Effect of positive end-expiratory pressure on inflammatory response in oleic acid-induced lung injury and whole-lung lavage-induced lung injury

Total alveolar lavage with oxygen fine bubble dispersion directly improves lipopolysaccharide-induced acute respiratory distress syndrome of rats

Severe respiratory disorder induced by pulmonary inflammation is one of the causes of acute respiratory distress syndrome, which still has high mortality. It is crucial to remove causative substances and inflammatory mediators early in order to inhibit the progression of pulmonary inflammation. Total alveolar lavage (TAL) may avert the inflammatory response by eliminating causative substances in certain inflammatory lung diseases. We developed an efficient TAL system and examined the efficacy of short-term TAL treatment performed for acute lung injury models of rats. In the first experiment with a severe lung injury model, 15 rats were divided into 3 groups: sham group, mechanical gas ventilation (MGV) treatment group, and TAL treatment group. The treatments were conducted for 5 min, 20 min after the provocation of inflammation. Two days after treatment, the TAL and MGV treatment groups exhibited significant differences in blood oxygen levels, mean arterial pressure, weight-loss ratio, and inflammatory cytokine levels in the lungs. In contrast, almost no differences were observed between the TAL treatment and sham groups. In the second experiment with a lethal lung injury model, the TAL treatment dramatically improved the survival rate of the rats compared to the MGV treatment groups (p = 0.0079). Histopathological analysis confirmed pronounced differences in neutrophil accumulation and thickening of the interstitial membrane between the TAL and MGV treatment groups in both experiments. These results indicate that as little as 5 min of TAL treatment can protect rats from acute lung injury by removing causative substances from the lungs.

A Physiologically Informed Strategy to Effectively Open, Stabilize, and Protect the Acutely Injured Lung

Acute respiratory distress syndrome (ARDS) causes a heterogeneous lung injury and remains a serious medical problem, with one of the only treatments being supportive care in the form of mechanical ventilation. It is very difficult, however, to mechanically ventilate the heterogeneously damaged lung without causing secondary ventilator-induced lung injury (VILI). The acutely injured lung becomes time and pressure dependent, meaning that it takes more time and pressure to open the lung, and it recollapses more quickly and at higher pressure. Current protective ventilation strategies, ARDSnet low tidal volume (LVt) and the open lung approach (OLA), have been unsuccessful at further reducing ARDS mortality. We postulate that this is because the LVt strategy is constrained to ventilating a lung with a heterogeneous mix of normal and focalized injured tissue, and the OLA, although designed to fully open and stabilize the lung, is often unsuccessful at doing so. In this review we analyzed the pathophysiology of ARDS that renders the lung susceptible to VILI. We also analyzed the alterations in alveolar and alveolar duct mechanics that occur in the acutely injured lung and discussed how these alterations are a key mechanism driving VILI. Our analysis suggests that the time component of each mechanical breath, at both inspiration and expiration, is critical to normalize alveolar mechanics and protect the lung from VILI. Animal studies and a meta-analysis have suggested that the time-controlled adaptive ventilation (TCAV) method, using the airway pressure release ventilation mode, eliminates the constraints of ventilating a lung with heterogeneous injury, since it is highly effective at opening and stabilizing the time- and pressure-dependent lung. In animal studies it has been shown that by “casting open” the acutely injured lung with TCAV we can (1) reestablish normal expiratory lung volume as assessed by direct observation of subpleural alveoli; (2) return normal parenchymal microanatomical structural support, known as alveolar interdependence and parenchymal tethering, as assessed by morphometric analysis of lung histology; (3) facilitate regeneration of normal surfactant function measured as increases in surfactant proteins A and B; and (4) significantly increase lung compliance, which reduces the pathologic impact of driving pressure and mechanical power at any given tidal volume.

Inhaled aerosolized insulin ameliorates hyperglycemia-induced inflammatory responses in the lungs in an experimental model of acute lung injury

Introduction

Previous studies have shown that patients with diabetes mellitus appear to have a lower prevalence of acute lung injury. We assumed that insulin prescribed to patients with diabetes has an anti-inflammatory property and pulmonary administration of insulin might exert beneficial effects much more than intravenous administration.

Methods

Twenty-eight mechanically ventilated rabbits underwent lung injury by saline lavage, and then the animals were allocated into a normoglycemia group (NG), a hyperglycemia group (HG), an HG treated with intravenous insulin (HG-VI) group or an HG treated with aerosolized insulin (HG-AI) group with continuous infusion of different fluid solutions and treatments: normal saline, 50% glucose, 50% glucose with intravenous insulin, or 50% glucose with inhaled aerosolized insulin, respectively. After four hours of treatment, the lungs and heart were excised en bloc, and then high-mobility group B1 concentration in bronchoalveolar lavage fluid, interleukin-8 and toll-like receptor 4 mRNA expression in bronchoalveolar lavage fluid cells, and lung myeloperoxidase activity were measured.

Results

Treatment with both aerosolized insulin and intravenous insulin attenuated toll-like receptor 4 mRNA expressions in the bronchoalveolar lavage fluid cells. Interleukin-8 and toll-like receptor 4 mRNA expression was significantly lower in the HG-AI group than in the HG-IV group. The lung myeloperoxidase activity in the normal healthy group showed significantly lower levels compared to the NG group but not different compared to those of the HG, HG-VI and HG-AI groups.

Conclusions

The results suggest that insulin attenuates inflammatory responses in the lungs augmented by hyperglycemia in acute lung injury and the insulin's efficacy may be better when administered by aerosol.

Vaporized Perfluorocarbon Confers Protection against Acute Lung Injury by Inhibiting MMP-9 Expression without Protective Effects in other Organs

OBJECTIVE: Vaporized perfluorocarbon (PFC) is a treatment for lung injury; this study investigated its mode of action and potential protective effects on other organs, which are unclear. METHODS: Acute lung injury was induced by lung lavage with artificial seawater in 32 female New Zealand White rabbits. Animals received either conventional mechanical ventilation (CMV), positive end-expiratory pressure under CMV (PEEP), vaporized PFC ventilation, or positive end-expiratory pressure with vaporized PFC ventilation (PEEP + PFC). Histopathology of the lung, small intestine, liver and kidney were investigated. Matrix metalloproteinase (MMP)-9 mRNA levels in the lung were analysed. RESULTS: Pathological injury of the lung was significantly alleviated in the PEEP, PFC and PEEP + PFC groups compared with the CMV group. Tissue damage in the liver, kidney and small intestine was similar between all groups. MMP-9 mRNA levels in the PEEP, PFC and PEEP + PFC groups were significantly lower than those in the CMV group. CONCLUSIONS: Vaporized PFC ventilation can significantly alleviate lung injury but has no significant protective effect on other organs. Alleviation of lung injury may be associated with MMP-9 inhibition.

Flexible bronchoscopy for children on extracorporeal membrane oxygenation for cardiac failure

OBJECTIVE

To describe the safety and use of flexible bronchoscopy in the management of respiratory complications in patients on extracorporeal membrane oxygenation for cardiac failure.

DESIGN

Retrospective cohort study.

SETTING

Pediatric intensive care unit at a tertiary care university hospital.

PATIENTS

Patients requiring extracorporeal membrane oxygenation for cardiac failure in the pediatric intensive care unit between 2003 and 2008.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Forty-eight patients required extracorporeal membrane oxygenation for cardiac failure (32 after surgery for congenital heart disease, 16 for acquired heart disease) during the study period. Seven patients (15%) underwent 17 flexible bronchoscopies. Median age and weight at extracorporeal membrane oxygenation cannulation was 10 days (range, 4 days to 27 yrs) and 3.2 kg (range, 2.8-66 kg), respectively. Median duration of extracorporeal membrane oxygenation in this group was longer than those not undergoing flexible bronchoscopy (314 vs. 114 hrs, p < .001). In all cases, flexible bronchoscopy indication was persistent atelectasis despite conventional ventilator adjustments. Activated clotting time during flexible bronchoscopy was maintained between 180 and 220 secs (normal, 80-150 secs) in all patients. No major complications occurred. A minor complication occurred in one of 17 flexible bronchoscopies (6%), scant oozing that stopped with epinephrine lavage. Findings included bronchus compression or narrowing in four patients and mucous plugging in three patients. Bronchoalveolar lavage specimens identified new ventilator-associated infections in three patients. In two patients with mucous plugging, serial bronchoscopies were accompanied by stepwise decreases in extracorporeal membrane oxygenation flow, thereby facilitating discontinuation from extracorporeal membrane oxygenation support.

CONCLUSIONS

In patients requiring extracorporeal membrane oxygenation for cardiac failure, flexible bronchoscopy can be performed safely, provide important diagnostic information to the bedside clinician, and, perhaps, therapeutic benefit to the patient.

Should mechanical ventilation be guided by esophageal pressure measurements?

PURPOSE OF REVIEW

Despite the well recognized role of mechanical ventilation in lung injury, appropriate surrogate markers to guide titration of ventilator settings remain elusive. One would like to strike a balance between protecting aerated units from overdistension while recruiting unstable units, thereby reducing tissue damage associated with their cyclic recruitment and derecruitment. To do so requires some estimate of the topographical distribution of parenchymal stress and strain.

RECENT FINDINGS

Recent studies have highlighted the importance of chest wall recoil and its effect on pleural pressure (Ppl) in determining lung stress. Although esophageal pressure (Pes) has traditionally been used to measure the average Ppl in normal upright patients, in recumbent acute lung injury/acute respiratory distress syndrome patients Pes-based estimates of Ppl are subject to untestable assumptions. Nevertheless, Pes measurements in recumbent patients with injured lungs strongly suggest that Ppl over dependent parts of the lung can exceed airway pressure by substantial amounts. Moreover, results of a pilot study in which Pes was used to titrate positive end-expiratory pressure (PEEP) suggest clinical benefit.

SUMMARY

Notwithstanding its theoretical limitations, esophageal manometry has shown promise in PEEP titration and deserves further evaluation in a larger trial on patients with injured lungs.

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.

Estabilidade do modelo animal de lesão pulmonar aguda induzida por ácido oleico

OBJETIVO: Avaliar a estabilidade das variáveis hemodinâmicas, da mecânica respiratória e de troca gasosa do modelo animal de lesão pulmonar aguda induzida por ácido oleico. MÉTODOS: Trata-se de um estudo experimental no qual foram utilizados 10 cães de raça indeterminada. As variáveis foram aferidas inicialmente e em 30, 60, 90 e 120 min após a administração do ácido oleico. Para analisar as medidas repetidas, foram testados efeitos lineares e quadráticos e foram utilizados ajustes de modelos lineares mistos com estruturas de variâncias e covariâncias diversificadas, dependendo da variável analisada. RESULTADOS: Observamos estabilidade da pressão arterial média aos 30 min, assim como da frequência cardíaca, da pressão arterial pulmonar e da pressão de capilar pulmonar aos 60 min. Frequência respiratória, volume corrente, volume minuto e trabalho respiratório estabilizaram aos 30 min. Quanto às variáveis de troca gasosa, PaO2, relação PaO2/FiO2 e fração de shunt pulmonar estabilizaram-se aos 30 min. As demais variáveis mantiveram-se em ascensão ou queda contínuas. CONCLUSÕES: O modelo de lesão pulmonar aguda induzida por ácido oleico é estável para algumas das variáveis testadas; porém, a estabilização se dá em momentos diferentes. As variáveis da mecânica respiratória e de troca gasosa estabilizaram em 30 min, e as hemodinâmicas, em 60 min.

Overview of the pathology of three widely used animal models of acute lung injury

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are syndromes of acute diffuse damage to the pulmonary parenchyma by a variety of local or systemic insults. Increased alveolar capillary membrane permeability was recognized as the common end organ injury and a central feature in all forms of ALI/ARDS. Although great strides have been made in understanding the pathogenesis of ALI/ARDS and in intensive care medicine, the treatment approach to ARDS is still relying on ventilatory and cardiovascular support based on the recognition of the clinical picture. In the course of evaluating novel treatment approaches to ARDS, 3 models of ALI induced in different species, i.e. the surfactant washout lavage model, the oleic acid intravenous injection model and the endotoxin injection model, were widely used. This review gives an overview of the pathological characteristics of these models from studies in pigs, dogs or sheep. We believe that a good morphological description of these models, both spatially and temporally, will help us gain a better understanding of the real pathophysiological picture and apply these models more accurately and liberally in evaluating novel treatment approaches to ARDS.