 describe the results of a retrospective study of postoperative pulmonary complications (PPCs) in 608 patients who underwent living donor liver transplantation over a period of 9 y. More than half of the patients developed pulmonary complications defined as respiratory failure, pneumonia, pulmonary edema, moderate-severe atelectasis, or pleural effusions within 7 d after the transplant. The authors found that a large number of intraoperative variables were associated with PPC including (not surprisingly) Model for End-stage Liver Disease score, ventilator driving pressures, positive end-expiratory pressure (PEEP) and compliance, fluid and blood administration, and duration of anesthesia. However, when using a multivariate analysis and focusing on intraoperative factors, greater driving pressure, and albumin levels at the end of surgery, prolonged hypotension and larger tidal volumes (but not PEEP) remained independently associated with PPC. Patient with PPCs had worse outcomes such as longer intensive care unit stay and worse graft and patient survival. This is the first, larger study of PPC after liver transplantation that investigates the effect of intraoperative variables and therefore factors that may be modifiable. Although any retrospective study can only identify associations and not prove causal relationships, this study provides us with evidence that may influence how we manage patients. Specifically, the association of driving pressures at the end of surgery confirms what we have learned from the nontransplant anesthesiology literature: intraoperative ventilator management matters. Almost 10 y ago, Futier et al2 demonstrated the benefit of intraoperative lung-protective ventilation including the use of PEEP to prevent PPC after abdominal surgery with the landmark randomized, controlled Intraoperative Protective Ventilation trial. The benefit of using PEEP shown in the Intraoperative Protective Ventilation trial could not be replicated in the present study. This may reflect more recent evidence that suggests that high driving pressure (and tidal volumes) and not just low PEEP are actually harmful,3 and PEEP should be individualized to the patient’s static compliance. The ongoing Prime-Air study (ClinicalTrials.gov Identifier: NCT04108130) is a large, multicenter, randomized, controlled trial of an anesthetic-center bundle of interventions that includes individualized PEEP. This study will likely provide us with a better understanding if and how individualized PEEP may be beneficial. Other factors identified by this study associated with PPCs such as low albumin levels at the end of surgery and intraoperative hypotension require more complex physiologic explanations and are not as easily modifiable. PPCs are usually defined as any serious respiratory complications after surgery independent of their etiology.4 Cardiogenic pulmonary edema, pneumonias, and pleural effusions are all considered PPCs, although they represent very different pathologies. PPC is a syndrome with often vague and subjective definitions. For example, the severity of atelectasis or pleural effusion is difficult to quantify and what some may consider normal postoperative changes may be considered PPC by others. The elegant solution to this problem by the present study was to assess for PPCs with radiograph and chart review by 2 pulmonologists. Although this method allows for the application of some common sense in the diagnosis of PPC, it is harder to quantify severity. For example, is severe atelectasis equally harmful than pneumonia? Unlike other organ injuries such as acute kidney injury or liver failure, there are no proven sensitive and specific biomarkers that allow us to identify PPCs and assess its severity. This should not discourage us as it is a great opportunity for future research that may dramatically transform clinical studies of PPCs and possible interventions. The present study is further encouraging as it demonstrates that interventions in the operating room affect complications and the anesthesiologist as an integral member of transplant team can contribute to better outcomes for our patients.

Positive end-expiratory pressure induced changes in airway driving pressure in mechanically ventilated COVID-19 Acute Respiratory Distress Syndrome patients

BackgroundThe profile of changes in airway driving pressure (dPaw) induced by positive-end expiratory pressure (PEEP) might aid for individualized protective ventilation. Our aim was to describe the dPaw versus PEEP curves behavior in ARDS from COVID-19 patients.MethodsPatients admitted in three hospitals were ventilated with fraction of inspired oxygen (FiO2) and PEEP initially adjusted by oxygenation-based table. Thereafter, PEEP was reduced from 20 until 6 cmH2O while dPaw was stepwise recorded and the lowest PEEP that minimized dPaw (PEEPmin_dPaw) was assessed. Each dPaw vs PEEP curve was classified as J-shaped, inverted-J-shaped, or U-shaped according to the difference between the minimum dPaw and the dPaw at the lowest and highest PEEP. In one hospital, hyperdistention and collapse at each PEEP were assessed by electrical impedance tomography (EIT).Results184 patients (41 including EIT) were studied. 126 patients (68%) exhibited a J-shaped dPaw vs PEEP profile (PEEPmin_dPaw of 7.5 ± 1.9 cmH2O). 40 patients (22%) presented a U (PEEPmin_dPaw of 12.2 ± 2.6 cmH2O) and 18 (10%) an inverted-J profile (PEEPmin_dPaw of 14,6 ± 2.3 cmH2O). Patients with inverted-J profiles had significant higher body mass index (BMI) and lower baseline partial pressure of arterial oxygen/FiO2 ratio. PEEPmin_dPaw was associated with lower fractions of both alveolar collapse and hyperinflation.ConclusionsA PEEP adjustment procedure based on PEEP-induced changes in dPaw is feasible and may aid in individualized PEEP for protective ventilation. The PEEP required to minimize driving pressure was influenced by BMI and was low in the majority of patients.

Neurological and respiratory effects of lung protective ventilation in acute brain injury patients without lung injury: brain vent, a single centre randomized interventional study

IntroductionLung protective ventilation (LPV) comprising low tidal volume (VT) and high positive end-expiratory pressure (PEEP) may compromise cerebral perfusion in acute brain injury (ABI). In patients with ABI, we investigated whether LPV is associated with increased intracranial pressure (ICP) and/or deranged cerebral autoregulation (CA), brain compensatory reserve and oxygenation.MethodsIn a prospective, crossover study, 30 intubated ABI patients with normal ICP and no lung injury were randomly assigned to receive low VT [6 ml/kg/predicted (pbw)]/at either low (5 cmH2O) or high PEEP (12 cmH2O). Between each intervention, baseline ventilation (VT 9 ml/kg/pbw and PEEP 5 cmH2O) were resumed. The safety limit for interruption of the intervention was ICP above 22 mmHg for more than 5 min. Airway and transpulmonary pressures were continuously monitored to assess respiratory mechanics. We recorded ICP by using external ventricular drainage or a parenchymal probe. CA and brain compensatory reserve were derived from ICP waveform analysis.ResultsWe included 27 patients (intracerebral haemorrhage, traumatic brain injury, subarachnoid haemorrhage), of whom 6 reached the safety limit, which required interruption of at least one intervention. For those without intervention interruption, the ICP change from baseline to “low VT/low PEEP” and “low VT/high PEEP” were 2.2 mmHg and 2.3 mmHg, respectively, and considered clinically non-relevant. None of the interventions affected CA or oxygenation significantly. Interrupted events were associated with high baseline ICP (p < 0.001), low brain compensatory reserve (p < 0.01) and mechanical power (p < 0.05).The transpulmonary driving pressure was 5 ± 2 cmH2O in both interventions. Partial arterial pressure of carbon dioxide was kept in the range 34–36 mmHg by adjusting the respiratory rate, hence, changes in carbon dioxide were not associated with the increase in ICP.ConclusionsThe present study found that most patients did not experience any adverse effects of LPV, neither on ICP nor CA. However, in almost a quarter of patients, the ICP rose above the safety limit for interrupting the interventions. Baseline ICP, brain compensatory reserve, and mechanical power can predict a potentially deleterious effect of LPV and can be used to personalize ventilator settings.Trial registrationNCT03278769. Registered September 12, 2017.Graphical