Acid aspiration-induced lung injury in rabbits is mediated by interleukin-8-dependent mechanisms

The response to recruitment worsens with progression of lung injury and fibrin accumulation in a mouse model of acid aspiration

Reopening the injured lung with deep inflation (DI) and positive end-expiratory pressure (PEEP) likely depends on the duration and severity of acute lung injury (ALI), key features of which include increased alveolar permeability and fibrin accumulation. We hypothesized that the response to DI and PEEP would worsen as ALI evolves and that this would correspond with increasing accumulation of alveolar fibrin. C57BL/6 mice were anesthetized and aspirated 75 μl of HCl (pH 1.8) or buffered normal saline. Subgroups were reanesthetized 4, 14, 24, and 48 h later. Following DI, tissue damping (G) and elastance (H) were measured periodically at PEEP of 1, 3, and 6 cmH2O, and air within the lung (thoracic gas volume) was quantified by microcomputed tomography. Following DI, G and H increased with time during progressive lung derecruitment, the latter confirmed by microcomputed tomography. The rise in H was greater in acid-injured mice than in controls ( P < 0.05) and also increased from 4 to 48 h after acid aspiration, reflecting progressively worsening injury. The rise in H was reduced by PEEP, but this effect was significantly blunted by 48 h ( P < 0.05), also confirmed by thoracic gas volume. Lung permeability and alveolar fibrin also increased over the 48-h study period, accompanied by increasing levels and transcription of the fibrinolysis inhibitor plasminogen activator inhibitor-1. Lung injury worsens progressively in mice during the 48 h following acid aspiration. This injury manifests as progressively increasing alveolar instability, likely due to surfactant dysfunction caused by increasing levels of alveolar protein and fibrin.

Impact of low and high tidal volumes on the rat alveolar epithelial type II cell proteome

RATIONALE

Mechanical ventilation with high tidal volumes leads to increased permeability, generation of inflammatory mediators, and damage to alveolar epithelial cells (ATII).

OBJECTIVES

To identify changes in the ATII proteome after two different ventilation strategies in rats.

METHODS

Rats (n = 6) were ventilated for 5 hours with high- and low tidal volumes (VTs) (high VT: 20 ml/kg; low VT: 6 ml/kg). Pooled nonventilated rats served as control animals. ATII cells were isolated and lysed, and proteins were tryptically cleaved into peptides. Cellular protein content was evaluated by peptide labeling of the ventilated groups with (18)O. Samples were fractionated by cation exchange chromatography and identified using electrospray tandem mass spectrometry. Proteins identified by 15 or more peptides were statistically compared using t tests corrected for the false discovery rate.

MEASUREMENTS AND MAIN RESULTS

High Vt resulted in a significant increase in airspace neutrophils without an increase in extravascular lung water. Compared with low-VT samples, high-VT samples showed a 32% decrease in the inositol 1,4,5-trisphosphate 3 receptor (p < 0.01), a 34% decrease in Na(+), K(+)-ATPase (p < 0.01), and a significantly decreased content in ATP synthase chains. Even low-VT samples displayed significant changes, including a 66% decrease in heat shock protein 90-beta (p < 0.01) and a 67% increase in mitochondrial pyruvate carboxylase (p < 0.01). Significant differences were found in membrane, acute phase, structural, and mitochondrial proteins.

CONCLUSIONS

After short-term exposure to high-VT ventilation, significant reductions in membrane receptors, ion channel proteins, enzymes of the mitochondrial energy system, and structural proteins in ATII cells were present. The data supports the two-hit concept that an unfavorable ventilatory strategy may make the lung more vulnerable to an additional insult.

Activation of the alpha7 nAChR reduces acid-induced acute lung injury in mice and rats

New evidence indicates that neural mechanisms can down-regulate acute inflammation. In these studies, we tested the potential role of the alpha7 nicotinic acetylcholine receptor (alpha7 nAChR) in a rodent model of acid-induced acute lung injury. We first determined that the alpha7 nAChR was expressed by alveolar macrophages and lung epithelial cells. Then, using an acid-induced acute lung injury mouse model, we found that nicotine, choline, and PNU-282,987 (a specific alpha7 nAChR agonist) decreased excess lung water and lung vascular permeability, and reduced protein concentration in the bronchoalveolar lavage (BAL). Deficiency of alpha7 nAChR resulted in a 2-fold increase in excess lung water and lung vascular permeability. The reduction of proinflammatory cytokines (macrophage inflammatory protein-2 and TNF-alpha) in the BAL with nicotine probably resulted from the suppression of NF-kappaB activation in alveolar macrophages. The beneficial effect of nicotine was also tested in rat model of acid-induced acute lung injury in which BAL protein and receptor for advanced glycation end products (RAGE), a marker of type I cell injury, were reduced by nicotine treatment. These results indicate that activation of alpha7 nAChR may provide a new therapeutic pathway for the treatment of acute lung injury.

Bench-to-bedside review: the role of activated protein C in maintaining endothelial tight junction function and its relationship to organ injury

Activated protein C (APC) has emerged as a novel therapeutic agent for use in selected patients with severe sepsis, even though the mechanism of its benefit is not well established. APC has anticoagulant, anti-inflammatory, antiapoptotic, and profibrinolytic properties, but it is not clear through which of these mechanisms APC exerts its benefit in severe sepsis. Focus has recently turned to the role of APC in maintaining endothelial barrier function, and in vitro and in vivo studies have examined this relationship. This article critically reviews these studies, with a focus on potential mechanisms of action.

Contributions of histamine, prostanoids, and neurokinins to edema elicited by edema toxin from Bacillus anthracis

Bacillus anthracis edema toxin (ET), composed of protective antigen and an adenylate cyclase edema factor (EF), elicits edema in host tissues, but the target cells and events leading from EF-mediated cyclic-AMP production to edema are unknown. We evaluated the direct effect of ET on several cell types in vitro and tested the possibility that mediators of vascular leakage, such as histamine, contribute to edema in rabbits given intradermal ET. ET increased the transendothelial electrical resistance of endothelial monolayers, a response that is mechanistically inconsistent with the in vivo vascular leakage induced by ET. Screening of several drugs by intradermal treatment prior to toxin injection demonstrated reduced ET-induced vascular leakage with a cyclo-oxygenase inhibitor (indomethacin), agents that interfere with histamine (pyrilamine or cromolyn), or a neurokinin antagonist (spantide). Systemic administration of indomethacin or celecoxib (cyclo-oxygenase inhibitors), pyrilamine, aprepitant (a neurokinin 1 receptor antagonist), or indomethacin with pyrilamine significantly reduced vascular leakage associated with ET. Although the effects of pyrilamine, cromolyn, or aprepitant on ET-induced vascular leakage suggest a possible role for mast cells (MC) and sensory neurons in ET-induced edema, ET did not elicit degranulation of human skin MC or substance P release from NT2N cells in vitro. Our results indicate that ET, acting indirectly or directly on a target yet to be identified, stimulates the production/release of multiple inflammatory mediators, specifically neurokinins, prostanoids, and histamine. These mediators, individually and through complex interactions, increase vascular permeability, and interventions directed at these mediators may benefit hosts infected with B. anthracis.

Animal models of transfusion-related acute lung injury

OBJECTIVE

To examine the existing animal models of transfusion-related acute lung injury (TRALI) for insight into disease pathogenesis.

DATA SOURCE

The data were taken from published research and from our own experimental results.

RESULTS

Animal models have disproved the microaggregate theory of acute lung injury from blood transfusions. The two major hypotheses of TRALI, passively transfused neutrophil and human leukocyte antigen antibodies and biologically active lipids that accumulate in older, cellular blood products, have been replicated in animal models. The proposed two-hit model of TRALI is also supported by animal studies. A new in vivo mouse model of TRALI based on major histocompatibility complex (MHC) I antibodies has replicated several features of human TRALI, focusing prominently on the role of neutrophils.

CONCLUSIONS

Experimental animal models support both the antibody and lipid theories of TRALI. The essential role of neutrophils to producing lung injury is common to all existing models of TRALI. There is a lack of clinically relevant animal models that explain why transfusion of donor antibodies to cognate antigens in the recipient does not always lead to TRALI.

Neutrophils and their Fc gamma receptors are essential in a mouse model of transfusion-related acute lung injury

Transfusion-related acute lung injury (TRALI) is the most common cause of transfusion-related mortality. To explore the pathogenesis of TRALI, we developed an in vivo mouse model based on the passive transfusion of an MHC class I (MHC I) mAb (H2Kd) to mice with the cognate antigen. Transfusion of the MHC I mAb to BALB/c mice produced acute lung injury with increased excess lung water, increased lung vascular and lung epithelial permeability to protein, and decreased alveolar fluid clearance. There was 50% mortality at a 2-hour time point after Ab administration. Pulmonary histology and immunohistochemistry revealed prominent neutrophil sequestration in the lung microvasculature that occurred concomitantly with acute peripheral blood neutropenia, all within 2 hours of administration of the mAb. Depletion of neutrophils by injection of anti-granulocyte mAb Gr-1 protected mice from lung injury following MHC I mAb challenge. FcRgamma-/- mice were resistant to MHC I mAb-induced lung injury, while adoptive transfer of wild-type neutrophils into the FcRgamma-/- animals restored lung injury following MHC I mAb challenge. In conclusion, in a clinically relevant in vivo mouse model of TRALI using an MHC I mAb, the mechanism of lung injury was dependent on neutrophils and their Fc gamma receptors.

PEEP has beneficial effects on inflammation in the injured and no deleterious effects on the noninjured lung after unilateral lung acid instillation

OBJECTIVE

In clinical lung injury areas of inflammation and structural alveolar alteration are unevenly distributed and interspaced between healthy or less injured lung areas. Positive end-expiratory pressure (PEEP) applied with mechanical ventilation (MV) may affect injured and healthy lung areas differently. We compared the effects of PEEP on the inflammatory response in injured and noninjured regions of the lung in an animal model of unilateral lung acid instillation.

SUBJECTS

Anesthetized, paralyzed, and ventilated rats.

INTERVENTIONS

Rats underwent left-endobronchial instillation with either hydrochloric acid or isotonic saline and were randomized 24 h later to MV using constant tidal volume (16 ml/kg) with either ZEEP, PEEP at 5 mmHg, or PEEP at 10 mmHg. After 4 h of MV the animals (n=9 or 10 per group) were killed and inflammatory markers assessed in left- and right-lung lavage fluid samples. In four additional animals per group differential lung perfusion was assessed.

RESULTS

Unilateral acid injury alone worsened oxygenation, decreased left-lung perfusion, and increased left-lung lavage neutrophil and macrophage counts and cytokine levels. MV with ZEEP further impaired oxygenation and further decreased left-lung perfusion in acid-injured animals. MV with high PEEP preserved oxygenation and significantly decreased left-lung lavage protein content and cell counts in acid-injured animals and had no deleterious effect on the right (noninjured) lung.

CONCLUSION

In this model of unilateral lung acid injury high PEEP attenuates the inflammatory cell response in the acid-injured lung, preserved oxygenation and has no deleterious effects in the opposite lung.

Interleukin-8 expression by mammary gland endothelial and epithelial cells following experimental mastitis infection with E. coli

Epithelial and endothelial cells play a pivotal role in initiating and controlling the movement of leukocytes into tissues during inflammation through the production of cytokines and chemokines such as interleukin-8 (IL-8). In situ hybridization with an IL-8 riboprobe was used to determine IL-8 mRNA expression by mammary gland epithelial and endothelial cells in cows with experimental Escherichia coli mastitis. Epithelial cells of the gland, especially surrounding the alveoli, had increased IL-8 mRNA levels at all time points at which tissue samples were collected (8, 12, and 24h) after E. coli challenge. Levels of IL-8 expression in the epithelial cells decreased at 24h post-infection. IL-8 expression by mammary gland endothelial cells was low, but did increase slightly at 24h post-infection. Both epithelial and endothelial cells of the mammary gland can contribute to the production of IL-8 that is typically seen in coliform mastitis.

Pharmacological therapy for acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is an Inflammatory process caused by a variety of direct and indirect injuries to the lungs. Despite improvements in supportive care and advances in ventilator management, mortality in patients with ARDS remains high. Multiple pharmacological interventions have been investigated but have not shown improved survival. Clinical trials using corticosterolds, prostaglandins, nitric oxide, prostacyclin, surfactant, lisofylline, ketoconazole, N-acetylcystelne, and fish oil have been unable to show a statistically significant Improvement in patient mortality. As more is understood about the pathophyslology of ARDS, treatment strategies such as increasing alveolar fluid clearance through activation of sodium channels, enhancing repair of alveolar epithelium with growth factors, inhibiting fibrin deposition, blocking proinflammatory transcription factors, preventing the effect of potent vasocontrictors such as endothelin, and using antibodies against key inflammatory cytokines are being explored. This review focuses on the pharmacological treatments studied clinically, proposed reasons for their lack of success, and new concepts emerging in ARDS therapy.

Is there a role for beta-adrenoceptor agonists in the management of acute lung injury and the acute respiratory distress syndrome?

Despite improvements in general supportive care and ventilatory strategies designed to limit lung injury, no specific pharmacological therapy has yet proven to be efficacious in the management of acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS). Based on experimental studies, as well as studies of the ex-vivo human lung, pulmonary edema fluid clearance from the alveolar space can be augmented by both inhaled and systemic beta2-adrenoceptor agonists (beta2-agonists). Additionally, in the presence of lung injury, beta2-agonists may reduce lung vascular permeability. Treatment with beta2-agonists may also increase the secretion of surfactant and have anti-inflammatory effects. In view of these potentially beneficial effects, beta2-agonist therapy should be evaluated for the treatment of lung injury in humans, particularly because they are already in wide clinical use and do not seem to have serious adverse effects in critically ill patients.

Expression and one-step ion-exchange purification of (AAR)IL-8 (human IL-8 receptor antagonist)

Interleukin-8 (IL-8) is C-X-C chemokine, which is produced by a variety of cells. IL-8 plays an important role in the inflammatory response and may be a therapeutic target for some inflammatory diseases. To develop an IL-8 receptor antagonist, (AAR)IL-8 (IL-8 receptor antagonist) was constructed and successfully expressed in Escherichia coli. (AAR)IL-8 could be easily purified by one-step SP-Sepharose fast flow column after the lysate of recombinant bacterial cells was heated at 70 degrees C for 10 min. The purity of (AAR)IL-8 is more than 95%. This purification process resulted in final purified yields of 4.29 mg (AAR)IL-8/g cell paste. In addition, the purified (AAR)IL-8 can significantly inhibit the chemotaxis that was induced by human IL-8 in vitro and in vivo. These results showed that this purification process is very simple and effective. It could be easily amplified at a larger scale. (AAR)IL-8 might find use as a new therapeutic IL-8 receptor antagonist for some acute and chronic inflammatory diseases.

Protease-activated receptor-2 activation induces acute lung inflammation by neuropeptide-dependent mechanisms

Protease-activated receptors (PARs) and tachykinin-immunoreactive fibers are located in the lung as sentries to respond to a variety of pathological stimuli. The effects of PAR activation on the lung have not been adequately studied. We report on the effects of instilling PAR-activating peptides (PAR-APs, including PAR1-, PAR2-, and PAR4-AP) into the lungs of ventilated or spontaneously breathing mice. PAR2-AP, but not PAR1-AP or PAR4-AP, caused a sharp increase in lung endothelial and epithelial permeability to protein, extravascular lung water, and airway tone. No responses to PAR2-AP were detected in PAR2 knockout mice. In bronchoalveolar lavage, PAR2 activation caused 8- and 5-fold increase in MIP-2 and substance P levels, respectively, and a 12-fold increase in the number of neutrophils. Ablation of sensory neurons (by capsaicin) markedly decreased the PAR2-mediated airway constriction, and virtually abolished PAR2-mediated pulmonary inflammation and edema, as did blockade of NK1 or NK2 receptors. Thus, PAR2 activation in the lung induces airway constriction, lung inflammation, and protein-rich pulmonary edema. These effects were either partly or completely neuropeptide dependent, suggesting that PAR2 can cause lung inflammation by a neurogenic mechanism.

Protective effect of endogenous beta-adrenergic tone on lung fluid balance in acute bacterial pneumonia in mice

Some investigators have reported that endogenous beta-adrenoceptor tone can provide protection against acute lung injury. Therefore, we tested the effects of beta-adrenoceptor inhibition in mice with acute Escherichia coli pneumonia. Mice were pretreated with propranolol or saline and then intratracheally instilled with live E. coli (10(7) colony-forming units). Hemodynamics, arterial blood gases, plasma catecholamines, extravascular lung water, lung permeability to protein, bacterial counts, and alveolar fluid clearance were measured. Acute E. coli pneumonia was established after 4 h with histological evidence of acute pulmonary inflammation, arterial hypoxemia, a threefold increase in lung vascular permeability, and a 30% increase in extravascular lung water as an increase in plasma catecholamine levels. beta-Adrenoceptor inhibition resulted in a marked increase in extravascular lung water that was explained by both an increase in lung vascular permeability and a reduction in net alveolar fluid clearance. The increase in extravascular lung water with propranolol pretreatment was not explained by an increase in systemic or vascular pressures. The increase in lung vascular permeability was explained in part by anti-inflammatory effects of beta-adrenoceptor stimulation because plasma macrophage inflammatory protein-2 levels were higher in the propranolol pretreatment group compared with controls. The decrease in alveolar fluid clearance with propranolol was explained by a decrease in catecholamine-stimulated fluid clearance. Together, these results indicate that endogenous beta-adrenoceptor tone has a protective effect in limiting accumulation of extravascular lung water in acute severe E. coli pneumonia in mice by two mechanisms: 1) reducing lung vascular injury and 2) upregulating the resolution of alveolar edema.

The beta-agonist lung injury trial (BALTI): a randomized placebo-controlled clinical trial

RATIONALE

Experimental data suggest that manipulation of alveolar fluid clearance with beta-agonists can accelerate the resolution of alveolar edema and improve survival.

OBJECTIVE

To determine if a sustained infusion of intravenous salbutamol (albuterol) would accelerate the resolution of alveolar edema in adult patients with acute lung injury (ALI) or acute respiratory distress syndrome (ARDS).

METHODS

This was a single-center, double-blind, randomized controlled trial. Patients with ALI/ARDS were randomized to treatment with intravenous salbutamol (15 microg kg(-1) h(-1)) or placebo for 7 d. The primary endpoint was extravascular lung water measured by thermodilution (PiCCO) at Day 7.

MEASUREMENTS AND MAIN RESULTS

Sixty-six patients were screened; of these, 40 met the inclusion criteria and were enrolled during 2001-2003. Patients in the salbutamol group had significantly lower lung water at Day 7 than the placebo group (9.2 +/- 6 vs. 13.2 +/- 3 ml kg(-1); 95% confidence interval difference, 0.2-8.3 ml kg(-1); p = 0.038). Plateau airway pressure was lower at Day 7 in the salbutamol group (23.9 +/- 3.8 cm H2O) versus placebo (29.5 +/- 7.2 cm H2O; p = 0.049). There was a trend toward lower Murray lung injury score at Day 7 in the salbutamol group (1.7 +/- 0.9) versus placebo (2.0 +/- 0.6; p = 0.2). Patients in the salbutamol group had a higher incidence of supraventricular arrhythmias (26 vs. 10%; p = 0.2).

CONCLUSION

Although further research is required to confirm the efficacy and safety of intravenous salbutamol in ALI/ARDS, this trial provides the first proof of principle that, in humans with ALI/ARDS, sustained treatment with intravenous beta-agonists reduces extravascular lung water.

Aspiration pneumonitis primes the host for an exaggerated inflammatory response during pneumonia

OBJECTIVE

Nosocomial pneumonia is a feared complication in the critically ill patient. Aspiration pneumonitis is frequently complicated by infections. The objective of this study was to determine the influence of aspiration pneumonitis on the host response to a common nosocomial respiratory pathogen.

DESIGN

Controlled, in vivo laboratory study.

SETTING

Research laboratory of a health sciences university.

SUBJECTS

Female C57Bl/6 mice.

INTERVENTIONS

Mice received hydrochloric acid or saline intratracheally followed 16 hrs later by Klebsiella pneumoniae.

MEASUREMENTS AND MAIN RESULTS

Hydrochloric acid induced a mild aspiration pneumonitis. Nonetheless, hydrochloric acid aspiration resulted in a markedly increased inflammatory response in the lung on infection with K. pneumoniae. This enhanced inflammatory reaction was accompanied by a greatly increased outgrowth of K. pneumoniae in lungs of mice previously exposed to hydrochloric acid. Preexisting aspiration pneumonitis also triggered mouse lungs in vivo and alveolar macrophages ex vivo for enhanced release of proinflammatory mediators on stimulation with Klebsiella lipopolysaccharide. Inhibition of tumor necrosis factor-alpha resulted in an increased inflammatory reaction and enhanced bacterial outgrowth in mice with primary K. pneumoniae pneumonia, whereas it had no effect in mice with preexisting aspiration pneumonitis.

CONCLUSIONS

These data indicate a) that aspiration pneumonitis renders the host more susceptible to respiratory tract infection with K. pneumoniae, concurrently priming the lung for an exaggerated inflammatory response; and b) that although tumor necrosis factor-alpha plays a major role in the host response to primary infection, it does not affect lung inflammation or defense after aspiration pneumonitis.

Inhibition of acid-induced lung injury by hyperosmolar sucrose in rats

RATIONALE

Acid aspiration causes acute lung injury (ALI). Recently, we showed that a brief intravascular infusion of hyperosmolar sucrose, given concurrently with airway acid instillation, effectively blocks the ensuing ALI.

OBJECTIVES

The objective of the present study was to determine the extent to which intravascular infusion of hyperosmolar sucrose might protect against acid-induced ALI when given either before or after acid instillation.

METHODS

Our studies were conducted in anesthetized rats and in isolated, blood-perfused rat lungs. We instilled HCl through the airway, and we quantified lung injury in terms of the extravascular lung water (EVLW) content, filtration coefficient (Kfc), and cell counts and protein concentration in the bronchoalveolar lavage. We infused hyperosmolar sucrose via the femoral vein.

RESULTS

In anesthetized rats, airway HCl instillation induced ALI as indicated by a 52% increase of EVLW and a threefold increase in Kfc. However, a 15-min intravenous infusion of hyperosmolar sucrose given up to 1 h before or 30 min after acid instillation markedly blunted the increases in EVLW, as well as the increases in cell count, and in protein concentration in the bronchoalveolar lavage. Hyperosmolar pretreatment also blocked the acid-induced increase of Kfc. Studies in isolated perfused lungs indicated that the protective effect of hyperosmolar sucrose was leukocyte independent.

CONCLUSIONS

We conclude that a brief period of vascular hyperosmolarity protects against acid-induced ALI when the infusion is administered shortly before, or shortly after, acid instillation in the airway. The potential applicability of hyperosmolar sucrose in therapy for ALI requires consideration.

IL-8 and airway neutrophilia in children with gastroesophageal reflux and asthma-like symptoms

Gastroesophageal reflux (GER) may induce respiratory symptoms (RS) through inhalation of acid gastric contents. To characterize the airway inflammation associated with this condition, 20 children [7.4 (0.9) yr old] with "difficult to treat" RS and a positive 24-h oesophageal pH monitoring (pHm) were studied and bronchoalveolar lavage (BAL) performed. The control group included 10 children [7.3 (1.3) yr], non-atopics, with a respiratory clinical history similar to the cases but no reflux, as demonstrated by a negative 24-h oesophageal pHm. On BAL samples, in addition to inflammatory indexes, the lipid-laden macrophage (LLM) index was determined as index of gastric content inhalation. As compared to controls, GER children had higher neutrophil proportion (P=0.002), higher LLM index (P=0.004) and higher concentrations of interleukin (IL)-8 (P=0.005), myeloperoxidase (MPO) (P=0.001) and elastase (P=0.045) in BAL fluid. In GER children, but not in controls, neutrophil proportion significantly correlated with LLM index (r=0.65, P=0.002), with IL-8 (r=0.62, P=0.003) and MPO levels (r=0.54, P=0.014) but not with elastase concentrations. These results suggest an active pathogenetic role of IL-8 in the recruitment and activation of neutrophils in the airways of children with GER, respiratory symptoms and BAL findings suggestive of gastric content aspiration.

Pneumonia versus aspiration pneumonitis in nursing home residents: prospective application of a clinical algorithm

OBJECTIVES

To prospectively evaluate a clinical algorithm for the diagnosis of pneumonitis and pneumonia in nursing home residents.

DESIGN

Prospective cohort study.

SETTING

Inpatient geriatrics unit.

PARTICIPANTS

Nursing home residents admitted to the hospital with suspected pneumonia.

MEASUREMENTS

Identification of pneumonitis and pneumonia using the algorithm; medical record review and abstraction of clinical data; hospital outcome and length of stay.

RESULTS

One hundred seventy episodes of suspected pneumonia were screened with the algorithm and classified into four groups: 25% pneumonia, 28% aspiration pneumonitis of 24 hours or less duration, 12% aspiration pneumonitis of more than 24 hours' duration, and 35% an aspiration event without pneumonitis. Presenting symptoms and signs, laboratory tests, severity of illness measures, or serum C-reactive protein levels did not distinguish between the four groups. Those with an aspiration event without pneumonitis tended to be treated less often with antibiotic therapy after admission (P=.004) and after discharge (P=.01). Of those who survived, there was no significant difference in mean hospital length of stay between the four groups. There was no significant difference in the percentage of case fatality between the four groups, but those with aspiration pneumonitis of 24 hours or less duration and with an aspiration event without pneumonitis had a lower mortality than the other two groups.

CONCLUSION

Distribution of episodes of suspected pneumonia by clinical category as determined using the algorithm was similar to that of the derivation study, as were case fatality rates in each category. These findings suggest that the algorithm may be useful for making the distinction between pneumonitis and pneumonia in nursing home residents; further studies are warranted.

Acid and particulate-induced aspiration lung injury in mice: importance of MCP-1

A model of aspiration lung injury was developed in WT C57BL/6 mice to exploit genetically modified animals on this background, i.e., MCP-1(-/-) mice. Mice were given intratracheal hydrochloric acid (ACID, pH 1.25), small nonacidified gastric particles (SNAP), or combined acid plus small gastric particles (CASP). As reported previously in rats, lung injury in WT mice was most severe for "two-hit" aspiration from CASP (40 mg/ml particulates) based on the levels of albumin, leukocytes, TNF-alpha, IL-1beta, IL-6, MCP-1, KC, and MIP-2 in bronchoalveolar lavage (BAL) at 5, 24, and 48 h. MCP-1(-/-) mice given 40 mg/ml CASP had significantly decreased survival compared with WT mice (32% vs. 80% survival at 24 h and 0% vs. 72% survival at 48 h). MCP-1(-/-) mice also had decreased survival compared with WT mice for CASP aspirates containing reduced particulate doses of 10-20 mg/ml. MCP-1(-/-) mice given 5 mg/ml CASP had survival similar to WT mice given 40 mg/ml CASP. MCP-1(-/-) mice also had differing responses from WT mice for several inflammatory mediators in BAL (KC or IL-6 depending on the particle dose of CASP and time of injury). Histopathology of WT mice with CASP (40 mg particles/ml) showed microscopic areas of compartmentalization with prominent granuloma formation by 24 h, whereas lung tissue from MCP-1(-/-) mice had severe diffuse pneumonia without granulomas. These results indicate that MCP-1 is important for survival in murine aspiration pneumonitis and appears to act partly to protect uninjured lung regions by promoting isolation and compartmentalization of tissue with active inflammation.

Early treatment with pentoxifylline reduces lung injury induced by acid aspiration in rats

STUDY OBJECTIVES

To evaluate the effect of pentoxifylline treatment on gas exchange and mortality immediately after bilateral instillation of hydrochloric acid.

DESIGN

Randomized, prospective, placebo-controlled trial.

SETTING

Animal laboratory of a university hospital.

SUBJECTS

Twenty-four, adult, male Sprague-Dawley rats.

METHODS

Sevoflurane-anesthetized rats (n = 12 in each group) underwent tracheostomy and insertion of a cannula into a hind paw vein and the left carotid artery. All animals received volume-controlled mechanical ventilation (zero positive end-expiratory pressure; fraction of inspired oxygen, 0.21). Acute lung injury was induced by instillation of 0.4 mL/kg 0.1 mol/L hydrochloric acid. The animals were randomized into two groups. The pentoxifylline group (n = 12) received a bolus of 20 mg/kg IV pentoxifylline after aspiration, followed by a continuous infusion of 6 mg/kg/h. The placebo group (n = 12) received an equivalent volume of saline solution. Arterial blood samples were collected for blood gas analysis 15 min and 0 min prior to aspiration and 30, 90, 180, 270, and 360 min after aspiration. Hemodynamic parameters, temperature, and ECG were recorded simultaneously. The primary end point was 6 h after aspiration. All surviving rats were killed by IV administration of pentobarbital. To assess morphologic changes due to lung injury, all animals underwent CT in inspiratory hold at the end of the experiment.

MEASUREMENTS AND RESULTS

No difference in baseline measurements was observed. In pentoxifylline-treated rats, Pao(2) was significantly increased (p < 0.05) at 30, 90, 180, 270, and 360 min. Mortality at 6 h was 17% in the pentoxifylline group vs 67% in the placebo group. Placebo-treated rats showed significant abnormalities in CT lung scans compared with the pentoxifylline group.

CONCLUSIONS

Acid aspiration impairs gas exchange and induces hypotension. Pentoxifylline administration shortly after acid instillation results in significant alleviation of impaired oxygenation, stabilization of BP with higher heart rates, and improved survival after 6 h.

Mild hypothermia reduces expression of intercellular adhesion molecule-1 (ICAM-1) and the accumulation of neutrophils after acid-induced lung injury in the rat

BACKGROUND

The pathophysiology of the acute phase of acid-induced lung injury (AILI) has been elucidated. However, once acute respiratory distress syndrome (ARDS) develops, the mortality rate remains high and there is, as yet, no effective therapy. There are reports that application of mild hypothermia is an effective treatment for ARDS. In this study, we hypothesize that mild hypothermia inhibits activation of neutrophils and expression of intercellular adhesion molecule-1 (ICAM-1) in an injured lung. We studied the effects of mild hypothermia on the expression of ICAM-1 and the accumulation of neutrophils after AILI in the rat.

METHODS

Male Sprague-Dawley rats were randomly allocated to one of the four groups: control normothermic group, induced mild hypothermia group, acid-instilled normothermic group, and acid-instilled group with mild hypothermia. At 6 h after instillation of acid, lungs were removed to measure neutrophil activity and to detect the expression of ICAM-1 in each group.

RESULTS

Oxygenation in acid-instilled rats was significantly impaired as compared to that in non-instilled groups, but induction of mild hypothermia gradually improved oxygenation. Expression of ICAM-1 was enhanced in the acid-instilled normothermic group. By contrast, no overexpression of ICAM-1 and its mRNA was detected in the acid-instilled hypothermic group. In addition, accumulation of neutrophils was markedly inhibited after exposure to mild hypothermia irrespective of the instillation of acid.

CONCLUSION

Our data suggest mild hypothermia can inhibit the adhesion, activation, and accumulation of neutrophils during the acute phase of AILI in the rat and may have the potential to reduce ongoing inflammation of ALI or ARDS.

Differential effects of sustained inflation recruitment maneuvers on alveolar epithelial and lung endothelial injury

OBJECTIVE

The role of recruitment maneuvers in mechanical ventilation for patients with the acute respiratory distress syndrome and acute lung injury remains uncertain in part due to a lack of data on the effects of specific recruitment maneuvers on lung injury severity. The primary objective of this study was to determine the effect of one type of recruitment maneuver--sustained inflation--on alveolar epithelial and lung endothelial injury in experimental acute lung injury.

DESIGN

Randomized experimental study.

SETTING

Academic research laboratory.

SUBJECTS

Forty-nine Sprague-Dawley rats.

INTERVENTIONS

Lung injury was induced in anesthetized, ventilated rats by instillation of acid (pH 1.5) into the airspaces. Rats were ventilated with a tidal volume of 6 mL/kg and a positive end-expiratory pressure of 5 cm H(2)O with or without a sustained inflation recruitment maneuver repeated every 30 mins. Each recruitment maneuver consisted of two 30-sec inflations to total lung capacity (30 cm H(2)O) 1 min apart.

MEASUREMENTS AND MAIN RESULTS

The use of recruitment maneuvers significantly improved oxygenation, compliance, end-expiratory lung volume, functional residual capacity, and deadspace fraction. Recruitment maneuvers reduced extravascular lung water and lung endothelial injury as measured by protein permeability (217 +/- 28 vs. 314 +/- 70 extravascular plasma equivalents [microL], p < .05). However, recruitment maneuvers did not prevent alveolar epithelial injury. Epithelial permeability and bronchoalveolar lavage RTI40 levels, a marker of type I cell injury, were similar with or without recruitment maneuvers. Recruitment maneuvers decreased epithelial fluid transport, a functional marker of epithelial injury. Recruitment maneuvers did not reduce markers of airspace inflammation.

CONCLUSIONS

Sustained inflation recruitment maneuvers improve respiratory mechanics and oxygenation and may protect the lung endothelium but do not reduce alveolar epithelial injury. Because of the differential effects of recruitment maneuvers on the lung endothelium and alveolar epithelium, the net effect in clinical acute lung injury may not be beneficial. Additional clinical studies will be needed to assess the net impact of recruitment maneuvers in patients with acute lung injury.

Progressive, severe lung injury secondary to the interaction of insults in gastric aspiration

This study examines lung injury and inflammation over 24 hours following intratracheal instillation of hydrochloric acid (acid), small nonacidic gastric particles (SNAP), or combined acid and small particles (CASP) in adult rats. The severity and duration of injury was significantly greater for CASP compared to acid or SNAP based on PaO2/FiO2, bronchoalveolar lavage (BAL) albumin, and BAL cell numbers. The inflammatory response associated with aspiration injury from CASP was distinct in several respects. Tumor necrosis factor (TNF)-alpha was greatly reduced in CASP compared to SNAP or acid, whereas interleukin (IL)-1beta was increased. Levels of cytokine-induced neutrophil chemoattractant (CINC)-1, monocyte chemoattractant protein (MCP)-1, and IL-10 in lavage were also significantly increased in animals injured with CASP compared to other forms of aspiration. Statistical analysis showed that BAL levels of IL-10 correlated most strongly with albumin leakage in aspiration-injured animals at 6 and 24 hours, followed by BAL levels of MCP-1. Additional cytokine cluster analyses indicated that levels of MCP-1 and CINC-1 in BAL from all injured animals were strongly correlated with inflammatory neutrophil numbers at 6 and 24 hours post aspiration, and that IL-10 levels in BAL were strongly correlated with inflammatory cell numbers at 24 hours. Preliminary blocking experiments showed that administration of anti-IL-10 antibody increased the albumin permeability index at 6 hours in SNAP and CASP animals, but anti-MCP-1 antibody did not affect the severity of injury. The results of this study support the possibility that different forms of aspiration are associated with identifiable cytokine profiles, and that specific cytokines, including IL-10 and MCP-1, may have utility as diagnostic or prognostic markers in clinical applications.

Chemokines in acute respiratory distress syndrome

A characteristic feature of all inflammatory disorders is the excessive recruitment of leukocytes to the site of inflammation. The loss of control in trafficking these cells contributes to inflammatory diseases. Leukocyte recruitment is a well-orchestrated process that includes several protein families including the large cytokine subfamily of chemotactic cytokines, the chemokines. Chemokines and their receptors are involved in the pathogenesis of several diseases. Acute lung injury that clinically manifests as acute respiratory distress syndrome (ARDS) is caused by an uncontrolled systemic inflammatory response resulting from clinical events including major surgery, trauma, multiple transfusions, severe burns, pancreatitis, and sepsis. Systemic inflammatory response syndrome involves activation of alveolar macrophages and sequestered neutrophils in the lung. The clinical hallmarks of ARDS are severe hypoxemia, diffuse bilateral pulmonary infiltrates, and normal intracardiac filling pressures. The magnitude and duration of the inflammatory process may ultimately determine the outcome in patients with ARDS. Recent evidence shows that activated leukocytes and chemokines play a key role in the pathogenesis of ARDS. The expanding number of antagonists of chemokine receptors for inflammatory disorders may hold promise for new medicines to combat ARDS.

JTE-607, a cytokine release blocker, attenuates acid aspiration-induced lung injury in rats

The present study was designed to clarify the effects of (-)-ethyl N-[3,5-dichloro-2-hydroxy-4-[2-(4-methyl-piperazin-1-yl)ethoxy]benzoyl]-l-phenylalaninate dihydrochloride (JTE-607), a novel multiple cytokine inhibitor, on hydrochloric acid (HCl) aspiration lung injury in rats. HCl (0.1 N, 2 ml kg(-1)) was instilled into male Sprague-Dawley rats that were pretreated with or without JTE-607 (30 or 75 mg kg(-1) h(-1)). As a control, normal saline (2 ml kg(-1)) was instilled in rats. All the animals were anesthetized with intraperitoneally injected pentobarbital sodium (40 mg kg(-1)). Bronchoalveolar lavage was performed 5 h (h) after HCl or normal saline instillation. In bronchoalveolar lavage fluid, the increases in total nuclear cell counts, neutrophil counts, optical density at 412 nm as an indication of pulmonary hemorrhage, concentrations of albumin, tumor necrosis factor (TNF)-alpha, interleukin (IL)-6 and cytokine-induced neutrophil chemoattractant induced by HCl instillation were significantly reduced by JTE-607 pretreatment. The level of expression of tumor necrosis factor-alpha and interleukin-6 mRNA in lung tissue was analyzed. The mean expression level of tumor necrosis factor-alpha and interleukin-6 mRNA in the JTE-607 group was lower than that in the HCl and NS groups. The wet-to-dry weight ratio was also determined, and JTE-607 at the dose of 75 mg kg(-1) h(-1) significantly attenuated the increased wet-to-dry weight ratio induced by HCl. These results suggest that JTE-607 can inhibit the production of inflammatory cytokines such as tumor necrosis factor-alpha, interleukin-6 and cytokine-induced neutrophil chemoattractant and attenuate acid-induced lung injury in rats. This agent might be therapeutically useful for lung injury.

Increased CXCL8 (IL-8) expression in Multiple Sclerosis

Multiple Sclerosis (MS) is a chronic inflammatory disease of the CNS which is characterized by large mononuclear cell infiltration and significant demyelination. CXCL8 is a chemo-attractant for both neutrophils and monocytes and triggers their firm adhesion to endothelium. In this study, we demonstrate that serum CXCL8 and CXCL8 secretion from PBMCs are significantly higher in untreated MS patients compared to controls and are significantly reduced in MS patients receiving interferon-beta1a therapy. We suggest that CXCL8 may serve as a marker of monocyte activity in MS and may play a role in monocyte recruitment to the CNS.

Topical interleukin-8 antibody attracts leukocytes in a piglet lavage model

OBJECTIVE

Acute respiratory distress syndrome (ARDS) in young infants is linked with a pulmonary inflammatory response part of which are increased interleukin-8 (IL-8) levels and migration of polymorphonuclear leukocytes (PMNL) into lung tissue. A topical application of an antibody against IL-8 might therefore decrease PMNL migration and improve lung function.

DESIGN

Randomized, controlled, prospective animal study.

SETTING

Research laboratory of a university children's hospital.

SUBJECTS AND INTERVENTIONS

Anesthetized, mechanically ventilated newborn piglets (n=22) underwent repeated airway lavage to remove surfactant and to induce lung inflammation. Piglets then received either surfactant alone (S, n=8), or a topical antibody against IL-8 admixed to surfactant (S+IL-8, n=8), or an air bolus injection (control, n=6).

MEASUREMENTS AND RESULTS

After 6 h of mechanical ventilation following intervention, oxygenation [S 169+/-51 (SD) vs S+IL-8 139+/-61 mmHg] and lung function (compliance: S 1.3+/-0.4 vs S+IL-8 0.9+/-0.4 ml/cmH(2)O/kg; extra-vascular lung-water: S 27+/-9 vs S+IL-8 52+/-28 ml/kg) were worse in the S+IL-8 group because reactive IL-8 production [S 810 (median, range 447-2323] vs S+IL-8 3485 (628-16180) pg/ml; P<0.05) with facilitated migration of PMNL into lung tissue occurred. Moreover, antibody application caused augmented chemotactic potency of IL-8 [linear regression of migrated PMNL and IL-8 levels: S r(2)=0.30 (P=ns) vs S+IL-8 r(2)=0.89 (P=0.0002)].

CONCLUSION

Topical anti-IL-8 treatment after lung injury increases IL-8 production, PMNL migration, and worsens lung function in our piglet lavage model. This effect is in contrast to current literature using pre-lung injury treatment protocols. Our data do not support anti-IL-8 treatment in young infants with ARDS.

Acute lung injury and acute respiratory distress syndrome in pregnancy

Acute respiratory failure can be the result of a variety of clinical conditions, such as congestive heart failure, pneumonia, pulmonary embolism, exacerbation of obstructive lung diseases, and acute respiratory distress syndrome (ARDS). This article focuses on developments related to acute lung injury and ARDS and reviews epidemiology, pathogenesis and therapeutic advances with an emphasis on the obstetric population. A brief discussion of tocolytic-induced pulmonary edema, preeclampsia, venous air embolism, and aspiration-related ARDS is included. Management of pregnant women with ARDS is outlined.

Hydrochloric acid-induced lung injury: effects of early partial liquid ventilation on survival rate, gas exchange, and pulmonary neutrophil accumulation

OBJECTIVE

Partial liquid ventilation can improve respiratory functions in acid-induced lung injury. We studied the effects of the interval between induction of injury and initiation of partial liquid ventilation on survival, gas exchange, and pulmonary neutrophil accumulation.

MATERIAL AND METHODS

Anesthetized rats were randomly assigned to one of five groups ( n = 6 per group). Group 1 served as the control group, in the other groups an extended lung injury was induced by intratracheal instillation of hydrochloric acid. Whereas lungs of group 2 were gas-ventilated, group 3 received an early partial liquid ventilation (5 min after acid instillation) and group 4 a delayed partial liquid ventilation (30 min after acid instillation, 5 ml/kg perfluorocarbon). Group 5 received an additional continuous perfluorocarbon application of 5 ml x kg(-1) x h(-1) (30 min after acid instillation). Blood gases were measured with an intravascular blood gas sensor.

RESULTS

Acid instillation resulted in a marked decrease in PO(2)-values within 30 min (from 481+/-37 mmHg to 128+/-71 mmHg, FiO(2) 1.0). Survival rate of the study period (12 h) was higher with early partial liquid ventilation. We observed no differences between groups in peak PO(2)-values during treatment. Histopathological examination, however, showed less pulmonary neutrophil accumulation in lungs of the early partial liquid ventilation group when compared to the delayed partial liquid ventilation group.

CONCLUSIONS

Our results suggest that early partial liquid ventilation increases survival after extended acid-induced lung injury. While effects on arterial oxygenation appear not to predict acute survival we observed less intrapulmonary neutrophil accumulation with early partial liquid ventilation.

Clinically relevant concentrations of beta2-adrenergic agonists stimulate maximal cyclic adenosine monophosphate-dependent airspace fluid clearance and decrease pulmonary edema in experimental acid-induced lung injury

OBJECTIVE

To determine whether clinically relevant airspace concentrations of beta2-adrenergic agonists stimulated maximal alveolar fluid clearance rates and to determine whether beta2 agonist therapy decreased pulmonary edema in experimental acute lung injury.

DESIGN

Prospective randomized laboratory investigation.

SETTING

University-affiliated laboratory.

SUBJECTS

Sprague Dawley rats.

INTERVENTIONS

Dibutyryl cyclic adenosine monophosphate (cAMP), salmeterol, albuterol, and isoproterenol in normal rat lung. Salmeterol in a rat model of acid-induced lung injury.

MEASUREMENTS AND MAIN RESULTS

Basal alveolar fluid clearance was 7.6 +/- 2.2 %/hr. Maximal cAMP-dependent alveolar fluid clearance rate was 32.9 +/- 10.9 %/hr (p <.05). Racemic albuterol 10(-5) M, salmeterol 10(-6) M, and isoproterenol 10(-6) M each stimulated alveolar fluid clearance to a level comparable to maximal cAMP-dependent alveolar fluid clearance. Compared with basal rates, alveolar fluid clearance was increased by both racemic albuterol 10(-6) M (14.5 +/- 3.0%, p <.05) and R-enantiomer 10(-6) M (15.0 +/- 4.6%, p <.05), but there was no difference between the two groups. Intra-alveolar salmeterol 10 (-6) M attenuated the degree of pulmonary edema following acid-induced lung injury. Extravascular lung water increased to only 180 +/- 30 microL with salmeterol treatment, compared with 296 +/- 65 microL in saline-treated rats 4 hrs after acid injury (p <.05). This decrease in lung water was accompanied by a 2.4-fold increase in the rate of alveolar fluid clearance at 4 hrs in the salmeterol-treated group. Lung endothelial permeability, expressed as extravascular plasma equivalents, was reduced to 64 +/- 9 microL with salmeterol compared with 119 +/- 51 microL in saline-treated rats 4 hrs after acid injury (p <.05).

CONCLUSIONS

Clinically relevant airspace concentrations of beta2-adrenergic agonists a) stimulate maximal cAMP-dependent airspace fluid clearance in normal lungs and b) reduce pulmonary edema in acid aspiration-induced lung injury by increasing alveolar fluid clearance and decreasing endothelial permeability. Clinical studies are required to determine whether beta2-adrenergic agonists improve outcome in patients with acute lung injury.

Pulmonary endothelium in acute lung injury: from basic science to the critically ill

BACKGROUND

Pulmonary endothelium is an active organ possessing numerous physiological, immunological, and metabolic functions. These functions may be altered early in acute lung injury (ALI) and further contribute to the development of acute respiratory distress syndrome (ARDS). Pulmonary endothelium is strategically located to filter the entire blood before it enters the systemic circulation; consequently its integrity is essential for the maintenance of adequate homeostasis in both the pulmonary and systemic circulations. Noxious agents that affect pulmonary endothelium induce alterations in hemodynamics and hemofluidity, promote interactions with circulating blood cells, and lead to increased vascular permeability and pulmonary edema formation.

OBJECTIVE

We highlight pathogenic mechanisms of pulmonary endothelial injury and their clinical implications in ALI/ARDS patients.

Cytokine-mediated inflammation in acute lung injury

Clinical acute lung injury (ALI) is a major cause of acute respiratory failure in critically ill patients. There is considerable experimental and clinical evidence that pro- and anti-inflammatory cytokines play a major role in the pathogenesis of inflammatory-induced lung injury from sepsis, pneumonia, aspiration, and shock. A recent multi-center clinical trial found that a lung-protective ventilatory strategy reduces mortality by 22% in patients with ALI. Interestingly, this protective ventilatory strategy was associated with a marked reduction in the number of neutrophils and the concentration of pro-inflammatory cytokines released into the airspaces of the injured lung. Further research is needed to establish the contribution of cytokines to both the pathogenesis and resolution of ALI.

Bench-to-bedside review: acute respiratory distress syndrome - how neutrophils migrate into the lung

Acute lung injury and its more severe form, acute respiratory distress syndrome, are major challenges in critically ill patients. Activation of circulating neutrophils and transmigration into the alveolar airspace are associated with development of acute lung injury, and inhibitors of neutrophil recruitment attenuate lung damage in many experimental models. The molecular mechanisms of neutrophil recruitment in the lung differ fundamentally from those in other tissues. Distinct signals appear to regulate neutrophil passage from the intravascular into the interstitial and alveolar compartments. Entry into the alveolar compartment is under the control of CXC chemokine receptor (CXCR)2 and its ligands (CXC chemokine ligand [CXCL]1–8). The mechanisms that govern neutrophil sequestration into the vascular compartment of the lung involve changes in the actin cytoskeleton and adhesion molecules, including selectins, β₂ integrins and intercellular adhesion molecule-1. The mechanisms of neutrophil entry into the lung interstitial space are currently unknown. This review summarizes mechanisms of neutrophil trafficking in the inflamed lung and their relevance to lung injury.

Surfactant lavage with lidocaine improves pulmonary function in piglets after HCl-induced acute lung injury

Acute respiratory distress syndrome (ARDS) is associated with significant morbidity and mortality. The pathophysiology of ARDS includes abnormalities of surfactant function as well as pulmonary inflammation. Immunomodulating drugs, like Lidocaine, have shown some success in decreasing inflammation in ARDS. We attempted to combine surfactant lavage's ability to reverse the surfactant dysfunction, while acting as a vehicle to deliver Lidocaine. Gravity-driven surfactant (Infasurf) lavage (35 ml/kg) was administered alone or mixed with Lidocaine after severe HCl acid injury (0.3 N; 3 cc/kg) in neonatal piglets. Treatment groups included: control (C) ( n = 5), surfactant lavage (SL) (35 ml/kg-diluted Infasurf) ( n = 7) and SL mixed with Lidocaine (SL+L) ( n = 7). About 26-27% of the lavage was retained (phospholipid 73-74 mg/kg; Lidocaine 1.8 mg/kg). Oxygenation progressively increased in the SL and SL+L groups over the 4-hour period (at 240 min: C = 99 +/- 14; SL = 154 +/- 39; SL+L = 230 +/- 40 mmHg) ( p < 0.05). PaCO(2) increased in all groups from 43 +/- 0.3 to 55 +/- 0.7 mmHg. Only SL+L showed a reduction in PaCO(2) (at 240 min: C = 54 +/- 4; SL = 53 +/- 7; SL+L = 49 +/- 2 mmHg) ( p < 0.05). Finally, SL and SL + L had superior characteristics during the quasi-static pressure volume (PV) procedure as compared to Control ( p < 0.05). In our HCl ALI model, SL improved oxygenation and quasi-static lung compliance over C. The pulmonary function effects of SL were further enhanced by the addition of Lidocaine to the surfactant suspension. Combining therapeutic agents with surfactant lavage may be an effective strategy in ALI.

Single‐Dose Activated Charcoal‐Backup and Reassess

Single-dose activated charcoal (SDAC) is frequently administered to poisoned patients. The assumption is that toxin absorption is prevented and that toxicity (as defined by morbidity and mortality) of the poisoning is decreased. Yet there is no evidence that SDAC improves outcome. Risks of this procedure have not been determined. The reported adverse events following SDAC administration are reviewed and risk:benefit ratio for this procedure is discussed.

Elastase inhibition reduced death associated with acid aspiration-induced lung injury in hamsters

This study examined whether the specific inhibition of neutrophil elastase by sivelestat sodium hydrate (sivelestat) reduced deaths associated with severe acute lung injury after hydrochloric acid (HCl) aspiration in hamsters. Animals that received a single intratracheal instillation of HCl (0.2 N, 200 microL) time-dependently died by occlusion of their trachea with inflammatory exudate. In a time course study, these animals developed severe lung injury, peaking 12 to 24 h after HCl instillation, as indicated by hemorrhage and a massive increase in the protein concentration of bronchoalveolar lavage fluid. These changes were closely correlated with neutrophil elastase activity in bronchoalveolar lavage fluid. Sivelestat (0.01, 0.1 and 1 mg/kg/h), when intravenously infused during the first 48 h post-HCl instillation, dose-dependently reduced death in HCl-instilled hamsters. In a separate experiment, analysis of bronchoalveolar lavage fluid parameters and partial pressure of arterial oxygen (PaO(2)) 8 h post-HCl instillation showed that sivelestat at 1 mg/kg/h, i.v. significantly improved both bronchoalveolar lavage fluid parameters and PaO(2) levels with evidence of the inhibition of neutrophil elastase activity in bronchoalveolar lavage fluid. These results suggest that neutrophil elastase plays a significant role in this type of severe acute lung injury that leads to death by respiratory failure.

Efficacy of partial liquid ventilation in improving acute lung injury induced by intratracheal acidified infant formula: determination of optimal dose and positive end-expiratory pressure level

OBJECTIVES

Partial liquid ventilation with fluorocarbon was successfully used for acute lung injury induced by oleic acid or lung lavage. Positive end-expiratory pressure (PEEP) during partial liquid ventilation enhances the efficacy of fluorocarbon. The aim of the current study was to assess whether partial liquid ventilation can repair lung damage induced by intratracheal acidified infant formula and to determine the optimal fluorocarbon dose and PEEP level.

DESIGN

Prospective, randomized animal study.

SETTING

University research laboratory.

SETTING AND SUBJECTS

Seventy-six male anesthetized rabbits.

INTERVENTIONS

For study 1, acute lung injury was induced by intratracheal acidified infant formula in four groups. Next, three groups received 10, 15, or 20 mL/kg fluorocarbon, and the fourth group was conventionally gas ventilated. For study 2, acute lung injury was induced in five groups. One group was gas ventilated at a PEEP of 5 cm H2O, whereas the other four groups received fluorocarbon (15 mL/kg) and were assigned to one of four PEEP levels (5, 7.5, 10, or 12.5 cm H2O). The lungs were ventilated with 100% oxygen for 4 hrs after acute lung injury.

MEASUREMENTS AND MAIN RESULTS

In study 1, fluorocarbon at doses of 15 and 20 mL/kg attenuated lung leukosequestration and edema and superoxide production of neutrophils, resulting in similar improvements in oxygenation, lung mechanics, and pathologic changes. The highest fluorocarbon dose caused mortality from pneumothorax. In study 2, the combination of PEEP with partial liquid ventilation improved gas exchange, lung compliance, pulmonary edema, and histologically observed damage. The beneficial effects of PEEP at 10 and 12.5 cm H2O were similar. Adverse side effects of 12.5 cm H2O PEEP included pneumothorax and hemodynamic instability.

CONCLUSIONS

The combination of fluorocarbon and PEEP improved the physiologic, biochemical, and histologic lung injury induced by acidified infant formula. The beneficial effects of partial liquid ventilation are due, in part, to inhibition of pulmonary neutrophil accumulation and activation with fluorocarbon. The optimal fluorocarbon dose and PEEP level in our model were 15 mL/kg and 10 cm H2O, respectively.

Neutrophil depletion attenuates interleukin-8 production in mild-overstretch ventilated normal rabbit lung

OBJECTIVE

Acute lung injury induced by lung overstretch is associated with neutrophil influx, but the pathogenic role of neutrophils in overstretch-induced lung injury remains unclear.

DESIGN

To assess the contribution of neutrophils, we compared the effects of noninjurious large tidal volume (Vt) ventilation on lungs in normal and neutrophil-depleted animals.

SETTING

Research animal laboratory.

SUBJECTS

Twenty-six male Japanese white rabbits.

INTERVENTIONS

Animals were mechanically ventilated for 4 hrs with one of the three following protocols: large Vt (20 mL/kg), small Vt (8 mL/kg), and large Vt (20 mL/kg) with neutrophil depletion achieved by a single dose of vinblastine injection (0.75 mg/kg) intravenously 4 days before the experiment.

MEASUREMENTS AND MAIN RESULTS

Large Vt ventilation produced alveolar neutrophil influx compared with low Vt (p =.002) without evidence of edema or increased epithelial permeability. The neutrophil influx was accompanied by increases in interleukin-8 in bronchoalveolar lavage fluid (p =.04). Immunohistochemistry of large Vt lungs showed increased interleukin-8 staining in bronchial epithelial cells, alveolar epithelium, alveolar macrophages, and smooth muscles of pulmonary vessels. Neutrophil depletion attenuated the interleukin-8 increase in the lung. Large Vt did not increase plasma interleukin-8 or tumor necrosis factor-alpha in plasma and bronchoalveolar lavage fluid. No expression of p-selectin or intercellular adhesion molecule-1 was observed.

CONCLUSIONS

Cyclic overstretching of normal rabbit lungs with noninjurious large Vt produced neutrophil influx and interleukin-8 increase in bronchoalveolar lavage fluid. Production of pulmonary interleukin-8 by lung overstretch might require the interaction between resident lung cells and migrated neutrophils. This study suggests that large Vt ventilation potentiates the predisposed, subclinical lung injury, such as nosocomial pneumonia or aspiration of gastric contents.

Flow cytometric detection of cell-associated interleukin-8 in alveolar macrophages in vivo from patients with hypersensitivity pneumonitis and sarcoidosis

In comparison with neutrophil-mediated lung diseases, such as acute respiratory distress syndrome, the involvement of IL-8 in lymphocyte-mediated lung diseases has not been fully investigated. Several reports have shown a slight increase in bronchoalveolar lavage fluid (BALF) IL-8 in patients with hypersensitivity pneumonitis (HP) and sarcoidosis (SAR), but the source of the IL-8 has not been clarified. In the present study, the in vivo production of IL-8 by alveolar macrophages (AMs) is examined in these patients by analyzing the cell-associated IL-8, using the flow cytometric method adopted previously. The IL-8 levels in the epithelial lining fluid (ELF) were also assessed. Initially, slight, but significant, increased levels of ELF IL-8 in HP and SAR were confirmed. Using flow cytometric analysis, a significant increase was found in the cell-associated IL-8 of the freshly isolated AMs in HP, but not in SAR, indicating in vivo production of IL-8 by AMs in HP. The cell-associated IL-8 of the AMs cultured with or without lipopolysaccharide was also analyzed. However, in contrast to previous findings in patients with idiopathic pulmonary fibrosis, no differences were found between SAR and HP patients and control subjects. Based on these findings, it is speculated that ELF IL-8 levels are slightly increased in HP and SAR, and they may contribute to the accumulation of neutrophils and possibly lymphocytes. However, the source of IL-8 may be different and AMs are the candidate source of IL-8 in HP, but not in SAR. The flow cytometric method may be useful in assessing cytokines production by AMs.

Dynamic mechanical consequences of deep inflation in mice depend on type and degree of lung injury

In a previous study (Allen G, Lundblad LK, Parsons P, and Bates JH. J Appl Physiol 93: 1709-1715, 2002), our laboratory used deep inflations (DI) in mice to show that recruitment of closed lung units can be a very transient phenomenon in lung injury. The purpose of this study was to investigate how this transience of lung recruitment depends on the nature and degree of acute lung injury. Mice were administered 50 microl of either saline (n = 8), 0.01 M (n = 9) or 0.025 M (n = 8) hydrochloric acid, or 50 microg (n = 10) or 150 microg (n = 6) of LPS and were mechanically ventilated 24-48 h later. At various levels of positive end-expiratory pressure, two DIs were delivered, and forced oscillations were used to obtain a measure of lung stiffness (H) periodically over 7 min. After LPS exposure, pressure-volume curve hysteresis and recovery in H after DI were no different from saline-exposed controls despite 500 times more neutrophils in bronchoalveolar lavage fluid. Pressure-volume hysteresis and recovery in H were increased in acid-exposed mice (P < 0.001) and were correlated with bronchoalveolar lavage fluid protein content (R = 0.81). Positive end-expiratory pressure reduced recovery in H in all groups (P < 0.01) but reduced pressure-volume hysteresis in the acid-injured groups only (P < 0.001). We conclude that the effects of DIs in acute lung injury depend on the degree of lung injury but only to the extent that this injury reflects a disruption of the air-liquid interface.

Bench-to-bedside review: beta2-Agonists and the acute respiratory distress syndrome

The acute respiratory distress syndrome (ARDS) is a devastating constellation of clinical, radiological and pathological signs characterized by failure of gas exchange and refractory hypoxia. Despite nearly 30 years of research, no specific pharmacological therapy has yet proven to be efficacious in manipulating the pathophysiological processes that underlie this condition. Several in vitro and in vivo animal or human studies suggest a potential role for β₂-agonists in the treatment of ARDS. These agents have been shown to reduce pulmonary neutrophil sequestration and activation, accelerate alveolar fluid clearance, enhance surfactant secretion, and modulate the inflammatory and coagulation cascades. They are also used widely in clinical practice and are well tolerated in critically ill patients. The present review examines the evidence supporting a role for β₂-agonists as a specific pharmacological intervention in patients with ARDS.

M1/70 attenuates blood-borne neutrophil oxidants, activation, and myofiber damage following stretch injury

The purpose of this study was to determine the role of the CD11b-dependent respiratory burst in neutrophil oxidant generation and activation, interleukin-8 (IL-8) production, and myofiber damage after muscle stretch injury by using the monoclonal antibody M1/70 to block this pathway. Twelve male New Zealand White rabbits were randomly assigned to a treatment group: M1/70 (n = 6), IgG isotype control (n = 3), or saline control (n = 3). After intravenous injection of the assigned agent under gas anesthesia, a standardized single-stretch injury was created in the right tibialis anterior, whereas the left tibialis anterior underwent a sham surgery. Blood-borne neutrophil oxidant generation and CD11b receptor density and plasma IL-8 levels were measured pre- and 24 h postinjury. Damage was assessed histologically at the hematoma site by counting torn myofibers. M1/70 group demonstrated decreased blood-borne neutrophil oxidant generation (P < 0.05) and CD11b receptor density (P < 0.05), an increase in plasma IL-8 concentration (P < 0.01), and less torn myofibers (P < 0.01) compared with IgG isotype or saline control groups. These data indicate that 1). CD11b-dependent respiratory burst is a major source of oxidants produced by the neutrophil, and that treatment with M1/70 2). attenuates neutrophil activation status, 3). increases plasma IL-8 concentration, and 4). minimizes myofiber damage 24 h postmuscle stretch injury.

Pressure-controlled ventilation attenuates lung microvascular injury in a rat model of activated charcoal aspiration

BACKGROUND

Previous animal data suggest that aspiration of activated charcoal is associated with pulmonary microvascular injury that may be related to excessive ventilator-induced airway pressures. The purpose of this study was to test the hypothesis that ventilator-induced airway trauma contributes to the lung vascular injury observed following activated charcoal aspiration.

METHODS

Capillary filtration coefficient (Kf,c), a sensitive measure of lung microvascular permeability, was determined isogravimetrically prior to and after intratracheal instillation of 0.4 ml/kg (12% weight/vol. solution, pH 7.4) activated charcoal oran equal volume of sterile water in isolated, perfused rat lungs in which ventilation was either pressure-controlled at 10cm H2O or volume-controlled at 5 ml/kg.

RESULTS

There was significant lung injury in both activated charcoal groups regardless of ventilation method compared to control lungs or lungs administered sterile water (p < 0.05 ANOVA). However, injury to pressure-controlled ventilated lungs was significantly less than lungs ventilated with traditional, volume-controlled ventilation.

CONCLUSION

The results of this investigation demonstrate that pressure-controlled ventilation reduces the lung microvascular injury observed following aspiration of activated charcoal as compared to traditional volume-controlled ventilation methods.

A potent inhibitor of cytosolic phospholipase A2, arachidonyl trifluoromethyl ketone, attenuates LPS-induced lung injury in mice

Acute respiratory distress syndrome (ARDS) is an acute lung injury of high mortality rate, and sepsis syndrome is one of the most frequent causes of ARDS. Metabolites of arachidonic acid, including thromboxanes and leukotrienes, are proinflammatory mediators and potentially involved in the development of ARDS. A key enzyme for the production of these inflammatory mediators is cytosolic phospholipase A(2) (cPLA(2)). Recently, it has been reported that arachidonyl trifluoromethyl ketone (ATK) is a potent inhibitor of cPLA(2). In the present study, we hypothesized that pharmacological intervention of cPLA(2) could affect acute lung injury. To test this hypothesis, we examined the effects of ATK in a murine model of acute lung injury induced by septic syndrome. The treatment with ATK significantly attenuated lung injury, polymorphonuclear neutrophil sequestration, and deterioration of gas exchange caused by lipopolysaccharide and zymosan administration. The current observations suggest that pharmacological intervention of cPLA(2) could be a novel therapeutic approach to acute lung injury caused by sepsis syndrome.

High tidal volume ventilation induces NOS2 and impairs cAMP- dependent air space fluid clearance

Tidal volume reduction during mechanical ventilation reduces mortality in patients with acute lung injury and the acute respiratory distress syndrome. To determine the mechanisms underlying the protective effect of low tidal volume ventilation, we studied the time course and reversibility of ventilator-induced changes in permeability and distal air space edema fluid clearance in a rat model of ventilator-induced lung injury. Anesthetized rats were ventilated with a high tidal volume (30 ml/kg) or with a high tidal volume followed by ventilation with a low tidal volume of 6 ml/kg. Endothelial and epithelial protein permeability were significantly increased after high tidal volume ventilation but returned to baseline levels when tidal volume was reduced. The basal distal air space fluid clearance (AFC) rate decreased by 43% (P < 0.05) after 1 h of high tidal volume but returned to the preventilation rate 2 h after tidal volume was reduced. Not all of the effects of high tidal volume ventilation were reversible. The cAMP-dependent AFC rate after 1 h of 30 ml/kg ventilation was significantly reduced and was not restored when tidal volume was reduced. High tidal volume ventilation also increased lung inducible nitric oxide synthase (NOS2) expression and air space total nitrite at 3 h. Inhibition of NOS2 activity preserved cAMP-dependent AFC. Because air space edema fluid inactivates surfactant and reduces ventilated lung volume, the reduction of cAMP-dependent AFC by reactive nitrogen species may be an important mechanism of clinical ventilator-associated lung injury.