Effect of design-related bias in studies of diagnostic tests for ventilator-associated pneumonia

Safety and clinical application of nonbronchoscopic bronchoalveolar lavage in preterm neonates with clinical ventilator-associated pneumonia

BACKGROUND

The safety and clinical application of nonbronchoscopic bronchoalveolar lavage (NB-BAL) in preterm neonates with ventilator-associated pneumonia (VAP) have not been fully investigated, and limited data on the feasibility of this method are available.

METHODS

Premature infants with clinically suspected VAP between October 2017 and June 2019 were enrolled, and NB-BAL was performed. The tolerance and safety of NB-BAL were prospectively recorded during the procedure, and the clinical applications of NB-BAL were observed.

RESULTS

A total of 46 NB-BAL procedures were performed in 31 neonates with clinically suspected VAP. The median (interquartile range) gestational age and birth body weight were 28.7 (26.7-31.3) weeks and 1055.0 (817.0-1475.0) grams, respectively. Overall, all episodes of the procedure were well tolerated, with only 9 (19.5%) episodes showing transient desaturation and one patient (2.2%) showing bradycardia during the NB-BAL procedure. There were no impairments in arterial blood gas, cardiopulmonary parameters or respiratory severity scores after NB-BAL. No significant complications occurred in any of the patients who received NB-BAL. No chronic comorbidities affected the safety and clinical application of NB-BAL in these mechanically ventilated preterm neonates. NB-BAL yielded a diagnosis in 32 (69.6%) of these VAP episodes. Staphylococcus aureus was the most common isolated bacterium and accounted for 7 (15.2%) confirmed cases of VAP in our study, followed by polymicrobial microorganisms (n = 6, 13.0%). The appropriate antibiotics were prescribed and modified according to the NB-BAL results in 25 (54.3%) cases of VAP.

CONCLUSIONS

NB-BAL is a safe and clinically applicable method for determining the etiology and diagnosis of VAP in the NICU, even in extremely preterm neonates with major chronic comorbidities. Further studies to investigate the diagnostic accuracy and impact of NB-BAL on VAP treatment in neonates are warranted in the future.

A rapid, real-time quantitative polymerase chain reaction test for the identification of pathogens in bronchoalveolar lavage samples

BACKGROUND

Standard bacteriologic culture techniques offer results within 2 days to 3 days, precluding a focused and timely antibiotic therapy in ventilated trauma patients. Our laboratory developed a real-time quantitative polymerase chain reaction (qPCR) test that can detect 25 different bacteria and fungi and methicillin resistance and offers results within 3 hours. The objective of this study was to compare the qPCR method to standard culture techniques.

METHODS

This was a prospective observational cohort study at a Level I trauma center from 2009 to 2012. Adult trauma patients on ventilation, receiving at least one bronchoalveolar lavage (BAL) with culture results were eligible for inclusion. DNA was isolated from the BAL samples and analyzed in 96-well plates using qPCR. Student's t tests were used to examine differences in mean qPCR cycle counts. Sensitivities, specificities, negative predictive values, and positive predictive values were calculated for the qPCR primer sets.

RESULTS

There were 28 BALs in the study. The qPCR method detected a total of 165 organisms, and culture methods found 54. The qPCR test had an overall sensitivity of 85%, specificity of 74%, negative predictive value of 98%, and positive predictive value of 27%. Those organisms that were only identified through qPCR had significantly less DNA than those identified through both qPCR and quantitative culture (28.8 vs. 23.3, p < 0.001). Concurrent antibiotic therapy was found to decrease the qPCR specificity in some primer sets, and methicillin resistance was only found in BAL samples that were concurrent with antibiotics.

CONCLUSION

The qPCR method shows promising initial diagnostic value. Many of the organisms not identified by quantitative culture had late cycle calls, suggesting that they might have been in quantities too low to result in culture identification. Once refined, our qPCR method has the potential to identify pathogens faster and earlier than standard quantitative culture methods, allowing for targeted antibiotic therapy within 3 hours.

LEVEL OF EVIDENCE

Diagnostic test, level II.

A systematic review classifies sources of bias and variation in diagnostic test accuracy studies

OBJECTIVE

To classify the sources of bias and variation and to provide an updated summary of the evidence of the effects of each source of bias and variation.

STUDY DESIGN AND SETTING

We conducted a systematic review of studies of any design with the main objective of addressing bias or variation in the results of diagnostic accuracy studies. We searched MEDLINE, EMBASE, BIOSIS, the Cochrane Methodology Register, and Database of Abstracts of Reviews of Effects (DARE) from 2001 to October 2011. Citation searches based on three key papers were conducted, and studies from our previous review (search to 2001) were eligible. One reviewer extracted data on the study design, objective, sources of bias and/or variation, and results. A second reviewer checked the extraction.

RESULTS

We summarized the number of studies providing evidence of an effect arising from each source of bias and variation on the estimates of sensitivity, specificity, and overall accuracy.

CONCLUSIONS

We found consistent evidence for the effects of case-control design, observer variability, availability of clinical information, reference standard, partial and differential verification bias, demographic features, and disease prevalence and severity. Effects were generally stronger for sensitivity than for specificity. Evidence for other sources of bias and variation was limited.

Glutamine supplemented parenteral nutrition to prevent ventilator-associated pneumonia in the intensive care unit

OBJECTIVE

Ventilator-associated pneumonia (VAP) is a form of nosocomial pneumonia that increases patient morbidity and mortality, length of hospital stay, and healthcare costs. Glutamine preserves the intestinal mucosal structure, increases immune function, and reduces harmful changes in gut permeability in patients receiving total parenteral nutrition (TPN). We hypothesized that TPN supplemented by glutamine might prevent the development of VAP in patients on mechanical ventilator support in the intensive care unit (ICU).

MATERIAL AND METHODS

With the approval of the ethics committee and informed consent from relatives, 60 patients who were followed in the ICU with mechanical ventilator support were included in our study. Patients were divided into three groups. The first group received enteral nutrition (n=20), and the second was prescribed TPN (n=20) while the third group was given glutamine-supplemented TPN (n=20). C-reactive protein (CRP), sedimentation rate, body temperature, development of purulent secretions, increase in the amount of secretions, changes in the characteristics of secretions and an increase in requirement of deep tracheal aspiration were monitored for seven days by daily examination and radiographs.

RESULTS

No statistically significant difference was found among groups in terms of development of VAP (p=0.622).

CONCLUSION

Although VAP developed at a lower rate in the glutamine-supplemented TPN group, no statistically significant difference was found among any of the groups. Glutamine-supplemented TPN may have no superiority over unsupplemented enteral and TPN in preventing VAP.

Comparison of bronchoscopic and non-bronchoscopic techniques for diagnosis of ventilator associated pneumonia

Background:

The diagnosis of ventilator associated pneumonia (VAP) remains a challenge because the clinical signs and symptoms lack both sensitivity and specificity and the selection of microbiologic diagnostic procedure is still a matter of debate.

Aims and Objective:

To study the role of various bronchoscopic and non-bronchoscopic diagnostic techniques for diagnosis of VAP.

Settings and Design:

This prospective comparative study was conducted in a medical ICU of a tertiary care center.

Materials and Methods:

Twenty-five patients, clinically diagnosed with VAP, were evaluated by bronchoscopic and non-bronchoscopic procedures for diagnosis. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of various bronchoscopic and non-bronchoscopic techniques were calculated, taking clinical pulmonary infection score (CPIS) of ≥6 as reference standard.

Results:

Our study has shown that for the diagnosis of VAP, bronchoscopic brush had a sensitivity, specificity, PPV and NPV of 94.9% [confidence interval (CI): 70.6–99.7], 57.1% (CI: 13.4–86.1), 85% (CI: 61.1–96) and 80% (CI: 21.9–98.7), respectively. Bronchoscopic bronchoalveolar lavage (BAL) had a sensitivity, specificity, PPV and NPV of 77.8% (CI: 51.9–92.6), 71.8% (CI: 24.1–94), 87.3% (CI: 60.4–97.8) and 55.5% (CI: 17.4–82.6), respectively. Sensitivity, specificity, PPV and NPV for non–bronchoscopic BAL (NBAL) were 83.3% (CI: 57.7–95.6), 71.43% (CI: 24.1–94), 88.2% (CI: 62.3–97.4) and 62.5% (CI: 20.2–88.2), respectively. Endotracheal aspirate (ETA) yield was only 52% and showed poor concordance with BAL (κ-0.351; P-0.064) and NBAL (k-0.272; P-0.161). There was a good microbiologic concordance among different bronchoscopic and non-bronchoscopic distal airway sampling techniques.

Conclusion:

NBAL is an inexpensive, easy, and useful technique for microbiologic diagnosis of VAP. Our findings, if verified, might simplify the approach for the diagnosis of VAP.

Year in review 2009: Critical Care--infection

In 2009 Critical Care provided important and clinically relevant research data for management and prevention of infections in critically ill patients. The present review summarises the results of these observational studies and clinical trials and discusses them in the context of the current relevant scientific and clinical background. In particular, we discuss recent epidemiologic data on nosocomial infections in intensive care units, present new approaches to prevention of ventilator-associated pneumonia, describe recent advances in biomarker-guided antibiotic stewardship and attempt to briefly summarise specific challenges related to the management of infections caused by multidrug-resistant microorganisms and influenza A (H1N1).

Determinants of outcome in patients with a clinical suspicion of ventilator-associated pneumonia

INTRODUCTION

In the absence of a reference standard, a probabilistic approach to the diagnosis of ventilator-associated pneumonia (VAP) has been proposed; and clinician judgment augmented by microbiological tests is used to guide therapy for patients having a clinical suspicion of VAP (CSVAP). However, the correlation of both clinician judgment at the time of CSVAP and the probability of VAP with clinical outcomes is unknown. In a cohort of patients with CSVAP, we sought to determine the correlation of clinician judgment and the probability of VAP with clinical outcomes. In addition, we studied the impact of the clinical and microbiological components of CSVAP on the processes of care and outcomes.

METHODS

We performed a retrospective analysis of data from a multicenter, randomized trial in 740 patients with CSVAP. Prospective clinician judgment of VAP probability at the time of CSVAP and retrospective adjudication of VAP were compared with clinical outcomes. The following determinants of CSVAP on outcomes were studied: time of CSVAP, index culture results, and the presence of bacteremia.

RESULTS

Neither clinician index of suspicion for VAP nor retrospective adjudication of VAP correlated with clinical outcomes. For CSVAP, occurrence >7 days after start of mechanical ventilation and negative index cultures were associated with worse outcomes. Bacteremia was associated with the development of increased organ dysfunction.

CONCLUSION

In patients with CSVAP, clinician judgment as to the probability of VAP does not correlate with processes of care and outcomes; and its use to group patients into those with and without VAP is of limited clinical utility.

The value of pretest probability and modified clinical pulmonary infection score to diagnose ventilator-associated pneumonia

PURPOSE

The aim of the study was to assess the utility of pretest probability and modified clinical pulmonary infection score CPIS in the diagnosis of late-onset ventilator-associated pneumonia (VAP).

MATERIALS AND METHODS

In 740 adults enrolled in a multicenter randomized trial, intensivists prospectively rated the pretest probability of VAP as low, moderate, or high based on their clinical judgment. The modified CPIS was calculated without considering culture results. Ventilator-associated pneumonia diagnosis was determined by 2 adjudicators using standardized definitions. We analyzed the relationship between pretest likelihood, CPIS, and VAP diagnosis.

RESULTS

Among the 739 patients analyzed, 14.5%, 39.6%, and 45.9% had low, moderate, and high pretest probability of VAP. Patients with high pretest probability had a lower PaO2/FiO2 ratio and a larger volume of secretions. High or moderate vs low pretest probability had high sensitivity (0.88; 95% confidence interval [CI], 0.87-0.89) and positive predictive value (0.87; 95% CI, 0.86-0.88) but low specificity (0.27; 95% CI, 0.21-0.35) and negative predictive value (0.29; 95% C,: 0.22-0.37) for the diagnosis of VAP. Therefore, 71% of patients who had a low pretest probability were actually infected (1 - negative predictive value). The area under the receiver operating characteristic curve for the modified CPIS was not significant (0.47; 95% CI, 0.42-0.53), meaning that no score threshold was clinically useful.

CONCLUSIONS

Pretest probability and a modified CPIS, which excludes culture results, are of limited utility in the diagnosis of late-onset VAP.

An Update on the Management of Nosocomial Pneumonia

Nosocomial pneumonia is the second most common hospital-acquired infection, after urinary tract infection; however, it carries with it a mortality rate estimated to be between 20% and 50%. Furthermore, patients with nosocomial pneumonia are hospitalized for an additional 7 to 9 days with an attributable cost of $40 000 or more per patient compared to patients without nosocomial pneumonia. While treatment options vary, initial empiric treatment of nosocomial pneumonia should include antimicrobials that will have activity against the organisms that will likely be encountered, including, but not limited to, methicillin-resistant Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter species, Klebsiella pneumoniae, Enterobacter subspecies, Serratia marcescens, and Stenotrophomonas maltophilia. During a time of increasing resistance, it is crucial that early recognition along with appropriate treatment and dosing strategies are employed to achieve successful outcomes. The goal of this article is to update clinicians about nosocomial pneumonia and provide information regarding caveats to selecting and dosing antimicrobials, so informed decisions can be made when treating this serious condition.

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.

Patterns and dynamics of airway colonisation in mechanically-ventilated patients

The aim of this study was to investigate the patterns and dynamics of the microbiota in the airways of ventilated patients. Seventy-four mechanically-ventilated patients were recruited consecutively, and oropharyngeal, tracheal and bronchoalveolar (BAL) fluid specimens were collected 48 h after intubation, and every 72 h thereafter until the patient was extubated or a total of five sample sets had been collected. Ventilator-associated pneumonia (VAP) pathogens were identified, quantified and genotyped. Microbial findings were highly correlated both between airway locations and over time when samples were taken no more than 72 h apart. If no VAP pathogen was present in the oral flora, it was unlikely to be found in a lower airway sample; i.e., the positive predictive value of the oropharyngeal sample was 0.73 (95% CI 0.67-0.80), and the negative predictive value was 0.95 (95% CI 0.92-0.99). Colonisation with Enterobacteriacae, non-fermentative bacteria and Staphylococcus aureus was monoclonal in the airways and over time, whereas colonisation with microbes normally found in the oropharynx, i.e., Haemophilus influenzae, Haemophilus parainfluenzae and Streptococcus pneumoniae, was polyclonal. When antibiotics were used, the chance of recovering VAP pathogens from all sampling sites was reduced three-fold. No correlation was observed between a bacterial count of > or =10(4) CFU/mL in BAL fluid and chest X-rays compatible with VAP.

Bronchoalveolar lavage cytological alveolar damage in patients with severe pneumonia

Introduction

Histological examination of lung specimens from patients with pneumonia shows the presence of desquamated pneumocytes and erythrophages. We hypothesized that these modifications should also be present in bronchoalveolar lavage fluid (BAL) from patients with hospital-acquired pneumonia.

Methods

We conducted a prospective study in mechanically ventilated patients with clinical suspicion of pneumonia. Patients were classified as having hospital-acquired pneumonia or not, in accordance with the quantitative microbiological cultures of respiratory tract specimens. A group of severe community-acquired pneumonias requiring mechanical ventilation during the same period was used for comparison. A specimen of BAL (20 ml) was taken for cytological analysis. A semiquantitative analysis of the dominant leukocyte population, the presence of erythrophages/siderophages and desquamated type II pneumocytes was performed.

Results

In patients with confirmed hospital-acquired pneumonia, we found that 13 out of 39 patients (33.3%) had erythrophages/siderophages in BAL, 18 (46.2%) had desquamated pneumocytes and 8 (20.5%) fulfilled both criteria. Among the patients with community-acquired pneumonia, 7 out of 15 (46.7%) had erythrophages/siderophages and 6 (40%) had desquamated pneumocytes on BAL cytology. Only four (26.7%) fulfilled both criteria. No patient without hospital-acquired pneumonia had erythrophages/siderophages and only 3 out of 18 (16.7%) had desquamated pneumocytes on BAL cytology.

Conclusion

Cytological analysis of BAL from patients with pneumonia (either community-acquired or hospital-acquired) shows elements of cytological alveolar damage as hemorrhage and desquamated type II pneumocytes much more frequently than in BAL from patients without pneumonia. These elements had a high specificity for an infectious cause of pulmonary infiltrates but low specificity. These lesions could serve as an adjunct to diagnosis in patients suspected of having ventilator-associated pneumonia.

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.

Quantitative cultures for diagnosing ventilator-associated pneumonia: a critique

The diagnosis of ventilator-associated pneumonia has been clouded by uncertainty, because a reference standard has never been established. The use of invasive procedures to obtain respiratory tract samples for culture, with quantitation of the bacteria isolated, has been the approach most commonly advocated. Quantitation of bacteria from lower respiratory tract specimens can be used to distinguish colonization from infection. We review the invasive procedures (bronchoalveolar lavage, protected specimen brushing, nonbronchoscopic bronchoalveolar lavage, and blinded bronchial sampling), the methods of quantitation used, the types of catheters used, the sample collection methods, and the criteria used as cutoffs for the quantitative cultures. Quantitation of lower respiratory tract samples is inherently unstable from a mathematical perspective, given the variability in the volume of fluid instilled and reaspirated and the magnitude and complexity of the area being sampled. We also briefly review the use of quantitation for bacterial infections other than pneumonia, including urinary tract infection and catheter-related bacteremia. The variability in both the methods and reference criteria in the studies reviewed show that the quantitation approach is neither standardized nor evidence based.

Diagnosis and Treatment of Ventilator-Associated Pneumonia

Ventilator-associated pneumonia (VAP) is the most common nosocomial infection in the ICU. Patients who acquire VAP have higher mortality rates and longer ICU and hospital stays. Because there are other potential causes of fever, leukocytosis, and pulmonary infiltrates, clinical diagnostic criteria are overly sensitive in the diagnosis of VAP. Employing quantitative cultures of bronchopulmonary secretions in the diagnostic algorithm leads to less antibiotic use and probably to lower mortality. With respect to microbiologic diagnosis, it is not clear that the use of a particular sampling method (bronchoscopic or nonbronchoscopic), when quantitatively cultured, is associated with better outcomes. Delayed administration of adequate antibiotic therapy is linked to an increased mortality rate. Hence, the focus of initial antibiotic therapy should be to rapidly provide antibiotic coverage for all likely pathogens and to then narrow or focus the antibiotic spectrum based on the results of quantitative cultures. Eight days of antibiotic therapy appears equivalent to 15 days of therapy except when treating nonlactose-fermenting Gram-negative organisms. In this latter situation, longer treatment durations appear to reduce the risk of recrudescence after discontinuation of antibiotic therapy. A guideline-based approach using the local hospital or ICU antibiogram can increase the likelihood that adequate initial antibiotic therapy is used and reduce the overall use of antibiotics and the associated selection pressure for multidrug-resistant organisms.

Diagnosis of ventilator-associated pneumonia: focus on nonbronchoscopic techniques (nonbronchoscopic bronchoalveolar lavage, including mini-BAL, blinded protected specimen brush, and blinded bronchial sampling) and endotracheal aspirates

The ideal diagnostic approach for ventilator-associated pneumonia currently is based on invasive procedures to obtain respiratory tract cultures. Given the lack of consensus and relatively poor acceptance of full bronchoscopic bronchoalveolar lavage (BAL) and protected specimen brush (PSB), less invasive procedures have been developed. We review the nonbronchoscopic procedures (nonbronchoscopic bronchoalveolar lavage, including mini-BAL, blinded protected specimen, and blinded bronchial sampling) and endotracheal aspiration. We provide a critique of the methods used, the types of catheters inserted, and the sample collection methods. Most studies were flawed in that antibiotic use before initiation of the procedure was not controlled. The variability of both the methods and the criteria for the gold standard in the numerous investigations show that these procedures are neither standardized nor proven to be accurate and often did not improve management. Pending future studies, use of endotracheal aspirates without the use of quantitation seems to be a reasonable approach for clinicians who are not committed to an invasive procedure.

Nosocomial pneumonia: state of the science

Nosocomial pneumonia is the leading cause of mortality due to hospital-acquired infections. A thorough understanding of the most recent developments in evaluating and managing nosocomial pneumonia is critical for infection control professionals and hospital epidemiologists, given the incidence and cost of this important patient safety problem. We review the evidence on pathogenesis, diagnosis, treatment, and prevention of both ventilator-associated and nonventilator-associated pneumonia. Key recommendations are then provided for diagnostic testing strategies, antibiotic selection, and treatment duration. We also summarize the most recent data on how to prevent hospital-acquired infection, in general, and nosocomial pneumonia, in particular.

Neumonía nosocomial causada por Staphylococcus aureus resistente a meticilina

Methicillin-resistant Staphylococcus aureus (MRSA) is an increasingly common cause of hospital acquired pneumonia (HAP) and the second most frequently isolated pathogen from patients who die from HAP. High-risk units for MRSA colonization such as intensive care (ICU's) are the most affected. Multiple risk factors for transmission of MRSA have been identified, including colonization pressure and severity of illness at ICU admission. On the other hand, the most important predisposing factor for MRSA infection is prolonged mechanical ventilation and/or previous antibiotic therapy. Controlling the spread of MRSA remains a major challenge for hospitals. Screening programs, together with contact precautions for cases with MRSA and judicious antimicrobial use are major factors for a successful control. Early appropriate initial therapy is of crucial importance and improves outcome. The standard therapy has been glycopeptides but, in spite of its in vitro activity, mortality in critically ill patients treated with glycopeptides has consistently been reported high, mainly due to their poor lung penetration. Linezolid shows better clinical cure and survival rates, but further studies are needed. As the treatment options for MRSA pneumonia are limited and inadequate, development of more effective drugs is mandatory.

The international sepsis forum consensus conference on definitions of infection in the intensive care unit

OBJECTIVE

To develop definitions of infection that can be used in clinical trials in patients with sepsis.

CONTEXT

Infection is a key component of the definition of sepsis, yet there is currently no agreement on the definitions that should be used to identify specific infections in patients with sepsis. Agreeing on a set of valid definitions that can be easily implemented as part of a clinical trial protocol would facilitate patient selection, help classify patients into prospectively defined infection categories, and therefore greatly reduce variability between treatment groups.

DESIGN AND METHODS

Experts in infectious diseases, clinical microbiology, and critical care medicine were recruited and allocated specific infection sites. They carried out a systematic literature review and used this, and their own experience, to prepare a draft definition. At a subsequent consensus conference, rapporteurs presented the draft definitions, and these were then refined and improved during discussion. Modifications were circulated electronically and subsequently agreed upon as part of an iterative process until consensus was reached.

RESULT

Consensus definitions of infection were developed for the six most frequent causes of infections in septic patients: pneumonia, bloodstream infections (including infective endocarditis), intravascular catheter-related sepsis, intra-abdominal infections, urosepsis, and surgical wound infections.

CONCLUSIONS

We have described standardized definitions of the common sites of infection associated with sepsis in critically ill patients. Use of these definitions in clinical trials should help improve the quality of clinical research in this field.

Pneumonia associada à ventilação mecânica: impacto da multirresistência bacteriana na morbidade e mortalidade

INTRODUÇÃO: A pneumonia associada à ventilação mecânica é a infecção hospitalar mais comum nas unidades de terapia intensiva. OBJETIVO: Determinar o impacto da multirresistência dos microorganismos na morbidade e mortalidade dos pacientes com pneumonia associada à ventilação mecânica. MÉTODO: Estudo de coorte retrospectivo. Em 40 meses consecutivos, 91 pacientes sob ventilação mecânica tiveram o diagnóstico de pneumonia. Os casos foram divididos entre causados por microorganismo multirresistente e causados por microorganismo sensível à antibioticoterapia. RESULTADOS: Pneumonia foi causada por microorganismo multirresistente em 75 casos (82,4%) e por microorganismo sensível 16 (17,6%) deles. As características clínicas e epidemiológicas não foram estatisticamente diferentes entre os grupos. O Staphylococcus aureus foi responsável por 27,5% dos episódios de pneumonia associada à ventilação mecânica e a Pseudomonas aeruginosa por 17,6%. A doença foi de início recente em 33 pacientes (36,3%) e de início tardio em 58 deles (63,7%). Os tempos de ventilação mecânica, de internação em unidade de terapia intensiva e de internação hospitalar total não diferiram. O tratamento empírico foi considerado inadequado em 42 pacientes com pneumonia por microorganismo multirresistente (56%) e em 4 com pneumonia por microorganismo sensível (25%) (p = 0,02). Óbito ocorreu em 46 pacientes com a pneumonia por microorganismo multirresistente (61,3%), e em 4 daqueles com pneumonia por microorganismo sensível (25%) (p = 0,008). CONCLUSÃO: A multirresistência bacteriana não determinou nenhum impacto na morbidade, mas esteve associada à maior mortalidade.

Diagnosis of infection in sepsis: An evidence-based review

OBJECTIVE

In 2003, critical care and infectious disease experts representing 11 international organizations developed management guidelines for the diagnosis of infection in sepsis that would be of practical use for the bedside clinician, under the auspices of the Surviving Sepsis Campaign, an international effort to increase awareness and improve outcome in severe sepsis.

DESIGN

The process included a modified Delphi method, a consensus conference, several subsequent smaller meetings of subgroups and key individuals, teleconferences, and electronic-based discussion among subgroups and among the entire committee.

METHODS

The modified Delphi methodology used for grading recommendations built on a 2001 publication sponsored by the International Sepsis Forum. We undertook a systematic review of the literature graded along five levels to create recommendation grades from A to E, with A being the highest grade. Pediatric considerations to contrast adult and pediatric management are in the article by Parker et al. on p. S591.

CONCLUSIONS

Obtaining a precise bacteriological diagnosis before starting antibiotic therapy is, when possible, of paramount importance for the success of therapeutic strategy during sepsis. Two to three blood cultures should be performed, preferably from a peripheral vein, without interval between samples to avoid delaying therapy. A quantitative approach is preferred in most cases when possible, in particular for catheter-related infections and ventilator-associated pneumonia. Diagnosing community-acquired pneumonia is complex, and a diagnostic algorithm is proposed. Appropriate samples are indicated during soft tissue and intraabdominal infections, but cultures obtained through the drains are discouraged.

Quantifying Uncertainty: Physicians' Estimates of Infection in Critically Ill Neonates and Children

To determine the diagnostic accuracy of physicians' prior probability estimates of serious infection in critically ill neonates and children, we conducted a prospective cohort study in 2 intensive care units. Using available clinical, laboratory, and radiographic information, 27 physicians provided 2567 probability estimates for 347 patients (follow-up rate, 92%). The median probability estimate of infection increased from 0% (i.e., no antibiotic treatment or diagnostic work-up for sepsis), to 2% on the day preceding initiation of antibiotic therapy, to 20% at initiation of antibiotic treatment (P<.001). At initiation of treatment, predictions discriminated well between episodes subsequently classified as proven infection and episodes ultimately judged unlikely to be infection (area under the curve, 0.88). Physicians also showed a good ability to predict blood culture-positive sepsis (area under the curve, 0.77). Treatment and testing thresholds were derived from the provided predictions and treatment rates. Physicians' prognoses regarding the presence of serious infection were remarkably precise. Studies investigating the value of new tests for diagnosis of sepsis should establish that they add incremental value to physicians' judgment.

Variation of infected cell count in bronchoalveolar lavage and timing of ventilator-associated pneumonia

OBJECTIVES

The aim of this study was to evaluate and compare the accuracy of the percentage of infected cells (%IC) in bronchoalveolar lavage (BAL) for ventilator-associated pneumonia (VAP) diagnosis according to its onset from the initiation of mechanical ventilation.

PATIENTS

One hundred and eight patients admitted to a surgical ICU were retrospectively included (1999-2001). A total of 171 cases of VAP were diagnosed on clinical, biological, chest X-ray and BAL results (threshold >/=10(4 )cfu/ml).

RESULTS

The %IC significantly decreased with the timing of VAP diagnosis: 12.2+/-12.1% for VAP occurring less than 7 days after the initiation of mechanical ventilation, 7.4+/-9.2% for VAP occurring between 7 and 15 days and 4.8+/-6.4% for VAP after 15 days ( p=0.0002), despite the same number of elements and proportion of polymorphonuclear neutrophils in BAL. In addition, a relationship between the %IC and the pathogen responsible for VAP was observed for P. aeruginosa [higher for VAP <7 days than for VAP 7-15 days ( p=0.01) and VAP >15 days ( p=0.006)] and S. aureus [lower for VAP >15 days than VAP 7-15 days ( p=0.04) and VAP <7 days ( p=0.04)]. Furthermore, the %IC in BAL was lower in patients undergoing antimicrobial therapy than in patients without antibiotics ( p=0.04). Three factors were independently associated with the %IC: quantitative culture of BAL (beta=0.42, p<0.0001), ongoing antimicrobial therapy (beta= -0.21, p=0.003) and onset of VAP (beta= -0.17, p=0.01).

CONCLUSIONS

A relationship between the %IC in BAL, duration of ventilation, quantitative culture of BAL and ongoing antimicrobial therapy has been proved in this study. The %IC for VAP diagnosis may not be accurate in patients with ongoing antibiotics and late onset infections (>7 days).

Blind and bronchoscopic sampling methods in suspected ventilator-associated pneumonia

OBJECTIVE

To compare four sampling methods: blind tracheal aspirate (blind TA), blind protected telescoping catheter (blind PTC), bronchoscopic PTC and bronchoscopic bronchoalveolar lavage (bronchoscopic BAL), for diagnosis of ventilator-associated pneumonia (VAP).

DESIGN

Prospective multicentre study.

SETTING

Five intensive care units in France.

PATIENTS

Sixty-three patients with mechanical ventilation for more than 48 h, no recent antibiotic change (<72 h) and suspected nosocomial pneumonia.

INTERVENTIONS

All patients underwent the four sampling methods. Direct examination and quantitative cultures of the four specimens were performed.

MEASUREMENTS AND RESULTS

Visible secretions expelled from the catheter were present 40 times (63%) for blind PTC and 45 times (71%) for bronchoscopic PTC. After exclusion of 11 uncertain cases, 34 VAP were diagnosed. Direct examination of PTC (either blind or bronchoscopic) did not differ from direct examination of bronchoscopic BAL in predicting VAP diagnosis and in guiding initial antibiotic treatment correctly. Compared to that of bronchoscopic BAL (0.98), the area under receiver operating characteristics (ROC) curve was smaller for blind TA (0.78, p=0.002), blind PTC (0.83, p=0.009) and bronchoscopic PTC (0.85, p=0.01). When samples with visible secretions expelled from the catheter were considered, blind and bronchoscopic PTC had areas under ROC curve close to that of bronchoscopic BAL (0.90, p=0.22 and 0.91, p=0.27, respectively).

CONCLUSIONS

Blind PTC appears to be a good alternative to bronchoscopic sampling for VAP diagnosis, provided that the sample contains visible secretions expelled from the catheter.

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.

Clinical pulmonary infection score for ventilator-associated pneumonia: accuracy and inter-observer variability

OBJECTIVE

Although quantitative microbiological cultures of samples obtained by bronchoscopy are considered the most specific tool for diagnosing ventilator-associated pneumonia, this labor-intensive invasive technique is not widely used. The Clinical Pulmonary Infection Score (CPIS), a diagnostic algorithm that relies on easily available clinical, radiographic, and microbiological criteria, could be an attractive alternative for diagnosing ventilator-associated pneumonia. Initially, the CPIS scoring system was validated upon 40 quantitative cultures of bronchoalveolar lavage fluid from 28 patients, and only few other studies have evaluated this scoring system since then. Therefore, little is known about the accuracy of this score.

DESIGN

We compared the scores of a slightly adjusted CPIS with results from quantitative cultures of bronchoalveolar lavage fluid in 99 consecutive patients with suspicion of ventilator-associated pneumonia, using growth of > or =10(4) cfu/ml in bronchoalveolar lavage fluid as a cut-off for diagnosing ventilator-associated pneumonia. In addition, the CPIS were calculated for 52 patients by two different intensivists to determine the inter-observer variability.

RESULTS

Ventilator-associated pneumonia was diagnosed in 69 (69.6%) patients. When using a CPIS >5 as diagnostic cutoff, the sensitivity of the score was 83% and its specificity was 17%. The area under the Receiver Operating Characteristic curve was 0.55. The level of agreement for prospectively measured Clinical Pulmonary Infection Score (< or =6 and >6) was poor (kappa =0.16).

CONCLUSIONS

When compared to quantitative cultures of bronchoalveolar lavage fluid, the CPIS has a low sensitivity and specificity for diagnosing ventilator-associated pneumonia with considerable inter-observer variability.

Diagnosis of hospital-acquired pneumonia: postmortem studies

Postmortem human and animal studies provided important insights into the relationship between histology and bacteriology in VAP. According to the results of these studies, VAP is a multifocal and polymicrobial infectious process. The lesions are predominately located in dependent segments of lower lobes. There is no straightforward relationship between the intensity of lung damage and the local microbial burden. Histobacteriologic discrepancy may explain why even such techniques as PSB and BAL can be unreliable for the diagnosis of VAP. The histopathologic examination of the lung tissue has been traditionally regarded as the gold standard for diagnosis of VAP. Even with histology, however, pneumonia is frequently difficult to define. For daily practice, antimicrobial decisions and the guidance of antimicrobial regimens should not rely exclusively on the results of quantitative cultures in the individual patient. Instead, finding a balance between clinical judgment and microbiologic results is crucial to manage patients with VAP appropriately.

Decision analysis of antibiotic and diagnostic strategies in ventilator-associated pneumonia

The optimal strategy for ventilator-associated pneumonia remains controversial. To clarify the tradeoffs involved, we performed a decision analysis. Strategies evaluated included antibiotic therapy with and without diagnostic testing. Tests that were explored included endotracheal aspirates, bronchoscopy with protected brush or bronchoalveolar lavage, and nonbronchoscopic mini-bronchoalveolar lavage (mini-BAL). Outcomes included dollar cost, antibiotic use, survival, cost-effectiveness, antibiotic use per survivor, and the outcome perspective of financial cost-antibiotic use per survivor. Initial coverage with three antibiotics was better than expectant management or one or two antibiotic approaches, leading to both improved survival (54% vs. 66%) and decreased cost (US dollars 55447 vs. US dollars 41483 per survivor). Testing with mini-BAL did not improve survival but did decrease costs (US dollars 41483 vs. US dollars 39967) and antibiotic use (63 vs. 39 antibiotic days per survivor). From the perspective of minimizing cost, minimizing antibiotic use, and maximizing survival, the best strategy was three antibiotics with mini-BAL.

Is the implementation of research findings in the critically ill hampered by the lack of universal definitions of illness?

In the design of clinical trials, a clear definition of disease is essential for enrollment of a homogeneous study population with a higher likelihood of demonstrating a benefit of an intervention. A definition that is applicable to standard clinical practice enhances the ability of clinicians to apply results of the clinical trial to patient care. Use of a universally accepted definition allows valid comparisons across multiple studies. Sepsis, the acute respiratory distress syndrome, and ventilator-associated pneumonia are examples of conditions for which universal definitions developed by panels of experts have facilitated the design of successful clinical trials. However, implementation of the results of some of these studies has been complicated by a lack of understanding or acceptance of disease definitions or by their overly inclusive nature. For example, the presence of Systemic Inflammatory Response Syndrome (SIRS) will identify most patients with sepsis, however, a significant number of patients with those clinical findings will have other underlying processes. Approved definitions for VAP are cumbersome, and adherence to those definitions in the design of clinical trials is poor. This has led to confusion regarding the accuracy of diagnostic tests and poor acceptance of evidence based guidelines by clinicians. When investigators and clinicians do not adhere to common definitions of disease, results of clinical trials may be applied inappropriately or ignored altogether. More specific identifiers of critical illnesses using specific biochemical or genetic markers are being explored. This approach may also be useful for staging disease.

The preventable proportion of nosocomial infections: an overview of published reports

The proportion of nosocomial infections potentially preventable under routine working conditions remains unclear. We performed a systematic review to describe multi-modal intervention studies, as well as studies assessing exogenous cross-infection published during the last decade, in order to give a crude estimate of the proportion of potentially preventable nosocomial infections. The evaluation of 30 reports suggests that great potential exists to decrease nosocomial infection rates, from a minimum reduction effect of 10% to a maximum effect of 70%, depending on the setting, study design, baseline infection rates and type of infection. The most important reduction effect was identified for catheter-related bacteraemia, whereas a smaller, but still substantial potential for prevention seems to exist for other types of infections. Based on these estimates, we consider at least 20% of all nosocomial infections as probably preventable, and hope that this overview will stimulate further research on feasible and cost-effective prevention of nosocomial infections for daily practice.

Acute respiratory distress syndrome after bacteremic sepsis does not increase mortality

To determine whether acute respiratory distress syndrome (ARDS) complicating bacteremic sepsis independently affects mortality in critically ill patients, we conducted a 3-year retrospective cohort study in a surgical intensive care unit. We included all consecutive patients with blood culture-positive sepsis and measured organ dysfunctions and mortality. Among 4,530 admissions, 196 cases of bacteremic sepsis were recorded. ARDS occurred in 31 (16%) of these patients. The case fatality rate was 58% in patients with ARDS compared with 31% in patients without ARDS. Using Cox proportional hazards regression with time-dependent variables, the unadjusted hazard ratio for death was 1.8 (95% confidence interval [CI], 1.0-3.2). After adjusting for comorbid factors that were present before the onset of sepsis, the hazard ratio was 2.2 (95% CI, 1.2-3.9). After further adjustment was made for nonpulmonary organ dysfunctions and microbiologic factors that were independently associated with mortality, the adjusted hazard ratio for ARDS was 0.6 (95% CI, 0.3-1.2). Among critically ill surgical patients, ARDS complicating bacteremic sepsis remains common, but it is not independently associated with short-term mortality, after adjusting for severity of illness and nonpulmonary organ dysfunctions evolving after the onset of sepsis.