PATHOPHYSIOLOGY OF PNEUMONIA

Data-driven classification and explainable-AI in the field of lung imaging

Detecting lung diseases in medical images can be quite challenging for radiologists. In some cases, even experienced experts may struggle with accurately diagnosing chest diseases, leading to potential inaccuracies due to complex or unseen biomarkers. This review paper delves into various datasets and machine learning techniques employed in recent research for lung disease classification, focusing on pneumonia analysis using chest X-ray images. We explore conventional machine learning methods, pretrained deep learning models, customized convolutional neural networks (CNNs), and ensemble methods. A comprehensive comparison of different classification approaches is presented, encompassing data acquisition, preprocessing, feature extraction, and classification using machine vision, machine and deep learning, and explainable-AI (XAI). Our analysis highlights the superior performance of transfer learning-based methods using CNNs and ensemble models/features for lung disease classification. In addition, our comprehensive review offers insights for researchers in other medical domains too who utilize radiological images. By providing a thorough overview of various techniques, our work enables the establishment of effective strategies and identification of suitable methods for a wide range of challenges. Currently, beyond traditional evaluation metrics, researchers emphasize the importance of XAI techniques in machine and deep learning models and their applications in classification tasks. This incorporation helps in gaining a deeper understanding of their decision-making processes, leading to improved trust, transparency, and overall clinical decision-making. Our comprehensive review serves as a valuable resource for researchers and practitioners seeking not only to advance the field of lung disease detection using machine learning and XAI but also from other diverse domains.

Inflammation-modulating nanoparticles for pneumonia therapy

Pneumonia is a common but serious infectious disease, and is the sixth leading cause for death. The foreign pathogens such as viruses, fungi, and bacteria establish an inflammation response after interaction with lung, leading to the filling of bronchioles and alveoli with fluids. Although the pharmacotherapies have shown their great effectiveness to combat pathogens, advanced methods are under developing to treat complicated cases such as virus-infection and lung inflammation or acute lung injury (ALI). The inflammation modulation nanoparticles (NPs) can effectively suppress immune cells and inhibit inflammatory molecules in the lung site, and thereby alleviate pneumonia and ALI. In this review, the pathological inflammatory microenvironments in pneumonia, which are instructive for the design of biomaterials therapy, are summarized. The focus is then paid to the inflammation-modulating NPs that modulate the inflammatory cells, cytokines and chemokines, and microenvironments of pneumonia for better therapeutic effects. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Respiratory Disease.

Anti-inflammatory Effects of Mesenchymal Stem Cells and Their Secretomes in Pneumonia

Mesenchymal stem cells (MSCs) are multipotent progenitor cells that play crucial roles in the microenvironment of injured tissues. The potential therapeutics of MSCs have attracted extensive attention for several diseases such as acute respiratory distress syndrome (ARDS) and novel coronavirus disease 2019 (COVID-19) pneumonia. MSC-extracellular vesicles have been isolated from MSC-conditioned media (MSC-CM) with similar functional effects as parent MSCs. The therapeutic role of MSCs can be achieved through the balance between the inflammatory and regenerative microenvironments. Clinical settings of MSCs and their extracellular vesicles remain promising for many diseases, such as ARDS and pneumonia. However, their clinical applications remain limited due to the cost of growing and storage facilities of MSCs with a lack of standardized MSC-CM. This review highlights the proposed role of MSCs in pulmonary diseases and discusses the recent advances of MSC application for pneumonia and other lung disorders.

FOCUSED IMPEDANCE METHOD TO DETECT LOCALIZED LUNG VENTILATION DISORDERS IN COMBINATION WITH CONVENTIONAL SPIROMETRY

Conventional spirometry gives information on the overall ventilation of a person's lung; it cannot detect localized disorders in ventilation as occurring in pulmonary edema, pneumonia, tumor, TB, etc. Here we propose a new technique involving the recently developed focused impedance method (FIM) in combination with conventional spirometry to detect localized lung ventilation disorders. Electrical impedance of lung tissue changes as a function of air content and FIM provides a measurement of localized electrical impedance with sensitivity down to reasonable depths inside the body using a few surface electrodes; here we used a six-electrode version. At least four quadrants of the lungs in the frontal plane can be separately measured using a hand-held probe with spring backed skin surface electrodes. Firstly, spatial sensitivity distribution of the six-electrode FIM was obtained using finite element simulation which verified the focusing effect and its depth sensitivity. Percent change in impedance between maximum inspiration and expiration were measured at four quadrants of the chest of a healthy male subject giving four different values; that at the lower right quadrant was found to be the maximum, as also expected based on anatomy. Changes in impedance at this quadrant of the same subject were found to vary proportionately with exhaled air volumes, measured using a bellows-type spirometer. Similar FIM measurements at lower right lung of seven healthy subjects were found to be almost proportional (R2 = 0.7) to the total exhaled air volumes (vital capacity). This was the basis of the new technique. For a healthy individual, the ratio of the local impedance change to vital capacity (VC) will fall within a certain range for each of the four lung quadrants. A lower value at any quadrant would indicate disorder within that quadrant, while a larger value would indicate disorder in a region outside the particular quadrant. The FIM electrode probe can then be moved to take measurements at the other quadrants to locate the region of disorder. This preliminary study indicates that FIM in combination with conventional spirometry could be used to detect localized ventilation defects.

Optimizing Treatment Outcomes in Severe Community-Acquired Pneumonia

Severe community-acquired pneumonia (CAP) is a life-threatening condition that requires intensive care unit (ICU) admission. Clinical presentation is characterized by the presence of respiratory failure, severe sepsis, or septic shock. Severe CAP accounts for approximately 5-35% of hospital-treated cases of pneumonia with the majority of patients having underlying comorbidities. The most common pathogens associated with this disease are Streptococcus pneumoniae, Legionella spp., Haemophilus influenzae, and Gram-negative enteric rods. Microbial investigation is probably helpful in the individual case but is likely to be more useful for defining local antimicrobial policies. The early and rapid initiation of empiric antimicrobial treatment is critical for a favorable outcome. It should include intravenous beta-lactam along with either a macrolide or a fluoroquinolone. Modifications of this basic regimen should be considered in the presence of distinct comorbid conditions and risk factors for specific pathogens. Other promising nonantimicrobial new therapies are currently being investigated. The assessment of severity of CAP helps physicians to identify patients who could be managed safely in an ambulatory setting. It may also play a crucial role in decisions about length of hospital stay and time of switching to oral antimicrobial therapy in different groups at risk. The most important adverse prognostic factors include advancing age, male sex, poor health of patient, acute respiratory failure, severe sepsis, septic shock, progressive radiographic course, bacteremia, signs of disease progression within the first 48-72 hours, and the presence of several different pathogens such as S. pneumoniae, Staphylococcus aureus, Gram-negative enteric bacilli, or Pseudomonas aeruginosa. However, some important topics of severity assessment remain controversial, including the definition of severe CAP. Prediction rules for complications or death from CAP, although far from perfect, should identify the majority of patients with severe CAP and be used to support decision-making by the physician. They may also contribute to the evaluation of processes and outcomes of care for patients with CAP.

Alcohol suppresses the granulopoietic response to pulmonary Streptococcus pneumoniae infection with enhancement of STAT3 signaling

Enhanced granulopoietic activity is crucial for host defense against bacterial pneumonia. Alcohol impairs this response. The underlying mechanisms remain obscure. G-CSF produced by infected lung tissue plays a key role in stimulating bone marrow granulopoiesis. This study investigated the effects of alcohol on G-CSF signaling in the regulation of marrow myeloid progenitor cell proliferation in mice with Streptococcus pneumoniae pneumonia. Chronic alcohol consumption plus acute alcohol intoxication suppressed the increase in blood granulocyte counts following intrapulmonary challenge with S. pneumoniae. This suppression was associated with a significant decrease in bone marrow granulopoietic progenitor cell proliferation. Alcohol treatment significantly enhanced STAT3 phosphorylation in bone marrow cells of animals challenged with S. pneumoniae. In vitro experiments showed that G-CSF-induced activation of STAT3-p27(Kip1) pathway in murine myeloid progenitor cell line 32D-G-CSFR cells was markedly enhanced by alcohol exposure. Alcohol dose dependently inhibited G-CSF-stimulated 32D-G-CSFR cell proliferation. This impairment of myeloid progenitor cell proliferation was not attenuated by inhibition of alcohol metabolism through either the alcohol dehydrogenase pathway or the cytochrome P450 system. These data suggest that alcohol enhances G-CSF-associated STAT3-p27(Kip1) signaling, which impairs granulopoietic progenitor cell proliferation by inducing cell cycling arrest and facilitating their terminal differentiation during the granulopoietic response to pulmonary infection.

Acute alcohol intoxication impairs the hematopoietic precursor cell response to pneumococcal pneumonia

BACKGROUND

Alcohol abuse is associated with an increased incidence and severity of pneumonia. In both the general population and individuals consuming excess alcohol, Streptococcus pneumoniae is the most frequent lung infection pathogen. Alcoholic patients with pneumonia frequently present with granulocytopenia, which is predictive of increased mortality. The mechanisms underlying this impaired granulopoietic response to pneumococcal pneumonia have yet to be elucidated.

METHODS

Acute alcohol intoxication was induced in mice 30 minutes before intrapulmonary infection with S. pneumoniae. Bone marrow, lung, and blood samples were collected. Bone marrow cells were also isolated from naïve mice and treated in vitro with plasma from mice infected with S. pneumoniae.

RESULTS

Alcohol intoxication impaired the pneumococcal-induced increase in granulocyte recruitment into the alveolar space, decreased bacterial clearance from the lung, and increased mortality. Pneumococcal pneumonia significantly increased bone marrow lineage(-) c-Kit(+) Sca-1(+) (LKS) cell number and colony-forming unit-granulocytes and monocyte (CFU-GM) activity of these cells. Both enhanced proliferation of LKS cells and re-expression of Sca-1 surface protein on downstream progenitor cells bearing lineage(-) c-Kit(+) Sca-1(-) surface markers accounted for the expansion of marrow LSK cells during pneumonia. Alcohol intoxication impaired these 2 mechanisms of LKS cell population expansion and was associated with a relative granulocytopenia during pneumococcal lung infection.

CONCLUSIONS

Alcohol inhibits the hematopoietic precursor cell response to pneumonia, which may serve as a mechanism underlying the granulocytopenia and impaired host defense in alcohol abusers with bacterial pneumonia.

[Intrapulmonary inflammatory response in critically ill patients with pneumonia]

OBJECTIVE

to evaluate the relationship between the microbiology result and cytokine expression in bronchoalveolar lavage (BAL).

DESIGN

An observational, prospective study.

SETTING

a 17-bed medical and surgical intensive care unit.

PATIENTS

Mechanically-ventilated patients with suspected pneumonia admitted to the ICU during a 27-month time period were consecutively enrolled.

INTERVENTIONS

BAL was performed with 150ml sterile isotonic saline solution in three aliquots of 50ml. Local anesthetics were not used during the procedure. A BAL sample was processed for a microbiologic quantitative culture and BAL cytokines IL-6, IL 8, TNFα, granulocyte colony-stimulating factor (G-CSF) and granulocyte-monocyte colony-stimulating factor (GM-CSF) were measured.

MAIN VARIABLES OF INTEREST

age, APACHE II score within the first 24 hours of admission, time on mechanical ventilation, ICU length of stay, mortality, previous antibiotic therapy, isolated bacteria and cytokines concentration were analyzed.

RESULTS

fifty-nine consecutive patients were included, and most of the patients (79.7%) had prior antibiotic therapy. Twenty-two patients (37.2%) had a positive BAL. In the group of patients with positive BAL, the TNFα concentration was significantly higher in the group of patients with positive BAL than in the BAL negative group.

CONCLUSIONS

there is a significant correlation between the microbiology result and the TNFα concentration in the BAL fluid. In mechanically-ventilated patients, TNFα in BAL has been associated with positive cultures despite prior antibiotic therapy.

Lymphocyte apoptosis in murine Pneumocystis pneumonia

BACKGROUND

Apoptosis of lymphocytes is important in the termination of an immune response to infection but has also been shown to have detrimental effects in animal models of systemic infection and sepsis. We sought to characterize lymphocyte apoptosis in an animal model of pneumonia due to Pneumocystis murina, an infection localized to the lungs.

METHODS

Control mice and mice depleted of CD4+ lymphocytes were inoculated with Pneumocystis. Apoptosis of lung and spleen lymphocytes was assayed by flow cytometry and PCR assay of apoptotic proteins.

RESULTS

In control mice, apoptosis of lung lymphocytes was maximal just after the infection was cleared from lung tissue and then declined. However, in CD4-depleted mice, apoptosis was also upregulated in recruited lymphocytes in spite of progressive infection. In splenic lymphocytes, apoptosis was observed early at 1 week after inoculation and then declined. Apoptosis of lung lymphocytes in control mice was associated with a decrease in mRNA for Bcl-2 and an increase in mRNA for Bim. In CD4-depleted mice, lavaged CD8+ cells did change intracellular Bcl-2 but showed increased mRNA for Bim.

CONCLUSION

Apoptosis of both pulmonary and extrapulmonary lymphocytes is part of the normal host response to Pneumocystis but is also triggered in CD4-deficient animals with progressive infection. In normal mice apoptosis of pulmonary lymphocytes may serve to terminate the immune response in lung tissue. Apoptosis of lung lymphocytes takes place via both the intrinsic and extrinsic apoptotic pathways and is associated with changes in both pro- and anti-apoptotic proteins.

The systemic and pulmonary LPS binding protein response to intratracheal lipopolysaccharide

LPS binding protein (LBP) is an acute-phase glycoprotein that facilitates LPS activation of immune cells through interactions with CD14 and Toll-like receptor 4. Initially, LBP production was thought to occur exclusively in the liver in response to stimulation with TNF-alpha, IL-1, and IL-6. More recently, it has been shown that type II pneumocytes are also capable of LBP production. Little is known, however, regarding the regulation and or distribution of this protein in response to localized intrapulmonary infection. We performed time-course experiments challenging C3H mice intratracheally with LPS (10 mug). In separate experiments, mice deficient in IL-6 were given the same dose of intratracheal LPS and euthanized 8 h later. Despite the intratracheal route of LPS administration, an increase in plasma LBP concentrations occurred earlier and was of greater magnitude than the increase observed in bronchoalveolar lavage fluid. Liver LBP mRNA increased to a greater extent than did lung LBP mRNA. Whereas the TNF-alpha response remained localized within the alveolar space, IL-6 was increased both locally and in plasma. Of several tissues analyzed, the lung was the greatest producer of IL-6 mRNA. Plasma LBP was significantly decreased in the IL-6-deficient mice compared with wild-type controls challenged with intratracheal LPS. We conclude that lung-derived IL-6 is an important mediator of hepatic LBP up-regulation. We speculate that the disruption of these lung-liver signaling pathways may be important to host response efforts to confine infection to the lung. If impaired, this may be one mechanism underlying the increased mortality observed in patients with liver disease who develop pneumonia.

Sequestration and homing of bone marrow-derived lineage negative progenitor cells in the lung during pneumococcal pneumonia

Background

Bone marrow (BM)-derived progenitor cells have been shown to have the potential to differentiate into a diversity of cell types involved in tissue repair. The characteristics of these progenitor cells in pneumonia lung is unknown. We have previously shown that Streptococcus pneumoniae induces a strong stimulus for the release of leukocytes from the BM and these leukocytes preferentially sequester in the lung capillaries. Here we report the behavior of BM-derived lineage negative progenitor cells (Lin- PCs) during pneumococcal pneumonia using quantum dots (QDs), nanocrystal fluorescent probes as a cell-tracking technique.

Methods

Whole BM cells or purified Lin- PCs, harvested from C57/BL6 mice, were labeled with QDs and intravenously transfused into pneumonia mice infected by intratracheal instillation of Streptococcus pneumoniae. Saline was instilled for control. The recipients were sacrificed 2 and 24 hours following infusion and QD-positive cells retained in the circulation, BM and lungs were quantified.

Results

Pneumonia prolonged the clearance of Lin- PCs from the circulation compared with control (21.7 ± 2.7% vs. 7.7 ± 0.9%, at 2 hours, P < 0.01), caused preferential sequestration of Lin- PCs in the lung microvessels (43.3 ± 8.6% vs. 11.2 ± 3.9%, at 2 hours, P < 0.05), and homing of these cells to both the lung (15.1 ± 3.6% vs. 2.4 ± 1.2%, at 24 hours, P < 0.05) and BM as compared to control (18.5 ± 0.8% vs. 9.5 ± 0.4%, at 24 hours, P < 0.01). Very few Lin- PCs migrated into air spaces.

Conclusion

In this study, we demonstrated that BM-derived progenitor cells are preferentially sequestered and retained in pneumonic mouse lungs. These cells potentially contribute to the repair of damaged lung tissue.

Bacterial Infections

In Osier’s time, bacterial pneumonia was a dreaded event, so important that he borrowed John Bunyan’s characterization of tuberculosis and anointed the pneumococcus, as the prime pathogen, “Captain of the men of death.”1 One hundred years later much has changed, but much remains the same. Pneumonia is now the sixth most common cause of death and the most common lethal infection in the United States. Hospital-acquired pneumonia is now the second most common nosocomial infection.2 It was documented as a complication in 0.6% of patients in a national surveillance study,3 and has been reported in as many as 20% of patients in critical care units.4 Furthermore, it is the leading cause of death among nosocomial infections.5 Leu and colleagues6 were able to associate one third of the mortality in patients with nosocomial pneumonia to the infection itself. The increase in hospital stay, which averaged 7 days, was statistically significant. It has been estimated that nosocomial pneumonia produces costs in excess of $500 million each year in the United States, largely related to the increased length of hospital stay.

TLR9 is required for protective innate immunity in Gram-negative bacterial pneumonia: role of dendritic cells

In this study, experiments were performed to determine the contribution of TLR9 to the generation of protective innate immunity against virulent bacterial pathogens of the lung. In initial studies, we found that the intratracheal administration of Klebsiella pneumoniae in wild-type (WT) BALB/c mice resulted in the rapid accumulation of dendritic cells (DC) expressing TLR9. As compared with WT mice, animals deficient in TLR9 (TLR9-/-) displayed significantly increased mortality that was associated with a >50-fold increase in lung CFU and a >400-fold increase in K. pneumoniae CFU in blood and spleen, respectively. Intrapulmonary bacterial challenge in TLR9-/- mice resulted in reduced lung DC accumulation and maturation as well as impaired activation of lung macrophages, NK cells, and alphabeta and gammadelta T cells. Mice deficient in TLR9 failed to generate an effective Th1 cytokine response following bacterial administration. The adoptive transfer of bone marrow-derived DC from syngeneic WT but not TLR9-/- mice administered intratracheally reconstituted antibacterial immunity in TLR9-/- mice. Collectively, our findings indicate that TLR9 is required for effective innate immune responses against Gram-negative bacterial pathogens and that approaches to maximize TLR9-mediated DC responses may serve as a means to augment antibacterial immunity in pneumonia.

Cyclic di-GMP stimulates protective innate immunity in bacterial pneumonia

Innate immunity is the primary mechanism by which extracellular bacterial pathogens are effectively cleared from the lung. We have previously shown that cyclic di-GMP (c-di-GMP [c-diguanylate]) is a novel small molecule immunomodulator and immunostimulatory agent that triggers protective host innate immune responses. Using a murine model of bacterial pneumonia, we show that local intranasal (i.n.) or systemic subcutaneous (s.c.) administration of c-di-GMP prior to intratracheal (i.t.) challenge with Klebsiella pneumoniae stimulates protective immunity against infection. Specifically, i.n. or s.c. administration of c-di-GMP 48 and 24 h prior to i.t. K. pneumoniae challenge resulted in significantly increased survival. Pretreatment with c-di-GMP resulted in a 5-fold reduction in bacterial CFU in the lung (P < 0.05) and an impressive >1,000-fold decrease in CFU in the blood (P < 0.01). c-di-GMP administration stimulated a robust innate response to bacterial challenge, characterized by enhanced accumulation of neutrophils and alphabeta T cells, as well as activated NK and alphabeta T lymphocytes, which was associated with earlier and more vigorous expression of chemokines and type I cytokines. Moreover, lung macrophages recovered from Klebsiella-infected mice pretreated with c-di-GMP expressed greater quantities of inducible nitric oxide synthase and nitric oxide ex vivo than did macrophages isolated from infected mice pretreated with the control, c-GMP. These findings demonstrate that c-di-GMP delivered in either a compartmentalized or systemic fashion stimulates protective innate immunity in the lung and protects mice against bacterial invasion. We propose that the cyclic dinucleotide c-di-GMP may be used clinically as an effective immunomodulator, immune enhancer, and vaccine adjuvant to protect against respiratory infection and pneumonia in humans and animals.

Conditional expression of interferon-γ to enhance host responses to pulmonary bacterial infection

Strategies to augment host defense against pulmonary infection run the risk of inducing excess pulmonary inflammation and tissue injury. To address this problem, we investigated conditional expression in lung tissue of the murine interferon-gamma (IFN-gamma) transgene. A recombinant adenoviral vector (AdTetIFN) was constructed by placing a murine IFN-gamma cDNA downstream of a tetracycline (Tet)-responsive promoter, inserted into a replication-defective adenoviral vector. Co-infection of target cells with AdTetIFN and a second vector encoding a reverse tetracycline controlled transactivator allowed doxycycline (Dox)-regulated IFN-gamma production. We then administered 10(8) plaque-forming units (PFU) of AdTetIFN to mice by intratracheal injection. When the mice were provided with Dox in drinking water (0.5mg/ml in 5% sucrose), there was significant release of IFN-gamma in lavage fluid by ELISA in comparison to mice on water/sucrose alone (399+/-74 pg/ml vs undetectable, p<0.01). IFN-gamma in lavage fluid was associated with upregulation of Class II Major histocompatibility complex markers on alveolar macrophages by flow cytometry, suggesting macrophage activation. We then injected AdTetIFN into mice three days prior to challenge with 10(4) CFU Klebsiella pneumoniae. Test mice were maintained on water+Dox and control mice on water+sucrose. Bacterial burden was assayed in lung tissue at serial intervals. At 24h after challenge, mice on doxycycline had significantly lower infection burden in comparison to mice on water/sucrose (0.77+/-0.05 colony forming units/lung for 10(8) PFU AdTetIFN plus Dox compared to 1.4+/-0.11 colony-forming units/lung for AdTetIFN without Dox, p<0.05). Survival of the vector treated mice given doxycycline in drinking water was also enhanced. Microscopic examination of lavaged cells showed a significant increase in pulmonary neutrophils in the AdTetIFN+Dox mice in comparison to AdTetIFN+sucrose mice (16+/-1.0 x 10(5) vs 10+0.8 cells/lung, p<0.05). We conclude that local release of IFN-gamma can be selectively activated to enhance neutrophil recruitment and host resistance to bacterial pneumonia.

Interferon-inducible protein 10, but not monokine induced by gamma interferon, promotes protective type 1 immunity in murine Klebsiella pneumoniae pneumonia

CXC chemokines that lack the ELR motif, including interferon-inducible protein 10 [IP-10 (CXCL10)] and monokine induced by gamma interferon (IFN-gamma) [MIG (CXCL9)], have been shown to mediate the generation of type 1 immune responses. In this study, we found that intrapulmonary administration of the gram-negative bacterium Klebsiella pneumoniae resulted in the local and systemic expression of IP-10, followed sequentially by MIG expression. MIG mRNA expression in the lungs of Klebsiella-infected mice required the endogenous production of IFN-gamma, whereas IP-10 was expressed in both an IFN-gamma-dependent and an IFN-gamma-independent fashion. Antibody-mediated neutralization of IP-10 resulted in reduced bacterial clearance and decreased survival, whereas bacterial clearance was unaltered in mice treated with anti-MIG antibody. Impaired bacterial clearance in anti-IP-10 antibody-treated mice was associated with significant reductions in the number and/or activational status of NK and NK-T cells, CD4+ T cells, and gammadelta T cells, as well as a reduction in the expression of IFN-gamma. Conversely, the transient transgenic expression of murine IP-10 using adenovirus-mediated gene transfer resulted in improved bacterial clearance when IP-10 adenovirus was given concomitant with intrapulmonary bacterial challenge. These results indicate that IP-10 is an important component of innate immunity against extracellular bacterial pathogens of the lung and may represent a candidate molecule for immunotherapy in the setting of severe respiratory tract infection.

Interleukin-10 haplotype associated with increased mortality in critically ill patients with sepsis from pneumonia but not in patients with extrapulmonary sepsis

STUDY OBJECTIVE

To test the hypothesis that haplotypes of the interleukin (IL)-10 gene are associated with clinical outcomes, comparing critically ill patients with sepsis from pneumonia vs those with extrapulmonary sepsis.

DESIGN

Genetic association study.

SETTING

Medical/surgical ICUs in a tertiary-care, university-affiliated teaching hospital.

PATIENTS

Of 550 white patients with sepsis, 158 had pneumonia as the principle cause of their sepsis and 392 had an extrapulmonary source of sepsis.

MEASUREMENTS

Haplotypes of the IL-10 gene were defined by measurement of haplotype tag single-nucleotide polymorphisms (SNPs). Primary outcome was 28-day survival. Secondary outcomes were days alive and free of organ dysfunction.

RESULTS

Three SNPs in the IL-10 gene (-592 C/A, +734 G/T, and +3367 G/A) identified four major haplotypes: CGG, AGG, CTA, and CTG. Patients with pneumonia who carried one or two copies of the CGG haplotype had greater 28-day mortality (51.4%) than patients who did not carry this haplotype (29.1%, p = 0.007). Carriers of CGG had significantly more cardiovascular dysfunction (and use of vasopressors), renal dysfunction (and requirement of dialysis), hepatic dysfunction, and hematologic dysfunction (p < 0.05 in each case). In contrast, in patients with an extrapulmonary source of infection there was no significant association of the CGG haplotype (or any measured IL-10 genotype) with 28-day mortality or organ dysfunction.

CONCLUSIONS

The IL-10 haplotype - 592C/734G/3367G is associated with increased mortality and organ dysfunction in critically ill patients with pulmonary sepsis but not in similarly ill patients with extrapulmonary sepsis. Therefore, polymorphisms within the IL-10 gene may be predictors of outcome in patients with sepsis from pneumonia.

[Guidelines for the management of community pneumonia in adult who needs hospitalization]

Community acquired pneumonia is still an important health problem. In Spain the year incidence is 162 cases per 100,000 inhabitants with 53,000 hospital admission costing 115 millions of euros per year. In the last years there have been significant advances in the knowledge of: aetiology, diagnostic tools, treatment alternatives and antibiotic resistance. The Spanish Societies of Intensive and Critical Care (SEMICYUC), Infectious Diseases and Clinical Microbiology (SEIMC) and Pulmonology and Thoracic Surgery (SEPAR) have produced these evidence-based Guidelines for the management of community acquired pneumonia in Adults. The main objective is to help physicians to make decisions about this disease. The different points that have been developed are: aetiology, diagnosis, treatment and prevention.

Escherichia coli pneumonia enhances granulopoiesis and the mobilization of myeloid progenitor cells into the systemic circulation

OBJECTIVE

The process by which hematopoietic tissues respond to a pulmonary infection remains poorly understood. This study investigated the potential role of lung-derived granulopoietic cytokines in facilitating this response.

DESIGN

Laboratory investigation.

SETTING

University laboratory.

SUBJECTS

Male Balb/c mice.

INTERVENTIONS

Mice were challenged with intratracheal Escherichia coli or granulocyte colony-stimulating factor (G-CSF). Bone marrow cells were isolated from normal mice and treated in vitro with G-CSF.

MEASUREMENTS AND MAIN RESULTS

Bronchoalveolar lavage fluid concentrations of G-CSF, macrophage inflammatory protein-2, and keratinocyte-derived chemokine were elevated 3 and 6 hrs after intratracheal E. coli. The increases in intrapulmonary G-CSF and keratinocyte-derived chemokine were associated with increases of their concentrations in the plasma. The numbers of granulocyte-macrophage colony forming units in bone marrow, spleen, and blood were increased 48 hrs after intratracheal E. coli or G-CSF. In addition, plasma G-CSF and the number of progenitor cells (lin-ckit+Sca-1(-)) in the blood were increased at 30 mins and 48 hrs, respectively, following intratracheal G-CSF. Signal transducer and activator of transcription-3 in bone marrow cells was activated following intratracheal E. coli or G-CSF in addition to activation by in vitro G-CSF stimulation.

CONCLUSIONS

During pulmonary infection, locally produced cytokines enter the circulation and may play an important role in initiating a granulopoietic response.

Diagnostic methods for the detection of anterograde aspiration in enterally fed patients

PURPOSE OF REVIEW

The diagnosis of aspiration and its origin in patients on enteral tube feeding is challenging to the physician and provides an important means to prevent pneumonia. This review examines the most recent studies and developments in the field with an approach to the technical aspects of diagnostic methods.

RECENT FINDINGS

The methods more commonly used to detect anterograde aspiration in clinical practice are fiberoptic endoscopic evaluation of swallowing and modified barium swallowing. Recent studies have shown that although these methods may provide the diagnosis of aspiration, their use for clinical monitoring is not appropriate. The studies comparing fiberoptic endoscopic evaluation of swallowing and modified barium swallowing have demonstrated that both tests present similar sensitivity, specificity and predictive values.

SUMMARY

The different methods used to diagnose anterograde aspiration are appropriate for clinical practice, with a low complication rate and few contraindications. In most instances, the early diagnosis of aspiration and evaluation of other factors such as laryngeal sensibility, may predict the occurrence of aspiration pneumonia.

Selective transport of cytokine-induced neutrophil chemoattractant from the lung to the blood facilitates pulmonary neutrophil recruitment

The CXC chemokines cytokine-induced neutrophil chemoattractant (CINC) and macrophage inflammatory protein-2 (MIP-2) are potent neutrophil chemoattractants in rats. We have previously shown that CINC, unlike MIP-2 and most other proinflammatory cytokines, is elevated in the systemic circulation in response to an intratracheal (IT) challenge. Therefore, we hypothesized that CINC generated within the lung selectively enters the vascular compartment to facilitate pulmonary neutrophil recruitment. Rats were administered IT LPS, and plasma CINC and MIP-2 levels were measured 90 min and 4 h after injection, along with mRNA expression in lung, spleen, liver, and kidney. Ninety minutes and 4 h after IT LPS, CINC and MIP-2 mRNA expression were largely confined to lung homogenate, but of the two chemokines, only CINC was present in plasma. In separate experiments, rats received IT injections of recombinant CINC and/or MIP-2. Here, plasma levels of CINC, but not MIP-2, were significantly increased throughout the 4-h observation period. This finding was verified by individually administering125I-labeled forms of each chemokine. Instillation of recombinant MIP-2 or CINC into the lung increased the number of neutrophils recovered in bronchoalveolar lavage fluid at 4 h, and this effect was enhanced when both chemokines were administered together. In addition, intravenous (IV) CINC, but not IV MIP-2, increased pulmonary neutrophil recruitment in response to IT MIP-2. Our results show that CINC, in contrast to MIP-2, is selectively transported from the lung to the systemic circulation, where it promotes neutrophil migration into the lung in response to a chemotactic stimulus.

The nasogastric feeding tube as a risk factor for aspiration and aspiration pneumonia

PURPOSE OF REVIEW

Aspiration is one of the most common complications in enterally fed patients. The source of aspiration is due to the accumulation of secretions in the pharynx of reflux gastric contents from the stomach into the pharynx. The true prevalence of aspiration is difficult to determine because of vague definitions, poor assessment methods, and varying levels of clinical recognition.

RECENT FINDINGS

There is evidence in the literature showing that the presence of a nasogastric feeding tube is associated with colonization and aspiration of pharyngeal secretions and gastric contents leading to a high incidence of Gram-negative pneumonia in patients on enteral nutrition. However, other aspects may be equally important and should also be considered when evaluating a patient suspected of having aspiration and aspiration pneumonia. The mechanisms responsible for aspiration in patients bearing a nasogastric feeding tube are (1). loss of anatomical integrity of the upper and lower esophageal sphincters, (2). increase in the frequency of transient lower esophageal sphincter relaxations, and (3). desensitization of the pharyngoglottal adduction reflex.

SUMMARY

Sometimes it is possible to differentiate whether the aspirate is gastric or pharyngeal. The kind of bacterial contamination is, however, more difficult to establish. Oral or dental disease, antibiotic therapy, systemic illness or malnutrition and reduction of salivary flow are responsible for colonization of Gram-negative bacteria in oral and pharyngeal flora in nasogastric-tube-fed patients. The use of a nasogastric feeding tube and the administration of food increase gastric pH and lead to colonization of gastric secretions. It has also been suggested that gastric bacteria could migrate upward along the tube and colonize the pharynx.

Community-acquired pneumonia in adults

The most common etiologic agent of CAP is Streptococcus pneumoniae. Atypical pathogens are the cause in approximately 20% to 30% of patients. Because the patients clinical presentation cannot be used to predict if a patient is infected with S. pneumoniae or an atypical pathogen, the initial empiric therapy should cover for these core organisms in all patients. In patients with CAP, the antibiotic spectrum of initial empiric therapy will escalate from an oral macrolide in an ambulatory patient without risk factors for resistant pathogens, to intravenous combination therapy, in a hospitalized patient in the intensive care unit with risk factors for resistant gram-negative organisms. The hospitalized patient can be switched safely from intravenous to oral therapy once he or she reaches clinical stability. The use of pneumococcal vaccine, influenza vaccine, and smoking-cessation programs is an important strategy to prevent CAP.

L-selectin is required for fMLP- but not C5a-induced margination of neutrophils in pulmonary circulation

To study the role of L-selectin in neutrophil (PMN) margination and sequestration in the pulmonary microcirculation, maximally active concentrations of C5a (900 pmol/g) and N-formylmethionyl-leucyl-phenylalanine (fMLP; 0.34 pmol/g) were injected into the jugular vein of wild-type or L-selectin-deficient C57BL/6 mice. In wild-type mice administered C5a or fMLP, 92 +/- 1% and 34 +/- 9%, respectively, of peripheral blood PMN were trapped mostly in the pulmonary circulation as determined by immunohistochemistry and myeloperoxidase activity. In wild-type mice treated with F(ab')(2) fragments of the L-selectin monoclonal antibody MEL-14 or in L-selectin-deficient mice, C5a-induced neutropenia was not significantly reduced, but the decrease in peripheral PMN in response to fMLP was completely abolished, indicating that L-selectin is necessary for fMLP- but not C5a-induced pulmonary margination. Immunostained lung sections of fMLP- or C5a-treated mice showed sequestered neutrophils in alveolar capillaries with no evidence of neutrophil aggregates. We conclude that chemoattractant-induced PMN margination in the pulmonary circulation can occur by two separate mechanisms, one of which requires L-selectin.

Defining severe community-acquired pneumonia

Based on the recognition of the main pathophysiologic features of pneumonia and currently available data on prognosis and clinical severity assessment, key points for a definition of severe pneumonia are as follows: 1. Independent predictors of pneumonia severity are factors reflecting acute respiratory failure and severe sepsis or septic shock. 2. In view of the dependence of the development of acute respiratory failure on pulmonary comorbidities, radiographic extension may prove to be an additional independent predictor of severe respiratory compromise. 3. Vital sign abnormalities other than acute respiratory failure and severe hypotension may be independent predictors of severity, particularly in patients presenting in early and asymptomatic stages of severe sepsis. 4. Several pathogens have been shown to have adverse prognostic potential. Because the cause is unknown at the initial evaluation, however, pathogens cannot form part of the criteria for the initial severity assessment. 5. Because pneumonia is a dynamic process, any assessment of severity takes place at an arbitrary point of disease evolution. It would be desirable to define a set of parameters reflecting initial severity as well as a state of increased risk for early deterioration toward severe pneumonia. 6. Severity stratification within the population of patients with severe pneumonia may open the prospect of identifying patients who may have the greatest benefit from intensive care.

Therapy of nosocomial pneumonia

HAP remains a major cause of morbidity and mortality among hospitalized patients. Although early appropriate therapy results in improved outcomes, the cause of HAP frequently is not known at the time antimicrobial therapy is initiated. Most cases of HAP result from microaspiration of oropharyngeal secretions previously colonized with pathogenic bacteria, and the spectrum of potential pathogens is broad. Taking several factors into account can narrow this spectrum, including severity of illness, length of stay before the onset of pneumonia, and presence of risk factors for specific pathogens. When therapy has been initiated, follow-up of microbial studies and careful monitoring of the patient's course is important. The clinical improvement, even when therapy is appropriate, frequently takes days; therapy should not be changed for the first 2 to 3 days unless frank deterioration is noted. Patients who fail to respond or experience clinical deterioration should be re-examined carefully, and thought should be given to the possibility of other noninfectious processes.

Leukotriene B4 augments neutrophil phagocytosis of Klebsiella pneumoniae

Neutrophils play a critical role in the clearance of bacteria from the lung and other organs by their capacity for phagocytosis and killing. Previously, we identified an important role for the leukotrienes in rat alveolar macrophage phagocytosis of Klebsiella pneumoniae. In this report, we explored the possibility that the leukotrienes play an important role in phagocytosis by neutrophils as well. Inhibition of endogenous leukotriene synthesis by 5-lipoxygenase knockout in mice or by pharmacologic means in human peripheral blood neutrophils attenuated phagocytosis of opsonized K. pneumoniae. Reduced phagocytosis was also observed in human neutrophils pretreated with a leukotriene B4 receptor but not a cysteinyl-leukotriene receptor antagonist. While leukotriene B4 reconstituted defective phagocytosis in leukotriene-deficient neutrophils and enhanced phagocytosis in neutrophils capable of leukotriene synthesis, leukotriene C4, leukotriene D4, 5-hydroperoxyeicosatetraenoic acid, and 5-oxo-eicosatetraenoic acid were ineffective. To determine the opsonin dependence of the leukotriene B4 augmentation of phagocytosis, we assessed the ability of leukotriene B4 to modulate neutrophil phagocytosis and the adherence of sheep erythrocytes opsonized with immunoglobulin G or the complement fragment C3bi. While leukotriene B4 augmented both Fc receptor- and complement receptor-mediated phagocytosis, increased adherence to leukotriene B4-treated neutrophils was limited to complement opsonized targets. In conclusion, we have identified a novel role for leukotriene B4 in the augmentation of neutrophil phagocytosis mediated by either the Fc or complement receptor.

The effects of granulocyte colony-stimulating factor and neutrophil recruitment on the pulmonary chemokine response to intratracheal endotoxin

Although G-CSF has been shown to increase neutrophil (polymorphonuclear leukocyte, PMN) recruitment into the lung during pulmonary infection, relatively little is known about the local chemokine profiles associated with this enhanced PMN delivery. We investigated the effects of G-CSF and PMN recruitment on the pulmonary chemokine response to intratracheal LPS. Rats pretreated twice daily for 2 days with an s.c. injection of G-CSF (50 microg/kg) were sacrificed at either 90 min or 4 h after intratracheal LPS (100 microg) challenge. Pulmonary recruitment of PMNs was not observed at 90 min post LPS challenge. Macrophage inflammatory protein-2 (MIP-2) and cytokine-induced neutrophil chemoattractant (CINC) concentrations in bronchoalveolar lavage (BAL) fluid were similar in animals pretreated with or without G-CSF at this time. G-CSF pretreatment enhanced pulmonary recruitment of PMNs (5-fold) and greatly reduced MIP-2 and CINC levels in BAL fluid at 4 h after LPS challenge. In vitro, the presence of MIP-2 and CINC after LPS stimulation of alveolar macrophages was decreased by coculturing with circulating PMNs but not G-CSF. G-CSF had no direct effect on LPS-induced MIP-2 and CINC mRNA expression by alveolar macrophages. Pulmonary recruited PMNs showed a significant increase in cell-associated MIP-2 and CINC. Cell-associated MIP-2 and CINC of circulating PMNs were markedly increased after exposure of these cells to the BAL fluid of LPS-challenged lungs. These data suggest that recruited PMNs are important cells in modulating the local chemokine response. G-CSF augments PMN recruitment and, thereby, lowers local chemokine levels, which may be one mechanism resulting in the subsidence of the host proinflammatory response.

Modulation of alveolar macrophage phagocytosis by leukotrienes is Fc receptor-mediated and protein kinase C-dependent

We have previously established an important role for leukotrienes (LTs) in augmenting rat alveolar macrophage (AM) phagocytosis of Klebsiella pneumoniae opsonized with complete immune serum (IS), which contains the two well-known opsonins, immunoglobulin (Ig) G and complement (C). In this report, the specific opsonin requirements for LT modulation of AM phagocytosis and the dependence of this response on protein kinase (PK) C activity were investigated. Phagocytosis of K. pneumoniae opsonized with IS, non-immune serum, or heat-inactivated immune serum and of inert targets (IgG-opsonized fluorescent microspheres or C-opsonized sheep red blood cells) was examined. Inhibition of endogenous LT synthesis or action attenuated, whereas the addition of exogenous LTs augmented, phagocytosis only of targets opsonized with IgG. LTs had no effect on phagocytosis of C-opsonized or unopsonized targets. LTs did not affect adherence of IgG-opsonized targets, implying instead an enhancement of internalization. Macrophage internalization of phagocytic targets has previously been shown to require PKC activity. Pretreatment of AMs with the PKC inhibitors staurosporine or calphostin C, or with phorbol 12-myristate 13-acetate to deplete PKC, completely inhibited the ability of LTB(4) and largely inhibited the ability of LTC(4) to augment phagocytosis of IgG-opsonized microspheres. These results demonstrate that LT enhancement is confined to Fc receptor (FcR)-mediated phagocytosis. Moreover, PKC activation represents an important mechanism by which LTs promote FcR-mediated phagocytosis.

Cytokine expression in severe pneumonia: a bronchoalveolar lavage study

OBJECTIVE

To assess the cytokine expression (tumor necrosis factor-alpha [TNF-alpha], interleukin [IL]-1beta, and IL-6) in severe pneumonia, both locally (in the lungs) and systemically (in blood).

DESIGN

Prospective sequential study with bronchoalveolar lavage (BAL) and blood sampling.

SETTING

Six-bed respiratory intensive care unit of a 1,000-bed teaching hospital.

PATIENTS

Thirty mechanically ventilated patients (>48 hrs) were allocated to either the pneumonia group (n = 20) or a control group (n = 10).

INTERVENTIONS

Protected specimen brush and BAL samples for quantitative cultures, and serum and BAL fluid TNF-alpha, IL-1beta, and IL-6 levels were measured on days 1, 3, and 7. In the control group, the procedure was done on day 1 only.

MEASUREMENTS AND MAIN RESULTS

Serum TNF-alpha levels were significantly higher in patients with pneumonia compared with controls (35 +/- 4 vs. 17 +/- 3 pg/mL, respectively, p = .001). IL-6 levels in serum and BAL fluid were higher in pneumonia than in control patients (serum, 837 +/- 260 vs. 94 +/- 35 pg/mL, respectively, p = .017; BAL fluid, 1176 +/- 468 vs. 234 +/- 83 pg/mL, respectively, p = .05). On days 1, 3, and 7 in patients with pneumonia, IL-1beta levels turned out to be higher in BAL fluid than in serum (71 +/- 17 vs. 2 +/-1 pg/mL on day 1; 49 +/- 8 vs. 6 +/- 2 pg/mL on day 3; and 47 +/- 16 vs. 3 +/- 2 pg/mL on day 7 for BAL fluid and serum, respectively, p < .05). No significant correlation between BAL fluid cytokine levels and lung bacterial burden was shown in presence of antibiotic treatment. Although no clear relationship was found between BAL fluid and serum cytokines and mortality, there was a trend toward higher serum IL-6 levels in nonsurvivors (1209 +/- 433 pg/mL) with pneumonia compared with survivors (464 +/- 260 pg/mL). In addition, serum TNF-alpha and IL-6 correlated with multiple organ failure score (r2 = .36, p = .004 for both) and with lung injury score (r2 = .30, p = .01, and r2 = .22, p = .03, for TNF-alpha and IL-6, respectively).

CONCLUSIONS

The present study describes the lung and systemic inflammatory response in severe pneumonia. The lung cytokine expression seems to be independent from the lung bacterial burden in the presence of antibiotic treatment. Because of the limited sample size, we did not find a clear relationship between serum and BAL fluid cytokine levels and outcome.

Severe community-acquired pneumonia. Risk factors and follow-up epidemiology

The aim of the study was to determine risk factors for severe community-acquired pneumonia (CAP) as well as to compare microbial patterns of severe CAP to a previous study from our respiratory intensive care unit (ICU) originating from 1984 to 1987. Patients admitted to the ICU according to clinical judgment were defined as having severe CAP. For the study of risk factors, a hospital-based case-control design was used, matching each patient with severe CAP to a patient hospitalized with CAP but not requiring ICU admission. Microbial investigation included noninvasive and invasive techniques. Overall, 89 patients with severe CAP were successfully matched to a control patient. The presence of an alcohol ingestion of >/= 80 g/d (odds ratio [OR] 3.9, 95% confidence interval [CI] 1.4 to 10.6, p = 0.008) was found to be an independent risk factor for severe CAP and prior ambulatory antimicrobial treatment (OR 0.37, 95% CI 0.17 to 0.79, p = 0.009) to be protective. Streptococcus pneumoniae (24%) continued to be the most frequent pathogen; however, 48% of strains were drug-resistant. "Atypical" bacterial pathogens were significantly more common (17% versus 6%, p = 0.006) and Legionella spp. less common (2% versus 14%, p = 0.004) than in our previous study, whereas gram-negative enteric bacilli (GNEB) and Pseudomonas aeruginosa continued to represent important pathogens (6% and 5%, respectively). Our findings provide additional evidence for the importance of the initiation of early empiric antimicrobial treatment for a favorable outcome of CAP. Variations of microbial patterns are only in part due to different epidemiological settings. Therefore, initial empiric antimicrobial treatment will also have to take into account local trends of changing microbial patterns.

5-Lipoxygenase reaction products modulate alveolar macrophage phagocytosis of Klebsiella pneumoniae

The leukotrienes are potent lipid mediators of inflammation formed by the 5-lipoxygenase-catalyzed oxidation of arachidonic acid. Although the effects of leukotrienes on neutrophil chemotaxis and activation have been established, their role in modulating innate host defense mechanisms is poorly understood. In a previous study (M. Bailie, T. Standiford, L. Laichalk, M. Coffey, R. Strieter, and M. Peters-Golden, J. Immunol. 157:5221-5224, 1996), we used 5-lipoxygenase knockout mice to establish a critical role for endogenous leukotrienes in pulmonary clearance and alveolar macrophage phagocytosis of Klebsiella pneumoniae. In the present study, we investigated the role of specific endogenous leukotrienes in phagocytosis of K. pneumoniae and explored the possibility that exogenous leukotrienes could restore phagocytosis in alveolar macrophages with endogenous leukotriene synthesis inhibition and enhance this process in leukotriene-competent cells. Rat alveolar macrophages produced leukotriene B4 (LTB4), LTC4, and 5-hydoxyeicosatetraenoic acid (5-HETE) during the process of phagocytosis, and the inhibition of endogenous leukotriene synthesis with zileuton and MK-886 dramatically attenuated phagocytosis. We also observed a reduction in phagocytosis when we treated alveolar macrophages with antagonists to the plasma membrane receptors for either LTB4, cysteinyl-leukotrienes, or both. In leukotriene-competent cells, LTC4 augmented phagocytosis to the greatest extent, followed by 5-HETE and LTB4. These 5-lipoxygenase reaction products demonstrated similar relative abilities to reconstitute phagocytosis in zileuton-treated rat alveolar macrophages and in alveolar macrophages from 5-lipoxygenase knockout mice. We conclude that endogenous synthesis of all major 5-lipoxygenase reaction products plays an essential role in phagocytosis. The restorative and pharmacologic effects of LTC4, LTB4, and 5-HETE may provide a basis for their exogenous administration as an adjunctive treatment for patients with gram-negative bacterial pneumonia.

Hospital-acquired pneumonia: epidemiology, etiology, and treatment

Despite improvements in diagnosis, treatment, and prevention, hospital-acquired pneumonia (HAP) remains the number one cause of nosocomial mortality. This article reviews the current knowledge regarding the incidence, epidemiology, and causes of HAP, with the appreciation that the available information is incomplete and that controversies are common, and thus the authors provide a rational approach to the initial management of HAP in immunocompetent adults. A discussion of therapy and what to do with patients who do not respond to the empiric therapy are included. The American Thoracic Society (ATS) statement on HAP has served as a foundation for this review but has been supplemented by newer literature that was not available when the ATS statement was developed.

Innate immunity, cytokines, and pulmonary host defense

Effective host defense against bacterial infection is dependent on the activation and recruitment of phagocytic cells. The initiation, maintenance, and resolution of this inflammatory response in the setting of bacterial pneumonia is dependent on the expression of cytokines. As the complexities of the host-pathogen interaction are further dissected and unraveled, immunologic manipulation of cytokine expression will likely become an important adjuvant therapy in the treatment of serious lung infections.

Acute ethanol intoxication suppresses the pulmonary inflammatory response in rats challenged with intrapulmonary endotoxin

The effects of acute ethanol intoxication on the functional activities of circulating and lung-recruited polymorphonuclear leukocytes (PMNs) and alveolar macrophages (AMs) were determined in rats challenged with intratracheal endotoxin to elucidate the mechanisms underlying the defects of pulmonary host defenses caused by acute ethanol intoxication. Acute ethanol Intoxication was induced by an intraperitoneal injection of 20% ethanol at a dose of 5.5 g of ethanol/kg. The control animals were injected with an equal amount of saline. Thirty min after intraperitoneal injection, rats were challenged with intratracheal endotoxin (300 micrograms/kg in 0.5 ml of saline) or saline. The rats were killed 3 h after intratracheal injection. CD11b/c expression on PMNs and phagocytosis and hydrogen peroxide generation of PMNs and AMs were determined by flow cytometry. Cytokine-Induced neutrophil chemoattractant (CINC) level in bronchoalveolar lavage fluid was measured with a specific ELISA. Intratracheal endotoxin caused a significant PMN recruitment into the lung in control animals. Acute ethanol intoxication completely suppressed the endotoxin-induced pulmonary recruitment of PMNs. Pulmonary-recruited PMNs exhibited a significant upregulation (8-fold) of CD11b/c expression when compared with circulating PMNs. This upregulation of CD11b/c expression was abolished by ethanol intoxication. Ethanol intoxication suppressed hydrogen peroxide generation by AMs and lung-recruited PMNs, and the phagocytosis of circulating PMNs. In contrast, acute ethanol intoxication did not affect pulmonary CINC production. These data indicate that the antiinflammatory effects of alcohol seem to be primarily based on the effects of ethanol on the PMNs themselves and not on the generation of certain chemotactic stimuli. In addition to the impairment of PMN recruitment, the suppression of AM and PMN activities also contributes to the mechanisms underlying ethanol-induced defects of pulmonary host defenses.

Ventilator-associated pneumonia due to Pseudomonas aeruginosa

OBJECTIVE

Ventilator-associated pneumonia (VAP) caused by Pseudomonas aeruginosa has been associated with higher case fatality rates than VAP caused by other bacterial etiologies. The causes of this excess mortality are unclear.

DESIGN

Retrospective review of 38 consecutive ventilated patients with Pseudomonas pneumonia, documented by highly reliable methods. Charts of five additional patients were unavailable for review.

SETTING

Medical ICUs of a university-affiliated Veterans Affairs Medical Center and a university-affiliated municipal hospital.

MEASUREMENTS

Prospectively collected hospital admission acute physiologic and chronic health examination (APACHE) II scores and cause of ICU admission. Retrospectively calculated organ failure and APACHE scores, VAP score. Clinical and microbiologic variables. Antibiotic treatment and outcome. Direct cause of death by standard definitions.

RESULTS

Overall mortality was 69% (26/38), significantly higher than the APACHE II predicted mortality of 42.6% (p=0.037). At least 38% (10/26) of deaths were directly attributable to Pseudomonas VAP. Multivariate analysis of factors associated with death found infectious cause for ICU admission (odds ratio [OR]=8.67; 95% confidence interval [CI], 0.86 to 85.94) and number of organ dysfunctions on the day of diagnosis (OR=1.73, 95% CI, 1.02 to 2.92) were significant. Septic shock from Pseudomonas VAP, septic shock from subsequent infection, and multiple organ dysfunction syndrome were the most common immediate causes of death. Mortality increased linearly with increasing APACHE III score on the day of diagnosis. Of initial antibiotic regimens, 67% (26/36) were considered failures. Persistent pneumonia occurred in 35% of patients while recurrent pneumonia was unusual (1/38).

CONCLUSIONS

Development of Pseudomonas pneumonia results in a mortality rate in excess of that due to the presenting illness. The attributable mortality determined by several means appears to approach 40%. The excess mortality appears to be related to the host defense response to the pneumonia rather than any characteristic of the pneumonia. Even standard antibiotic regimens fail frequently and do not prevent the excess mortality. Since at least 38% of deaths can be directly attributable to the Pseudomonas pneumonia, improvement in therapy is needed.