Volatile anesthetics for lung- and diaphragm-protective sedation.

This review explores the complex interactions between sedation and invasive ventilation and examines the potential of volatile anesthetics for lung- and diaphragm-protective sedation. In the early stages of invasive ventilation, many critically ill patients experience insufficient respiratory drive and effort, leading to compromised diaphragm function. Compared with common intravenous agents, inhaled sedation with volatile anesthetics better preserves respiratory drive, potentially helping to maintain diaphragm function during prolonged periods of invasive ventilation. In turn, higher concentrations of volatile anesthetics reduce the size of spontaneously generated tidal volumes, potentially reducing lung stress and strain and with that the risk of self-inflicted lung injury. Taken together, inhaled sedation may allow titration of respiratory drive to maintain inspiratory efforts within lung- and diaphragm-protective ranges. Particularly in patients who are expected to require prolonged invasive ventilation, in whom the restoration of adequate but safe inspiratory effort is crucial for successful weaning, inhaled sedation represents an attractive option for lung- and diaphragm-protective sedation. A technical limitation is ventilatory dead space introduced by volatile anesthetic reflectors, although this impact is minimal and comparable to ventilation with heat and moisture exchangers. Further studies are imperative for a comprehensive understanding of the specific effects of inhaled sedation on respiratory drive and effort and, ultimately, how this translates into patient-centered outcomes in critically ill patients.

High PEEP with recruitment maneuvers versus Low PEEP During General Anesthesia for Surgery - a Bayesian individual patient data meta-analysis of three randomized clinical trials.

BACKGROUND: The influence of high positive end-expiratory pressure (PEEP) with recruitment maneuvers on the occurrence of postoperative pulmonary complications after surgery is still not definitively established. Bayesian analysis can help to gain further insights from the available data and provide a probabilistic framework that is easier to interpret. Our objective was to estimate the posterior probability that the use of high PEEP with recruitment maneuvers is associated with reduced postoperative pulmonary complications in patients with intermediate-to-high risk under neutral, pessimistic, and optimistic expectations regarding the treatment effect. METHODS: Multilevel Bayesian logistic regression analysis on individual patient data from three randomized clinical trials carried out on surgical patients at Intermediate-to-High Risk for postoperative pulmonary complications. The main outcome was the occurrence of postoperative pulmonary complications in the early postoperative period. We studied the effect of high PEEP with recruitment maneuvers versus Low PEEP Ventilation. Priors were chosen to reflect neutral, pessimistic, and optimistic expectations of the treatment effect. RESULTS: Using a neutral, pessimistic, or optimistic prior, the posterior mean odds ratio (OR) for High PEEP with recruitment maneuvers compared to Low PEEP was 0.85 (95% Credible Interval [CrI] 0.71 to 1.02), 0.87 (0.72 to 1.04), and 0.86 (0.71 to 1.02), respectively. Regardless of prior beliefs, the posterior probability of experiencing a beneficial effect exceeded 90%. Subgroup analysis indicated a more pronounced effect in patients who underwent laparoscopy (OR: 0.67 [0.50 to 0.87]) and those at high risk for PPCs (OR: 0.80 [0.53 to 1.13]). Sensitivity analysis, considering severe postoperative pulmonary complications only or applying a different heterogeneity prior, yielded consistent results. CONCLUSION: High PEEP with recruitment maneuvers demonstrated a moderate reduction in the probability of PPC occurrence, with a high posterior probability of benefit observed consistently across various prior beliefs, particularly among patients who underwent laparoscopy.

Impaired oxygenation after lung resection: Incidence and perioperative risk factors.

STUDY OBJECTIVE: To estimate the incidence of postoperative oxygenation impairment after lung resection in the era of lung-protective management, and to identify perioperative factors associated with that impairment. DESIGN: Registry-based retrospective cohort study. SETTING: Two large academic hospitals in the United States. PATIENTS: 3081 ASA I-IV patients undergoing lung resection. MEASUREMENTS: 79 pre- and intraoperative variables, selected for inclusion based on a causal inference framework. The primary outcome of impaired oxygenation, an early marker of lung injury, was defined as at least one of the following within seven postoperative days: (1) SpO2 < 92%; (2) imputed PaO2/FiO2 < 300 mmHg [(1) or (2) occurring at least twice within 24 h]; (3) intensive oxygen therapy (mechanical ventilation or > 50% oxygen or high-flow oxygen). MAIN RESULTS: Oxygenation was impaired within seven postoperative days in 70.8% of patients (26.6% with PaO2/FiO2 < 200 mmHg or intensive oxygen therapy). In multivariable analysis, each additional cmH2O of intraoperative median driving pressure was associated with a 7% higher risk of impaired oxygenation (OR 1.07; 95%CI 1.04 to 1.10). Higher median intraoperative FiO2 (OR 1.23; 95%CI 1.14 to 1.31 per 0.1) and PEEP (OR 1.12; 95%CI 1.04 to 1.21 per 1 cm H2O) were also associated with increased risk. History of COPD (OR 2.55; 95%CI 1.95 to 3.35) and intraoperative albuterol administration (OR 2.07; 95%CI 1.17 to 3.67) also showed reliable effects. CONCLUSIONS: Impaired postoperative oxygenation is common after lung resection and is associated with potentially modifiable pre- and intraoperative respiratory factors.

Effects of Positive End-expiratory Pressure on Pulmonary Perfusion Distribution and Intrapulmonary Shunt during One-lung Ventilation in Pigs: A Randomized Crossover Study.

BACKGROUND: During one-lung ventilation (OLV), positive end-expiratory pressure (PEEP) can improve lung aeration but might overdistend lung units and increase intrapulmonary shunt. The authors hypothesized that higher PEEP shifts pulmonary perfusion from the ventilated to the nonventilated lung, resulting in a U-shaped relationship with intrapulmonary shunt during OLV. METHODS: In nine anesthetized female pigs, a thoracotomy was performed and intravenous lipopolysaccharide infused to mimic the inflammatory response of thoracic surgery. Animals underwent OLV in supine position with PEEP of 0 cm H2O, 5 cm H2O, titrated to best respiratory system compliance, and 15 cm H2O (PEEP0, PEEP5, PEEPtitr, and PEEP15, respectively, 45 min each, Latin square sequence). Respiratory, hemodynamic, and gas exchange variables were measured. The distributions of perfusion and ventilation were determined by IV fluorescent microspheres and computed tomography, respectively. RESULTS: Compared to two-lung ventilation, the driving pressure increased with OLV, irrespective of the PEEP level. During OLV, cardiac output was lower at PEEP15 (5.5 ± 1.5 l/min) than PEEP0 (7.6 ± 3 l/min) and PEEP5 (7.4 ± 2.9 l/min; P = 0.004), while the intrapulmonary shunt was highest at PEEP0 (PEEP0: 48.1% ± 14.4%; PEEP5: 42.4% ± 14.8%; PEEPtitr: 37.8% ± 11.0%; PEEP15: 39.0% ± 10.7%; P = 0.027). The relative perfusion of the ventilated lung did not differ among PEEP levels (PEEP0: 65.0% ± 10.6%; PEEP5: 68.7% ± 8.7%; PEEPtitr: 68.2% ± 10.5%; PEEP15: 58.4% ± 12.8%; P = 0.096), but the centers of relative perfusion and ventilation in the ventilated lung shifted from ventral to dorsal and from cranial to caudal zones with increasing PEEP. CONCLUSIONS: In this experimental model of thoracic surgery, higher PEEP during OLV did not shift the perfusion from the ventilated to the nonventilated lung, thus not increasing intrapulmonary shunt.

Comparative effects of variable versus conventional volume-controlled one-lung ventilation on gas exchange and respiratory system mechanics in thoracic surgery patients: A randomized controlled clinical trial.

BACKGROUND: Mechanical ventilation with variable tidal volumes (V-VCV) has the potential to improve lung function during general anesthesia. We tested the hypothesis that V-VCV compared to conventional volume-controlled ventilation (C-VCV) would improve intraoperative arterial oxygenation and respiratory system mechanics in patients undergoing thoracic surgery under one-lung ventilation (OLV). METHODS: Patients were randomized to V-VCV (n = 39) or C-VCV (n = 39). During OLV tidal volume of 5 mL/kg predicted body weight (PBW) was used. Both groups were ventilated with a positive end-expiratory pressure (PEEP) of 5 cm H2O, inspiration to expiration ratio (I:E) of 1:1 (during OLV) and 1:2 during two-lung ventilation, the respiratory rate (RR) titrated to arterial pH, inspiratory peak-pressure ≤ 40 cm H2O and an inspiratory oxygen fraction of 1.0. RESULTS: Seventy-five out of 78 Patients completed the trial and were analyzed (dropouts were excluded). The partial pressure of arterial oxygen (PaO2) 20 min after the start of OLV did not differ among groups (V-VCV: 25.8 ± 14.6 kPa vs C-VCV: 27.2 ± 15.3 kPa; mean difference [95% CI]: 1.3 [-8.2, 5.5], P = 0.700). Furthermore, intraoperative gas exchange, intraoperative adverse events, need for rescue maneuvers due to desaturation and hypercapnia, incidence of postoperative pulmonary and extra-pulmonary complications, and hospital free days at day 30 after surgery did not differ between groups. CONCLUSIONS: In thoracic surgery patients under OLV, V-VCV did not improve oxygenation or respiratory system mechanics compared to C-VCV. Ethical Committee: EK 420092019. TRIAL REGISTRATION: at the German Clinical Trials Register: DRKS00022202 (16.06.2020).

Association Between Age- and Sex-Specific Body Mass Index Percentile and Multiple Intubation Attempts: A Retrospective Cohort Analysis.

BACKGROUND: Obesity distorts airways and slightly complicates intubations in adults, but whether obesity complicates pediatric intubations remains unclear. We, therefore, tested the primary hypothesis that increasing age- and sex-specific body mass index (BMI) percentile is associated with difficult intubation, defined as >1 intubation attempt. METHODS: We conducted a retrospective analysis of pediatric patients between 2 and 18 years of age who had noncardiac surgery with oral endotracheal intubation. We assessed the association between BMI percentile and difficult intubation, defined as >1 intubation attempt, using a confounder-adjusted multivariable logistic regression model. Secondarily, we assessed whether the main association depended on preoperative substantial airway abnormality status or age group. RESULTS: A total of 9339 patients were included in the analysis. Median [quartiles] age- and sex-specific BMI percentile was 70 [33, 93], and 492 (5.3%) patients had difficult intubation. There was no apparent association between age- and sex-specific BMI percentile and difficult intubation. The estimated odds ratio (OR) for having difficult intubation for a 10-unit increase in BMI percentile was 0.98 (95% confidence interval [CI], 0.95-1.005) and was consistent across the 3 age groups of early childhood, middle childhood, and early adolescence (interaction P = .53). Patients with preoperative substantial airway abnormalities had lower odds of difficult intubation per 10-unit increase in BMI percentile, with OR (95% CI) of 0.83 (0.70-0.98), P = .01. CONCLUSIONS: Age- and sex-specific BMI percentile was not associated with difficult intubation in children between 2 and 18 years of age. As in adults, obesity in children does not much complicate intubation.

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 OBJECTIVE: We 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. DESIGN: Prospective, two-centre substudy of the international, multicentre, two-arm, randomized-controlled PROBESE trial. SETTING: Operating rooms of two European University Hospitals. PATIENTS: Forty-eight adult obese patients undergoing abdominal surgery. INTERVENTIONS: Intra-operative protective ventilation with either PEEP of 12 cmH2O and repeated RM (HighPEEP+RM) or 4 cmH2O without RM (LowPEEP). MEASUREMENTS: The 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 RESULTS: Twenty-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). CONCLUSIONS: In 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 REGISTRATION: The PROBESE study was registered at www. CLINICALTRIALS: gov, identifier: NCT02148692 (submission for registration on May 23, 2014).

Modulation of the hippo-YAP pathway by cyclic stretch in rat type 2 alveolar epithelial cells-a proof-of-concept study.

Background: Mechanical ventilation (MV) is a life supporting therapy but may also cause lung damage. This phenomenon is known as ventilator-induced lung injury (VILI). A potential pathomechanisms of ventilator-induced lung injury may be the stretch-induced production and release of cytokines and pro-inflammatory molecules from the alveolar epithelium. Yes-associated protein (YAP) might be regulated by mechanical forces and involved in the inflammation cascade. However, its role in stretch-induced damage of alveolar cells remains poorly understood. In this study, we explored the role of YAP in the response of alveolar epithelial type II cells (AEC II) to elevated cyclic stretch in vitro. We hypothesize that Yes-associated protein activates its downstream targets and regulates the interleukin-6 (IL-6) expression in response to 30% cyclic stretch in AEC II. Methods: The rat lung L2 cell line was exposed to 30% cyclic equibiaxial stretch for 1 or 4 h. Non-stretched conditions served as controls. The cytoskeleton remodeling and cell junction integrity were evaluated by F-actin and Pan-cadherin immunofluorescence, respectively. The gene expression and protein levels of IL-6, Yes-associated protein, Cysteine-rich angiogenic inducer 61 (Cyr61/CCN1), and connective tissue growth factor (CTGF/CCN2) were studied by real-time polymerase chain reaction (RT-qPCR) and Western blot, respectively. Verteporfin (VP) was used to inhibit Yes-associated protein activation. The effects of 30% cyclic stretch were assessed by two-way ANOVA. Statistical significance as accepted at p < 0.05. Results: Cyclic stretch of 30% induced YAP nuclear accumulation, activated the transcription of Yes-associated protein downstream targets Cyr61/CCN1 and CTGF/CCN2 and elevated IL-6 expression in AEC II after 1 hour, compared to static control. VP (2 µM) inhibited Yes-associated protein activation in response to 30% cyclic stretch and reduced IL-6 protein levels. Conclusion: In rat lung L2 AEC II, 30% cyclic stretch activated YAP, and its downstream targets Cyr61/CCN1 and CTGF/CCN2 and proinflammatory IL-6 expression. Target activation was blocked by a Yes-associated protein inhibitor. This novel YAP-dependent pathway could be involved in stretch-induced damage of alveolar cells.

Distribution of transpulmonary pressure during one-lung ventilation in pigs at different body positions.

Background. Global and regional transpulmonary pressure (PL) during one-lung ventilation (OLV) is poorly characterized. We hypothesized that global and regional PL and driving PL (ΔPL) increase during protective low tidal volume OLV compared to two-lung ventilation (TLV), and vary with body position. Methods. In sixteen anesthetized juvenile pigs, intra-pleural pressure sensors were placed in ventral, dorsal, and caudal zones of the left hemithorax by video-assisted thoracoscopy. A right thoracotomy was performed and lipopolysaccharide administered intravenously to mimic the inflammatory response due to thoracic surgery. Animals were ventilated in a volume-controlled mode with a tidal volume (VT) of 6 mL kg-1 during TLV and of 5 mL kg-1 during OLV and a positive end-expiratory pressure (PEEP) of 5 cmH2O. Global and local transpulmonary pressures were calculated. Lung instability was defined as end-expiratory PL<2.9 cmH2O according to previous investigations. Variables were acquired during TLV (TLVsupine), left lung ventilation in supine (OLVsupine), semilateral (OLVsemilateral), lateral (OLVlateral) and prone (OLVprone) positions randomized according to Latin-square sequence. Effects of position were tested using repeated measures ANOVA. Results. End-expiratory PL and ΔPL were higher during OLVsupine than TLVsupine. During OLV, regional end-inspiratory PL and ΔPL did not differ significantly among body positions. Yet, end-expiratory PL was lower in semilateral (ventral: 4.8 ± 2.9 cmH2O; caudal: 3.1 ± 2.6 cmH2O) and lateral (ventral: 1.9 ± 3.3 cmH2O; caudal: 2.7 ± 1.7 cmH2O) compared to supine (ventral: 4.8 ± 2.9 cmH2O; caudal: 3.1 ± 2.6 cmH2O) and prone position (ventral: 1.7 ± 2.5 cmH2O; caudal: 3.3 ± 1.6 cmH2O), mainly in ventral (p ≤ 0.001) and caudal (p = 0.007) regions. Lung instability was detected more often in semilateral (26 out of 48 measurements; p = 0.012) and lateral (29 out of 48 measurements, p < 0.001) as compared to supine position (15 out of 48 measurements), and more often in lateral as compared to prone position (19 out of 48 measurements, p = 0.027). Conclusion. Compared to TLV, OLV increased lung stress. Body position did not affect stress of the ventilated lung during OLV, but lung stability was lowest in semilateral and lateral decubitus position.

An anesthesia-centered bundle to reduce postoperative pulmonary complications: The PRIME-AIR study protocol.

BACKGROUND: Postoperative pulmonary complications (PPCs) are a major cause of morbidity and mortality after open abdominal surgery. Optimized perioperative lung expansion may minimize the synergistic factors responsible for the multiple-hit perioperative pulmonary dysfunction. This ongoing study will assess whether an anesthesia-centered bundle focused on perioperative lung expansion results in decreased incidence and severity of PPCs after open abdominal surgery. METHODS: Prospective multicenter randomized controlled pragmatic trial in 750 adult patients with at least moderate risk for PPCs undergoing prolonged (≥2 hour) open abdominal surgery. Participants are randomized to receive either a bundle intervention focused on perioperative lung expansion or usual care. The bundle intervention includes preoperative patient education, intraoperative protective ventilation with individualized positive end-expiratory pressure to maximize respiratory system compliance, optimized neuromuscular blockade and reversal management, and postoperative incentive spirometry and early mobilization. Primary outcome is the distribution of the highest PPC severity by postoperative day 7. Secondary outcomes include the proportion of participants with: PPC grades 1-2 through POD 7; PPC grades 3-4 through POD 7, 30 and 90; intraoperative hypoxemia, rescue recruitment maneuvers, or cardiovascular events; and any major extrapulmonary postoperative complications. Additional secondary and exploratory outcomes include individual PPCs by POD 7, length of postoperative oxygen therapy or other respiratory support, hospital resource use parameters, Patient-Reported Outcomes Measurements (PROMIS®) questionnaires for dyspnea and fatigue collected before and at days 7, 30 and 90 after surgery, and plasma concentrations of lung injury biomarkers (IL6, IL-8, RAGE, CC16, Ang-2) analyzed from samples obtained before, end of, and 24 hours after surgery. DISCUSSION: Participant recruitment for this study started January 2020; results are expected in 2024. At the conclusion of this trial, we will determine if this anesthesia-centered strategy focused on perioperative lung expansion reduces lung morbidity and healthcare utilization after open abdominal surgery. TRIAL REGISTRATION: ClinicalTrial.gov NCT04108130.

Spin and fragility in anaesthesia studies: when sirens sing into anaesthetists' ears.

Spin and fragility are common in randomised controlled trials published in anaesthesia journals. Staying with the facts and addressing only the primary endpoint in the conclusion of clinical research reports might help reduce spin. Routinely reporting the fragility index, in turn, could deliver information about robustness, enhancing the transparency of positive dichotomous results. It is in the best interest of clinical research that authors, reviewers, and journals come together to reduce spin and address the fragility of randomised controlled trials.

Variable ventilation versus stepwise lung recruitment manoeuvres for lung recruitment: A comparative study in an experimental model of atelectasis.

BACKGROUND: Variable ventilation recruits alveoli in atelectatic lungs, but it is unknown how it compares with conventional recruitment manoeuvres. OBJECTIVES: To test whether mechanical ventilation with variable tidal volumes and conventional recruitment manoeuvres have comparable effects on lung function. DESIGN: Randomised crossover study. SETTING: University hospital research facility. ANIMALS: Eleven juvenile mechanically ventilated pigs with atelectasis created by saline lung lavage. INTERVENTIONS: Lung recruitment was performed using two strategies, both with an individualised optimal positive-end expiratory pressure (PEEP) associated with the best respiratory system elastance during a decremental PEEP trial: conventional recruitment manoeuvres (stepwise increase of PEEP) in pressure-controlled mode) followed by 50 min of volume-controlled ventilation (VCV) with constant tidal volume, and variable ventilation, consisting of 50 min of VCV with random variation in tidal volume. MAIN OUTCOME MEASURES: Before and 50 min after each recruitment manoeuvre strategy, lung aeration was assessed by computed tomography, and relative lung perfusion and ventilation (0% = dorsal, 100% = ventral) were determined by electrical impedance tomography. RESULTS: After 50 min, variable ventilation and stepwise recruitment manoeuvres decreased the relative mass of poorly and nonaerated lung tissue (percent lung mass: 35.3 ±â€Š6.2 versus 34.2 ±â€Š6.6, P  = 0.303); reduced poorly aerated lung mass compared with baseline (-3.5 ±â€Š4.0%, P  = 0.016, and -5.2 ±â€Š2.8%, P  < 0.001, respectively), and reduced nonaerated lung mass compared with baseline (-7.2 ±â€Š2.5%, P  < 0.001; and -4.7 ±â€Š2.8%, P  < 0.001 respectively), while the distribution of relative perfusion was barely affected (variable ventilation: -0.8 ±â€Š1.1%, P  = 0.044; stepwise recruitment manoeuvres: -0.4 ±â€Š0.9%, P  = 0.167). Compared with baseline, variable ventilation and stepwise recruitment manoeuvres increased Pa O 2 (172 ±â€Š85mmHg, P  = 0.001; and 213 ±â€Š73 mmHg, P  < 0.001, respectively), reduced Pa CO 2 (-9.6 ±â€Š8.1 mmHg, P  = 0.003; and -6.7 ±â€Š4.6 mmHg, P  < 0.001, respectively), and decreased elastance (-11.4 ±â€Š6.3 cmH 2 O, P  < 0.001; and -14.1 ±â€Š3.3 cmH 2 O, P  < 0.001, respectively). Mean arterial pressure decreased during stepwise recruitment manoeuvres (-24 ±â€Š8 mmHg, P  = 0.006), but not variable ventilation. CONCLUSION: In this model of lung atelectasis, variable ventilation and stepwise recruitment manoeuvres effectively recruited lungs, but only variable ventilation did not adversely affect haemodynamics. TRIAL REGISTRATION: This study was registered and approved by Landesdirektion Dresden, Germany (DD24-5131/354/64).

Effect of patient-ventilator asynchrony on lung and diaphragmatic injury in experimental acute respiratory distress syndrome in a porcine model.

BACKGROUND: Patient-ventilator asynchrony during mechanical ventilation may exacerbate lung and diaphragm injury in spontaneously breathing subjects. We investigated whether subject-ventilator asynchrony increases lung or diaphragmatic injury in a porcine model of acute respiratory distress syndrome (ARDS). METHODS: ARDS was induced in adult female pigs by lung lavage and injurious ventilation before mechanical ventilation by pressure assist-control for 12 h. Mechanically ventilated pigs were randomised to breathe spontaneously with or without induced subject-ventilator asynchrony or neuromuscular block (n=7 per group). Subject-ventilator asynchrony was produced by ineffective, auto-, or double-triggering of spontaneous breaths. The primary outcome was mean alveolar septal thickness (where thickening of the alveolar wall indicates worse lung injury). Secondary outcomes included distribution of ventilation (electrical impedance tomography), lung morphometric analysis, inflammatory biomarkers (gene expression), lung wet-to-dry weight ratio, and diaphragmatic muscle fibre thickness. RESULTS: Subject-ventilator asynchrony (median [interquartile range] 28.8% [10.4] asynchronous breaths of total breaths; n=7) did not increase mean alveolar septal thickness compared with synchronous spontaneous breathing (asynchronous breaths 1.0% [1.6] of total breaths; n=7). There was no difference in mean alveolar septal thickness throughout upper and lower lung lobes between pigs randomised to subject-ventilator asynchrony vs synchronous spontaneous breathing (87.3-92.2 µm after subject-ventilator asynchrony, compared with 84.1-95.0 µm in synchronised spontaneous breathing;). There were also no differences between groups in wet-to-dry weight ratio, diaphragmatic muscle fibre thickness, atelectasis, lung aeration, or mRNA expression levels for inflammatory cytokines pivotal in ARDS pathogenesis. CONCLUSIONS: Subject-ventilator asynchrony during spontaneous breathing did not exacerbate lung injury and dysfunction in experimental porcine ARDS.

Changes in lung aeration and respiratory function after open abdominal surgery: A quantitative magnetic resonance imaging study.

BACKGROUND: Atelectasis is one of the most common respiratory complications in patients undergoing open abdominal surgery. Peripheral oxygen saturation (SpO2 ) and forced vital capacity (FVC) are bedside indicators of postoperative respiratory dysfunction. The aim of this study was to describe the changes in lung aeration, using quantitative analysis of magnetic resonance imaging (MRI) and the diagnostic accuracy of SpO2 and FVC to detect postoperative atelectasis. METHODS: Post-hoc analysis of a randomized trial conducted at a University Hospital in Dresden, Germany. Patients undergoing pre- and postoperative lung MRI were included. MRI signal intensity was analyzed quantitatively to define poorly and nonaerated lung compartments. Postoperative atelectasis was defined as nonaerated lung volume above 2% of the total lung volume in the respective MRI investigation. RESULTS: This study included 45 patients, 27 with and 18 patients without postoperative atelectasis. Patients with atelectasis had higher body mass index (p = .024), had more preoperative poorly aerated lung volume (p = .049), a lower preoperative SpO2 (p = .009), and a lower preoperative FVC (p = .029). The amount of atelectasis correlated with preoperative SpO2 (Spearman's ρ = -.51, p < .001) and postoperative SpO2 (ρ = -.60, p < .001), and with preoperative FVC (ρ = -.29, p = .047) and postoperative FVC (ρ = -.40, p = .006). A postoperative SpO2 ≤ 94% had 74% sensitivity and 78% specificity to detect atelectasis, while postoperative FVC ≤ 50% had 56% sensitivity and 100% specificity to detect atelectasis. CONCLUSION: SpO2 and FVC correlated with the amount of postoperative non-aerated lung volume, showing acceptable diagnostic accuracy in bedside detection of postoperative atelectasis.

Static Stretch Increases the Pro-Inflammatory Response of Rat Type 2 Alveolar Epithelial Cells to Dynamic Stretch.

Background: Mechanical ventilation (MV) inflicts stress on the lungs, initiating or increasing lung inflammation, so-called ventilator-induced lung injury (VILI). Besides overdistention, cyclic opening-and-closing of alveoli (atelectrauma) is recognized as a potential mechanism of VILI. The dynamic stretch may be reduced by positive end-expiratory pressure (PEEP), which in turn increases the static stretch. We investigated whether static stretch modulates the inflammatory response of rat type 2 alveolar epithelial cells (AECs) at different levels of dynamic stretch and hypothesized that static stretch increases pro-inflammatory response of AECs at given dynamic stretch. Methods: AECs, stimulated and not stimulated with lipopolysaccharide (LPS), were subjected to combinations of static (10, 20, and 30%) and dynamic stretch (15, 20, and 30%), for 1 and 4 h. Non-stretched AECs served as control. The gene expression and secreted protein levels of interleukin-6 (IL-6), monocyte chemoattractant protein-1 (MCP-1), and macrophage inflammatory protein 2 (MIP-2) were studied by real-time polymerase chain reaction (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA), respectively. The effects of static and dynamic stretch were assessed by two-factorial ANOVA with planned effects post-hoc comparison according to Sidák. Statistical significance was considered for p < 0.05. Results: In LPS-stimulated, but not in non-stimulated rat type 2 AECs, compared to non-stretched cells: 1) dynamic stretch increased the expression of amphiregulin (AREG) (p < 0.05), MCP-1 (p < 0.001), and MIP-2 (<0.05), respectively, as well as the protein secretion of IL-6 (p < 0.001) and MCP-1 (p < 0.05); 2) static stretch increased the gene expression of MCP-1 (p < 0.001) and MIP-2, but not AREG, and resulted in higher secretion of IL-6 (p < 0.001), but not MCP-1, while MIP-2 was not detectable in the medium. Conclusion: In rat type 2 AECs stimulated with LPS, static stretch increased the pro-inflammatory response to dynamic stretch, suggesting a potential pro-inflammatory effect of PEEP during mechanical ventilation at the cellular level.