Recruitment maneuvers modulate epithelial and endothelial cell response according to acute lung injury etiology. Crit Care Med. 2013;41:e256-e265. [PMID: 23887231 DOI: 10.1097/ccm.0b013e31828a3c13]

Restoration of Pulmonary Compliance after Laparoscopic Gynecologic Surgery Using a Recruitment Maneuver

BACKGROUND/OBJECTIVES

This study aimed to investigate the hypothesis that an alveolar recruitment maneuver can restore lung compliance to initial values after laparoscopic gynecological surgery.

METHODS

A total of 31 patients who underwent laparoscopic gynecological surgery were enrolled. Protective mechanical ventilation was applied, and the radial artery was catheterized in all patients. An alveolar recruitment maneuver (incremental and decremental positive end-expiratory pressure) was applied ten minutes after the release of pneumoperitoneum. The respiratory mechanics and blood gas results were recorded at eight different time points: after induction of anesthesia (T1), in the lithotomy position (T2), in the Trendelenburg position (T3), 10 and 90 min after insufflation of carbon dioxide (T4 and T5), in the supine position (T6), after desufflation (T7), and 10 min after an alveolar recruitment maneuver at the end of surgery (T8).

RESULTS

Pneumoperitoneum and the Trendelenburg position caused a decline of 15 units in compliance (T7 vs. T1; p < 0.05) compared to baseline. After the alveolar recruitment maneuver, compliance increased by 17.5% compared with the mean value of compliance at time T1 (T8 vs. T1; p < 0.05). The recruitment maneuver had favorable results in patients with low initial compliance (41.5 mL/cmH2O, IQR: 9.75 mL/cmH2O), high Body Mass Index 30.32 kg/m2 (IQR: 1.05 kg/m2), and high initial plateau airway pressure (16.5 cmH2O, IQR: 0.75 cmH2O).

CONCLUSIONS

Lung compliance does not return to initial values after performing laparoscopic gynecological procedures. However, after the release of pneumoperitoneum, an alveolar recruitment maneuver is beneficial as it improves compliance and gas exchange.

Protective Effects of Atractylodis lancea Rhizoma on Lipopolysaccharide-Induced Acute Lung Injury via TLR4/NF-κB and Keap1/Nrf2 Signaling Pathways In Vitro and In Vivo

Acute lung injury (ALI) is a syndrome caused by an excessive inflammatory response characterized by intractable hypoxemia both inside and outside the lung, for which effective therapeutic drugs are lacking. Atractylodis rhizoma, a traditional Chinese medicine, has excellent anti-inflammatory and antiviral properties in addition to protecting the integrity of the cellular barrier. However, few studies of Atractylodis rhizoma for the treatment of ALI have been published, and its mechanism of action remains unclear. In the present study, the chemical composition of the ethanolic extract of Atractylodis rhizoma (EEAR) was initially clarified by high performance liquid chromatography (HPLC), after which it was studied in vivo using a lipopolysaccharide (LPS)-induced ALI rat model. Treatment with EEAR significantly reduced the lung wet/dry (W/D) ratio, neutrophil infiltration, and malondialdehyde (MDA) and myeloperoxidase (MPO) formation, and enhanced superoxide dismutase (SOD) and glutathione (GSH) depletion in rats with ALI, thereby improving lung barrier function and effectively reducing lung injury. In addition, EEAR significantly reduced histopathological changes, decreased the expression of inflammatory factors (such as tumor necrosis factor-α (TNF-α), interleukin-1 beta (IL-1β), inducible nitric oxide synthase (INOS), and cyclooxygenase-2 (COX-2)), and inhibited the activation of the NF-κB signaling pathway, thus reducing inflammation. In addition, EEAR was found to also reduce oxidative stress in ALI by upregulating the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and its downstream proteins heme oxygenase-1 (HO-1) and NADPH quinone acceptor oxidoreductase 1 (NQO-1). EEAR also reduced LPS-induced inflammatory factor expression in THP-1 cells in vitro by inhibition of the NF-κB signaling pathway, and reduced damage from lipopolysaccharide (LPS)-induced oxidative stress in THP-1 cells by promoting the expression of Nrf2 and its downstream targets HO-1 and NQO-1, the molecular mechanism of which was consistent with in vivo observations. Therefore, we conclude that EEAR attenuates oxidative stress and inflammatory responses via TLR4/NF-κB and Keap1/Nrf2 signaling pathways to alleviate LPS-induced ALI, suggesting that Atractylodis rhizoma is a potential drug candidate for the treatment of ALI.

Effects of different fluid management on lung and kidney during pressure-controlled and pressure-support ventilation in experimental acute lung injury

Optimal fluid management is critical during mechanical ventilation to mitigate lung damage. Under normovolemia and protective ventilation, pulmonary tensile stress during pressure-support ventilation (PSV) results in comparable lung protection to compressive stress during pressure-controlled ventilation (PCV) in experimental acute lung injury (ALI). It is not yet known whether tensile stress can lead to comparable protection to compressive stress in ALI under a liberal fluid strategy (LF). A conservative fluid strategy (CF) was compared with LF during PSV and PCV on lungs and kidneys in an established model of ALI. Twenty-eight male Wistar rats received endotoxin intratracheally. After 24 h, they were treated with CF (minimum volume of Ringer's lactate to maintain normovolemia and mean arterial pressure ≥70 mmHg) or LF (~4 times higher than CF) combined with PSV or PCV (VT  = 6 ml/kg, PEEP = 3 cmH2 O) for 1 h. Nonventilated animals (n = 4) were used for molecular biology analyses. CF-PSV compared with LF-PSV: (1) decreased the diffuse alveolar damage score (10 [7.8-12] vs. 25 [23-31.5], p = 0.006), mainly due to edema in axial and alveolar parenchyma; (2) increased birefringence for occludin and claudin-4 in lung tissue and expression of zonula-occludens-1 and metalloproteinase-9 in lung. LF compared with CF reduced neutrophil gelatinase-associated lipocalin and interleukin-6 expression in the kidneys in PSV and PCV. In conclusion, CF compared with LF combined with PSV yielded less lung epithelial cell damage in the current model of ALI. However, LF compared with CF resulted in less kidney injury markers, regardless of the ventilatory strategy.

Pharmacological treatment to reduce pulmonary morbidity after esophagectomy

Esophagectomy for esophageal cancer is one of the most invasive procedures in gastrointestinal surgery. An invasive surgical procedure causes postoperative lung injury through the surgical procedure and one-lung ventilation during anesthesia. Lung injury developed by inflammatory response to surgical insults and oxidative stress is associated with pulmonary morbidity after esophagectomy. Postoperative pulmonary complications negatively affect the long-term outcomes; therefore, an effort to reduce lung injury improves overall survival after esophagectomy. Although significant evidence has not been established, various pharmacological treatments for reducing lung injury, such as administration of a corticosteroid, neutrophil elastase inhibitor, and vitamins are considered to have efficacy for pulmonary morbidity. In this review we survey the following topics: mediators during the perioperative periods of esophagectomy and the efficacy of pharmacological therapies for patients with esophagectomy on pulmonary complications.

The impact of fluid status and decremental PEEP strategy on cardiac function and lung and kidney damage in mild-moderate experimental acute respiratory distress syndrome

BACKGROUND

We evaluated the effects of abrupt versus gradual PEEP decrease, combined with standard versus high-volume fluid administration, on cardiac function, as well as lung and kidney damage in an established model of mild-moderate acute respiratory distress syndrome (ARDS).

METHODS

Wistar rats received endotoxin intratracheally. After 24 h, they were treated with Ringer's lactate at standard (10 mL/kg/h) or high (30 mL/kg/h) dose. For 30 min, all animals were mechanically ventilated with tidal volume = 6 mL/kg and PEEP = 9 cmH2O (to keep alveoli open), then randomized to undergo abrupt or gradual (0.2 cmH2O/min for 30 min) PEEP decrease from 9 to 3 cmH2O. Animals were then further ventilated for 10 min at PEEP = 3 cmH2O, euthanized, and their lungs and kidneys removed for molecular biology analysis.

RESULTS

At the end of the experiment, left and right ventricular end-diastolic areas were greater in animals treated with high compared to standard fluid administration, regardless of PEEP decrease rate. However, pulmonary arterial pressure, indicated by the pulmonary acceleration time (PAT)/pulmonary ejection time (PET) ratio, was higher in abrupt compared to gradual PEEP decrease, independent of fluid status. Animals treated with high fluids and abrupt PEEP decrease exhibited greater diffuse alveolar damage and higher expression of interleukin-6 (a pro-inflammatory marker) and vascular endothelial growth factor (a marker of endothelial cell damage) compared to the other groups. The combination of standard fluid administration and gradual PEEP decrease increased zonula occludens-1 expression, suggesting epithelial cell preservation. Expression of club cell-16 protein, an alveolar epithelial cell damage marker, was higher in abrupt compared to gradual PEEP decrease groups, regardless of fluid status. Acute kidney injury score and gene expression of kidney injury molecule-1 were higher in the high versus standard fluid administration groups, regardless of PEEP decrease rate.

CONCLUSION

In the ARDS model used herein, decreasing PEEP abruptly increased pulmonary arterial hypertension, independent of fluid status. The combination of abrupt PEEP decrease and high fluid administration led to greater lung and kidney damage. This information adds to the growing body of evidence that supports gradual transitioning of ventilatory patterns and warrants directing additional investigative effort into vascular and deflation issues that impact lung protection.

Lung ultrasound for the assessment of lung recruitment in neonates with massive pneumothorax during extracorporeal membrane oxygenation: a case report

Bedside lung ultrasound may be an effective method for the assessment of lung recruitment in newborns with extracorporeal membrane oxygenation (ECMO). We report a case of a neonate who had severe hypoxemia with persistent pulmonary hypertension and massive pneumothorax due to meconium aspiration syndrome and was treated with ECMO. Positive pressure mechanical ventilation resulted in persistent massive air leakage from the disrupted pulmonary tissue. When ECMO was initiated, a "total lung rest" ventilation strategy was used to facilitate healing of the lung rupture and absorption of the pneumothorax. After complete absorption of the pneumothorax, lung recruitment was performed by progressively increasing the positive end-expiratory pressure under the guidance of lung ultrasound. Bedside lung ultrasound was successfully used to assess pneumothorax absorption and improvement of pulmonary inflammation and successfully guided the recruitment of collapsed alveoli and the withdrawal of ECMO.

Effects of two stepwise lung recruitment strategies on respiratory function and haemodynamics in anaesthetised pigs: A randomised crossover study

BACKGROUND

Lung recruitment manoeuvres and positive end-expiratory pressure (PEEP) can improve lung function during general anaesthesia. Different recruitment manoeuvre strategies have been described in large international trials: in the protective ventilation using high vs. low PEEP (PROVHILO) strategy, tidal volume (VT) was increased during volume-controlled ventilation; in the individualised peri-operative open-lung approach vs. standard protective ventilation in abdominal surgery (iPROVE) strategy, PEEP was increased during pressure-controlled ventilation.

OBJECTIVES

To compare the effects of the PROVHILO strategy and the iPROVE strategy on respiratory and haemodynamic variables.

DESIGN

Randomised crossover study.

SETTING

University hospital research facility.

ANIMALS

A total of 20 juvenile anaesthetised pigs.

INTERVENTIONS

Animals were assigned randomly to one of two sequences: PROVHILO strategy followed by iPROVE strategy or vice-versa (n = 10/sequence). In the PROVHILO strategy, VT was increased stepwise by 4 ml kg-1 at a fixed PEEP of 12 cmH2O until a plateau pressure of 30 to 35 cmH2O was reached. In the iPROVE strategy, at fixed driving pressure of 20 cmH2O, PEEP was increased up to 20 cmH2O followed by PEEP titration according to the lowest elastance of the respiratory system (ERS).

MAIN OUTCOME MEASURES

We assessed regional transpulmonary pressure (Ptrans), respiratory system mechanics, gas exchange and haemodynamics, as well as the centre of ventilation (CoV) by electrical impedance tomography.

RESULTS

During recruitment manoeuvres with the PROVHILO strategy compared with the iPROV strategy, dorsal Ptrans was lower at end-inspiration (16.3 ± 2.7 vs. 18.6 ± 3.1 cmH2O, P = 0.001) and end-expiration (4.8 ± 2.6 vs. 8.8 ± 3.4 cmH2O, P  < 0.001), and mean arterial pressure (MAP) was higher (77 ± 11 vs. 60 ± 14 mmHg, P < 0.001). At 1 and 15 min after recruitment manoeuvres, ERS was higher in the PROVHILO strategy than the iPROVE strategy (24.6 ± 3.9 vs. 21.5 ± 3.4 and 26.7 ± 4.3 vs. 24.0 ± 3.8 cmH2O l-1; P  < 0.001, respectively). At 1 min, PaO2 was lower in PROVHILO compared with iPROVE strategy (57.1 ± 6.1 vs. 59.3 ± 5.1 kPa, P = 0.013), but at 15 min, values did not differ. CoV did not differ between strategies.

CONCLUSION

In anaesthetised pigs, the iPROVE strategy compared with the PROVHILO strategy increased dorsal Ptrans at the cost of lower MAP during recruitment manoeuvres, and decreased ERS thereafter, without consistent improvement of oxygenation or shift of the CoV.

TRIAL REGISTRATION

This study was registered and approved by the Landesdirektion Dresden, Germany (DD24-5131/338/28).

Perioperative Open-lung Approach, Regional Ventilation, and Lung Injury in Cardiac Surgery

BACKGROUND

In the Protective Ventilation in Cardiac Surgery (PROVECS) randomized, controlled trial, an open-lung ventilation strategy did not improve postoperative respiratory outcomes after on-pump cardiac surgery. In this prespecified subanalysis, the authors aimed to assess the regional distribution of ventilation and plasma biomarkers of lung epithelial and endothelial injury produced by that strategy.

METHODS

Perioperative open-lung ventilation consisted of recruitment maneuvers, positive end-expiratory pressure (PEEP) = 8 cm H2O, and low-tidal volume ventilation including during cardiopulmonary bypass. Control ventilation strategy was a low-PEEP (2 cm H2O) low-tidal volume approach. Electrical impedance tomography was used serially throughout the perioperative period (n = 56) to compute the dorsal fraction of ventilation (defined as the ratio of dorsal tidal impedance variation to global tidal impedance variation). Lung injury was assessed serially using biomarkers of epithelial (soluble form of the receptor for advanced glycation end-products, sRAGE) and endothelial (angiopoietin-2) lung injury (n = 30).

RESULTS

Eighty-six patients (age = 64 ± 12 yr; EuroSCORE II = 1.65 ± 1.57%) undergoing elective on-pump cardiac surgery were studied. Induction of general anesthesia was associated with ventral redistribution of tidal volumes and higher dorsal fraction of ventilation in the open-lung than the control strategy (0.38 ± 0.07 vs. 0.30 ± 0.10; P = 0.004). No effect of the open-lung strategy on the dorsal fraction of ventilation was noted at the end of surgery after median sternotomy closure (open-lung = 0.37 ± 0.09 vs. control = 0.34 ± 0.11; P = 0.743) or in extubated patients at postoperative day 2 (open-lung = 0.63 ± 0.18 vs. control = 0.59 ± 0.11; P > 0.999). Open-lung ventilation was associated with increased intraoperative plasma sRAGE (7,677 ± 3,097 pg/ml vs. 6,125 ± 1,400 pg/ml; P = 0.037) and had no effect on angiopoietin-2 (P > 0.999).

CONCLUSIONS

In cardiac surgery patients, open-lung ventilation provided larger dorsal lung ventilation early during surgery without a maintained benefit as compared with controls at the end of surgery and postoperative day 2 and was associated with higher intraoperative plasma concentration of sRAGE suggesting lung overdistension.

EDITOR’S PERSPECTIVE

Chest physiotherapy: An important adjuvant in critically ill mechanically ventilated patients with COVID-19

In late 2019, an outbreak of a novel human coronavirus causing respiratory disease was identified in Wuhan, China. The virus spread rapidly worldwide, reaching pandemic status. Chest computed tomography scans of patients with coronavirus disease-2019 (COVID-19) have revealed different stages of respiratory involvement, with extremely variable lung presentations, which require individualized ventilatory strategies in those who become critically ill. Chest physiotherapy has proven to be effective for improving long-term respiratory physical function among ICU survivors. The ARIR recently reported the role of chest physiotherapy in the acute phase of COVID-19, pointing out limitation of some procedures due to the limited experience with this disease in the ICU setting. Evidence on the efficacy of chest physiotherapy in COVID-19 is still lacking. In this line, the current review discusses the important role of chest physiotherapy in critically ill mechanically ventilated patients with COVID-19, around the weaning process, and how it can be safely applied with careful organization, including the training of healthcare staff and the appropriate use of personal protective equipment to minimize the risk of viral exposure.

Gradually Increasing Tidal Volume May Mitigate Experimental Lung Injury in Rats

BACKGROUND

This study hypothesized that, in experimental mild acute respiratory distress syndrome, lung damage caused by high tidal volume (VT) could be attenuated if VT increased slowly enough to progressively reduce mechanical heterogeneity and to allow the epithelial and endothelial cells, as well as the extracellular matrix of the lung to adapt. For this purpose, different strategies of approaching maximal VT were tested.

METHODS

Sixty-four Wistar rats received Escherichia coli lipopolysaccharide intratracheally. After 24 h, animals were randomly assigned to receive mechanical ventilation with VT = 6 ml/kg for 2 h (control); VT = 6 ml/kg during hour 1 followed by an abrupt increase to VT = 22 ml/kg during hour 2 (no adaptation time); VT = 6 ml/kg during the first 30 min followed by a gradual VT increase up to 22 ml/kg for 30 min, then constant VT = 22 ml/kg during hour 2 (shorter adaptation time); and a more gradual VT increase, from 6 to 22 ml/kg during hour 1 followed by VT = 22 ml/kg during hour 2 (longer adaptation time). All animals were ventilated with positive end-expiratory pressure of 3 cm H2O. Nonventilated animals were used for molecular biology analysis.

RESULTS

At 2 h, diffuse alveolar damage score and heterogeneity index were greater in the longer adaptation time group than in the control and shorter adaptation time animals. Gene expression of interleukin-6 favored the shorter (median [interquartile range], 12.4 [9.1-17.8]) adaptation time compared with longer (76.7 [20.8 to 95.4]; P = 0.02) and no adaptation (65.5 [18.1 to 129.4]) time (P = 0.02) strategies. Amphiregulin, metalloproteinase-9, club cell secretory protein-16, and syndecan showed similar behavior.

CONCLUSIONS

In experimental mild acute respiratory distress syndrome, lung damage in the shorter adaptation time group compared with the no adaptation time group was attenuated in a time-dependent fashion by preemptive adaptation of the alveolar epithelial cells and extracellular matrix. Extending the adaptation period increased cumulative power and did not prevent lung damage, because it may have exposed animals to injurious strain earlier and for a longer time, thereby negating any adaptive benefit.

Biological Response to Time-Controlled Adaptive Ventilation Depends on Acute Respiratory Distress Syndrome Etiology

OBJECTIVES

To compare a time-controlled adaptive ventilation strategy, set in airway pressure release ventilation mode, versus a protective mechanical ventilation strategy in pulmonary and extrapulmonary acute respiratory distress syndrome with similar mechanical impairment.

DESIGN

Animal study.

SETTING

Laboratory investigation.

SUBJECTS

Forty-two Wistar rats.

INTERVENTIONS

Pulmonary acute respiratory distress syndrome and extrapulmonary acute respiratory distress syndrome were induced by instillation of Escherichia coli lipopolysaccharide intratracheally or intraperitoneally, respectively. After 24 hours, animals were randomly assigned to receive 1 hour of volume-controlled ventilation (n = 7/etiology) or time-controlled adaptive ventilation (n = 7/etiology) (tidal volume = 8 mL/kg). Time-controlled adaptive ventilation consisted of the application of continuous positive airway pressure 2 cm H2O higher than baseline respiratory system peak pressure for a time (Thigh) of 0.75-0.85 seconds. The release pressure (Plow = 0 cm H2O) was applied for a time (Tlow) of 0.11-0.18 seconds. Tlow was set to target an end-expiratory flow to peak expiratory flow ratio of 75%. Nonventilated animals (n = 7/etiology) were used for Diffuse Alveolar Damage and molecular biology markers analyses.

MEASUREMENT AND MAIN RESULTS

Time-controlled adaptive ventilation increased mean respiratory system pressure regardless of acute respiratory distress syndrome etiology. The Diffuse Alveolar Damage score was lower in time-controlled adaptive ventilation compared with volume-controlled ventilation in pulmonary acute respiratory distress syndrome and lower in time-controlled adaptive ventilation than nonventilated in extrapulmonary acute respiratory distress syndrome. In pulmonary acute respiratory distress syndrome, volume-controlled ventilation, but not time-controlled adaptive ventilation, increased the expression of amphiregulin, vascular cell adhesion molecule-1, and metalloproteinase-9. Collagen density was higher, whereas expression of decorin was lower in time-controlled adaptive ventilation than nonventilated, independent of acute respiratory distress syndrome etiology. In pulmonary acute respiratory distress syndrome, but not in extrapulmonary acute respiratory distress syndrome, time-controlled adaptive ventilation increased syndecan expression.

CONCLUSION

In pulmonary acute respiratory distress syndrome, time-controlled adaptive ventilation led to more pronounced beneficial effects on expression of biomarkers related to overdistension and extracellular matrix homeostasis.

Effects of pressure support ventilation on ventilator-induced lung injury in mild acute respiratory distress syndrome depend on level of positive end-expiratory pressure: A randomised animal study

BACKGROUND

Harmful effects of spontaneous breathing have been shown in experimental severe acute respiratory distress syndrome (ARDS). However, in the clinical setting, spontaneous respiration has been indicated only in mild ARDS. To date, no study has compared the effects of spontaneous assisted breathing with those of fully controlled mechanical ventilation at different levels of positive end-expiratory pressure (PEEP) on lung injury in ARDS.

OBJECTIVE

To compare the effects of assisted pressure support ventilation (PSV) with pressure-controlled ventilation (PCV) on lung function, histology and biological markers at two different PEEP levels in mild ARDS in rats.

DESIGN

Randomised controlled experimental study.

SETTING

Basic science laboratory.

PARTICIPANTS

Thirty-five Wistar rats (weight ± SD, 310 ± 19) g received Escherichia coli lipopolysaccharide (LPS) intratracheally. After 24 h, the animals were anaesthetised and randomly allocated to either PCV (n=14) or PSV (n=14) groups. Each group was further assigned to PEEP = 2 cmH2O or PEEP = 5 cmH2O. Tidal volume was kept constant (≈6 ml kg). Additional nonventilated animals (n=7) were used as a control for postmortem analysis.

MAIN OUTCOME MEASURES

Ventilatory and mechanical parameters, arterial blood gases, diffuse alveolar damage score, epithelial integrity measured by E-cadherin tissue expression, and biological markers associated with inflammation (IL-6 and cytokine-induced neutrophil chemoattractant, CINC-1) and type II epithelial cell damage (surfactant protein-B) were evaluated.

RESULTS

In both PCV and PSV, peak transpulmonary pressure was lower, whereas E-cadherin tissue expression, which is related to epithelial integrity, was higher at PEEP = 5 cmH2O than at PEEP = 2 cmH2O. In PSV, PEEP = 5 cmH2O compared with PEEP = 2 cmH2O was associated with significantly reduced diffuse alveolar damage score [median (interquartile range), 11 (8.5 to 13.5) vs. 23 (19 to 26), P = 0.005] and expressions of IL-6 and CINC-1 (P = 0.02 for both), whereas surfactant protein-B mRNA expression increased (P = 0.03). These changes suggested less type II epithelial cell damage at a PEEP of 5 cmH2O. Peak transpulmonary pressure correlated positively with IL-6 [Spearman's rho (ρ) = 0.62, P = 0.0007] and CINC-1 expressions (ρ = 0.50, P = 0.01) and negatively with E-cadherin expression (ρ = -0.67, P = 0.0002).

CONCLUSION

During PSV, PEEP of 5 cmH2O, but not a PEEP of 2 cmH2O, reduced lung damage and inflammatory markers while maintaining epithelial cell integrity.

Ventilation in patients with intra-abdominal hypertension: what every critical care physician needs to know

The incidence of intra-abdominal hypertension (IAH) is high and still underappreciated by critical care physicians throughout the world. One in four to one in three patients will have IAH on admission, while one out of two will develop IAH within the first week of Intensive Care Unit stay. IAH is associated with high morbidity and mortality. Although considerable progress has been made over the past decades, some important questions remain regarding the optimal ventilation management in patients with IAH. An important first step is to measure intra-abdominal pressure (IAP). If IAH (IAP > 12 mmHg) is present, medical therapies should be initiated to reduce IAP as small reductions in intra-abdominal volume can significantly reduce IAP and airway pressures. Protective lung ventilation with low tidal volumes in patients with respiratory failure and IAH is important. Abdominal-thoracic pressure transmission is around 50%. In patients with IAH, higher positive end-expiratory pressure (PEEP) levels are often required to avoid alveolar collapse but the optimal PEEP in these patients is still unknown. During recruitment manoeuvres, higher opening pressures may be required while closely monitoring oxygenation and the haemodynamic response. During lung-protective ventilation, whilst keeping driving pressures within safe limits, higher plateau pressures than normally considered might be acceptable. Monitoring of the respiratory function and adapting the ventilatory settings during anaesthesia and critical care are of great importance. This review will focus on how to deal with the respiratory derangements in critically ill patients with IAH.

Effects of Stepwise Lung Recruitment Maneuvers in Patients with Early Acute Respiratory Distress Syndrome: A Prospective, Randomized, Controlled Trial

Since the clinical benefit of lung recruitment maneuvers (LRMs) is still conflicting, we performed this prospective, randomized, controlled study to investigate whether LRMs should be used in the routine management of acute respiratory distress syndrome (ARDS). This trial was conducted in four intensive care units (ICUs) to compare application of a modified stepwise LRMs with solely lung-protective ventilation in patients with moderate to severe ARDS within 72 h from the onset. The primary outcome was 28-day mortality, and the secondary outcomes were ventilator-free days and ICU-free days. We collected data on 120 ARDS patients from 2009 to 2012, and there was no difference in 28-day mortality between the two groups (28.3% vs. 30.0%, p = 0.84). However, among survivors, patients in the LRM group had a significant longer median duration of ventilator-free days (18 vs. 13 days; p = 0.04) and ICU-free days (16 vs. 11 days; p = 0.03) at 28 days than in the control group. The respiratory system compliance was significantly higher in the LRM group from day 1 to day 7. The occurrence rate of barotrauma was similar in both groups. We concluded that LRMs combined with lung-protective ventilation in early ARDS may improve patient outcomes.

Acute Lung Injury in Response to Intratracheal Instillation of Lipopolysaccharide in an Animal Model of Emphysema Induced by Elastase

The response of lungs with emphysema to an acute lung injury (ALI) remains unclear. This study compared the lung response to intratracheal instillation of lipopolysaccharide (LPS) in rats with and without emphysema. Twenty-four Wistar rats were randomized to four groups: control group (C-G), ALI group (ALI-G), emphysema group (E-G), emphysema and ALI group (E-ALI-G). Euthanasia and the following analysis were performed 24 h after ALI induction: lung histology, bronchoalveolar lavage (BAL), mRNA expression of inflammatory mediators, and blood gas measures. The histological analysis showed that animals of ALI-G (0.55 ± 0.15) and E-ALI-G (0.69 ± 0.08) had a higher ALI score compared to C-G (0.12 ± 0.04) and E-G (0.16 ± 0.04) (p < 0.05). The analysis of each component of the score demonstrated that ALI-G and E-ALI-G had greater alveolar and interstitial neutrophil infiltration, as well as greater amount of alveolar proteinaceous debris. Comparing the two groups that received LPS, there was a trend of higher ALI in the E-ALI-G, specially due to a higher neutrophil infiltration in the alveolar spaces and a higher septal thickening. Total cell count (E-G = 3.09 ± 0.83; ALI-G = 4.45 ± 1.9; E-ALI-G = 5.9 ± 2.1; C-G = 0.73 ± 0.37 × 10⁵) and neutrophil count (E-G = 0.69 ± 0.35; ALI-G = 2.53 ± 1.09; E-ALI-G = 3.86 ± 1.4; C-G = 0.09 ± 0.07 × 10⁵) in the BAL were higher in the groups E-G, ALI-G, and E-ALI-G when compared to C-G (p < 0.05). The IL-6, TNF-α, and CXCL2 mRNA expressions were higher in the animals that received LPS (ALI-G and E-ALI-G) compared to the C-G and E-G (p < 0.05). No statistically significant difference was observed in the BAL cellularity and in the expression of inflammatory mediators between the ALI-G and the E-ALI-G. The severity of ALI in response to intratracheal instillation of LPS did not show difference in rats with and without intratracheal-induced emphysema.

Comparison of different degrees of variability in tidal volume to prevent deterioration of respiratory system elastance in experimental acute lung inflammation

BACKGROUND

Variable ventilation improves respiratory function, but it is not known whether the amount of variability in tidal volume (VT) can be reduced in recruited lungs without a deterioration of respiratory system elastance.

METHODS

Acute lung inflammation was induced by intratracheal instillation of lipopolysaccharide in 35 Wistar rats. Twenty-eight animals were anaesthetized and ventilated in volume-controlled mode. Lungs were recruited by random variation of VT (mean 6 ml kg(-1), coefficient of variation 30%, normal distribution) for 30 min. Animals were randomly assigned to different amounts of VT variability (n=7 for 90 min per group): 30, 15, 7.5, or 0%. Lung function, diffuse alveolar damage, and gene expression of biological markers associated with cell mechanical stress, inflammation, and fibrogenesis were assessed. Seven animals were not ventilated and served as controls for post-mortem analyses.

RESULTS

A VT variability of 30%, but not 15, 7.5, or 0%, prevented deterioration of respiratory system elastance [Mean (SD) -7.5 (8.7%), P<0.05; 21.1 (9.6%), P<0.05; 43.3 (25.9), P<0.05; and 41.2 (16.4), P<0.05, respectively]. Diffuse alveolar damage was lower with a VT variability of 30% than with 0% and without ventilation, because of reduced oedema and haemorrhage. A VT variability of 30, 15, or 7.5% reduced the gene expression of amphiregulin, cytokine-induced neutrophil chemoattractant-1, and tumour necrosis factor α compared with a VT variability of 0%.

CONCLUSIONS

In this model of acute lung inflammation, a VT variability of 30%, compared with 15 and 7.5%, was necessary to avoid deterioration of respiratory system elastance and was not associated with lung histological damage.

Ventilator-induced lung injury during controlled ventilation in patients with acute respiratory distress syndrome: less is probably better

INTRODUCTION

Mechanical ventilation is required to support respiratory function in the acute respiratory distress syndrome (ARDS), but it may promote lung damage, a phenomenon known as ventilator-induced lung injury (VILI). Areas covered: Several mechanisms of VILI have been described, such as: inspiratory and/or expiratory stress inducing overdistension (volutrauma); interfaces between collapsed or edema-filled alveoli with surrounding open alveoli, acting as stress raisers; alveoli that repetitively open and close during tidal breathing (atelectrauma); and peripheral airway dynamics. In this review, we discuss: the definition and classification of ARDS; ventilatory parameters that act as VILI determinants (tidal volume, respiratory rate, positive end-expiratory pressure, peak, plateau, driving and transpulmonary pressures, energy, mechanical power, and intensity); and the roles of prone positioning and muscle paralysis. We seek to provide an up-to-date overview of the evidence in the field from a clinical perspective. Expert commentary: To prevent VILI, mechanical ventilation strategies should minimize inspiratory/expiratory stress, dynamic/static strain, energy, mechanical power, and intensity, as well as mitigate the hemodynamic consequences of positive-pressure ventilation. In patients with moderate to severe ARDS, prone positioning can reduce lung damage and improve survival. Overall, volutrauma seems to be more harmful than atelectrauma. Extracorporeal support should be considered in selected cases.

Anesthesia and fast-track in video-assisted thoracic surgery (VATS): from evidence to practice

In thoracic surgery, the introduction of video-assisted thoracoscopic techniques has allowed the development of fast-track protocols, with shorter hospital lengths of stay and improved outcomes. The perioperative management needs to be optimized accordingly, with the goal of reducing postoperative complications and speeding recovery times. Premedication performed in the operative room should be wisely administered because often linked to late discharge from the post-anesthesia care unit (PACU). Inhalatory anesthesia, when possible, should be preferred based on protective effects on postoperative lung inflammation. Deep neuromuscular blockade should be pursued and carefully monitored, and an appropriate reversal administered before extubation. Management of one-lung ventilation (OLV) needs to be optimized to prevent not only intraoperative hypoxemia but also postoperative acute lung injury (ALI): protective ventilation strategies are therefore to be implemented. Locoregional techniques should be favored over intravenous analgesia: the thoracic epidural, the paravertebral block (PVB), the intercostal nerve block (ICNB), and the serratus anterior plane block (SAPB) are thoroughly reviewed and the most common dosages are reported. Fluid therapy needs to be administered critically, to avoid both overload and cardiovascular compromisation. All these practices are analyzed singularly with the aid of the most recent evidences aimed at the best patient care. Finally, a few notes on some of the latest trends in research are presented, such as non-intubated video-assisted thoracoscopic surgery (VATS) and intravenous lidocaine.

Variability in Tidal Volume Affects Lung and Cardiovascular Function Differentially in a Rat Model of Experimental Emphysema

In experimental elastase-induced emphysema, mechanical ventilation with variable tidal volumes (V_T) set to 30% coefficient of variation (CV) may result in more homogenous ventilation distribution, but might also impair right heart function. We hypothesized that a different CV setting could improve both lung and cardiovascular function. Therefore, we investigated the effects of different levels of V_T variability on cardiorespiratory function, lung histology, and gene expression of biomarkers associated with inflammation, fibrogenesis, epithelial cell damage, and mechanical cell stress in this emphysema model. Wistar rats (n = 35) received repeated intratracheal instillation of porcine pancreatic elastase to induce emphysema. Seven animals were not ventilated and served as controls (NV). Twenty-eight animals were anesthetized and assigned to mechanical ventilation with a V_T CV of 0% (BASELINE). After data collection, animals (n = 7/group) were randomly allocated to V_T CVs of 0% (VV₀); 15% (VV₁₅); 22.5% (VV_22.5); or 30% (VV₃₀). In all groups, mean V_T was 6 mL/kg and positive end-expiratory pressure was 3 cmH₂O. Respiratory system mechanics and cardiac function (by echocardiography) were assessed continuously for 2 h (END). Lung histology and molecular biology were measured post-mortem. VV_22.5 and VV₃₀ decreased respiratory system elastance, while VV₁₅ had no effect. VV₀, VV₁₅, and VV_22.5, but not VV₃₀, increased pulmonary acceleration time to pulmonary ejection time ratio. VV_22.5 decreased the central moment of the mean linear intercept (D2 of Lm) while increasing the homogeneity index (1/β) compared to NV (77 ± 8 μm vs. 152 ± 45 μm; 0.85 ± 0.06 vs. 0.66 ± 0.13, p < 0.05 for both). Compared to NV, VV₃₀ was associated with higher interleukin-6 expression. Cytokine-induced neutrophil chemoattractant-1 expression was higher in all groups, except VV_22.5, compared to NV. IL-1β expression was lower in VV_22.5 and VV₃₀ compared to VV₀. IL-10 expression was higher in VV_22.5 than NV. Club cell protein 16 expression was higher in VV_22.5 than VV₀. SP-D expression was higher in VV₃₀ than NV, while SP-C was higher in VV₃₀ and VV_22.5 than VV_0. In conclusion, VV_22.5 improved respiratory system elastance and homogeneity of airspace enlargement, mitigated inflammation and epithelial cell damage, while avoiding impairment of right cardiac function in experimental elastase-induced emphysema.

Sevoflurane, Compared With Isoflurane, Minimizes Lung Damage in Pulmonary but Not in Extrapulmonary Acute Respiratory Distress Syndrome in Rats

BACKGROUND

Volatile anesthetics modulate inflammation in acute respiratory distress syndrome (ARDS). However, it is unclear whether they act differently depending on ARDS etiology. We hypothesized that the in vivo and in vitro effects of sevoflurane and isoflurane on lung damage would not differ in pulmonary (p) and extrapulmonary (exp) ARDS.

METHODS

Twenty-four Wistar rats were randomized to undergo general anesthesia (1-2 minutes) with sevoflurane and isoflurane. Animals were then further randomized to receive Escherichia coli lipopolysaccharide (LPS) intratracheally (ARDSp) or intraperitoneally (ARDSexp), and 24 hours after ARDS induction, they were subjected to 60 minutes of sevoflurane or isoflurane anesthesia at 1 minimal alveolar concentration. The primary outcome measure was interleukin (IL)-6 mRNA expression in lung tissue. Secondary outcomes included gas exchange, lung mechanics, histology, and mRNA expression of IL-10, nuclear factor erythroid 2-related factor-2 (Nrf2), surfactant protein (SP)-B, vascular cell adhesion molecule-1, epithelial amiloride-sensitive Na-channel subunits α and γ, and sodium-potassium-adenosine-triphosphatase pump subunits α1 (α1-Na,K-ATPase) and β1 (β1-Na,K-ATPase). Additional ARDSp and ARDSexp animals (n = 6 per group) were anesthetized with sodium thiopental but not mechanically ventilated (NV) to serve as controls. Separately, to identify how sevoflurane and isoflurane act on type II epithelial cells, A549 human lung epithelial cells were stimulated with LPS (20 µg/mL) for 24 hours, and SP-B expression was quantified after further exposure to sevoflurane or isoflurane (1 minimal alveolar concentration ) for 60 minutes.

RESULTS

In ARDSp, sevoflurane reduced IL-6 expression to a greater degree than isoflurane (P = .04). Static lung elastance (P = .0049) and alveolar collapse (P = .033) were lower in sevoflurane than isoflurane, whereas Nrf2 (P = .036), SP-B (P = .042), and β1-Na,K-ATPase (P = .038) expressions were higher in sevoflurane. In ARDSexp, no significant differences were observed in lung mechanics, alveolar collapse, or molecular parameters between sevoflurane and isoflurane. In vitro, SP-B expression was higher in sevoflurane than isoflurane (P = .026).

CONCLUSIONS

Compared with isoflurane, sevoflurane did not affect lung inflammation in ARDSexp, but it did reduce lung inflammation in ARDSp.

Recruitment maneuvers in acute respiratory distress syndrome

The rationale for the use of recruitment maneuvers (RMs) in acute respiratory distress syndrome (ARDS) is to promote alveolar recruitment, leading to an increased end-expiratory lung volume and thus decreased ventilator-induced lung injury (VILI). RMs consists of a transient increase in transpulmonary pressure that can re-open previously collapsed alveoli. RMs represents a physiological response to lung aggression in different conditions by re-opening the collapsed part of the lung and decreasing lung oedema. This process can be accomplished through a variety of methods. The RM that has probably been used most commonly is sustained inflation, but recruitment can be achieved by a prolonged sigh, leading to a lesser increase in transpulmonary pressure for a longer period of time. This extended sigh seems to be more efficient, with less haemodynamic compromise. Knowledge of physiological determinants is crucial to selecting good levels of pressure and time required to perform an efficient and well-tolerated RM. Identifying ARDS patients who may benefit from RMs is a major issue, depending essentially on the amount of recruitable lung involved. In any case, however, RMs should be done at the early phase of ARDS.

Lung Functional and Biologic Responses to Variable Ventilation in Experimental Pulmonary and Extrapulmonary Acute Respiratory Distress Syndrome

OBJECTIVES

The biologic effects of variable ventilation may depend on the etiology of acute respiratory distress syndrome. We compared variable and conventional ventilation in experimental pulmonary and extrapulmonary acute respiratory distress syndrome.

DESIGN

Prospective, randomized, controlled experimental study.

SETTINGS

University research laboratory.

SUBJECTS

Twenty-four Wistar rats.

INTERVENTIONS

Acute respiratory distress syndrome was induced by Escherichia coli lipopolysaccharide administered intratracheally (pulmonary acute respiratory distress syndrome, n = 12) or intraperitoneally (extrapulmonary acute respiratory distress syndrome, n = 12). After 24 hours, animals were randomly assigned to receive conventional (volume-controlled ventilation, n = 6) or variable ventilation (n = 6). Nonventilated animals (n = 4 per etiology) were used for comparison of diffuse alveolar damage, E-cadherin, and molecular biology variables. Variable ventilation was applied on a breath-to-breath basis as a sequence of randomly generated tidal volume values (n = 600; mean tidal volume = 6 mL/kg), with a 30% coefficient of variation (normal distribution). After randomization, animals were ventilated for 1 hour and lungs were removed for histology and molecular biology analysis.

MEASUREMENTS AND MAIN RESULTS

Variable ventilation improved oxygenation and reduced lung elastance compared with volume-controlled ventilation in both acute respiratory distress syndrome etiologies. In pulmonary acute respiratory distress syndrome, but not in extrapulmonary acute respiratory distress syndrome, variable ventilation 1) decreased total diffuse alveolar damage (median [interquartile range]: volume-controlled ventilation, 12 [11-17] vs variable ventilation, 9 [8-10]; p < 0.01), interleukin-6 expression (volume-controlled ventilation, 21.5 [18.3-23.3] vs variable ventilation, 5.6 [4.6-12.1]; p < 0.001), and angiopoietin-2/angiopoietin-1 ratio (volume-controlled ventilation, 2.0 [1.3-2.1] vs variable ventilation, 0.7 [0.6-1.4]; p < 0.05) and increased relative angiopoietin-1 expression (volume-controlled ventilation, 0.3 [0.2-0.5] vs variable ventilation, 0.8 [0.5-1.3]; p < 0.01). In extrapulmonary acute respiratory distress syndrome, only volume-controlled ventilation increased vascular cell adhesion molecule-1 messenger RNA expression (volume-controlled ventilation, 7.7 [5.7-18.6] vs nonventilated, 0.9 [0.7-1.3]; p < 0.05). E-cadherin expression in lung tissue was reduced in volume-controlled ventilation compared with nonventilated regardless of acute respiratory distress syndrome etiology. In pulmonary acute respiratory distress syndrome, E-cadherin expression was similar in volume-controlled ventilation and variable ventilation; in extrapulmonary acute respiratory distress syndrome, however, it was higher in variable ventilation than in volume-controlled ventilation.

CONCLUSIONS

Variable ventilation improved lung function in both pulmonary acute respiratory distress syndrome and extrapulmonary acute respiratory distress syndrome. Variable ventilation led to more pronounced beneficial effects in biologic marker expressions in pulmonary acute respiratory distress syndrome compared with extrapulmonary acute respiratory distress syndrome but preserved E-cadherin in lung tissue only in extrapulmonary acute respiratory distress syndrome, thus suggesting lower damage to epithelial cells.

Variable Ventilation Improved Respiratory System Mechanics and Ameliorated Pulmonary Damage in a Rat Model of Lung Ischemia-Reperfusion

Lung ischemia-reperfusion injury remains a major complication after lung transplantation. Variable ventilation (VV) has been shown to improve respiratory function and reduce pulmonary histological damage compared to protective volume-controlled ventilation (VCV) in different models of lung injury induced by endotoxin, surfactant depletion by saline lavage, and hydrochloric acid. However, no study has compared the biological impact of VV vs. VCV in lung ischemia-reperfusion injury, which has a complex pathophysiology different from that of other experimental models. Thirty-six animals were randomly assigned to one of two groups: (1) ischemia-reperfusion (IR), in which the left pulmonary hilum was completely occluded and released after 30 min; and (2) Sham, in which animals underwent the same surgical manipulation but without hilar clamping. Immediately after surgery, the left (IR-injured) and right (contralateral) lungs from 6 animals per group were removed, and served as non-ventilated group (NV) for molecular biology analysis. IR and Sham groups were further randomized to one of two ventilation strategies: VCV (n = 6/group) [tidal volume (V_T) = 6 mL/kg, positive end-expiratory pressure (PEEP) = 2 cmH₂O, fraction of inspired oxygen (FiO₂) = 0.4]; or VV, which was applied on a breath-to-breath basis as a sequence of randomly generated V_T values (n = 1200; mean V_T = 6 mL/kg), with a 30% coefficient of variation. After 5 min of ventilation and at the end of a 2-h period (Final), respiratory system mechanics and arterial blood gases were measured. At Final, lungs were removed for histological and molecular biology analyses. Respiratory system elastance and alveolar collapse were lower in VCV than VV (mean ± SD, VCV 3.6 ± 1.3 cmH₂0/ml and 2.0 ± 0.8 cmH₂0/ml, p = 0.005; median [interquartile range], VCV 20.4% [7.9–33.1] and VV 5.4% [3.1–8.8], p = 0.04, respectively). In left lungs of IR animals, VCV increased the expression of interleukin-6 and intercellular adhesion molecule-1 compared to NV, with no significant differences between VV and NV. Compared to VCV, VV increased the expression of surfactant protein-D, suggesting protection from type II epithelial cell damage. In conclusion, in this experimental lung ischemia-reperfusion model, VV improved respiratory system elastance and reduced lung damage compared to VCV.

Distensibility index of the inferior vena cava in experimental acute respiratory distress syndrome

We determined the accuracy of distensibility index of inferior vena cava (dIVC) for evaluation of fluid responsiveness in rats with acute respiratory distress syndrome (ARDS) and validated this index for use in rat models. In protocol 1, E. coli lipopolysaccharide was administered in Wistar rats (n=7). After 24h, animals were mechanically ventilated, and stroke volume (SV) and dIVC quantified after blood drainage and subsequent volume expansion (albumin 20%). A receiver operating characteristic (ROC) curve was plotted to determine the optimal dIVC cutoff. In protocol 2, rats (n=10) were divided into fluid-responders (SV increase >5%) and nonresponders (SV increase <5%). The dIVC cutoff obtained from protocol 1 was 25%. Fluid responders had a 2.5 relative risk of low dIVC (<25%). The sensitivity, specificity, positive predictive, and negative predictive values for dIVC were 74%, 62%, 59%, and 76%, respectively. In conclusion, a dIVC threshold <25% was associated with positive response after volume expansion and could be used to titrate fluids in endotoxin-induced ARDS.

Emphysema induced by elastase enhances acute inflammatory pulmonary response to intraperitoneal LPS in rats

Abnormalities in lungs caused by emphysema might alter their response to sepsis and the occurrence of acute lung injury (ALI). This study compared the extension of ALI in response to intraperitoneal lipopolysaccharide (LPS) injection in Wistar rats with and without emphysema induced by elastase. Adult male Wistar rats were randomized into four groups: control, emphysema without sepsis, normal lung with sepsis and emphysema with sepsis. Sepsis was induced, and 24 h later the rats were euthanised. The following analysis was performed: blood gas measurements, bronchoalveolar lavage (BAL), lung permeability and histology. Animals that received LPS showed significant increase in a lung injury scoring system, inflammatory cells in bronchoalveolar lavage (BAL) and IL-6, TNF-α and CXCL2 mRNA expression in lung tissue. Animals with emphysema and sepsis showed increased alveolocapillary membrane permeability, demonstrated by higher BAL/serum albumin ratio. In conclusion, the presence of emphysema induced by elastase increases the inflammatory response in the lungs to a systemic stimulus, represented in this model by the intraperitoneal injection of LPS.

Variable ventilation improves pulmonary function and reduces lung damage without increasing bacterial translocation in a rat model of experimental pneumonia

Background

Variable ventilation has been shown to improve pulmonary function and reduce lung damage in different models of acute respiratory distress syndrome. Nevertheless, variable ventilation has not been tested during pneumonia. Theoretically, periodic increases in tidal volume (V_T) and airway pressures might worsen the impairment of alveolar barrier function usually seen in pneumonia and could increase bacterial translocation into the bloodstream. We investigated the impact of variable ventilation on lung function and histologic damage, as well as markers of lung inflammation, epithelial and endothelial cell damage, and alveolar stress, and bacterial translocation in experimental pneumonia.

Methods

Thirty-two Wistar rats were randomly assigned to receive intratracheal of Pseudomonas aeruginosa (PA) or saline (SAL) (n = 16/group). After 24-h, animals were anesthetized and ventilated for 2 h with either conventional volume-controlled (VCV) or variable volume-controlled ventilation (VV), with mean V_T = 6 mL/kg, PEEP = 5cmH₂O, and FiO₂ = 0.4. During VV, tidal volume varied randomly with a coefficient of variation of 30% and a Gaussian distribution. Additional animals assigned to receive either PA or SAL (n = 8/group) were not ventilated (NV) to serve as controls.

Results

In both SAL and PA, VV improved oxygenation and lung elastance compared to VCV. In SAL, VV decreased interleukin (IL)-6 expression compared to VCV (median [interquartile range]: 1.3 [0.3–2.3] vs. 5.3 [3.6–7.0]; p = 0.02) and increased surfactant protein-D expression compared to NV (2.5 [1.9–3.5] vs. 1.2 [0.8–1.2]; p = 0.0005). In PA, compared to VCV, VV reduced perivascular edema (2.5 [2.0–3.75] vs. 6.0 [4.5–6.0]; p < 0.0001), septum neutrophils (2.0 [1.0–4.0] vs. 5.0 [3.3–6.0]; p = 0.0008), necrotizing vasculitis (3.0 [2.0–5.5] vs. 6.0 [6.0–6.0]; p = 0.0003), and ultrastructural lung damage scores (16 [14–17] vs. 24 [14–27], p < 0.0001). Blood colony-forming-unit (CFU) counts were comparable (7 [0–28] vs. 6 [0–26], p = 0.77). Compared to NV, VCV, but not VV, increased expression amphiregulin, IL-6, and cytokine-induced neutrophil chemoattractant (CINC)-1 (2.1 [1.6–2.5] vs. 0.9 [0.7–1.2], p = 0.025; 12.3 [7.9–22.0] vs. 0.8 [0.6–1.9], p = 0.006; and 4.4 [2.9–5.6] vs. 0.9 [0.8–1.4], p = 0.003, respectively). Angiopoietin-2 expression was lower in VV compared to NV animals (0.5 [0.3–0.8] vs. 1.3 [1.0–1.5], p = 0.01).

Conclusion

In this rat model of pneumonia, VV improved pulmonary function and reduced lung damage as compared to VCV, without increasing bacterial translocation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-016-0476-7) contains supplementary material, which is available to authorized users.

Fast Versus Slow Recruitment Maneuver at Different Degrees of Acute Lung Inflammation Induced by Experimental Sepsis

BACKGROUND

Large tidal volume (VT) breaths or "recruitment maneuvers" (RMs) are used commonly to open collapsed lungs, but their effectiveness may depend on how the RM is delivered. We hypothesized that a stepped approach to RM delivery ("slow" RM) compared with a nonstepped ("fast" RM), when followed by decremental positive end-expiratory pressure (PEEP) titration to lowest dynamic elastance, would (1) yield a more homogeneous inflation of the lungs, thus reducing the PEEP obtained during post-RM titration; (2) produce less lung morphofunctional injury, regardless of the severity of sepsis-induced acute lung inflammation; and (3) result in less biological damage in severe, but not in moderate, acute lung inflammation.

METHODS

Sepsis was induced by cecal ligation and puncture surgery in 51 Wistar rats. After 48 hours, animals were anesthetized, mechanically ventilated (VT = 6 mL/kg), and stratified by PO2/fraction of inspired oxygen ratio into moderate (≥300) and severe (<300) acute lung inflammation groups. Each group was then subdivided randomly into 3 subgroups: (1) nonrecruited; (2) RM with continuous positive airway pressure (30 cm H2O for 30 seconds; CPAPRM or fast RM); and (3) RM with stepwise airway pressure increase (5 cm H2O/step, 8.5 seconds/step, 6 steps, 51 seconds; STEPRM or slow RM), with a maximum pressure hold for 10 seconds. All animals underwent decremental PEEP titration to determine the level of PEEP required to optimize dynamic compliance after RM and were then ventilated for 60 minutes with VT = 6 mL/kg, respiratory rate = 80 bpm, fraction of inspired oxygen = 0.4, and the newly adjusted PEEP for each animal. Respiratory mechanics, hemodynamics, and arterial blood gases were measured before and at the end of 60-minute mechanical ventilation. Lung histology and biological markers of inflammation and damage inflicted to endothelial cells were evaluated at the end of the 60-minute mechanical ventilation.

RESULTS

Respiratory system mean airway pressure was lower in STEPRM than that in CPAPRM. The total RM time was greater, and the RM rise angle was lower in STEPRM than that in CPAPRM. In both moderate and severe acute lung inflammation groups, STEPRM reduced total diffuse alveolar damage score compared with the score in nonrecruited rats. In moderate acute lung inflammation, STEPRM rats compared with CPAPRM rats had less endothelial cell damage and angiopoietin (Ang)-2 expression. In severe acute lung inflammation, STEPRM compared with CPAPRM reduced hyperinflation, endothelial cell damage, Ang-2, and intercellular adhesion molecule-1 expressions. RM rise angle correlated with Ang-2 expression.

CONCLUSIONS

Compared with CPAPRM, STEPRM reduced biological markers associated with endothelial cell damage and ultrastructural endothelial cell injury in both moderate and severe sepsis-induced acute lung inflammation.

Comparison between Variable and Conventional Volume-Controlled Ventilation on Cardiorespiratory Parameters in Experimental Emphysema

Emphysema is characterized by loss of lung tissue elasticity and destruction of structures supporting alveoli and capillaries. The impact of mechanical ventilation strategies on ventilator-induced lung injury (VILI) in emphysema is poorly defined. New ventilator strategies should be developed to minimize VILI in emphysema. The present study was divided into two protocols: (1) characterization of an elastase-induced emphysema model in rats and identification of the time point of greatest cardiorespiratory impairment, defined as a high specific lung elastance associated with large right ventricular end-diastolic area; and (2) comparison between variable (VV) and conventional volume-controlled ventilation (VCV) on lung mechanics and morphometry, biological markers, and cardiac function at that time point. In the first protocol, Wistar rats (n = 62) received saline (SAL) or porcine pancreatic elastase (ELA) intratracheally once weekly for 4 weeks, respectively. Evaluations were performed 1, 3, 5, or 8 weeks after the last intratracheal instillation of saline or elastase. After identifying the time point of greatest cardiorespiratory impairment, an additional 32 Wistar rats were randomized into the SAL and ELA groups and then ventilated with VV or VCV (n = 8/group) [tidal volume (V_T) = 6 mL/kg, positive end-expiratory pressure (PEEP) = 3 cmH₂O, fraction of inspired oxygen (FiO₂) = 0.4] for 2 h. VV was applied on a breath-to-breath basis as a sequence of randomly generated V_T values (mean V_T = 6 mL/kg), with a 30% coefficient of variation. Non-ventilated (NV) SAL and ELA animals were used for molecular biology analysis. The time point of greatest cardiorespiratory impairment, was observed 5 weeks after the last elastase instillation. At this time point, interleukin (IL)-6, cytokine-induced neutrophil chemoattractant (CINC)-1, amphiregulin, angiopoietin (Ang)-2, and vascular endothelial growth factor (VEGF) mRNA levels were higher in ELA compared to SAL. In ELA animals, VV reduced respiratory system elastance, alveolar collapse, and hyperinflation compared to VCV, without significant differences in gas exchange, but increased right ventricular diastolic area. Interleukin-6 mRNA expression was higher in VCV and VV than NV, while surfactant protein-D was increased in VV compared to NV. In conclusion, VV improved lung function and morphology and reduced VILI, but impaired right cardiac function in this model of elastase induced-emphysema.

Recruitment maneuvers in acute respiratory distress syndrome: The safe way is the best way

Acute respiratory distress syndrome (ARDS) represents a serious problem in critically ill patients and is associated with in-hospital mortality rates of 33%-52%. Recruitment maneuvers (RMs) are a simple, low-cost, feasible intervention that can be performed at the bedside in patients with ARDS. RMs are characterized by the application of airway pressure to increase transpulmonary pressure transiently. Once non-aerated lung units are reopened, improvements are observed in respiratory system mechanics, alveolar reaeration on computed tomography, and improvements in gas exchange (functional recruitment). However, the reopening process could lead to vascular compression, which can be associated with overinflation, and gas exchange may not improve as expected (anatomical recruitment). The purpose of this review was to discuss the effects of different RM strategies - sustained inflation, intermittent sighs, and stepwise increases of positive end-expiratory pressure (PEEP) and/or airway inspiratory pressure - on the following parameters: hemodynamics, oxygenation, barotrauma episodes, and lung recruitability through physiological variables and imaging techniques. RMs and PEEP titration are interdependent events for the success of ventilatory management. PEEP should be adjusted on the basis of respiratory system mechanics and oxygenation. Recent systematic reviews and meta-analyses suggest that RMs are associated with lower mortality in patients with ARDS. However, the optimal RM method (i.e., that providing the best balance of benefit and harm) and the effects of RMs on clinical outcome are still under discussion, and further evidence is needed.

Lung Injury After One-Lung Ventilation: A Review of the Pathophysiologic Mechanisms Affecting the Ventilated and the Collapsed Lung

Lung injury is the leading cause of death after thoracic surgery. Initially recognized after pneumonectomy, it has since been described after any period of 1-lung ventilation (OLV), even in the absence of lung resection. Overhydration and high tidal volumes were thought to be responsible at various points; however, it is now recognized that the pathophysiology is more complex and multifactorial. All causative mechanisms known to trigger ventilator-induced lung injury have been described in the OLV setting. The ventilated lung is exposed to high strain secondary to large, nonphysiologic tidal volumes and loss of the normal functional residual capacity. In addition, the ventilated lung experiences oxidative stress, as well as capillary shear stress because of hyperperfusion. Surgical manipulation and/or resection of the collapsed lung may induce lung injury. Re-expansion of the collapsed lung at the conclusion of OLV invariably induces duration-dependent, ischemia-reperfusion injury. Inflammatory cytokines are released in response to localized injury and may promote local and contralateral lung injury. Protective ventilation and volatile anesthesia lessen the degree of injury; however, increases in biochemical and histologic markers of lung injury appear unavoidable. The endothelial glycocalyx may represent a common pathway for lung injury creation during OLV, because it is damaged by most of the recognized lung injurious mechanisms. Experimental therapies to stabilize the endothelial glycocalyx may afford the ability to reduce lung injury in the future. In the interim, protective ventilation with tidal volumes of 4 to 5 mL/kg predicted body weight, positive end-expiratory pressure of 5 to 10 cm H2O, and routine lung recruitment should be used during OLV in an attempt to minimize harmful lung stress and strain. Additional strategies to reduce lung injury include routine volatile anesthesia and efforts to minimize OLV duration and hyperoxia.

Impact of Chest Wall Modifications and Lung Injury on the Correspondence Between Airway and Transpulmonary Driving Pressures

OBJECTIVE

Recent interest has arisen in airway driving pressure (DP(AW)), the quotient of tidal volume (V(T)), and respiratory system compliance (C(RS)), which could serve as a direct and easily measured marker for ventilator-induced lung injury risk. We aimed to test the correspondence between DP(AW) and transpulmonary driving pressure (DP(TP))-the quotient of V(T) and lung compliance (C(L)), in response to intra-abdominal hypertension and changes in positive end-expiratory pressure during different models of lung pathology.

DESIGN

Well-controlled experimental setting that allowed reversible modification of chest wall compliance (C(CW)) in a variety of models of lung pathology.

SETTING

Large animal laboratory of a university-affiliated hospital.

SUBJECTS

Ten deeply anesthetized swine.

INTERVENTIONS

Application of intra-abdominal pressures of 0 and 20 cm H2O at positive end-expiratory pressure of 1 and 10 cm H2O, under volume-controlled mechanical ventilation in the settings of normal lungs (baseline), unilateral whole-lung atelectasis, and unilateral and bilateral lung injuries caused by saline lavage.

MEASUREMENTS AND MAIN RESULTS

Pulmonary mechanics including esophageal pressure and calculations of DP(AW), DP(TP), C(RS), C(L), and C(CW). When compared with normal intra-abdominal pressures, intra-abdominal hypertension increased DP(AW), during both "normal lung conditions" (p < 0.0001) and "unilateral atelectasis" (p = 0.0026). In contrast, DP(TP) remained virtually unaffected by changes in positive end-expiratory pressure or intra-abdominal pressures in both conditions. During unilateral lung injury, both DPA(W) and DP(TP) were increased by the presence of intra-abdominal hypertension (p < 0.0001 and p = 0.0222, respectively). During bilateral lung injury, intra-abdominal hypertension increased both DP(AW) (at positive end-expiratory pressure of 1 cm H2O, p < 0.0001; and at positive end-expiratory pressure of 10 cm H2O, p = 0.0091) and DP(TP) (at positive end-expiratory pressure of 1 cm H2O, p = 0.0510; and at positive end-expiratory pressure of 10 cm H2O, p = 0.0335).

CONCLUSIONS

Our data indicate that DP(AW) is influenced by reductions in chest wall compliance and by underlying lung properties. As with other measures of pulmonary mechanics that are based on unmodified P(AW), caution is advised in attempting to attribute hazard or safety to any specific absolute value of DP(AW).

The effects of lung recruitment maneuvers on exhaled breath condensate pH

Exhaled breath condensate (EBC) pH serves as a surrogate marker of airway lining fluid (ALF) pH and can be used to evaluate airway acidification (AA). AA is known to be present in acute respiratory distress syndrome (ARDS) and can be evaluated via continuous EBC pH measurement during mechanical ventilation. Lung recruitment maneuvers (LRMs) are utilized in the treatment of ARDS, however, their impact on EBC pH has never been explored. Here we described the acute effects of two commonly used LRMs on EBC pH. In a prospective, non-randomized, serial exposure study, 10 intubated pediatric subjects with acute respiratory distress syndrome sequentially underwent: a period of baseline ventilation, sustained inflation (SI) maneuver of 40 cm H2O for 40 s, open lung ventilation, staircase recruitment strategy (SRS) (which involves a systematic ramping of plateau pressures in 5 cm H2O increments, starting at 30 cm H2O), and PEEP titration. Maximum lung recruitment during the SRS is defined as a PaO2 + PaCO2 of  >400 mmHg. Following lung recruitment, PEEP titration was conducted from 20 cm H2O in 2 cm H2O decrements until a PaO2 + PaCO2 was  <380 and then increased by 2 cm H2O. EBC pH, arterial blood gases, lung mechanics, hemodynamics, and function residual capacity were obtained following each phase of the LRM and observational period. Seven out of 10 patients were able to reach maximum lung recruitment. Baseline EBC pH (6.38   ±   0.37) did not correlate with disease severity defined by PaO2/FiO2 ratio or oxygenation index (OI). Average EBC pH differed between phases and decreased after LRM (p = 0.001). EBC pH is affected by LRMs. EBC acidification following LRMs may represent a washout effect of opening acidic lung units and ventilating them or acute AA resulting from LRM.

FG-4497: a new target for acute respiratory distress syndrome?

The morbidity and mortality rates associated with acute respiratory distress syndrome (ARDS) remain high and the development of new therapeutic strategies is urgently required. Some pharmacological treatments, proposed or under evaluation for ARDS, seek to protect the endothelium and consequently mitigate fluid extravasation into the alveolar space. FG-4497 is a new compound which acts as a prolyl hydroxylase domain 2 inhibitor and mimics hypoxia in the activation of hypoxia-inducible factor-2α signaling, decreasing VE-cadherin phosphorylation and thus promoting integrity of adherens junctions. In this special report, we discuss the pharmacological characteristics of FG-4497, its effect on lung parenchyma and other organs and future perspectives in ARDS. In short, FG-4497 may be considered a novel pharmacological option targeting endothelial cell repair in lung diseases such as ARDS. Further experimental and clinical studies are warranted to better understand the mechanisms of action of FG-4497 in different types of lung injury.

Pulmonar recruitment in acute respiratory distress syndrome. What is the best strategy?

Supporting patients with acute respiratory distress syndrome (ARDS), using a protective mechanical ventilation strategy characterized by low tidal volume and limitation of positive end-expiratory pressure (PEEP) is a standard practice in the intensive care unit. However, these strategies can promote lung de-recruitment, leading to the cyclic closing and reopening of collapsed alveoli and small airways. Recruitment maneuvers (RM) can be used to augment other methods, like positive end-expiratory pressure and positioning, to improve aerated lung volume. Clinical practice varies widely, and the optimal method and patient selection for recruitment maneuvers have not been determined, considerable uncertainty remaining regarding the appropriateness of RM. This review aims to discuss recent findings about the available types of RM, and compare the effectiveness, indications and adverse effects among them, as well as their impact on morbidity and mortality in ARDS patients. Recent developments include experimental and clinical evidence that a stepwise extended recruitment maneuver may cause an improvement in aerated lung volume and decrease the biological impact seen with the traditionally used sustained inflation, with less adverse effects. Prone positioning can reduce mortality in severe ARDS patients and may be an useful adjunct to recruitment maneuvers and advanced ventilatory strategies, such noisy ventilation and BIVENT, which have been useful in providing lung recruitment.

Effects of a recruitment maneuver on plasma levels of soluble RAGE in patients with diffuse acute respiratory distress syndrome: a prospective randomized crossover study

PURPOSE

The soluble form of the receptor for advanced glycation end-products (sRAGE) is a promising marker for epithelial dysfunction, but it has not been fully characterized as a biomarker of acute respiratory distress syndrome (ARDS). Whether sRAGE could inform on the response to ventilator settings has been poorly investigated, and whether a recruitment maneuver (RM) may influence plasma sRAGE remains unknown.

METHODS

Twenty-four patients with moderate/severe, nonfocal ARDS were enrolled in this prospective monocentric crossover study and randomized into a "RM-SHAM" group when a 6-h-long RM sequence preceded a 6-h-long sham evaluation period, or a "SHAM-RM" group (inverted sequences). Protective ventilation was applied, and RM consisted of the application of 40 cmH2O airway pressure for 40 s. Arterial blood was sampled for gas analyses and sRAGE measurements, 5 min pre-RM (or 40-s-long sham period), 5, 30 min, 1, 4, and 6 h after the RM (or 40-s-long sham period).

RESULTS

Mean PaO2/FiO2, tidal volume, PEEP, and plateau pressure were 125 mmHg, 6.8 ml/kg (ideal body weight), and 13 and 26 cmH2O, respectively. Median baseline plasma sRAGE levels were 3,232 pg/ml. RM induced a significant decrease in sRAGE (-1,598 ± 859 pg/ml) in 1 h (p = 0.043). At 4 and 6 h post-RM, sRAGE levels increased back toward baseline values. Pre-RM sRAGE was associated with RM-induced oxygenation improvement (AUC 0.84).

CONCLUSIONS

We report the first kinetics study of plasma sRAGE after RM in ARDS. Our findings reinforce the value of plasma sRAGE as a biomarker of ARDS.

Advances in ventilator-associated lung injury: prevention is the target

Mechanical ventilation (MV) is the main supportive treatment in respiratory failure due to different etiologies. However, MV might aggravate ventilator-associated lung injury (VALI). Four main mechanisms leading to VALI are: 1) increased stress and strain, induced by high tidal volume (VT); 2) increased shear stress, i.e. opening and closing, of previously atelectatic alveolar units; 3) distribution of perfusion and 4) biotrauma. In severe acute respiratory distress syndrome patients, low VT, higher levels of positive end expiratory pressure, long duration prone position and neuromuscular blockade within the first 48 hours are associated to a better outcome. VALI can also occur by using high VT in previously non injured lungs. We believe that prevention is the target to minimize injurious effects of MV. This review aims to describe pathophysiology of VALI, the possible prevention and treatment as well as monitoring MV to minimize VALI.

Effects of sigh during pressure control and pressure support ventilation in pulmonary and extrapulmonary mild acute lung injury

INTRODUCTION

Sigh improves oxygenation and lung mechanics during pressure control ventilation (PCV) and pressure support ventilation (PSV) in patients with acute respiratory distress syndrome. However, so far, no study has evaluated the biological impact of sigh during PCV or PSV on the lung and distal organs in experimental pulmonary (p) and extrapulmonary (exp) mild acute lung injury (ALI).

METHODS

In 48 Wistar rats, ALI was induced by Escherichia coli lipopolysaccharide either intratracheally (ALIp) or intraperitoneally (ALIexp). After 24 hours, animals were anesthetized and mechanically ventilated with PCV or PSV with a tidal volume of 6 mL/kg, FiO2 = 0.4, and PEEP = 5 cmH2O for 1 hour. Both ventilator strategies were then randomly assigned to receive periodic sighs (10 sighs/hour, Sigh) or not (non-Sigh, NS). Ventilatory and mechanical parameters, arterial blood gases, lung histology, interleukin (IL)-1β, IL-6, caspase-3, and type III procollagen (PCIII) mRNA expression in lung tissue, and number of apoptotic cells in lung, liver, and kidney specimens were analyzed.

RESULTS

In both ALI etiologies: (1) PCV-Sigh and PSV-Sigh reduced transpulmonary pressure, and (2) PSV-Sigh reduced the respiratory drive compared to PSV-NS. In ALIp: (1) PCV-Sigh and PSV-Sigh decreased alveolar collapse as well as IL-1β, IL-6, caspase-3, and PCIII expressions in lung tissue, (2) PCV-Sigh increased alveolar-capillary membrane and endothelial cell damage, and (3) abnormal myofibril with Z-disk edema was greater in PCV-NS than PSV-NS. In ALIexp: (1) PSV-Sigh reduced alveolar collapse, but led to damage to alveolar-capillary membrane, as well as type II epithelial and endothelial cells, (2) PCV-Sigh and PSV-Sigh increased IL-1β, IL-6, caspase-3, and PCIII expressions, and (3) PCV-Sigh increased the number of apoptotic cells in the lung compared to PCV-NS.

CONCLUSIONS

In these models of mild ALIp and ALIexp, sigh reduced alveolar collapse and transpulmonary pressures during both PCV and PSV; however, improved lung protection only during PSV in ALIp.

The biological effects of higher and lower positive end-expiratory pressure in pulmonary and extrapulmonary acute lung injury with intra-abdominal hypertension

Introduction

Mechanical ventilation with high positive end-expiratory pressure (PEEP) has been used in patients with acute respiratory distress syndrome (ARDS) and intra-abdominal hypertension (IAH), but the role of PEEP in minimizing lung injury remains controversial. We hypothesized that in the presence of acute lung injury (ALI) with IAH: 1) higher PEEP levels improve pulmonary morphofunction and minimize lung injury; and 2) the biological effects of higher PEEP are more effective in extrapulmonary (exp) than pulmonary (p) ALI.

Methods

In 48 adult male Wistar rats, ALIp and ALIexp were induced by Escherichia coli lipopolysaccharide intratracheally and intraperitoneally, respectively. After 24 hours, animals were anesthetized and mechanically ventilated (tidal volume of 6 mL/kg). IAH (15 mmHg) was induced and rats randomly assigned to PEEP of 5 (PEEP5), 7 (PEEP7) or 10 (PEEP10) cmH₂O for 1 hour.

Results

In both ALIp and ALIexp, higher PEEP levels improved oxygenation. PEEP10 increased alveolar hyperinflation and epithelial cell damage compared to PEEP5, independent of ALI etiology. In ALIp, PEEP7 and PEEP10 increased lung elastance compared to PEEP5 (4.3 ± 0.7 and 4.3 ± 0.9 versus 3.1 ± 0.3 cmH₂O/mL, respectively, P <0.01), without changes in alveolar collapse, interleukin-6, caspase-3, type III procollagen, receptor for advanced glycation end-products, and vascular cell adhesion molecule-1 expressions. Moreover, PEEP10 increased diaphragmatic injury compared to PEEP5. In ALIexp, PEEP7 decreased lung elastance and alveolar collapse compared to PEEP5 (2.3 ± 0.5 versus 3.6 ± 0.7 cmH₂O/mL, P <0.02, and 27.2 (24.7 to 36.8) versus 44.2 (39.7 to 56.9)%, P <0.05, respectively), while PEEP7 and PEEP10 increased interleukin-6 and type III procollagen expressions, as well as type II epithelial cell damage compared to PEEP5.

Conclusions

In the current models of ALI with IAH, in contrast to our primary hypothesis, higher PEEP is more effective in ALIp than ALIexp as demonstrated by the activation of biological markers. Therefore, higher PEEP should be used cautiously in the presence of IAH and ALI, mainly in ALIexp.