Elastin fibers and the diagnosis of bacterial pneumonia in the adult respiratory distress syndrome

Clinical practice guidelines for hospital-acquired pneumonia and ventilator-associated pneumonia in adults

Hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) are important causes of morbidity and mortality, with mortality rates approaching 62%. HAP and VAP are the second most common cause of nosocomial infection overall, but are the most common cause documented in the intensive care unit setting. In addition, HAP and VAP produce the highest mortality associated with nosocomial infection. As a result, evidence-based guidelines were prepared detailing the epidemiology, microbial etiology, risk factors and clinical manifestations of HAP and VAP. Furthermore, an approach based on the available data, expert opinion and current practice for the provision of care within the Canadian health care system was used to determine risk stratification schemas to enable appropriate diagnosis, antimicrobial management and nonantimicrobial management of HAP and VAP. Finally, prevention and risk-reduction strategies to reduce the risk of acquiring these infections were collated. Future initiatives to enhance more rapid diagnosis and to effect better treatment for resistant pathogens are necessary to reduce morbidity and improve survival.

Lung parenchymal mechanics in health and disease

The mechanical properties of lung tissue are important determinants of lung physiological functions. The connective tissue is composed mainly of cells and extracellular matrix, where collagen and elastic fibers are the main determinants of lung tissue mechanical properties. These fibers have essentially different elastic properties, form a continuous network along the lungs, and are responsible for passive expiration. In the last decade, many studies analyzed the relationship between tissue composition, microstructure, and macrophysiology, showing that the lung physiological behavior reflects both the mechanical properties of tissue individual components and its complex structural organization. Different lung pathologies such as acute respiratory distress syndrome, fibrosis, inflammation, and emphysema can affect the extracellular matrix. This review focuses on the mechanical properties of lung tissue and how the stress-bearing elements of lung parenchyma can influence its behavior.

Diagnosis of ventilator-associated pneumonia: a systematic review of the literature

INTRODUCTION

Early, accurate diagnosis is fundamental in the management of patients with ventilator-associated pneumonia (VAP). The aim of this qualitative review was to compare various criteria of diagnosing VAP in the intensive care unit (ICU) with a special emphasis on the value of clinical diagnosis, microbiological culture techniques, and biomarkers of host response.

METHODS

A MEDLINE search was performed using the keyword 'ventilator associated pneumonia' AND 'diagnosis'. Our search was limited to human studies published between January 1966 and June 2007. Only studies of at least 25 adult patients were included. Predefined variables were collected, including year of publication, study design (prospective/retrospective), number of patients included, and disease group.

RESULTS

Of 572 articles fulfilling the initial search criteria, 159 articles were chosen for detailed review of the full text. A total of 64 articles fulfilled the inclusion criteria and were included in our review. Clinical criteria, used in combination, may be helpful in diagnosing VAP, however, the considerable inter-observer variability and the moderate performance should be taken in account. Bacteriologic data do not increase the accuracy of diagnosis as compared to clinical diagnosis. Quantitative cultures obtained by different methods seem to be rather equivalent in diagnosing VAP. Blood cultures are relatively insensitive to diagnose pneumonia. The rapid availability of cytological data, including inflammatory cells and Gram stains, may be useful in initial therapeutic decisions in patients with suspected VAP. C-reactive protein, procalcitonin, and soluble triggering receptor expressed on myeloid cells are promising biomarkers in diagnosing VAP.

CONCLUSION

An integrated approach should be followed in diagnosing and treating patients with VAP, including early antibiotic therapy and subsequent rectification according to clinical response and results of bacteriologic cultures.

Microbial investigation in ventilator-associated pneumonia

Ventilator-associated pneumonia (VAP) is a serious infectious condition in intensive care unit (ICU) patients, currently related to a high mortality rate. Therefore, this complication of mechanical ventilation requires a prompt diagnosis and adequate antibiotic treatment. The detection of the causative organism is imperative for guiding an appropriate therapy as there is strong evidence of the adverse effect of inadequate empirical treatment on outcome. The major difficulty of the microbial investigation is to obtain the sample from the lower respiratory tract, mainly because of the potential contamination with upper airways flora, which may result in a misinterpretation of the cultures. Microbial investigation in VAP is based on the culture of samples obtained from lower respiratory tract by noninvasive or invasive methods. The most common techniques of sampling are the endotracheal aspirate (ETA), which is considered a noninvasive method, the protected specimen brush (PSB) and the bronchoalveolar lavage (BAL), both being invasive methods of investigation. The latter were designed as an attempt to avoid the colonizing flora of the upper airways. The best of these diagnostic approaches is still controversial. In terms of outcome, there is strong evidence that the impact of both invasive and noninvasive methods seems to be similar. In terms of cost, however, the endotracheal aspirate is less expensive compared to BAL or PSB. On the other hand, invasive methods could be particularly beneficial in patients who are not responding to the initial empirical antibiotic treatment. The rationale for the quantitative culture of the respiratory samples is to differentiate between infection and colonization of lower airways, because the bacterial colonization is a frequent event in mechanically ventilated patients. The thresholds currently employed for the diagnosis of the pneumonia are the following: ETA samples, > or = 10(5)-10(6) colony forming units (cfu).mL(-1); PSB samples, > or =10(3) cfu.mL(-1); and BAL samples, > or =10(4) cfu.mL(-1). Intending to provide a practical approach to the issue, the present manuscript reviews the available noninvasive (blood culture, endotracheal aspirate) and invasive (protected specimen brush, bronchoalveolar lavage, blinded methods and lung biopsy) techniques used for the diagnosis of ventilator-associated pneumonia.

Architectural remodelling in acute and chronic interstitial lung disease: fibrosis or fibroelastosis?

AIMS

Pulmonary fibrosis in acute and chronic lung disease has been much investigated, but little attention has been directed at the elastic tissue in these situations. Our aim was to verify whether elastic deposition accompanies collagen deposition in the repairing process of acute and chronic lung injury.

METHODS AND RESULTS

We measured, by image analysis, the content of fibres of the collagenous and elastic systems of the alveolar septum in histological slides sampled from autopsied lungs, using the picrosirius-polarization method and Weigert's resorcin-fuchsin stain, respectively. Five groups were studied: I, 10 normal patients; II, 10 patients with cardiogenic pulmonary oedema; III, 23 adult respiratory distress syndrome (ARDS) patients in the early phase; IV, 14 ARDS patients in the late fibroproliferative phase; and V, 10 idiopathic pulmonary fibrosis patients. The first two groups were used as controls. The content of fibres of the collagenous and elastic systems was significantly increased in groups IV and V as compared to the other groups.

CONCLUSIONS

Our results indicate that deposition of elastic system fibres is present in the fibroproliferative phase of ARDS and in usual interstitial pneumonia and suggest that this event may contribute to the alveolar mechanical dysfunction and remodelling that occur in acute and chronic interstitial lung disease.