Injurious ventilatory strategies increase cytokines and c-fos m-RNA expression in an isolated rat lung model

Cytoskeleton and mechanotransduction in the pathophysiology of ventilator-induced lung injury

Although mechanical ventilation is an important therapy, it can result in complications. One major complication is ventilator-induced lung injury, which is caused by alveolar hyperdistension, leading to an inflammatory process, with neutrophilic infiltration, hyaline membrane formation, fibrogenesis and impaired gas exchange. In this process, cellular mechanotransduction of the overstretching stimulus is mediated by means of the cytoskeleton and its cell-cell and cell-extracellular matrix interactions, in such a way that the mechanical stimulus of ventilation is translated into an intracellular biochemical signal, inducing endothelial activation, pulmonary vascular permeability, leukocyte chemotaxis, cytokine production and, possibly, distal organ failure. Clinical studies have shown the relationship between pulmonary distension and mortality in patients with ventilator-induced lung injury. However, although the cytoskeleton plays a fundamental role in the pathogenesis of ventilator-induced lung injury, there have been few in vivo studies of alterations in the cytoskeleton and in cytoskeleton-associated proteins during this pathological process.

[Mechanotransduction and the bronchoalveolar epithelium]

The bronchoalveolar epithelium is submitted to numerous mechanical strains. These strains induce a specific cellular activity at the tissue level. This type of activation has been studied in respiratory medicine, mainly in the context of mechanical ventilation and asthma. The phenomenon of mechanotransduction is linked to various epithelial cellular activities such as epithelium repair, extracellular matrix remodelling, inflammatory mediator release and mucociliary regulation. In this review, the main studies related to bronchoalveolar epithelial mechanotransduction are reported to bring a new perspective on this little known biological phenomenon. A better understanding of the physiological and pathological aspects will potentially offer new treatment approaches for bronchial diseases.

Pulmonary-derived phosphoinositide 3-kinase gamma (PI3Kγ) contributes to ventilator-induced lung injury and edema

BACKGROUND

Ventilator-induced lung injury (VILI) occurs in part by increased vascular permeability and impaired alveolar fluid clearance. Phosphoinositide 3-kinase gamma (PI3Kγ) is activated by mechanical stress, induces nitric oxide (NO) production, and participates in cyclic adenosine monophosphate (cAMP) hydrolysis, each of which contributes to alveolar edema. We hypothesized that lungs lacking PI3Kγ or treated with PI3Kγ inhibitors would be protected from ventilation-induced alveolar edema and lung injury.

METHODS

Using an isolated and perfused lung model, wild-type (WT) and PI3Kγ-knockout (KO) mice underwent negative-pressure cycled ventilation at either -25 cmH₂O and 0 cmH₂O positive end-expiratory pressure (PEEP) (HIGH STRESS) or -10 cmH₂O and -3 cmH₂O PEEP (LOW STRESS).

RESULTS

Compared with WT, PI3Kγ-knockout mice lungs were partially protected from VILI-induced derangement of respiratory mechanics (lung elastance) and edema formation [bronchoalveolar lavage (BAL) protein concentration, wet/dry ratio, and lung histology]. In PI3Kγ-knockout mice, VILI induced significantly less phosphorylation of protein kinase B (Akt), endothelial nitric oxide synthase (eNOS), production of nitrate and nitrotyrosine, as well as hydrolysis of cAMP, compared with wild-type animals. PI3Kγ wild-type lungs treated with AS605240, an inhibitor of PI3Kγ kinase activity, in combination with enoximone, an inhibitor of phosphodiesterase-3 (PDE3)-induced cAMP hydrolysis, were protected from VILI at levels comparable to knockout lungs.

CONCLUSIONS

Phosphoinositide 3-kinase gamma in resident lung cells mediates part of the alveolar edema induced by high-stress ventilation. This injury is mediated via altered Akt, eNOS, NO, and/or cAMP signaling. Anti-PI3Kγ therapy aimed at resident lung cells represents a potential pharmacologic target to mitigate VILI.

Linking lung function and inflammatory responses in ventilator-induced lung injury

Despite decades of research, the mechanisms of ventilator-induced lung injury are poorly understood. We used strain-dependent responses to mechanical ventilation in mice to identify associations between mechanical and inflammatory responses in the lung. BALB/c, C57BL/6, and 129/Sv mice were ventilated using a protective [low tidal volume and moderate positive end-expiratory pressure (PEEP) and recruitment maneuvers] or injurious (high tidal volume and zero PEEP) ventilation strategy. Lung mechanics and lung volume were monitored using the forced oscillation technique and plethysmography, respectively. Inflammation was assessed by measuring numbers of inflammatory cells, cytokine (IL-6, IL-1β, and TNF-α) levels, and protein content of the BAL. Principal components factor analysis was used to identify independent associations between lung function and inflammation. Mechanical and inflammatory responses in the lung were dependent on ventilation strategy and mouse strain. Three factors were identified linking 1) pulmonary edema, protein leak, and macrophages, 2) atelectasis, IL-6, and TNF-α, and 3) IL-1β and neutrophils, which were independent of responses in lung mechanics. This approach has allowed us to identify specific inflammatory responses that are independently associated with overstretch of the lung parenchyma and loss of lung volume. These data provide critical insight into the mechanical responses in the lung that drive local inflammation in ventilator-induced lung injury and the basis for future mechanistic studies in this field.

Use of invasive mechanical ventilation in Australian emergency departments

OBJECTIVE

There are few published reports describing the use of invasive mechanical ventilation in EDs. We explored the characteristics of patients receiving mechanical ventilation, the ventilator modes and parameters used as well as the duration of ventilation and the nature of ventilator decision-making in Australian ED.

METHODS

We conducted a 2 month prospective survey of adult patients who received invasive mechanical ventilation in 24 Australian ED. Data forms were completed by ED staff during the patient's ED presentation. We documented ventilator settings post intubation, after a 1 h stabilization period, and immediately before ED discharge or extubation. The person responsible for selection of ventilator settings was noted at each time point.

RESULTS

Data were recorded on 307 patients. Altered mental status (179/307 [58%, 95% CI 53-64]) was the most common indication for mechanical ventilation. Volume-controlled modes were most frequently used at all measured time points; with a median tidal volume of 8 mL/kg. Responsibility for initial selection of ventilator settings was shared between ED physicians (157/307 [51%, 95% CI 46-57]), ED nurses (111/307 [36%, 95% CI 31-42]) and ICU or paramedic staff (9/307 [3%, 95% CI 1-5]) (not recorded 30/307 [10%, 95% CI 6-13]). Ongoing responsibility for titration of ventilation was more commonly that of the ED nurse.

CONCLUSION

The application of mechanical ventilation was similar to descriptions reported in the critical care literature both in Australia and internationally. Decision-making responsibilities were shared by ED medical and nursing staff.

The physical basis of ventilator-induced lung injury

Although mechanical ventilation (MV) is a life-saving intervention for patients with acute respiratory distress syndrome (ARDS), it can aggravate or cause lung injury, known as ventilator-induced lung injury (VILI). The biophysical characteristics of heterogeneously injured ARDS lungs increase the parenchymal stress associated with breathing, which is further aggravated by MV. Cells, in particular those lining the capillaries, airways and alveoli, transform this strain into chemical signals (mechanotransduction). The interaction of reparative and injurious mechanotransductive pathways leads to VILI. Several attempts have been made to identify clinical surrogate measures of lung stress/strain (e.g., density changes in chest computed tomography, lower and upper inflection points of the pressure-volume curve, plateau pressure and inflammatory cytokine levels) that could be used to titrate MV. However, uncertainty about the topographical distribution of stress relative to that of the susceptibility of the cells and tissues to injury makes the existence of a single 'global' stress/strain injury threshold doubtful.

Acute lung injury in preterm newborn infants: mechanisms and management

Respiratory morbidity and mortality remain common in preterm infants. The immature preterm lung is especially prone to injury. This process often starts in-utero due to maternal chorioamnionitis, priming the lung for further injury in response to post-natal ventilation, oxygen and nosocomial infection. Pulmonary inflammation has been strongly implicated in the pathway leading to lung injury in this population of infants. Several therapeutic approaches have been attempted to prevent acute lung injury or to limit its progress. The mechanisms of acute lung injury in preterm infants; their clinical correlates and available therapeutic approaches are reviewed here.

Assessing the impact of lung hyperinflation maneuver on systemic inflammatory response and lung collapse in patients undergoing surgeries under spontaneous ventilation

BACKGROUND AND OBJECTIVES

Lung hyperinflation maneuvers (LHM) reverse intraoperative atelectasis; however, they can lead to pulmonary-induced systemic inflammatory response. The objective of this study was to determine the impact of LHM on systemic inflammatory response and lung structure in patients undergoing subarachnoid block.

METHODS

After approval by the Ethics Committee of the institution and signing the informed consent, 20 patients undergoing small and medium surgical procedures were randomly separated into two groups: 1) control (CG), and 2) LHM (LHMG). One hour after the spinal anesthesia, LHM was performed in LHMG by applying bilevel positive pressure in the airways (BIPAP) with an expiratory pressure of 20 cmH(2)O and inspiratory pressure of 20 cmH(2)O for 1 to 2 minutes. Blood levels of TNFalpha, IL-1, IL-6, IL-8, IL-10, and IL-12 were determined by flow cytometry at baseline and at 90, 180, and 780 minutes. Lung volumes and weights were determined using CT scans obtained immediately after the surgery.

RESULTS

The use of LHM resulted in a reduction in the fraction of non-aerated pulmonary parenchyma (7.5 +/- 4.3%, in the Control Group, vs. 4 +/- 2.1%, in the LHM Group, p = 0.02) without changing pulmonary volumes. A progressive increase in plasma levels of IL-1, IL-6, IL-8, and IL-10, similar in both groups, was observed. Plasma levels of TNFalpha and IL-12 were undetectable during the study.

CONCLUSIONS

The use of LHM reduced the incidence of atelectasis, but it did not amplify the inflammatory response in patients with normal lungs undergoing small and medium surgeries under subarachnoid block.

Highly conserved transcriptional responses to mechanical ventilation of the lung

Cross-species analysis of microarray data has shown improved discriminating power between healthy and diseased states. Computational approaches have proven effective in deciphering the complexity of human disease by identifying upstream regulatory elements and the transcription factors that interact with them. Here we used both methods to identify highly conserved transcriptional responses during mechanical ventilation, an important therapeutic treatment that has injurious side effects. We generated control and ventilated whole lung samples from the premature baboon model of bronchopulmonary dysplasia (BPD), processed them for microarray, and combined them with existing whole lung oligonucleotide microarray data from 85 additional control samples from mouse, rat, and human and 19 additional ventilated samples from mouse and rat. Of the 2,531 orthologs shared by all 114 samples, 60 were modulated by mechanical ventilation [false discovery rate (FDR)-adjusted q value (q(FDR)) = 0.005, ANOVA]. These included transcripts encoding the transcription factors ATF3 and FOS. Because of compelling known roles for these transcription factors, we used computational methods to predict their targets in the premature baboon model of BPD, which included elastin (ELN), gastrin-releasing polypeptide (GRP), and connective tissue growth factor (CTGF). This approach identified highly conserved transcriptional responses to mechanical ventilation and may facilitate identification of therapeutic targets to reduce the side effects of this valuable treatment.

Management of mechanical ventilation during laparoscopic surgery

Laparoscopy is widely used in the surgical treatment of a number of diseases. Its advantages are generally believed to lie on its minimal invasiveness, better cosmetic outcome and shorter length of hospital stay based on surgical expertise and state-of-the-art equipment. Thousands of laparoscopic surgical procedures performed safely prove that mechanical ventilation during anaesthesia for laparoscopy is well tolerated by a vast majority of patients. However, the effects of pneumoperitoneum are particularly relevant to patients with underlying lung disease as well as to the increasing number of patients with higher-than-normal body mass index. Moreover, many surgical procedures are significantly longer in duration when performed with laparoscopic techniques. Taken together, these factors impose special care for the management of mechanical ventilation during laparoscopic surgery. The purpose of the review is to summarise the consequences of pneumoperitoneum on the standard monitoring of mechanical ventilation during anaesthesia and to discuss the rationale of using a protective ventilation strategy during laparoscopic surgery. The consequences of chest wall derangement occurring during pneumoperitoneum on airway pressure and central venous pressure, together with the role of end-tidal-CO2 monitoring are emphasised. Ventilatory and non-ventilatory strategies to protect the lung are discussed.

Mechanical ventilation in trauma

PURPOSE OF REVIEW

The purpose of this review is to evaluate new concepts in mechanical ventilation in trauma. We begin with the keystone of physiology prior to embarking on a discussion of several new modes of mechanical ventilation. We will discuss the use of noninvasive ventilation as a mode to prevent intubation and then go on to airway pressure release ventilation, high-frequency oscillatory ventilation, and computer-based, closed loop ventilation.

RECENT FINDINGS

The importance of preventing further injury in mechanical ventilation lies at the heart of the introduction of several new strategies of mechanical ventilation. New modes of ventilation have been developed to provide lung recruitment and alveolar stabilization at the lowest possible pressure.

SUMMARY

The old modes of continuous positive airway pressure and bilevel positive airway pressure have been actively introduced in clinical practice in the case of trauma patients. Used with proper pain management protocols, there has been a decrease in the incidence of intubation in blunt thoracic trauma. Airway pressure release ventilation has been gaining a role in the management of thoracic injury and may lead to less incidence of physiologic trauma to mechanically ventilated patients. High-frequency oscillatory ventilation has been shown to be effective in patient care by its ability to open and recruit the lung in trauma patients and in those with acute respiratory distress syndrome but it may not have a role in patients with inhalational injury. Closed loop ventilation is a technology that may better control major pulmonary parameters and lead to more rapid titration from the ventilator to spontaneous breathing.

Inflammatory response to oxygen and endotoxin in newborn rat lung ventilated with low tidal volume

Herein, we determined the contribution of mechanical ventilation, hyperoxia and inflammation, individually or combined, to the cytokine/chemokine response of the neonatal lung. Eight-day-old rats were ventilated for 8 h with low ( approximately 3.5 mL/kg), moderate ( approximately 12.5 mL/kg), or high ( approximately 25 mL/kg) tidal volumes (VT) and the cytokine/chemokine response was measured. Next, we tested whether low-VT ventilation with 50% oxygen or a preexisting inflammation induced by lipopolysaccharide (LPS) would modify this response. High-, moderate-, and low-VT ventilation significantly elevated CXCL-2 and IL-6 mRNA levels. Low-VT ventilation with 50% oxygen significantly increased IL-6 and CXCL-2 expression versus low-VT ventilation alone. LPS pretreatment combined with low-VT ventilation with 50% oxygen amplified IL-6 mRNA expression when compared with low VT alone or low VT + 50% O2 treatment. In contrast, low VT up-regulated CXCL-2 levels were reduced to nonventilated levels when LPS-treated newborn rats were ventilated with 50% oxygen. Thus, low-VT ventilation triggers the expression of acute phase cytokines and CXC chemokines in newborn rat lung, which is amplified by oxygen but not by a preexisting inflammation. Depending on the individual cytokine or chemokine, the combination of both oxygen and inflammation intensifies or abrogates the low VT-induced inflammatory response.

Changes of splanchnic perfusion after applying positive end expiratory pressure in patients with acute respiratory distress syndrome

Background:

Positive end-expiratory pressure (PEEP) improves oxygenation and can prevent ventilator- induced lung injury in patients with acute respiratory distress syndrome (ARDS). Nevertheless, PEEP can also induce detrimental effects by its influence on the cardiovascular system. The purpose of this study was to assess the effects of PEEP on gastric mucosal perfusion while applying a protective ventilatory strategy in patients with ARDS.

Materials and Methods:

Thirty-two patients were included in the study. A pressure–volume curve was traced and ideal PEEP, defined as lower inflection point + 2cmH₂O, was determined. Gastric tonometry was measured continuously (Tonocap). After baseline measurements, 10, 15 and 20cmH₂O PEEP and ideal PEEP were applied for 30 min each. By the end of each period, hemodynamics, CO₂ gap (gastric minus arterial partial pressures), and ventilatory measurements were taken.

Results:

PEEP had no effect on CO₂ gap (median [range], baseline: 18 [2–30] mmHg; PEEP 10: 18 [0–40] mmHg; PEEP 15: 17 [0–39] mmHg; PEEP 20: 16 [4–39] mmHg; ideal PEEP: 19 [9–39] mmHg; P = 0.19). Cardiac index also remained unchanged (baseline: 4.7 [2.6–6.2] l min⁻¹ m⁻²; PEEP 10: 4.4 [2.5–7] l min⁻¹ m⁻²; PEEP 15: 4.4 [2.2–6.8] l min⁻¹ m⁻²; PEEP 20: 4.8 [2.4–6.3] l min⁻¹ m⁻²; ideal PEEP: 4.9 [2.4–6.3] l min⁻¹ m⁻²; P = 0.09).

Conclusion:

PEEP of 10–20 cmH₂O does not affect splanchnic perfusion and is hemodynamically well tolerated in most patients with ARDS, including those receiving inotropic supports.

Alveolar recruitment maneuvers in acute lung injury/acute respiratory distress syndrome

Mechanical ventilation can worsen lung damage in acute lung injury and acute respiratory distress syndrome. The use of low tidal volumes is one of the strategies that has been shown to reduce lung injury and improve outcomes in this situation. However, low tidal volumes may lead to alveolar derecruitment and worsening of hypoxia. Recruitment maneuvers along with positive end-expiratory pressure may help to prevent derecruitment. Although recruitment maneuvers have been shown to improve oxygenation, improved clinical outcomes have not been demonstrated. The optimal recruitment strategy and the type of patients who might benefit are also unclear. This review summarizes the impact of recruitment maneuvers on lung mechanics and physiology, techniques of application, and the clinical situations in which they may be useful.

Mechanical ventilation modulates Toll-like receptor signaling pathway in a sepsis-induced lung injury model

BACKGROUND

Experimental and clinical studies on sepsis have demonstrated activation of the innate immune response following the initial host-bacterial interaction. In addition, mechanical ventilation (MV) can induce a pulmonary inflammatory response. How these two responses interact when present simultaneously remains to be elucidated. We hypothesized that MV modulates innate host response during sepsis by influencing Toll-like receptor (TLR) signaling.

DESIGN

Prospective, randomized, controlled animal study.

SUBJECTS

Male, septic Sprague-Dawley rats.

INTERVENTIONS

Sepsis was induced by cecal ligation and perforation. At 18 h, surviving animals had the cecum removed and were randomized to spontaneous breathing or two strategies of MV for 4 h: high (20 ml/kg) tidal volume (V (T)) with no positive end-expiratory pressure (PEEP) versus low V (T) (6 ml/kg) plus 10 cmH(2)O PEEP.

MEASUREMENTS AND MAIN RESULTS

Histological evaluation, TLR-2, TLR-4, inhibitory kappaB alpha (IkappaBalpha), interleukin-1 receptor-associated kinase-3 (IRAK-3) gene expression, protein levels and immunohistochemical lung localization, inflammatory cytokines gene expression, and protein serum concentrations were analyzed. MV with low V (T) plus PEEP attenuated sepsis-associated TLR-4 activation, and produced a significant decrease of IRAK-3 gene expression and protein levels, a significant increase of IkappaBalpha, and a decrease in lung gene expression and serum levels of cytokines. High-V (T) MV caused a significant increase of TLR-4 and IRAK-3 protein levels, lung and systemic cytokines, and mortality, and a significant decrease of IkappaBalpha.

CONCLUSIONS

Our findings suggest a novel mechanism that could partially explain how MV modulates the innate immune response in the lung by interfering with cellular signaling pathways that are activated in response to pathogens.

The physical basis of ventilator-induced lung injury

Although mechanical ventilation (MV) is a life-saving intervention for patients with acute respiratory distress syndrome (ARDS), it can aggravate or cause lung injury, known as ventilator-induced lung injury (VILI). The biophysical characteristics of heterogeneously injured ARDS lungs increase the parenchymal stress associated with breathing, which is further aggravated by MV. Cells, in particular those lining the capillaries, airways and alveoli, transform this strain into chemical signals (mechanotransduction). The interaction of reparative and injurious mechanotransductive pathways leads to VILI. Several attempts have been made to identify clinical surrogate measures of lung stress/strain (e.g., density changes in chest computed tomography, lower and upper inflection points of the pressure-volume curve, plateau pressure and inflammatory cytokine levels) that could be used to titrate MV. However, uncertainty about the topographical distribution of stress relative to that of the susceptibility of the cells and tissues to injury makes the existence of a single 'global' stress/strain injury threshold doubtful.

How I manage the adult potential organ donor: donation after neurological death (part 1)

The need for organ donation has become a growing concern over that last decade as the gap between organ donors and those awaiting transplant widens. According to UNOS, as of 8/2009, there were 102,962 patients on the transplant waiting list and only 6,004 donors in 2009 (UNOS.org. Accessed 4/8/2009). In 2008, an estimated 17 patients died each day awaiting transplant (OPTN.org). Though currently most organ donations come after brain death (DND or donation after neurological death), tissue donation (cornea, skin, bone, and musculoskeletal tissue), and donation after cardiac death (DCD) and are also possible. The term "extended criteria donor" refers to potential donors over 60 years of age or age 50-59 years plus 2 of the 3 following criteria: stroke as the cause of death, creatnine > 1.5 meq/dl, or a history of hypertension. Historically, extended criteria donors have had a lower organ yield per donor. In order to preserve the choice of organ donation for the family, intensive management of the potential organ donor is necessary. Since each potential donor could save seven lives or more, nihilism in the care of such patients can have far reaching ramifications. This article describes intensive care management practices that can optimize organ donation.

Spatial distribution of sequential ventilation during mechanical ventilation of the uninjured lung: an argument for cyclical airway collapse and expansion

Background

Ventilator-induced lung injury (VILI) is a recognized complication of mechanical ventilation. Although the specific mechanism by which mechanical ventilation causes lung injury remains an active area of study, the application of positive end expiratory pressure (PEEP) reduces its severity. We have previously reported that VILI is spatially heterogeneous with the most severe injury in the dorsal-caudal lung. This regional injury heterogeneity was abolished by the application of PEEP = 8 cm H₂O. We hypothesized that the spatial distribution of lung injury correlates with areas in which cyclical airway collapse and recruitment occurs.

Methods

To test this hypothesis, rabbits were mechanically ventilated in the supine posture, and regional ventilation distribution was measured under four conditions: tidal volumes (V_T) of 6 and 12 ml/kg with PEEP levels of 0 and 8 cm H₂O.

Results

We found that relative ventilation was sequentially redistributed towards dorsal-caudal lung with increasing tidal volume. This sequential ventilation redistribution was abolished with the addition of PEEP.

Conclusions

These results suggest that cyclical airway collapse and recruitment is regionally heterogeneous and spatially correlated with areas most susceptible to VILI.

Lung-lung interaction in isolated perfused unilateral hyperventilated rat lungs

The technique of conducting high tidal volume (TV) ventilation-induced lung inflammation including remote organs is still open to discussion, and our aim is to investigate this issue in isolated ventilated rat lungs perfused with salt solution. Selective right lung (RL) hyperventilation (TV of 15 mL/kg with air containing 5% CO(2) on zero or 2.5 cm H(2)0 end expiratory pressure [ZEEP or PEEP] in addition to left lung (LL) on 2.5 cm H(2)0 continuous positive airway pressure (CPAP) for 60 min, was realized after 30 min both lungs ventilation by occluding the left main bronchus, and it was allocated to the following 5 groups: groups 1 and 2 underwent hyperventilation under ZEEP, groups 3 and 4 underwent hyper ventilation under PEEP with recirculation or nonrecirculation (R-ZEEP or NR-ZEEP and R-PEEP or NR-PEEP), and group 5 served as the control group. Recirculation means the same perfusate recirculates the system throughout the procedure. The wet/dry ratio and protein content of bronchoalveolar lavage fluid (Prot-BALF), cytokine messenger RNAs (mRNAs), localization of tumor necrosis factor-alpha (TNF-alpha) by immunofluorescence double staining, and TNF-alpha concentration in the perfusate and BALF in each lung were measured and compared between groups by Kruskal-Wallis test. Lung injury (increased wet/dry ratio, Prot-BALF, and TNF-alpha on endothelial and epithelial cells) was shown in the hyperventilated RLs with ZEEP compared with their corresponding CPAP LLs. PEEP prevented these injuries. Lung injury was also demonstrated in the recirculated LL compared with the nonrecirculated LL (Prot-BALF, TNF-alpha and interleukin-1beta [IL-1beta] mRNAs: the LL of the R-ZEEP is greater than the LL of NR-ZEEP by P < 0.01). Unilateral hyperventilated lungs with ZEEP induced TNF-alpha, increased permeability, and injured the control lung via perfusion.

Mechanical ventilation aggravates transfusion-related acute lung injury induced by MHC-I class antibodies

PURPOSE

Transfusion-related acute lung injury (TRALI) occurs more often in critically ill patients than in a general hospital population, possibly due to the presence of underlying inflammatory conditions that may prime pulmonary neutrophils. Mechanical ventilation may be a risk factor for developing TRALI. We examined the influence of mechanical ventilation (MV) on the development of TRALI, combining a murine MV model causing ventilator-induced lung injury with a model of antibody-induced TRALl.

METHODS

BALB/c mice (n = 84) were ventilated for 5 h with low (7.5 ml/kg) or high (15 ml/kg) tidal volume, a positive end-expiratory pressure of 2 cm H(2)O and a fraction of inspired oxygen of 50%. After 3 h of MV, TRALI was induced by infusion of MHC-I antibodies (4.5 mg/kg); controls received vehicle. Non-ventilated animals receiving vehicle, isotype or MHC-I antibodies served as additional controls.

RESULTS

All animals receiving MHC-I antibodies developed TRALI within 2 h. In mice in which TRALI was induced, MV with low tidal volumes aggravated pulmonary injury, as evidenced by an increase in neutrophil influx, pulmonary and systemic levels of cytokines and lung histopathological changes compared to unventilated controls. The use of high tidal volume ventilation resulted in a further increase in protein leakage and pulmonary edema.

CONCLUSIONS

Mechanical ventilation (MV) synergistically augmented lung injury during TRALI, which was even further enhanced by the use of injurious ventilator settings. Results suggest that MV may be a risk factor for the onset of TRALI and may aggravate the course of disease.

Hypercapnic acidosis in ventilator-induced lung injury

RATIONALE

Permissive hypercapnia is established in lung injury management. Therapeutic hypercapnia causes benefit or harm, depending on the context. Ventilator-associated lung injury has a wide spectrum of candidate mechanisms, affording multiple opportunities for intervention such as hypercapnia to exert benefit or harm.

OBJECTIVES

To confirm (1) that hypercapnia attenuates in vivo ventilator-induced lung injury (VILI); (2) biological plausibility of such protection (e.g., dose-response, time series, inflammatory profile); and (3) that the associated biochemical events are consistently beneficial.

METHODS

A mouse model of VILI was established in vivo. Injurious ventilation was established, hypercapnia applied and markers of inflammation measured.

MEASUREMENTS

Lung injury was quantified by gas exchange, elastance, microvascular leak, histology and levels of cytokines and eicosanoids, cyclooxygenase and tissue nitrotyrosine.

MAIN RESULTS

Injurious ventilation caused significant lung injury (mechanics, microvascular leak, histology) and release of inflammatory cytokines, chemokines and eicosanoids. Hypercapnia attenuated these responses, with dose-response and time-dependent effects. No adverse effects of hypercapnia were observed in controls. Hypercapnia suppressed the transcription (mRNA) and translation (protein) of the major inducible prostanoid-generating enzyme (COX-2), but the effects on the downstream eicosanoids were modest. However, hypercapnia significantly increased lung tissue nitrotyrosine-at PaCO(2) levels that were protective.

CONCLUSIONS

Hypercapnia provided consistent and biologically plausible in vivo protection against VILI, but elevated lung tissue levels of nitro-tyrosine as previously described in sepsis. Clinicians and those designing clinical trials need to be aware of the potential for detrimental effects when using hypercapnia in order to balance benefits versus harm with this approach.

Do soluble mediators cause ventilator-induced lung injury and multi-organ failure?

BACKGROUND

Significant advances in the management of patients with acute respiratory distress syndrome have been few in the recent past despite considerable efforts in clinical testing and experimental work. The biotrauma hypothesis of ventilator-associated lung injury (VALI), suggesting that mechanical ventilation induces the release of injurious mediators from the lung, implies that pharmaceutical interventions targeting these circulating pathogenic mediators would be clinically beneficial. Among the commonly reported classes of ventilation-associated mediators are cytokines, coagulation factors, hormones (e.g., angiotensin-II), lipid-derived mediators and oxidants, yet proof of their pathogenicity is lacking.

DISCUSSION

This review discusses evidence surrounding the roles of these mediators in VALI and describes how definitive proof could be provided based on Koch's postulates, using an isolated perfused lung model. According to this experimental concept, candidate mediators would fulfill certain criteria, including increased accumulation in perfusate during injurious ventilation and induction of injury during non-injurious ventilation. Accumulation of mediators in the perfusate would facilitate isolation and characterization by standard biochemical means, from broad determination of physical and chemical properties to precise identification of individual molecules (e.g., by modern "omic" approaches such as mass spectrometry). Finally, confirmation by exogenous administration of mediators or antagonists can assess effects on injury and its mechanisms such as cell permeability or cytotoxicity.

CONCLUSIONS

Adaptation of Koch's postulates to the biotrauma hypothesis of VALI could provide important insights. Translation of the acquired knowledge into clinical testing is challenged by the heterogeneity of the patient population (e.g., etiology, co-morbidity, genetics or concomitant therapy) and the specificity and efficacy of the therapeutic intervention on the cellular/molecular level.

Comparison of acid-induced inflammatory responses in the rat lung during high frequency oscillatory and conventional mechanical ventilation

BACKGROUND

The present study was performed to compare the effects of high frequency oscillatory ventilation (HFOV) with conventional mechanical ventilation (CMV) on pulmonary inflammatory responses in a rat acid-induced lung injury model.

METHODS

Anesthetized rats were instilled intratracheally with HCl (0.1 N, 2 mL/kg) and then randomly divided into three mechanical ventilation settings: HFOV (an oscillatory frequency of 15 Hz, mean airway pressure (MAP) of 9 cmH(2)O), CMV at tidal volume of 12 and 6 mL/kg for 5 h.

RESULTS

After HCl instillation, HFOV significantly attenuated the increases in neutrophil infiltration and TNF-α concentration in bronchoalveolar lavage fluid compared with the CMV groups. During HFOV, there was an inhibition of an increase in TNF-α mRNA expression and a decrease in SP-A mRNA expression induced by acid instillation.

CONCLUSION

This animal study demonstrates that HFOV is a suitable form of mechanical ventilation to prevent inflammatory responses in acid-induced lung injury.

Comparison of the effect of LPS and PAM3 on ventilated lungs

BACKGROUND

While lipopolysaccharide (LPS) from Gram-negative bacteria has been shown to augment inflammation in ventilated lungs information on the effect of Gram-positive bacteria is lacking. Therefore the effect of LPS and a lipopetide from Gram-positive bacteria, PAM3, on ventilated lungs were investigated.

METHODS

C57/Bl6 mice were mechanically ventilated. Sterile saline (sham) and different concentrations of LPS (1 microg and 5 microg) and PAM3 (50 nM and 200 nM) were applied intratracheally. Lung function parameters and expression of MIP-2 and TNFalpha as well as influx of neutrophils were measured.

RESULTS

Mechanical ventilation increased resistance and decreased compliance over time. PAM3 but not LPS significantly increased resistance compared to sham challenge (P < 0.05). Both LPS and PAM3 significantly increased MIP-2 and TNFalpha mRNA expression compared to sham challenge (P < 0.05). The numbers of neutrophils were significantly increased after LPS at a concentration of 5 microg compared to sham (P < 0.05). PAM3 significantly increased the numbers of neutrophils at both concentrations compared to sham (P < 0.05).

CONCLUSIONS

These data suggest that PAM3 similar to LPS enhances ventilator-induced inflammation. Moreover, PAM3 but not LPS increases pulmonary resistance in ventilated lungs. Further studies are warranted to define the role of lipopetides in ventilator-associated lung injury.

Clinical application of ventilator modes: Ventilatory strategies for lung protection

INTRODUCTION

Identification of the mortality reducing effect of lung protective ventilation using low tidal volumes and pressure limitation is one of the biggest advances in the application of mechanical ventilation. Yet studies continue to demonstrate low adoption of this style of ventilation. Critical care nurses in Australia and New Zealand have a high level of responsibility and autonomy for mechanical ventilation and weaning practices and therefore require in-depth knowledge of ventilator technology, its clinical application and the current evidence for effective ventilation strategies.

AIM

To present an overview of current knowledge and research relating to lung protective ventilation.

METHOD

A multidatabase literature search using the terms protective ventilation, open lung, high frequency oscillatory ventilation, airway pressure release ventilation, and weaning.

RESULTS

Based on clinical trials and physiological evidence lung protective strategies using low tidal volumes and moderate levels of PEEP have been recommended as strategies to prevent tidal alveolar collapse and overdistension in patients with ALI/ARDS. Evidence now suggests these strategies may also be beneficial in patients with normal lungs. Lung protective ventilation may be applied with either volume or pressure-controlled ventilation. Pressure-controlled ventilation allows regulation over injurious peak inspiratory pressures; however no study has identified the superiority of pressure-controlled ventilation over low tidal volume strategies using volume-control. Other lung protective ventilation strategies include moderate to high positive-end expiratory pressure, recruitment manoeuvres, high frequency oscillatory ventilation, and airway pressure release ventilation though definitive trials identifying consistently improved patient outcomes are still needed. No ventilation strategy can be more lung protective than the timely discontinuation of mechanical ventilation. Despite the above recommendations, evidence suggests the decision to commence weaning and attempt extubation continue to be delayed. Critical care nurses play a vital role in the recognition of patients capable of spontaneous breathing and ready for extubation. Organisational interventions such as weaning protocols as well as computerised weaning systems may have less effect when nurses are able to manage weaning processes effectively.

CONCLUSIONS

Lung protective ventilatory strategies are not consistently applied and weaning and extubation continue to be delayed. Critical care nurses need to establish a strong knowledge base to promote effective and appropriate management of patients requiring mechanical ventilation.

Risk and protective factors for major complications after pneumonectomy for lung cancer

Pneumonectomy carries a high-risk for postoperative complications. The aim of the study was to identify factors that may predispose to the development of major postoperative complications after pneumonectomy for lung cancer. All consecutive patients from January 2000 to December 2005 were retrospectively studied. Major postoperative complications were defined by respiratory failure, pulmonary embolism, pneumonia, shock, cardiogenic pulmonary oedema, myocardial ischaemia or symptomatic cardiac arrhythmia. One hundred and twenty-nine patients were included. The overall hospital mortality rate was 10.8%, and complications occurred in 42.6%. Multivariate analysis revealed that patients with American Society of Anesthesiologist (ASA) class >2 [odds ratio (OR) 8.26; 95% confidence interval (CI), 3.19-36.55] and liberal fluid administration during surgery (OR, 1.96 for each litre; 95% CI, 1.45-3.16) to be risk factor for major cardiopulmonary complication or mortality. Preoperative haemoglobin > or =10 g/dl (OR, 0.19; 95% CI, 0.01-0.91) and low tidal volume administrated during surgery (< or =7.35 ml/kg; OR, 0.36; 95% CI, 0.10-0.92) were identified as protective factors. Pneumonectomy remains a high-risk surgery. Postoperative complications may be influenced by the comorbidities but also the management of fluid infusion and mechanical ventilation during the surgical procedure.

Mechanical ventilation modulates TLR4 and IRAK-3 in a non-infectious, ventilator-induced lung injury model

BACKGROUND

Previous experimental studies have shown that injurious mechanical ventilation has a direct effect on pulmonary and systemic immune responses. How these responses are propagated or attenuated is a matter of speculation. The goal of this study was to determine the contribution of mechanical ventilation in the regulation of Toll-like receptor (TLR) signaling and interleukin-1 receptor associated kinase-3 (IRAK-3) during experimental ventilator-induced lung injury.

METHODS

Prospective, randomized, controlled animal study using male, healthy adults Sprague-Dawley rats weighing 300-350 g. Animals were anesthetized and randomized to spontaneous breathing and to two different mechanical ventilation strategies for 4 hours: high tidal volume (VT) (20 ml/kg) and low VT (6 ml/kg). Histological evaluation, TLR2, TLR4, IRAK3 gene expression, IRAK-3 protein levels, inhibitory kappa B alpha (IkappaBalpha), tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL6) gene expression in the lungs and TNF-alpha and IL-6 protein serum concentrations were analyzed.

RESULTS

High VT mechanical ventilation for 4 hours was associated with a significant increase of TLR4 but not TLR2, a significant decrease of IRAK3 lung gene expression and protein levels, a significant decrease of IkappaBalpha, and a higher lung expression and serum concentrations of pro-inflammatory cytokines.

CONCLUSIONS

The current study supports an interaction between TLR4 and IRAK-3 signaling pathway for the over-expression and release of pro-inflammatory cytokines during ventilator-induced lung injury. Our study also suggests that injurious mechanical ventilation may elicit an immune response that is similar to that observed during infections.

Mild endotoxemia during mechanical ventilation produces spatially heterogeneous pulmonary neutrophilic inflammation in sheep

BACKGROUND

There is limited information on the regional inflammatory effects of mechanical ventilation and endotoxemia on the production of acute lung injury. Measurement of F-fluorodeoxyglucose (F-FDG) uptake with positron emission tomography allows for the regional, in vivo and noninvasive, assessment of neutrophilic inflammation. The authors tested whether mild endotoxemia combined with large tidal volume mechanical ventilation bounded by pressures within clinically acceptable limits could yield measurable and anatomically localized neutrophilic inflammation.

METHODS

Sheep were mechanically ventilated with plateau pressures = 30-32 cm H2O and positive end-expiratory pressure = 0 for 2 h. Six sheep received intravenous endotoxin (10 ng x kg x min), whereas six did not (controls), in sequentially performed studies. The authors imaged with positron emission tomography the intrapulmonary kinetics of infused N-nitrogen and F-FDG to compute regional perfusion and F-FDG uptake. Transmission scans were used to assess aeration.

RESULTS

Mean gas fraction and perfusion distribution were similar between groups. In contrast, a significant increase in F-FDG uptake was observed in all lung regions of the endotoxin group. In this group, F-FDG uptake in the middle and dorsal regions was significantly larger than that in the ventral regions. Multivariate analysis showed that the F-FDG uptake was associated with regional aeration (P < 0.01) and perfusion (P < 0.01).

CONCLUSIONS

Mild short-term endotoxemia in the presence of heterogeneous lung aeration and mechanical ventilation with pressures within clinically acceptable limits produces marked spatially heterogeneous increases in pulmonary neutrophilic inflammation. The dependence of inflammation on aeration and perfusion suggests a multifactorial basis for that finding. F-FDG uptake may be a sensitive marker of pulmonary neutrophilic inflammation in the studied conditions.

Substance P receptor blockade decreases stretch-induced lung cytokines and lung injury in rats

Overdistension of lung tissue during mechanical ventilation causes cytokine release, which may be facilitated by the autonomic nervous system. We used mechanical ventilation to cause lung injury in rats, and studied how cervical section of the vagus nerve, or substance P (SP) antagonism, affected the injury. The effects of 40 or 25 cmH(2)O high airway pressure injurious ventilation (HV(40) and HV(25)) were studied and compared with low airway pressure ventilation (LV) and spontaneous breathing (controls). Lung mechanics, lung weight, gas exchange, lung myeloperoxidase activity, lung concentrations of interleukin (IL)-1 beta and IL-6, and amounts of lung SP were measured. Control rats were intact, others were bivagotomized, and in some animals we administered the neurokinin-1 (NK-1) receptor blocking agent SR140333. We first determined the durations of HV(40) and HV(25) that induced the same levels of lung injury and increased lung contents of IL-1 beta and IL-6. They were 90 min and 120 min, respectively. Both HV(40) and HV(25) increased lung SP, IL-1 beta and IL-6 levels, these effects being markedly reduced by NK-1 receptor blockade. Bivagotomy reduced to a lesser extent the HV(40)- and HV(25)-induced increases in SP but significantly reduced cytokine production. Neither vagotomy nor NK-1 receptor blockade prevented HV(40)-induced lung injury but, in the HV(25) group, they made it possible to maintain lung injury indices close to those measured in the LV group. This study suggests that both neuronal and extra-neuronal SP might be involved in ventilator-induced lung inflammation and injury. NK-1 receptor blockade could be a pharmacological tool to minimize some adverse effects of mechanical ventilation.

Increased cardiac microvascular permeability and activation of cardiac endothelial nitric oxide synthase in high tidal volume ventilation-induced lung injury

Background: Positive pressure ventilation with large tidal volumes has been shown to cause lung injury via the serine/threonine kinase-protein kinase B (Akt) and endothelial nitric oxide synthase (eNOS)-pathways. However, the effects of high tidal volume (VT) ventilation on the heart are unclear. Objectives: Evaluate the effect of VT ventilation on the cardiac vascular permeability and intracellular Akt and eNOS signaling pathway. Methods: C57BL/6 and Akt knock-out (heterozygotes, +/−) mice were exposed to high VT (30 mL/kg) mechanical ventilation with room air for one and/or five hours. Results: High VT ventilation increased cardiac microvascular permeability and eNOS phosphorylation in a timedependent manner. Serum cardiac troponin I was increased after one hour of high VT ventilation. Cardiac Akt phosphorylation was accentuated after one hour and attenuated after five hours of high VT ventilation. Pharmacological inhibition of Akt with LY294002 and high VT ventilation of Akt+/− mice attenuated cardiac Akt phosphorylation, but not eNOS phosphorylation. Conclusion: High VT ventilation increased cardiac myocardial injury, microvascular permeability, and eNOS phosphorylation. Involvement of cardiac Akt in high VT ventilation was transient.

Low tidal volume and high positive end-expiratory pressure mechanical ventilation results in increased inflammation and ventilator-associated lung injury in normal lungs

BACKGROUND

Protective mechanical ventilation with low tidal volume (Vt) and low plateau pressure reduces mortality and decreases the length of mechanical ventilation in patients with acute respiratory distress syndrome. Mechanical ventilation that will protect normal lungs during major surgical procedures of long duration may improve postoperative outcomes. We performed an animal study comparing 3 ventilation strategies used in the operating room in normal lungs. We compared the effects on pulmonary mechanics, inflammatory mediators, and lung tissue injury.

METHODS

Female pigs were randomized into 3 groups. Group H-Vt/3 (n = 6) was ventilated with a Vt of 15 mL/kg predicted body weight (PBW)/positive end-expiratory pressure (PEEP) of 3 cm H(2)O, group L-Vt/3 (n = 6) with a Vt of 6 mL/kg PBW/PEEP of 3 cm H(2)O, and group L-Vt/10 (n = 6) with a Vt of 6 mL/kg PBW/PEEP of 10 cm H(2)O, for 8 hours. Hemodynamics, airway mechanics, arterial blood gases, and inflammatory markers were monitored. Bronchoalveolar lavage (BAL) was analyzed for inflammatory markers and protein concentration. The right lower lobe was assayed for mRNA of specific cytokines. The right lower lobe and right upper lobe were evaluated histologically.

RESULTS

In contrast to groups H-Vt/3 and L-Vt/3, group L-Vt/10 exhibited a 6-fold increase in inflammatory mediators in BAL (P < 0.001). Cytokines in BAL were similar in groups H-Vt/3 and L-Vt/3. Group H-Vt/3 had a significantly lower lung injury score than groups L-Vt/3 and L-Vt/10.

CONCLUSION

Comparing intraoperative strategies, ventilation with high PEEP resulted in increased production of inflammatory markers. Low PEEP resulted in lower levels of inflammatory markers. High Vt/low PEEP resulted in less histologic lung injury.

Comparison of two ventilatory strategies in elderly patients undergoing major abdominal surgery

BACKGROUND

'Open lung' ventilation is commonly used in patients with acute lung injury and has been shown to improve intraoperative oxygenation in obese patients undergoing laparoscopic surgery. The feasibility of an 'open lung' ventilatory strategy in elderly patients under general anaesthesia has not previously been assessed.

METHODS

'Open lung' ventilation (recruitment manoeuvres, tidal volume 6 ml kg(-1) predicted body weight, and 12 cm H(2)O PEEP) (RM group) was compared with conventional ventilation (no recruitment manoeuvres, tidal volume 10 ml kg(-1) predicted body weight, and zero end-expiratory pressure) in elderly patients (>65 yr) undergoing major open abdominal surgery with regard to oxygenation, respiratory system mechanics, and haemodynamic stability. We also monitored the serum levels of the interleukins (IL)-6 and IL-8 before and after surgery to determine whether the systemic inflammatory response to surgery depends on the ventilatory strategy used.

RESULTS

Twenty patients were included in each group. The RM group tolerated open lung ventilation without significant haemodynamic instability. Intraoperative Pa(o(2)) improved in the RM group (P<0.01) and deteriorated in controls (P=0.01), but postoperative Pa(o(2)) was similar in both groups. The RM group had improved breathing mechanics as evidenced by increased dynamic compliance (36%) and decreased airway resistance (21%). Both IL-6 and IL-8 significantly increased after surgery, but the magnitude of increase did not differ between the groups.

CONCLUSIONS

A lung recruitment strategy in elderly patients is well tolerated and improves intraoperative oxygenation and lung mechanics during laparotomy.

Mechanical ventilation with high tidal volume induces inflammation in patients without lung disease

INTRODUCTION

Mechanical ventilation (MV) with high tidal volumes may induce or aggravate lung injury in critical ill patients. We compared the effects of a protective versus a conventional ventilatory strategy, on systemic and lung production of tumor necrosis factor-alpha (TNF-alpha) and interleukin-8 (IL-8) in patients without lung disease.

METHODS

Patients without lung disease and submitted to mechanical ventilation admitted to one trauma and one general adult intensive care unit of two different university hospitals were enrolled in a prospective randomized-control study. Patients were randomized to receive MV either with tidal volume (VT) of 10 to 12 ml/kg predicted body weight (high VT group) (n = 10) or with VT of 5 to 7 ml/kg predicted body weight (low VT group) (n = 10) with an oxygen inspiratory fraction (FIO2) enough to keep arterial oxygen saturation >90% with positive end-expiratory pressure (PEEP) of 5 cmH2O during 12 hours after admission to the study. TNF-alpha and IL-8 concentrations were measured in the serum and in the bronchoalveolar lavage fluid (BALF) at admission and after 12 hours of study observation time.

RESULTS

Twenty patients were enrolled and analyzed. At admission or after 12 hours there were no differences in serum TNF-alpha and IL-8 between the two groups. While initial analysis did not reveal significant differences, standardization against urea of logarithmic transformed data revealed that TNF-alpha and IL-8 levels in bronchoalveolar lavage (BAL) fluid were stable in the low VT group but increased in the high VT group (P = 0.04 and P = 0.03). After 12 hours, BALF TNF-alpha (P = 0.03) and BALF IL-8 concentrations (P = 0.03) were higher in the high VT group than in the low VT group.

CONCLUSIONS

The use of lower tidal volumes may limit pulmonary inflammation in mechanically ventilated patients even without lung injury.

CLINICAL TRIAL REGISTRATION

NCT00935896.

Chorioamnionitis alters the response to surfactant in preterm infants

OBJECTIVE

To study the association between antenatal exposure to chorioamnionitis and the neonatal response to surfactant.

STUDY DESIGN

Prospective observational cohort of 301 preterm infants of gestational age < or = 32.0 weeks, 146 of whom received surfactant according to standardized criteria. Fraction of inspired oxygen (FiO(2)) requirement (using analysis of variance) and time to extubation (using Kaplan-Meier and Cox regression analyses) were compared between groups based on the presence of histological chorioamnionitis (HC) with or without fetal involvement (HC-, n = 88; HC + F-, n = 25; HC + F+, n = 33) and between infants who developed bronchopulmonary dysplasia (BPD) or died (n = 57) and BPD-free survivors (n = 89). Multiple logistic regression was performed to investigate the association between HC and BPD.

RESULTS

Compared with HC- infants, HC + F+ infants had significantly greater FiO(2) requirement and prolonged time to extubation postsurfactant, not accounted for by differences in gestational age and birth weight. Infants with BPD/death had a strikingly similar pattern of increased FiO(2) requirement postsurfactant. Moreover, in infants who received surfactant, HC + F+ status was associated with increased risk for BPD (odds ratio [OR] = 3.40; 95% confidence interval [CI] = 1.02-11.3; P = .047) and for BPD/death (OR = 2.72; 95% CI = 1.00-7.42; P = .049).

CONCLUSIONS

An impaired surfactant response was observed in preterm infants with severe chorioamnionitis and may be involved in the association between chorioamnionitis, mechanical ventilation, and the development of BPD.

Acute lung injury in patients with severe brain injury: a double hit model

The presence of pulmonary dysfunction after brain injury is well recognized. Acute lung injury (ALI) occurs in 20% of patients with isolated brain injury and is associated with a poor outcome. The "blast injury" theory, which proposes combined "hydrostatic" and "high permeability" mechanisms for the formation of neurogenic pulmonary edema, has been challenged recently by the observation that a systemic inflammatory response may play an integral role in the development of pulmonary dysfunction associated with brain injury. As a result of the primary cerebral injury, a systemic inflammatory reaction occurs, which induces an alteration in blood-brain barrier permeability and infiltration of activated neutrophils into the lung. This preclinical injury makes the lungs more susceptible to the mechanical stress of an injurious ventilatory strategy. Tight CO2 control is a therapeutic priority in patients with acute brain injury, but the use of high tidal volume ventilation may contribute to the development of ALI. Establishment of a therapeutic regimen that allows the combination of protective ventilation with the prevention of hypercapnia is, therefore, required. Moreover, in patients with brain injury, hypoxemia represents a secondary insult associated with a poor outcome. Optimal oxygenation may be achieved by using an adequate FiO2 and by application of positive end-expiratory pressure (PEEP). PEEP may, however, affect the cerebral circulation by hemodynamic and CO2-mediated mechanisms and the effects of PEEP on cerebral hemodynamics should be monitored in these patients and used to titrate its application.

Lung recruitment assessed by total respiratory system input reactance

PURPOSE

ALI and ARDS are associated with lung volume derecruitment, usually counteracted by PEEP and recruitment maneuvers (RM), which should be accurately tailored to the patient's needs. The aim of this study was to investigate the possibility of monitoring the amount of derecruited lung by the forced oscillation technique (FOT).

METHODS

We studied six piglets (26 +/- 2.5 kg) ventilated by a mechanical ventilator connected to a FOT device that produced sinusoidal pressure forcing at 5 Hz. The percentage of non-aerated lung tissue (V (tiss)NA%) was measured by whole-body CT scans at end-expiration with zero end-expiratory pressure. Respiratory system oscillatory input reactance (X (rs)) was measured simultaneously to CT and used to derive oscillatory compliance (C (X5)), which we used as an index of recruited lung. Measurements were performed at baseline and after several interventions in the following sequence: mono-lateral reabsorption atelectasis, RM, bi-lateral derecruitment induced by broncho-alveolar lavage and a second RM.

RESULTS

By pooling data from all experimental conditions and all pigs, C (X5) was linearly correlated to V (tiss)NA% (r (2) = 0.89) regardless of the procedure used to de-recruit the lung (reabsorption atelectasis or pulmonary lavage). Separate correlation analysis on single pigs showed similar regression equations, with an even higher coefficient of determination (r (2) = 0.91 +/- 0.07).

CONCLUSION

These results suggest that FOT and the measurement of C (X5) could be a useful tool for the non-invasive measurement of lung volume recruitment/derecruitment.

Interplay Between Cytokine-Induced and Cyclic Equibiaxial Deformation-Induced Nitric Oxide Production and Metalloproteases Expression in Human Alveolar Epithelial Cells

Ventilator-induced lung overdistension has been a growing concern in the management of mechanically ventilated patients. Mechanical ventilation triggers or enhances the net inflammatory and tissue remodeling activities. Although it has been shown that proinflammatory and tissue remodeling factors play important roles during airway remodeling, the interplay between them is not well understood. Thus, our objective was to study and characterize the molecular mechanism of cyclic equibiaxial deformation-induced airway inflammation and remodeling either in the presence or absence of a pre-existing inflammatory condition. This study was done using an in vitro dynamic model, which can simulate different mechanical ventilative conditions. Type II alveolar epithelial cell (A549) monolayers were exposed to the different levels of mechanical ventilative conditions using the Flexcell^® Tension Plus^™ 4000T system, which generated the different levels of cyclic equibiaxial deformation (5, 10, 15, and 20%) at 0.2 Hz deformation frequency. The production of nitric oxide (NO), the expression of metalloprotease-2 (MMP-2)/tissue inhibitor metalloprotease-2 (TIMP-2), and the activation of MMP-2 were measured under the different levels of cyclic equibiaxial deformation either in the presence or absence of TNF-α. Our study indicated that cyclic equibiaxial deformation-induced production of NO and MMP-2/TIMP-2. Higher levels of cyclic equibiaxial deformation increased the expression of the active form of MMP-2. In particular, in the presence of TNF-α, the more active form of MMP-2 was detected during both cyclic equibiaxial deformation and remodeling periods.

Neurally adjusted ventilatory assist decreases ventilator-induced lung injury and non-pulmonary organ dysfunction in rabbits with acute lung injury

OBJECTIVE

To determine if neurally adjusted ventilatory assist (NAVA) that delivers pressure in proportion to diaphragm electrical activity is as protective to acutely injured lungs (ALI) and non-pulmonary organs as volume controlled (VC), low tidal volume (Vt), high positive end-expiratory pressure (PEEP) ventilation.

DESIGN

Prospective, randomized, laboratory animal study.

SUBJECTS

Twenty-seven male New Zealand white rabbits.

INTERVENTIONS

Anesthetized rabbits with hydrochloric acid-induced ALI were randomized (n = 9 per group) to 5.5 h NAVA (non-paralyzed), VC (paralyzed; Vt 6-ml/kg), or VC (paralyzed; Vt 15-ml/kg). PEEP was adjusted to hemodynamic goals in NAVA and VC6-ml/kg, and was 1 cmH2O in VC15-ml/kg.

MEASUREMENTS AND MAIN RESULTS

PaO2/FiO2; lung wet-to-dry ratio; lung histology; interleukin-8 (IL-8) concentrations in broncho-alveolar-lavage (BAL) fluid, plasma, and non-pulmonary organs; plasminogen activator inhibitor type-1 and tissue factor in BAL fluid and plasma; non-pulmonary organ apoptosis rate; creatinine clearance; echocardiography. PEEP was similar in NAVA and VC6-ml/kg. During NAVA, Vt was lower (3.1 +/- 0.9 ml/kg), whereas PaO2/ FiO2, respiratory rate, and PaCO2 were higher compared to VC6-ml/kg (p<0.05 for all). Variables assessing ventilator-induced lung injury (VILI), IL-8 levels, non-pulmonary organ apoptosis rate, and kidney as well as cardiac performance were similar in NAVA compared to VC6-ml/kg. VILI and non-pulmonary organ dysfunction was attenuated in both groups compared to VC15-ml/kg.

CONCLUSIONS

In anesthetized rabbits with early experimental ALI, NAVA is as effective as VC6-ml/kg in preventing VILI, in attenuating excessive systemic and remote organ inflammation, and in preserving cardiac and kidney function.

Global gene expression patterns in the post-pneumonectomy lung of adult mice

Background

Adult mice have a remarkable capacity to regenerate functional alveoli following either lung resection or injury that exceeds the regenerative capacity observed in larger adult mammals. The molecular basis for this unique capability in mice is largely unknown. We examined the transcriptomic responses to single lung pneumonectomy in adult mice in order to elucidate prospective molecular signaling mechanisms used in this species during lung regeneration.

Methods

Unilateral left pneumonectomy or sham thoracotomy was performed under general anesthesia (n = 8 mice per group for each of the four time points). Total RNA was isolated from the remaining lung tissue at four time points post-surgery (6 hours, 1 day, 3 days, 7 days) and analyzed using microarray technology.

Results

The observed transcriptomic patterns revealed mesenchymal cell signaling, including up-regulation of genes previously associated with activated fibroblasts (Tnfrsf12a, Tnc, Eln, Col3A1), as well as modulation of Igf1-mediated signaling. The data set also revealed early down-regulation of pro-inflammatory cytokine transcripts and up-regulation of genes involved in T cell development/function, but few similarities to transcriptomic patterns observed during embryonic or post-natal lung development. Immunohistochemical analysis suggests that early fibroblast but not myofibroblast proliferation is important during lung regeneration and may explain the preponderance of mesenchymal-associated genes that are over-expressed in this model. This again appears to differ from embryonic alveologenesis.

Conclusion

These data suggest that modulation of mesenchymal cell transcriptome patterns and proliferation of S100A4 positive mesenchymal cells, as well as modulation of pro-inflammatory transcriptome patterns, are important during post-pneumonectomy lung regeneration in adult mice.

Acute respiratory distress syndrome: insights gained from clinical and translational research

Acute lung injury and its more severe form acute respiratory distress syndrome (ARDS) are characterized by diffuse impairment of alveolocapillary membrane in the settings of different predisposing conditions such as sepsis, trauma and shock. Many intrahospital exposures, including aspiration, delayed resuscitation, high tidal volume mechanical ventilation and non critical use of transfusions may contribute or worsen ARDS. Therapy is targeted to treatment of predisposing condition, life supportive measures and prevention of nosocomial complications. Rigorous adherence to lung-protective mechanical ventilation is critical to prevent ventilator induced lung injury and decrease mortality. Although survival of ARDS patients has improved in the last decades ARDS mortality rates are still high and survivors encounter significant physical and psychological impairments.