Effects of PEEP levels following repeated recruitment maneuvers on ventilator-induced lung injury

Roles of alpha-7 nicotinic acetylcholine receptors and spleen in the lung injury induced by a repeated saline lavage in rat

BACKGROUND

The study aimed to determine whether or notα7 nicotinic acetylcholine receptors (α7nAChR) induce anti-inflammatory effects directly in the lung or through the spleen pathway in a sterile model of lung injury by saline lavage.

METHODS

Male Sprague Dawley rats were divided into seven groups; Sham, splenectomy (SPX), saline lavage (LAV), LAV treated with α7nAChR agonist nicotine (LAV + NIC), and LAV treated with NIC and a selective α7nAChR antagonist MLA (LAV+MLA+NIC), LAV and splenectomy (LAV+SPX), and LAV+SPX treated with nicotine (LAV+SPX+NIC). Tracheostomy and catheterization of the femoral artery were performed under deep anesthesia. Animals were subjected to volume-controlled ventilation and lung injury by 10 repeated saline lavages. Splenectomy was achieved one week before the induction of lung injury. The recovery phase lasted for 3 h, and drugs were injected 1 h after the last lavage.

RESULTS

Mean arterial blood pressure (MBP), heart rate (HR), PaO₂, PaO₂/FiO₂ ratio, and pH decreased, whereas, maximal inspiratory (MIP) and expiratory (MEP) pressures, and PaCO₂ increased 1 h after the saline lavage. Nicotine corrected entirely all the above parameters in the LAV + NIC group. MLA or SPX prevented the effects of nicotine on the above parameters, except that MLA had no extra effect on MIP or MEP. In addition, nicotine improved lung compliance in the LAV + NIC and LAV + SPX + NIC groups, though it was inhibited by MLA in the LAV + MLA + NIC group. The increases of plasma and lung tissue malondialdehyde (MDA) in the LAV group were diminished by nicotine, whereas, MLA and SPX prevented these reductions. Besides, nicotine could reduce plasma MDA in the LAV + SPX + NIC group. Total BAL cell count, protein BAL/protein plasma ratio, and lung histological scores were attenuated by nicotine in the LAV + NIC group, whereas, MLA reversed the mentioned alterations in the LAV + MLA + NIC group. However, splenectomy could not stop the decreasing effect of nicotine on the total BAL cell in the LAV + SPX + NIC group.

CONCLUSIONS

In this study, we indicated that α7nAChR and spleen play roles in cholinergic anti-inflammatory pathways in saline lavage-induced lung injury. However, our results are in favor of at least some direct effects of α 7nAChR in the lung.

Comparison of Up-Front Minimally Invasive Esophagectomy versus Open Esophagectomy on Quality of Life for Esophageal Squamous Cell Cancer

This study investigates whether minimally invasive esophagectomy (MIE) is a safe and effective way for patients with resectable esophageal cancer by comparing the short-term quality of life (QOL) after minimally invasive esophagectomy and open esophagectomy (OE). A total number of 104 patients who underwent esophagectomy from January 2013 to March 2014 were enrolled in this study. These patients were divided into two groups (MIE and OE group). Three scoring scales of quality of life were used to evaluate QOL before the operation and at the first, third, sixth and twelfth months after MIE or OE, which consist of Karnofshy performance scale (KPS), the European Organization for Research and Treatment questionnaire QLQC-30 (EORTC QLQC-30) and esophageal cancer supplement scale (OES-18). The MIE group was higher than the OE group in one-year survival rate (92.54% vs. 72.00%). Significant differences between the two groups were observed in intraoperative bleeding volume (158.53 ± 91.07 mL vs. 228.97 ± 109.33 mL, p = 0.001), and the incidence of postoperative pneumonia (33.33% vs. 58.62%, p = 0.018). The KPS of MIE group was significantly higher than the OE group at the first (80 vs. 70, p = 0.004 < 0.05), third (90 vs. 80, p = 0.006 < 0.05), sixth (90 vs. 80, p = 0.007 < 0.05) and twelfth months (90 vs. 80, p = 0.004 < 0.05) after surgery. The QLQC-30 score of MIE group was better than OE group at first and twelfth months after the operation. The OES-18 score of MIE group was significantly better than OE group at first, sixth and twelfth months after surgery. The short-term quality of life in MIE group was better than OE group.

Lung injury in brain ischemia/reperfusion is exacerbated by mechanical ventilation with moderate tidal volume in rats

Ischemic stroke is one of the most frequent causes of injury in the central nervous system which may lead to multiorgan dysfunction, including in the lung. The aim of this study was to investigate whether brain ischemia/reperfusion with or without mechanical ventilation leads to lung injury. Male Sprague-Dawley rats were assigned to four groups: Sham, 1-h brain ischemia (MCAO)/24-h reperfusion (I/R), mechanical ventilation with moderate tidal volume (MTV), and I/R+MTV. The pulmonary capillary permeability (K_fc) was measured in the isolated perfused lung. Mean arterial blood pressure (MAP), heart rate (HR), blood-gas variables, histopathological parameters, lung glutathione peroxidase, and TNF-α were measured. K_fc in the I/R, MTV, and I/R+MTV groups were higher than that in the Sham group. In the I/R, MTV, and I/R+MTV groups, arterial partial pressures of oxygen and the arterial partial pressure of oxygen/fraction of inspired oxygen ratios were lower, whereas arterial partial pressures of carbon dioxide were higher than those in the Sham group. The histopathological score in the I/R group was more than that in the Sham group, and in the MTV and I/R+MTV groups were higher than those in the Sham and I/R groups. Furthermore, there were stepwise rises in TNF-α in the I/R, MTV, and I/R+MTV groups, respectively. There was no significant difference in MAP between groups. However, HR in the MTV group was higher than that in the Sham group. Brain ischemia/reperfusion leads to pulmonary capillary endothelial damage and the impairment of gas exchange in the alveolar-capillary barrier, which is exacerbated by mechanical ventilation with moderate tidal volume partially linked to inflammatory reactions.

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.

Dual effects of human neutrophil peptides in a mouse model of pneumonia and ventilator-induced lung injury

BACKGROUND

Pneumonia is a major cause of high morbidity and mortality in critically illness, and frequently requires support with mechanical ventilation. The latter can lead to ventilator-induced lung injury characterized by neutrophil infiltration. The cationic human neutrophil peptides (HNP) stored in neutrophils can kill microorganisms, but excessive amount of HNP released during phagocytosis may contribute to inflammatory responses and worsen lung injury. Based on our previous work, we hypothesized that blocking the cell surface purinergic receptor P2Y₆ will attenuate the HNP-induced inflammatory responses while maintaining their antimicrobial activity in pneumonia followed by mechanical ventilation.

METHODS

Plasma HNP levels were measured in patients with pneumonia who received mechanical ventilation and in healthy volunteers. FVB littermate control and HNP transgenic (HNP⁺) mice were randomized to receive P. aeruginosa intranasally. The P2Y₆ antagonist (MRS2578) or vehicle control was given after P. aeruginosa instillation. Additional mice underwent mechanical ventilation at either low pressure (LP) or high pressure (HP) ventilation 48 h after pneumonia, and were observed for 24 h.

RESULTS

Plasma HNP concentration increased in patients with pneumonia as compared to healthy subjects. The bacterial counts in the bronchoalveolar lavage fluid (BALF) were lower in HNP⁺ mice than in FVB mice 72 h after P. aeruginosa instillation. However, upon receiving HP ventilation, HNP⁺ mice had higher levels of cytokines and chemokines in BALF than FVB mice. These inflammatory responses were attenuated by the treatment with MRS2578 that did not affect the microbial effects of HNP.

CONCLUSIONS

HNP exerted dual effects by exhibiting antimicrobial activity in pneumonia alone condition while enhancing inflammatory responses in pneumonia followed by HP mechanical ventilation. Blocking P2Y₆ can attenuate the inflammation without affecting the antibacterial property of HNP. The P2Y₆ receptor may be a novel therapeutic target in attenuation of the leukocyte-mediated excessive host responses in inflammatory lung diseases.

Driving-pressure-independent protective effects of open lung approach against experimental acute respiratory distress syndrome

Background

The open lung approach (OLA) reportedly has lung-protective effects against acute respiratory distress syndrome (ARDS). Recently, lowering of the driving pressure (ΔP), rather than improvement in lung aeration per se, has come to be considered as the primary lung-protective mechanism of OLA. However, the driving pressure-independent protective effects of OLA have never been evaluated in experimental studies. We here evaluated whether OLA shows protective effects against experimental ARDS even when the ΔP is not lowered.

Methods

Lipopolysaccharide was intratracheally administered to rats to establish experimental ARDS. After 24 h, rats were mechanically ventilated and randomly allocated to the OLA or control group. In the OLA group, 5 cmH₂O positive end-expiratory pressure (PEEP) and recruitment maneuver (RM) were applied. Neither PEEP nor RM was applied to the rats in the control group. Dynamic ΔP was kept at 15 cmH₂O in both groups. After 6 h of mechanical ventilation, rats in both groups received RM to inflate reversible atelectasis of the lungs. Arterial blood gas analysis, lung computed tomography, histological evaluation, and comprehensive biochemical analysis were performed.

Results

OLA significantly improved lung aeration, arterial oxygenation, and gas exchange. Even after RM in both groups, the differences in these parameters between the two groups persisted, indicating that the atelectasis-induced respiratory dysfunction observed in the control group is not an easily reversible functional problem. Lung histological damage was severe in the dorsal dependent area in both groups, but was attenuated by OLA. White blood cell counts, protein concentrations, and tissue injury markers in the broncho-alveolar lavage fluid (BALF) were higher in the control than in the OLA group. Furthermore, levels of CXCL-7, a platelet-derived chemokine, were higher in the BALF from the control group, indicating that OLA protects the lungs by suppressing platelet activation.

Conclusions

OLA shows protective effects against experimental ARDS, even when the ΔP is not decreased. In addition to reducing ΔP, maintaining lung aeration seems to be important for lung protection in ARDS.

Electronic supplementary material

The online version of this article (10.1186/s13054-018-2154-2) contains supplementary material, which is available to authorized users.

Effects of positive end-expiratory pressure and recruitment maneuvers in a ventilator-induced injury mouse model

Background

Positive-pressure mechanical ventilation is an essential therapeutic intervention, yet it causes the clinical syndrome known as ventilator-induced lung injury. Various lung protective mechanical ventilation strategies have attempted to reduce or prevent ventilator-induced lung injury but few modalities have proven effective. A model that isolates the contribution of mechanical ventilation on the development of acute lung injury is needed to better understand biologic mechanisms that lead to ventilator-induced lung injury.

Objectives

To evaluate the effects of positive end-expiratory pressure and recruitment maneuvers in reducing lung injury in a ventilator-induced lung injury murine model in short- and longer-term ventilation.

Methods

5–12 week-old female BALB/c mice (n = 85) were anesthetized, placed on mechanical ventilation for either 2 hrs or 4 hrs with either low tidal volume (8 ml/kg) or high tidal volume (15 ml/kg) with or without positive end-expiratory pressure and recruitment maneuvers.

Results

Alteration of the alveolar-capillary barrier was noted at 2 hrs of high tidal volume ventilation. Standardized histology scores, influx of bronchoalveolar lavage albumin, proinflammatory cytokines, and absolute neutrophils were significantly higher in the high-tidal volume ventilation group at 4 hours of ventilation. Application of positive end-expiratory pressure resulted in significantly decreased standardized histology scores and bronchoalveolar absolute neutrophil counts at low- and high-tidal volume ventilation, respectively. Recruitment maneuvers were essential to maintain pulmonary compliance at both 2 and 4 hrs of ventilation.

Conclusions

Signs of ventilator-induced lung injury are evident soon after high tidal volume ventilation (as early as 2 hours) and lung injury worsens with longer-term ventilation (4 hrs). Application of positive end-expiratory pressure and recruitment maneuvers are protective against worsening VILI across all time points. Dynamic compliance can be used guide the frequency of recruitment maneuvers to help ameloriate ventilator-induced lung injury.

A double blind randomized experimental study on the use of IgM-enriched polyclonal immunoglobulins in an animal model of pneumonia developing shock

BACKGROUND

Patients with severe pneumonia often develop septic shock. IgM-enriched immunoglobulins have been proposed as a potential adjuvant therapy for septic shock. While in vitro data are available on the possible mechanisms of action of IgM-enriched immunoglobulins, the results of the in vivo experimental studies are non-univocal and, overall, unconvincing. We designed this double blinded randomized controlled study to test whether IgM-enriched immunoglobulins administered as rescue treatment in a pneumonia model developing shock, could either limit lung damage and/or contain systemic inflammatory response.

METHODS

Thirty-eight Sprague Dawley rats were ventilated with injurious ventilation for 30min to prime the lung. The rats were subsequently randomized to received intratracheal instillation of either lipopolysaccharide (LPS) (12mg/kg) or placebo followed by 3.5h of protective mechanical ventilation. IgM-enriched immunoglobulins at 25mg/h (0.5mL/h) or saline were intravenously administered in the last hour of mechanical ventilation. During the experiment, gas exchange and hemodynamic measurements were recorded. Thereafter, the animals were sacrificed, and blood and organs were stored for cytokines measurements.

RESULTS

Despite similar lung and hemodynamic findings, the administration of IgM-enriched immunoglobulins compared to placebo significantly modulates the inflammatory response by increasing IL-10 levels in the bloodstream and by decreasing TNF-α in bronchoalveolar lavage (BAL) fluid. Furthermore, in vitro data suggest that IgM-enriched immunoglobulins induce monocytes production of IL-10 after LPS stimulation.

CONCLUSIONS

In an in vivo model of pneumonia developing shock, IgM-enriched immunoglobulins administered as rescue treatment enhance the anti-inflammatory response by increasing blood levels of IL-10 and reducing TNF-α in BAL fluid.

High PEEP levels are associated with overdistension and tidal recruitment/derecruitment in ARDS patients

BACKGROUND

Positive end-expiratory pressure (PEEP) improves gas exchange and respiratory mechanics, and it may decrease tissue injury and inflammation. The mechanisms of this protective effect are not fully elucidated. Our aim was to determine the intrinsic effects of moderate and higher levels of PEEP on tidal recruitment/derecruitment, hyperinflation, and lung mechanics, in patients with acute respiratory distress syndrome (ARDS).

METHODS

Nine patients with ARDS of mainly pulmonary origin were ventilated sequential and randomly using two levels of PEEP: 9 and 15 cmH2 O, and studied with dynamic computed tomography at a fix transversal lung region. Tidal recruitment/derecruitment and hyperinflation were determined as non-aerated tissue and hyperinflated tissue variation between inspiration and expiration, expressed as percentage of total weight. We also assessed the maximal amount of non-aerated and hyperinflated tissue weight.

RESULTS

PEEP 15 cmH2 O was associated with decrease in non-aerated tissue in all the patients (P < 0.01). However, PEEP 15 cmH2 O did not decrease tidal recruitment/derecruitment compared to PEEP 9 cmH2 O (P = 1). In addition, PEEP 15 cmH2 O markedly increased maximal hyperinflation (P < 0.01) and tidal hyperinflation (P < 0.05). Lung compliance decreased with PEEP 15 cmH2 O (P < 0.001).

CONCLUSION

In this series of patients with ARDS of mainly pulmonary origin, application of high levels of PEEP did not decrease tidal recruitment/derecruitment, but instead consistently increased tidal and maximal hyperinflation.

Lung mechanical changes following bronchoaspiration in a porcine model: differentiation of direct and indirect mechanisms

Bronchoaspiration results in local deterioration of lung function through direct damage and/or indirect systemic effects related to neurohumoral pathways. We distinguished these effects by selectively intubating the two main bronchi in pigs while a PEEP of 4 or 10cm H2O was maintained. Gastric juice was instilled only into the right lung. Lung mechanical and ventilation defects were assessed by measuring unilateral pulmonary input impedance (ZL,s) and the third phase slope of the capnogram (SIII) for each lung side separately before the aspiration and for 120min thereafter. Marked transient elevations in ZL,s parameters and SIII were observed in the affected lung after aspiration. Elevating PEEP did not affect these responses in the ZL,s parameters, whereas it prevented the SIII increases. None of these indices changed in the intact left lung. These findings furnish evidence of the predominance of the local direct damage over the indirect systemic effects in the development of the deterioration of lung function, and demonstrate the benefit of an initially elevated PEEP following aspiration.

Recruitment Maneuver Does not Increase the Risk of Ventilator Induced Lung Injury

BACKGROUND

Mechanical ventilation (MV) may induce lung injury.

AIMS

To assess and evaluate the role of different mechanical ventilation strategies on ventilator-induced lung injury (VILI) in comparison to a strategy which includes recruitment manoeuvre (RM).

STUDY DESIGN

Randomized animal experiment.

METHODS

Thirty male Sprague-Dawley rats were anaesthetised, tracheostomised and divided into 5 groups randomly according to driving pressures; these were mechanically ventilated with following peak alveolar opening (Pao) and positive end-expiratory pressures (PEEP) for 1 hour: Group 15-0: 15 cmH2O Pao and 0 cmH2O PEEP; Group 30-10: 30 cmH2O Pao and 10 cmH2O PEEP; Group 30-5: 30 cmH2O Pao and 5 cmH2O PEEP; Group 30-5&RM: 30 cmH2O Pao and 5 cmH2O PEEP with additional 45 cmH2O CPAP for 30 seconds in every 15 minutes; Group 45-0: 45 cmH2O Pao and 0 cmH2O PEEP Before rats were sacrificed, blood samples were obtained for the evaluation of cytokine and chemokine levels; then, the lungs were subsequently processed for morphologic evaluation.

RESULTS

Oxygenation results were similar in all groups; however, the groups were lined as follows according to the increasing severity of morphometric evaluation parameters: Group 15-0: (0±0.009) < Group 30-10: (0±0.14) < Group 30-5&RM: (1±0.12) < Group 30-5: (1±0.16) < Group 45-0: (2±0.16). Besides, inflammatory responses were the lowest in 30-5&RM group compared to all other groups. TNF-α, IL-1β, IL-6, MCP-1 levels were significantly different between group 30-5&RM and group 15-0 vs. group 45-0 in each group.

CONCLUSION

RM with low PEEP reduces the risk of ventilator-induced lung injury with a lower release of systemic inflammatory mediators in response to mechanical ventilation.

Mechanical stress induces lung fibrosis by epithelial-mesenchymal transition

OBJECTIVES

Many mechanically ventilated patients with acute respiratory distress syndrome develop pulmonary fibrosis. Stresses induced by mechanical ventilation may explain the development of fibrosis by a number of mechanisms (e.g., damage the alveolar epithelium, biotrauma). The objective of this study was t test the hypothesis that mechanical ventilation plays an important role in the pathogenesis of lung fibrosis.

METHODS

C57BL/6 mice were randomized into four groups: healthy controls; hydrochloric acid aspiration alone; vehicle control solution followed 24 hrs later by mechanical ventilation (peak inspiratory pressure 22 cm H(2)O and positive end-expiratory pressure 2 cm H(2)O for 2 hrs); and acid aspiration followed 24 hrs later by mechanical ventilation. The animals were monitored for up to 15 days after acid aspiration. To explore the direct effects of mechanical stress on lung fibrotic formation, human lung epithelial cells (BEAS-2B) were exposed to mechanical stretch for up to 48 hrs.

MEASUREMENT AND MAIN RESULTS

Impaired lung mechanics after mechanical ventilation was associated with increased lung hydroxyproline content, and increased expression of transforming growth factor-β, β-catenin, and mesenchymal markers (α-smooth muscle actin and vimentin) at both the gene and protein levels. Expression of epithelial markers including cytokeratin-8, E-cadherin, and prosurfactant protein B decreased. Lung histology demonstrated fibrosis formation and potential epithelia-mesenchymal transition. In vitro direct mechanical stretch of BEAS-2B cells resulted in similar fibrotic and epithelia-mesenchymal transition formation.

CONCLUSIONS

Mechanical stress induces lung fibrosis, and epithelia-mesenchymal transition may play an important role in mediating the ventilator-induced lung fibrosis.

Influence of propofol and volatile anaesthetics on the inflammatory response in the ventilated lung

BACKGROUND

The immunomodulatory effects of volatile anaesthetics in vitro and the protective effect of propofol in lung injury spurred us to study the effects of volatile anaesthetics and propofol on lung tissue in vivo.

METHODS

Twenty-seven pigs were randomized to 4-h general anaesthesia with propofol (8 mg/kg/h, group P, n=9), sevoflurane [minimum alveolar concentration (MAC)=1.0, group S, n=9) or desflurane (MAC=1.0, group D, n=9). Four healthy animals served as the no-ventilation group. Bronchoalveolar lavage fluid (BALF) was obtained to measure the cell counts, platelet-activating factor acetylhydrolase (PAF-AcH), phospholipase A(2) (PLA(2)) and superoxide dismutase (SOD) activity. Lung tissues were evaluated histologically and for caspase-3 expression.

RESULTS

Volatile anaesthetics reduced PAF-AcH levels without affecting PLA(2) activity and resulted in decreased alveolar macrophage and increased lymphocyte counts in BALF (sevoflurane: 29 ± 23%; desflurane: 26 ± 6%, both P<0.05 compared with 4 ± 2% in the no-ventilation group). These findings were accompanied by atelectasis and inflammatory cells' infiltration in the inhalational anaesthetics groups. Also, sevoflurane reduced SOD activity and both sevoflurane and desflurane induced significant caspase-3 expression. In contrast, propofol resulted in a minor degree of inflammation and preserved BALF cells' composition without triggering apoptosis.

CONCLUSION

Halogenated anaesthetics seem to trigger an immune lymphocytic response in the lung, inducing significant apoptosis and impairment of PAF-AcH. In contrast, propofol preserves anti-inflammatory and anti-oxidant defences during mechanical ventilation, thus preventing the emergence of apoptosis.

Maintaining end-expiratory transpulmonary pressure prevents worsening of ventilator-induced lung injury caused by chest wall constriction in surfactant-depleted rats

OBJECTIVE

To see whether in acute lung injury 1) compression of the lungs caused by thoracoabdominal constriction degrades lung function and worsens ventilator-induced lung injury; and 2) maintaining end-expiratory transpulmonary pressure by increasing positive end-expiratory pressure reduces the deleterious effects of chest wall constriction.

DESIGN

Experimental study in rats.

SETTING

Physiology laboratory.

INTERVENTIONS

Acute lung injury was induced in three groups of nine rats by saline lavage. Nine animals immediately killed served as a control group. Group L had lavage only, group LC had the chest wall constricted with an elastic binder, and group LCP had the same chest constriction but with positive end-expiratory pressure raised to maintain end-expiratory transpulmonary pressure. After lavage, all groups were ventilated with the same pattern for 1½ hrs.

MEASUREMENTS AND MAIN RESULTS

Transpulmonary pressure, measured with an esophageal balloon catheter, lung volume changes, arterial blood gasses, and pH were assessed during mechanical ventilation. Lung wet-to-dry ratio, albumin, tumor necrosis factor-α, interleukin-1β, interleukin-6, interleukin-10, and macrophage inflammatory protein-2 in serum and bronchoalveolar lavage fluid and serum E-selectin and von Willebrand Factor were measured at the end of mechanical ventilation. Lavage caused hypoxemia and acidemia, increased lung resistance and elastance, and decreased end-expiratory lung volume. With prolonged mechanical ventilation, lung mechanics, hypoxemia, and wet-to-dry ratio were significantly worse in group LC. Proinflammatory cytokines except E-selectin were elevated in serum and bronchoalveolar lavage fluid in all groups with significantly greater levels of tumor necrosis factor-α, interleukin-1β, and interleukin-6 in group LC, which also exhibited significantly worse bronchiolar injury and greater heterogeneity of airspace expansion at a fixed transpulmonary pressure than other groups.

CONCLUSIONS

Chest wall constriction in acute lung injury reduces lung volume, worsens hypoxemia, and increases pulmonary edema, mechanical abnormalities, proinflammatory mediator release, and histologic signs of ventilator-induced lung injury. Maintaining end-expiratory transpulmonary pressure at preconstriction levels by adding positive end-expiratory pressure prevents these deleterious effects.

Esophageal pressures in acute lung injury: do they represent artifact or useful information about transpulmonary pressure, chest wall mechanics, and lung stress?

Acute lung injury can be worsened by inappropriate mechanical ventilation, and numerous experimental studies suggest that ventilator-induced lung injury is increased by excessive lung inflation at end inspiration or inadequate lung inflation at end expiration. Lung inflation depends not only on airway pressures from the ventilator but, also, pleural pressure within the chest wall. Although esophageal pressure (Pes) measurements are often used to estimate pleural pressures in healthy subjects and patients, they are widely mistrusted and rarely used in critical illness. To assess the credibility of Pes as an estimate of pleural pressure in critically ill patients, we compared Pes measurements in 48 patients with acute lung injury with simultaneously measured gastric and bladder pressures (Pga and P(blad)). End-expiratory Pes, Pga, and P(blad) were high and varied widely among patients, averaging 18.6 +/- 4.7, 18.4 +/- 5.6, and 19.3 +/- 7.8 cmH(2)O, respectively (mean +/- SD). End-expiratory Pes was correlated with Pga (P = 0.0004) and P(blad) (P = 0.0104) and unrelated to chest wall compliance. Pes-Pga differences were consistent with expected gravitational pressure gradients and transdiaphragmatic pressures. Transpulmonary pressure (airway pressure - Pes) was -2.8 +/- 4.9 cmH(2)O at end exhalation and 8.3 +/- 6.2 cmH(2)O at end inflation, values consistent with effects of mediastinal weight, gravitational gradients in pleural pressure, and airway closure at end exhalation. Lung parenchymal stress measured directly as end-inspiratory transpulmonary pressure was much less than stress inferred from the plateau airway pressures and lung and chest wall compliances. We suggest that Pes can be used to estimate transpulmonary pressures that are consistent with known physiology and can provide meaningful information, otherwise unavailable, in critically ill patients.

[Peri-operative atelectasis and alveolar recruitment manoeuvres]

Respiratory complications are a significant cause of post-operative morbidity and mortality. Peri-operative atelectasis, in particular, affects 90% of surgical patients and its effects can be prolonged, due to changes in respiratory mechanics, pulmonary circulation and hypoxaemia. Alveolar collapse is caused by certain predisposing factors, mainly by compression and absorption mechanisms. To prevent or treat these atelectasis several therapeutic strategies have been proposed, such as alveolar recruitment manoeuvres, which has become popular in the last few years. Its application in patients with alveolar collapse, but without a previous significant acute lung lesion, has some special features, therefore its use is not free of uncertainties and complications. This review describes the frequency, pathophysiology, importance and treatment of peri-operative atelectasis. Special attention is paid to treatment with recruitment manoeuvres, with the purpose of providing a basis for the their rational and appropriate use.

Lung volume recruitment maneuvers and respiratory system mechanics in mechanically ventilated mice

The study aim was to establish how recruitment maneuvers (RMs) influence lung mechanics and to determine whether RMs produce lung injury. Healthy BALB/c mice were allocated to receive positive end-expiratory pressure (PEEP) at 2 or 6 cmH(2)O and volume- (20 or 40 mL/kg) or pressure-controlled (25 cmH(2)O) RMs every 5 or 75 min for 150 min. The low-frequency forced oscillation technique was used to measure respiratory input impedance. Large RMs resulting in peak airway opening pressures (P(ao))>30 cmH(2)O did not increase inflammatory response or affect transcutaneous oxygen saturation but significantly lowered airway resistance, tissue damping and tissue elastance; the latter changes are likely associated with the bimodal pressure-volume behavior observed in mice. PEEP increase alone and application of RMs producing peak P(ao) below 25 cmH(2)O did not prevent or reverse changes in lung mechanics; whereas frequent application of substantial RMs on top of elevated PEEP levels produced stable lung mechanics without signs of lung injury.

Protective effects of adenosine A2A receptor agonist in ventilator-induced lung injury in rats

OBJECTIVES

Mechanical ventilation is associated with overwhelming inflammatory responses that are associated with ventilator-induced lung injury (VILI) in patients with acute respiratory distress syndrome. The activation of adenosine A2A receptors has been reported to attenuate inflammatory cascades.

HYPOTHESIS

The administration of A2A receptors agonist ameliorates VILI.

METHODS

Rats were subjected to hemorrhagic shock and resuscitation as a first hit to induce systemic inflammation. The animals randomly received the selective A2A receptor agonist CGS-21680 or a vehicle control in a blinded fashion at the onset of resuscitation phase. They were then randomized to receive mechanical ventilation as a second hit with a high tidal volume of 20 mL/kg and zero positive end-expiratory pressure, or a low tidal volume of 6 mL/kg with positive end-expiratory pressure of 5 cm H2O.

RESULTS

The administration of CGS-21680 attenuated lung injury as evidenced by a decrease in respiratory elastance, lung edema, lung injury scores, neutrophil recruitment in the lung, and production of inflammatory cytokines, compared with the vehicle-treated animals.

CONCLUSIONS

The selective A2A receptor agonist may have a place as a novel therapeutic approach in reducing VILI.

Update on one-lung ventilation: the use of continuous positive airway pressure ventilation and positive end-expiratory pressure ventilation--clinical application

PURPOSE OF REVIEW

The purpose of this review is to examine the evidence for and the clinical use of continuous positive airway pressure (CPAP) and positive end-expiratory pressure (PEEP) for the management of one-lung ventilation during thoracic surgery. CPAP and PEEP use are important as we are increasingly challenged with patients with less respiratory reserve and greater comorbidity leading to the need for greater clinical management and more interventions during one-lung ventilation for thoracic surgery to prevent perioperative complications.

RECENT FINDINGS

The focus of this article is on the most recent literature with selected classic articles. First, the supportive literature and rationale for application of PEEP, CPAP or both during thoracic surgery are reviewed, relative to the threats of hypoxemia, hyperoxia and mechanical lung injury. The second part of the article focuses on the clinical use of PEEP and CPAP. Algorithms for the application of CPAP and PEEP to patients both at risk and not at risk of acute lung injury are presented.

SUMMARY

CPAP and PEEP are useful not only to treat hypoxia and atelectasis as the consequence of one-lung ventilation, perhaps more importantly, also as part of a protective lung-ventilation strategy to ameliorate mechanical stress and prevent acute lung injury.

Hemodynamic effects of PEEP in a porcine model of HCl-induced mild acute lung injury

BACKGROUND

Positive end-expiratory pressure (PEEP) and sustained inspiratory insufflations (SI) during acute lung injury (ALI) are suggested to improve oxygenation and respiratory mechanics. We aimed to investigate the hemodynamic effects of PEEP with and without alveolar recruiting maneuver in a mild ALI model induced by inhalation of hydrochloric acid.

METHODS

Thirty-two pigs were randomly allocated into four groups (Control-PEEP, Control-SI, ALI-PEEP and ALI-SI). ALI was induced by intratracheal instillation of hydrochloric acid. PEEP values were progressively increased and decreased from 5, 10, 15 and 20 cmH2O in all groups. Three SIs maneuvers of 30 cmH2O for 20 s were applied to the assignable groups between each PEEP level. Transesophageal echocardiography (TEE), global hemodynamics, oxygenation indexes and gastric tonometry were measured 5 min after the maneuvers had been concluded and at each established value of PEEP (5, 10, 15 and 20 cmH2O).

RESULTS

The cardiac index, ejection fraction and end-diastolic volume of right ventricle were significantly (P < 0.001) decreased with PEEP in both Control and ALI groups. Left ventricle echocardiography showed a significant decrease in end-diastolic volume at 20 cmH2O of PEEP (P < 0.001). SIs did not exert any significant hemodynamic effects either early (after 5 min) or late (after 3 h).

CONCLUSIONS

In a mild ALI model induced by inhalation of hydrochloric acid, significant hemodynamic impairment characterized by cardiac function deterioration occurred during PEEP increment, but SI, probably due to low applied values (30 cmH2O), did not exert further negative hemodynamic effects. PEEP should be used cautiously in ALI caused by acid gastric content inhalation.