Up to 18% of obese patients undergoing surgery have postoperative pulmonary complications,¹ which is almost twice the risk among normal weight or overweight patients.^2,3 Postoperative pulmonary complications prolong hospitalization and increase mortality.^3,4 In 2012, it was estimated that more than 310 million surgical procedures were conducted worldwide.⁵ Given that the global prevalence of obesity is increasing,^6,7 the burden of postoperative pulmonary complications will increase if the number of surgical procedures remains unchanged over the coming decades.

Objective: Volutrauma and atelectrauma promote ventilator-induced lung injury, but their relative contribution to inflammation in ventilator-induced lung injury is not well established. The aim of this study was to determine the impact of volutrauma and atelectrauma on the distribution of lung inflammation in experimental acute respiratory distress syndrome. Design: Laboratory investigation. Setting: University-hospital research facility. Subjects: Ten pigs (five per group; 34.7–49.9 kg) Interventions: Animals were anesthetized and intubated, and saline lung lavage was performed. Lungs were separated with a double-lumen tube. Following lung recruitment and decremental positive end-expiratory pressure trial, animals were randomly assigned to 4 hours of ventilation of the left (ventilator-induced lung injury) lung with tidal volume of approximately 3 mL/kg and 1) high positive end-expiratory pressure set above the level where dynamic compliance increased more than 5% during positive end-expiratory pressure trial (volutrauma); or 2) low positive end-expiratory pressure to achieve driving pressure comparable with volutrauma (atelectrauma). The right (control) lung was kept on continuous positive airway pressure of 20 cm H₂O, and Co ₂ was partially removed extracorporeally. Measurements and Main Results: Regional lung aeration, specific [¹⁸F]fluorodeoxyglucose uptake rate, and perfusion were assessed using computed and positron emission tomography. Volutrauma yielded higher [¹⁸F]fluorodeoxyglucose uptake rate in the ventilated lung compared with atelectrauma (median [interquartile range], 0.017 [0.014–0.025] vs 0.013 min^–1 [0.010–0.014 min^–1]; p < 0.01), mainly in central lung regions. Volutrauma yielded higher [¹⁸F]fluorodeoxyglucose uptake rate in ventilator-induced lung injury versus control lung (0.017 [0.014–0.025] vs 0.011 min^–1 [0.010–0.016 min^–1]; p < 0.05), whereas atelectrauma did not. Volutrauma decreased blood fraction at similar perfusion and increased normally as well as hyperaerated lung compartments and tidal hyperaeration. Atelectrauma yielded higher poorly and nonaerated lung compartments, and tidal recruitment. Driving pressure increased in atelectrauma. Conclusions: In this model of acute respiratory distress syndrome, volutrauma promoted higher lung inflammation than atelectrauma at comparable low tidal volume and lower driving pressure, suggesting that static stress and strain are major determinants of ventilator-induced lung injury.

Introduction: In patients with acute respiratory distress syndrome (ARDS) fluid therapy might be necessary. The aim of this systematic review and meta-analysis is to determine the effects of colloid therapy compared to crystalloids on mortality and oxygenation in adults with ARDS. Methods: Randomized controlled trials (RCTs) were identified through a systematic literature search of MEDLINE, EMBASE, CENTRAL and LILACS. Articles published up to 15^th February 2013 were independently screened, abstracted, and assessed (Cochrane Risk of Bias Tool) to provide evidence-based therapy recommendations. RCTs were eligible if they compared colloid versus crystalloid therapy on lung function, inflammation, damage or mortality in adults with ARDS. Primary outcome parameters were respiratory mechanics, gas exchange lung inflammation and damage as well as hospital mortality. Kidney function, need for renal replacement therapy, hemodynamic stabilization and intensive care unit (ICU) length of stay served as secondary outcomes. Results: A total of 3 RCTs out of 4130 potential trials found in the databases were selected for qualitative and quantitative analysis totaling 206 patients who received either albumin or saline. Overall risk of bias was unclear to high in the identified trials. Calculated pooled risk of death was not statistically significant (albumin 34 of 100 (34.0%) versus 40 of 104 (38.5%), relative risk (RR) = 0.89, 95% confidence interval (CI) 0.62 to 1.28, P = 0.539). Weighted mean difference (WMD) in PaO₂/FiO₂ (mmHg) improved in the first 48 hours (WMD = 62, 95% CI 47 to 77, P <0.001, I ² = 0%) after therapy start and remained stable after 7 days (WMD = 20, 95% CI 4 to 36, P = 0.017, I ² = 0%). Conclusions: There is a high need for RCTs investigating the effects of colloids in ARDS patients. Based on the findings of this review, colloid therapy with albumin improved oxygenation but did not affect mortality.

To describe and evaluate the effects of the new noisy pressure support ventilation (noisy PSV) on lung physiologic variables. Crossover design with four modes of mechanical ventilation. Experimental research facility of a university hospital. A total of 12 pigs weighing 25.0–36.5 kg. Animals were anesthetized, the trachea was intubated, and lungs were ventilated with a mechanical ventilator (volume-controlled mode). Acute lung injury was then induced by surfactant depletion. Biphasic intermittent airway pressure/airway pressure release ventilation (BIPAP/APRV) was initiated, and anesthesia depth was decreased to allow spontaneous breathing. After that, each animal was ventilated with four different modes of assisted mechanical ventilation (1 hr each, Latin squares sequence): 1) PSV, 2) PSV combined with intermittent sighs (PSV + Sighs), 3) BIPAP/APRV + spontaneous breathing, and 4) noisy PSV with random variation of pressure support (normal distribution). The mean level of pressure support was set identical in all PSV forms. We found that noisy PSV increased tidal volume variability compared with PSV and PSV + Sighs (19% vs. 5% and 7%, respectively, p < .05) independently from the inspiratory effort; improved oxygenation and reduced venous admixture but did not affect the amount of nonaerated lung tissue as compared with other assisted ventilation modes; reduced mean airway pressure at comparable minute ventilation; redistributed pulmonary blood flow toward nondependent lung regions similar to other PSV forms, whereas BIPAP/APRV + spontaneous breathing did not; and reduced the inspiratory effort and cardiac output in comparison with BIPAP/APRV + spontaneous breathing. In the surfactant depletion model of acute lung injury, the new noisy PSV increased the variability of the respiratory pattern and improved oxygenation by a redistribution of perfusion toward the ventilated nondependent lung regions with simultaneous lower mean airway pressure, comparable minute ventilation, and no increase in the inspiratory effort or cardiac output.

Ischemic stroke causes brain inflammation, which we postulate may result in lung damage. Several studies have focused on stroke-induced immunosuppression and lung infection; however, the possibility that strokes may trigger lung inflammation has been overlooked. We hypothesized that even focal ischemic stroke might induce acute systemic and pulmonary inflammation, thus altering respiratory parameters, lung tissue integrity, and alveolar macrophage behavior. Forty-eight Wistar rats were randomly assigned to ischemic stroke (Stroke) or sham surgery (Sham). Lung function, histology, and inflammation in the lung, brain, bronchoalveolar lavage fluid (BALF), and circulating plasma were evaluated at 24 h. In vitro, alveolar macrophages from naïve rats (unstimulated) were exposed to serum or BALF from Sham or Stroke animals to elucidate possible mechanisms underlying alterations in alveolar macrophage phagocytic capability. Alveolar macrophages and epithelial and endothelial cells of Sham and Stroke animals were also isolated for evaluation of mRNA expression of interleukin (IL)-6 and tumor necrosis factor (TNF)-α. Twenty-four hours following ischemic stroke, the tidal volume, expiratory time, and mean inspiratory flow were increased. Compared to Sham animals, the respiratory rate and duty cycle during spontaneous breathing were reduced, but this did not affect lung mechanics during mechanical ventilation. Lungs from Stroke animals showed clear evidence of increased diffuse alveolar damage, pulmonary edema, and inflammation markers. This was associated with an increase in ultrastructural damage, as evidenced by injury to type 2 pneumocytes and endothelial cells, cellular infiltration, and enlarged basement membrane thickness. Protein levels of proinflammatory mediators were documented in the lung, brain, and plasma (TNF-α and IL-6) and in BALF (TNF-α). The phagocytic ability of macrophages was significantly reduced. Unstimulated macrophages isolated from naïve rats only upregulated expression of TNF-α and IL-6 following exposure to serum from Stroke rats. Exposure to BALF from Stroke or Sham animals did not change alveolar macrophage behavior, or gene expression of TNF-α and IL-6. IL-6 expression was increased in macrophages and endothelial cells from Stroke animals. In rats, focal ischemic stroke is associated with brain–lung crosstalk, leading to increased pulmonary damage and inflammation, as well as reduced alveolar macrophage phagocytic capability, which seems to be promoted by systemic inflammation.