Diagnostic testing for ventilator-associated pneumonia

Transcriptomic depression of immunological synapse as a signature of ventilator-associated pneumonia

Background

Ventilator-associated pneumonia (VAP) is one of the most commonly encountered intensive care unit (ICU) acquired infections worldwide. The objective of the study was to identify the immune alteration occurring in patients suffering from VAP at the transcriptomic level and explore its potential use for clinical diagnoses of this disease.

Methods

We performed a prospective observational study in five medical ICUs. Immunological gene expression profiles in the blood of VAP patients were compared with those of controls by using whole transcriptome microarrays and droplet digital polymerase chain reaction (ddPCR) in the first 24 hours following diagnosis.

Results

VAP patients showed significantly lower expression levels of HLA-DOA, HLA-DMA, HLA-DMB, ICOS, ICOSLG, IL2RA, CD1, CD3, CD28 and CD40LG. The molecules coded by these genes participate of the immunological synapse. CD1C, CD40LG and ICOS showed the highest values of area under the receiver operating characteristic curve (AUROC) with a good balance between sensibility and specificity.

Conclusions

Patients with VAP show a transcriptomic depression of genes participating of the immunological synapse. It takes a commonplace event, namely VAP, and highlights a quite significant underlying immune suppressive state. In effect this small study will change how we regard VAP, and proposes that we regard it as an infection in an immune compromised host, and that immunity has a central role for ICU acquired infections. This may in time change clinical practice, as it has profound implications for the role of protocolised care, or bundles, in the prevention of VAP. Quantifying the expression in blood of this genes using ddPCR could be a useful approach for the diagnosis of VAP.

Differences in hospital- and ventilator-associated pneumonia due to Staphylococcus aureus (methicillin-susceptible and methicillin-resistant) between Europe and Latin America: a comparison of the EUVAP and LATINVAP study cohorts

PURPOSE

A comparison is made of epidemiological variables (demographic and clinical characteristics) and outcomes in patients with hospital-acquired pneumonia (HAP) or ventilator-associated pneumonia (VAP) caused by methicillin-susceptible and methicillin-resistant Staphylococcus aureus (MSSA and MRSA) in the Latin American VAP (LATINVAP) vs. the European Union VAP (EUVAP) cohorts of patients admitted to intensive care units (ICUs).

METHODS

The EUVAP project was a prospective, multicenter observational study reporting 827 patients with HAP/VAP in 27 ICUs from 9 European countries. The LATINVAP project was a multicenter prospective observational study, with an identical design, performed in 17 ICUs from 4 Latin American countries involving 99 patients who developed HAP/VAP. Episodes of VAP/HAP caused by S. aureus, MSSA, and MRSA were compared in both cohorts.

RESULTS

Forty-five patients had S. aureus HAP/VAP in the EUVAP cohort vs. 11 patients in the LATINVAP cohort. More patients had MRSA in the LATINVAP study than in the EUVAP (45% vs. 33%). ICU mortality among patients with MSSA HAP/VAP in EUVAP was 10% vs. 50% for LATINVAP (OR=9.75, p=0.01). Fifteen patients in the EUVAP cohort developed MRSA HAP/VAP as opposed to 5 in LATINVAP. In the EUVAP study there was an ICU mortality rate of 33.3%. In the LATINVAP cohort, the ICU mortality rate was 60% (OR for death=3.0; 95%CI 0.24-44.7).

CONCLUSION

MRSA pneumonia was associated with poorer outcomes in comparison with MSSA. Our study suggests significant variability among European and Latin American ICU practices that may influence clinical outcomes. Furthermore, patients with pneumonia in Latin America have different outcomes.

[Infection associated with the use of assisted-ventilation devices]

The second most important infectious complication in hospitalised patients is pneumonia, and it hits first place in the Intensive Care Unit (ICU). Almost 80% of the episodes of health-care pneumonia happens when patient is under mechanical ventilation, causing ventilator-associated pneumonia (VAP). VAP is associated with the highest rates of mortality in ICU infections, mainly if due to Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA). It also increases days under mechanical ventilation and the length of stay in ICU and hospital. Although all the diagnostic procedures, the diagnosis of VAP is based basically in the clinics: X-ray infiltrates and purulent endotracheal secretions are the cornerstone of the diagnosis. We should evaluate and screen any risk factor for multiresistant pathogens. If we have an early VAP and no risk factors, the majority of empiric antibiotic strategies are useful, but if we have a patient with more than one week under mechanical ventilation, previous antibiotic use, and risk factors for multiresistant pathogens, we should then individualize empiric antibiotic treatment.

Diagnosis of ventilator-associated pneumonia: is there a gold standard and a simple approach?

PURPOSE OF REVIEW

Diagnosis of ventilator-associated pneumonia remains controversial. Different approaches are advocated, but none has yet demonstrated superiority. Diagnosis based on clinical data and aetiological diagnosis of ventilator-associated pneumonia episodes are two concepts that should be combined in an integrative evaluation for ventilator-associated pneumonia. Recent findings in diagnosis are reviewed here.

RECENT FINDINGS

Studies of various diagnostic strategies have been conducted to evaluate whether they influence outcome. Strategies include use of biomarkers (e.g. C-reactive protein and procalcitonin) and use of clinical scores to render the diagnostic process more objective. The appropriateness of the available aetiological diagnostic techniques and their reliability in the absence of a 'gold standard' for diagnosis were also recently addressed. It remains controversial whether type of culture (quantitative or nonquantitative) or sampling method (invasive or noninvasive) influences aetiological diagnosis or outcomes in ventilator-associated pneumonia. It is unlikely that any single approach is the optimal diagnostic assessment whenever ventilator-associated pneumonia is suspected.

SUMMARY

Microbiological data should always be used in association with clinical data when assessing patients with suspected ventilator-associated pneumonia. Integration of these data might be the most simple and effective strategy for diagnosing ventilator-associated pneumonia.

The simple and the simpler in pneumonia diagnosis

In the absence of a perfect 'gold standard' for diagnosing pneumonia, comparing diagnostic performance between techniques remains controversial. El Solh and coworkers present a study evaluating use of quantitative endotracheal aspirate culture to enhance diagnostic accuracy in pneumonia patients admitted from nursing homes. We discuss the use of quantitative cultures and thresholds to differentiate between colonization and infection in pneumonia patients; we also consider the inaccuracy of diagnostic studies, which compromises the reproducibility of these data in clinical practice.

Direct examination and cultures of bronchoalveolar lavage in pneumonia diagnosis: a comparative experimental study

OBJECTIVE

To assess the accuracy of direct examination and quantitative cultures of BAL to diagnose pneumonia with or without antibiotic treatment.

DESIGN

Experimental rat models.

INTERVENTIONS

Pneumonia was induced by intratracheal inoculation of S. pneumoniae (10(9) cfu/ml) or P. aeruginosa (10(8)cfu/ml). Controls (n = 10) received sterile inoculum. Study animals received penicillin (n = 19) or saline (n = 18) (pneumococcal model); amikacin (n = 13), ceftazidime (n = 11), or saline (n = 13) (Pseudomonas model). BAL was assessed 48 h after infection. The animals were killed for histopathological analysis.

RESULTS

All study animals developed pneumonia, which was more extensive in the pneumococcal than in the Pseudomonas model. In pneumococcal pneumonia the sensitivity of BAL cultures (10(3) cfu/ml or higher) was 77.8% with saline and 21.0% with penicillin. In the Pseudomonas ceftazidime group all specimens were negative, precluding diagnosis. The sensitivity of cultures with amikacin was 23.1% vs. 30.8% with saline. In the pneumococcal model intracellular organism (ICO) count of 2% or higher had a sensitivity of 100% for detecting pneumonia with saline and 57.9% with penicillin. In the Pseudomonas model the sensitivity of ICO was 69.2% with both amikacin and saline and 36.3% with ceftazidime. The sensitivity of neutrophil count above 50% in pneumococcal pneumonia was 77.8% and 64.7% with saline and penicillin, respectively, and 69.2%, 61.5%, and 81.8% with saline, amikacin, and ceftazidime, respectively, in Pseudomonas pneumonia.

CONCLUSIONS

BAL-positive intracellular organisms were more accurate than cultures for the diagnosis of recent pneumonia, and were less affected by antibiotic treatment.

Ventilator-associated pneumonia: diagnosis, treatment, and prevention

While critically ill patients experience a life-threatening illness, they commonly contract ventilator-associated pneumonia. This nosocomial infection increases morbidity and likely mortality as well as the cost of health care. This article reviews the literature with regard to diagnosis, treatment, and prevention. It provides conclusions that can be implemented in practice as well as an algorithm for the bedside clinician and also focuses on the controversies with regard to diagnostic tools and approaches, treatment plans, and prevention strategies.

Hospital-acquired pneumonia in the 21st century: a review of existing treatment options and their impact on patient care

Hospital-acquired pneumonia is a common nosocomial infection, with significant morbidity and mortality, and represents a major therapeutic challenge to clinicians. The therapeutic approach must be patient-oriented and institution-specific. The specific risk factors of each patient, such as previous antibiotic exposure, underlying diseases, length of hospital stay and the local patterns of antimicrobial resistance, should guide physicians in their decision of the initial optimal empirical therapy. Delays in the initiation or inappropriate/inadequate initial therapy are related to increased mortality and worse outcomes. In responding patients, as soon as culture data are available, efforts should be made to change the initial broad spectrum antibiotic regimen to a more targeted one (de-escalation). The optimal duration of treatment is a matter of debate, but courses longer than 1 week are rarely justified.

Enfoque clínico del paciente con neumonía asociada a ventilación mecánica

Ventilator-associated pneumonia (VAP) is the most frequent infection in the intensive care unit. The importance of this entity lies not only in its high incidence but also in the significant mortality it produces. Therefore, a new episode of VAP should be clinically suspected when new or persistent radiological opacity, purulent respiratory secretions and other signs of sepsis (fever and leukocytosis) are present. In these patients, at the very least, tracheal aspirate samples with quantitative culture and direct staining should be immediately obtained, followed by prompt initiation of empirical broad-spectrum antibiotic therapy. The choice of initial antibiotic therapy should be patient-based, taking into account the risk factors associated especially with VAP caused by Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus, because of the high associated mortality. To evaluate resolution of VAP, we analyze various clinical variables (based mainly on resolution of fever and hypoxemia) and microbiologic information. Once the microorganism responsible for VAP has been isolated, antibiotic therapy can be adapted, based on de-escalation, to reduce the emergence of resistant bacteria. Recent studies suggest that shorter antibiotic regimens reduce the emergence of antibiotic-resistant pathogens, cost and adverse events.

Advances in the management of pneumonia in the intensive care unit: review of current thinking

Interventions to prevent pneumonia in the intensive care unit should combine multiple measures targeting the invasive devices, microorganisms and protection of the patient. Microbiological investigation is useful for evaluating the quality of the respiratory sample, and permits early modification of the regimen in light of the microbiological findings. Once pneumonia develops, the appropriateness of the initial antibiotic regimen is a vital determinant of outcome. Three questions should be formulated: (1) is the patient at risk of acquiring methicillin-resistant Staphylococcus aureus, (2) is Acinetobacter baumannii a problem in the institution, and (3) is the patient at risk of acquiring Pseudomonas aeruginosa? Antibiotic therapy should be started immediately and must circumvent any pathogen resistance mechanisms developed after previous antibiotic exposure. Therefore, antibiotic choice should be institution-specific and patient-oriented.

Concordância entre o aspirado traqueal e o lavado broncoalveolar no diagnóstico das pneumonias associadas à ventilação mecânica

INTRODUÇÃO: Os exames de cultura e o exame bacterioscópico pelo método de coloração de Gram (GRAM) do aspirado traqueal ainda são objeto de controvérsias com relação ao diagnóstico etiológico na pneumonia associada à ventilação mecânica (PAV). OBJETIVO: Avaliar a concordância entre os resultados do GRAM e da cultura quantitativa do aspirado traqueal e do lavado broncoalveolar nos pacientes com PAV. MÉTODO: Foram estudados de modo prospectivo os pacientes internados no período de outubro de 2001 a agosto de 2002, que estavam há mais de 48hs sob ventilação mecânica, e que apresentavam suspeita clínica de PAV. No momento da suspeita clínica foi realizado o aspirado traqueal seguido do lavado broncoalveolar. O diagnóstico de PAV foi confirmado com a suspeita clínica associada à cultura quantitativa do lavado broncoalveolar 10(4)ufc/ml. RESULTADOS: Dos 119 pacientes sob ventilação mecânica, 32 (26,8%) tiveram suspeita clínica de PAV, com confirmação diagnóstica em 25 (78%) deles. A comparação entre o GRAM do aspirado traqueal e a cultura do lavado broncoalveolar mostrou uma moderada concordância (coeficiente de Kappa de 0,56). Houve concordância entre a cultura quantitativa do aspirado traqueal e do lavado broncoalveolar em 22/25 (88%) e discordância em 3/25 (12%) casos (coeficiente de Kappa de 0,71). A sensibilidade e a especificidade do aspirado traqueal para o diagnóstico de PAV com o ponto de corte 10 6 ufc/ml foram de 71% e 72%, respectivamente. CONCLUSÃO: A combinação do GRAM com a cultura quantitativa do aspirado traqueal pode contribuir para a avaliação diagnóstica da PAV.

Pneumonia in the intensive care unit

OBJECTIVE

To update the state-of-the-art on pneumonia in adult patients in the intensive care unit (ICU), with special emphasis on new developments in management.

METHODS

We searched MEDLINE, using the following keywords: hospital-acquired pneumonia, ventilator-associated pneumonia and healthcare-associated pneumonia, diagnosis, therapy, prevention.

RESULTS

Interventions to prevent pneumonia in the ICU should combine multiple measures targeting the invasive devices, microorganisms, and protection of the patient. Once pneumonia develops, the appropriateness of the initial antibiotic regimen is a vital determinant of outcome. Three questions should be formulated: a) Is the patient at risk of methicillin-resistant Staphylococcus aureus?; b) Is Acinetobacter baumannii a problem in the institution?; and c) is the patient at risk of Pseudomonas aeruginosa? Antibiotic therapy should be started immediately and must circumvent pathogen-resistance mechanisms developed after previous antibiotic exposure. Therefore, antibiotic choice should be institution specific and patient oriented. Microbiologic investigation is useful on evaluating the quality of the respiratory sample and permits early modification of the regimen in light of the microbiologic findings.

CONCLUSION

A decision tree outlining an approach to the evaluation and management of ventilator-associated pneumonia is provided.

Ventilator-associated pneumonia after heart surgery: a prospective analysis and the value of surveillance

OBJECTIVE

To determine the frequency, etiology, and risk factors of ventilator-associated pneumonia (VAP) and purulent tracheobronchitis (TBX) in patients who have undergone heart surgery. To study the predictive role of systematic surveillance cultures.

DESIGN

Prospective study.

SETTING

Heart surgery intensive care unit.

PATIENTS

Intubated heart surgical patients.

INTERVENTIONS

Systematic tracheal aspirate and protected brush catheter cultures of all intubated patients.

MEASUREMENTS AND MAIN RESULTS

Studied were the frequency of lower respiratory tract infection in ventilated patients and the role of surveillance cultures. The frequency of VAP was 7.87% (34.5 per 1,000 days of mechanical ventilation), and the criteria for purulent tracheobronchitis was fulfilled by 8.15% of patients (31.13 per 1,000 days of mechanical ventilation). After multivariate analysis, the variables independently associated with the development of respiratory tract infection were central nervous system disorder (relative risk [RR] = 4.7), ulcer disease (RR = 3.6), New York Heart Association score >/=3 (RR = 4), need for mechanical circulatory support (RR = 6.8), duration of mechanical ventilation >96 hrs (RR = 12.3), and reintubation (RR = 63.7). Mortality in our study was as follows: VAP patients, 57.1%; purulent tracheobronchitis patients, 20.7%; colonized patients, 11.5%; and noncolonized patients, 1.6%. Regular surveillance cultures were taken from all ventilated patients to assess the anticipative value of the cultures in predicting respiratory tract infection. A total of 1,626 respiratory surveillance samples were obtained. Surveillance cultures effectively predicted only one episode of VAP and one of tracheobronchitis.

CONCLUSIONS

Patients undergoing heart surgery have a high frequency of VAP. VAP is associated with a poor prognosis. In this study, surveillance cultures failed as an anticipative diagnostic method.

Therapy of ventilator-associated pneumonia. A patient-based approach based on the ten rules of "The Tarragona Strategy"

Therapy of ventilator-associated pneumonia should be a patient-based approach focusing on some key features are listed here: early initial therapy should be based on broad-spectrum antibiotics. Empirical treatment may be targeted after direct staining and should be modified according to good-quality quantitative microbiological findings, but should never be withdrawn in presence of negative direct staining or delayed until microbiological results are available. Courses of therapy should be given at high doses according to pharmacodynamic and tissue penetration properties. Prolonging antibiotic treatment does not prevent recurrences. Methicillin-sensitive Staphylococcus aureus should be expected in comatose patients. Methicillin-resistant Staphylococcus aureus should not be expected in patients without previous antibiotic coverage. Pseudomonas aeruginosa should be covered with combination therapy. Antifungal therapy, even when Candida spp is isolated in significant concentrations, is not recommended for intubated nonneutropenic patients. Vancomycin, given at the standard doses and route of administration for the treatment of VAP caused by Gram-positive pathogens, is associated with poor outcomes. The choice of initial antibiotic should be based on the patient's previous antibiotic exposure and comorbidities, and local antibiotic susceptibility patterns, which should be updated regularly.

International Conference for the Development of Consensus on the Diagnosis and Treatment of Ventilator-associated Pneumonia

Ventilator-associated pneumonia (VAP) is an important health problem that still generates great controversy. A consensus conference attended by 12 researchers from Europe and Latin America was held to discuss strategies for the diagnosis and treatment of VAP. Commonly asked questions concerning VAP management were selected for discussion by the participating researchers. Possible answers to the questions were presented to the researchers, who then recorded their preferences anonymously. This was followed by open discussion when the results were known. In general, peers thought that early microbiological examinations are warranted and contribute to improving the use of antibiotherapy. Nevertheless, no consensus was reached regarding choices of antimicrobial agents or the optimal duration of therapy. Piperacillin/tazobactam was the preferred choice for empiric therapy, followed by a cephalosporin with antipseudomonal activity and a carbapenem. All the peers agreed that the pathogens causing VAP and multiresistance patterns in their ICUs were substantially different from those reported in studies in the United States. Pathogens and multiresistance patterns also varied from researcher to researcher inside the group. Consensus was reached on the importance of local epidemiology surveillance programs and on the need for customized empiric antimicrobial choices to respond to local patterns of pathogens and susceptibilities.

Ventilator-associated pneumonia or not? Contemporary diagnosis

Ventilator-associated pneumonia (VAP) is pneumonia in patients who have been on mechanical ventilation for > or =48 hours. VAP is most accurately diagnosed by quantitative culture and microscopy examination of lower respiratory tract secretions, which are best obtained by bronchoscopically directed techniques such as the protected specimen brush and bronchoalveolar lavage. These techniques have acceptable repeatability, and interpretation of results is unaffected by antibiotics administered concurrently for infection at extrapulmonary sites as long as antimicrobial therapy has not been changed for <72 hours before bronchoscopy.

Pulmonary Infections in Ventilated Patients: Diagnostic and Therapeutic Options

The diagnosis of pulmonary infections in the ventilated patient has threatened the foundations of medicine. Although the lifesaving techniques of endotracheal intubation (developed for the treatment of diphtheria) and artificial ventilation (developed for the management of poliomyelitis) contribute greatly to medical care, they have resulted in the production of the "progress"-related infection of ventilator-associated pneumonia (VAP). Modern ventilator therapy is a substantial technologic advance from earlier days and, as technology inherently does, has removed some of the human element, the main foundation of Oslerian medical practice. The time-honored clinical diagnosis based on physical examination by an experienced physician has been seriously compromised in the approach to VAP.