Gram staining for the treatment of peritonsillar abscess

Objective. To examine whether Gram staining can influence the choice of antibiotic for the treatment of peritonsillar abscess. Methods. Between 2005 and 2009, a total of 57 cases of peritonsillar abscess were analyzed with regard to cultured bacteria and Gram staining. Results. Only aerobes were cultured in 16% of cases, and only anaerobes were cultured in 51% of cases. Mixed growth of aerobes and anaerobes was observed in 21% of cases. The cultured bacteria were mainly aerobic Streptococcus, anaerobic Gram-positive cocci, and anaerobic Gram-negative rods. Phagocytosis of bacteria on Gram staining was observed in 9 cases. The bacteria cultured from these cases were aerobic Streptococcus, anaerobic Gram-positive cocci, and anaerobic Gram-negative rods. The sensitivity of Gram staining for the Gram-positive cocci and Gram-negative rods was 90% and 64%, respectively. The specificity of Gram staining for the Gram-positive cocci and Gram-negative rods was 62% and 76%, respectively. Most of the Gram-positive cocci were sensitive to penicillin, but some of anaerobic Gram-negative rods were resistant to penicillin. Conclusion. When Gram staining shows only Gram-positive cocci, penicillin is the treatment of choice. In other cases, antibiotics effective for the penicillin-resistant organisms should be used.

Influence of the collection and oxygenation method on quantitative bacterial composition in bronchoalveolar lavage fluid samples from healthy dogs

The purpose of the study was to evaluate the effects on quantitative and qualitative microbial content of endoscopic bronchoalveolar lavage fluid (BALF) in healthy dogs using a laryngeal mask airway (LMA). It was hypothesised that oropharyngeal protection might prevent contamination of BALF with oropharyngeal microflora. Ten healthy Beagle dogs were randomly assigned to two groups and underwent endoscopic BAL on two occasions, either via an open unprotected oropharynx with oxygen supply provided via a nasal catheter (NT) or through a sterile LMA. For the second sampling, groups were switched. BALF analysis included quantitative microbial culture, nucleated cell counts and cytology. The mean (+/-SD) number of colony forming units (CFU)/mL found in the BALF using the LMA was 25,610+/-22,943 in the right lung (RL) and 22,510+/-18,779 in the left (LL). With the NT technique, the figures were 21,068+/-19,375 for the RL and 16,060+/-15,523 for the LL, respectively. Nucleated cell counts/microL were 691.0+/-181.6 (RL) and 734.0+/-171.6 (LL) for LMA, and 772.0+/-251.0 (RL) and 748+/-163.2 (LL) for NT. No significant differences were detected either in the number of CFU/mL or in the diversity of bacterial species with the two methods. A significant increase in BALF bacterial counts (with reduced species diversity) was observed on the second compared to the first sampling regardless of the method used. Protection of the oral cavity and oropharynx using an LMA had no significant influence on BALF bacterial counts. The findings suggest that with careful endoscope insertion, the risk of contamination of BALF by resident and transient oropharyngeal microflora can be negligible.

[Acute forms of diffuse interstitial hypoxemic pneumonia in immunocompetent patients]

The large majority of patients with acute respiratory failure present diffuse pulmonary opacities resulting from pulmonary embolism, intra-alveolar hemorrhage, or a classical cause of ARDS. In a small number of patients however, these opacities correspond to diffuse interstitial pneumonia. This should be suspected in light of the context, the time of formation, and the unusual respiratory and/or extrarespiratory signs. If there is a clinical doubt, thoracic scan and bronchoalveolar lavage should be performed together with infectious and immunology tests. Treatment depends on the cause and/or the type of lesion.

Ventilator-associated pneumonia

Ventilator-associated pneumonia is the most common nosocomial infection. Mortality rates, morbidity, and costs are all increased in the patient with VAP, and every measure should thus be taken to prevent its development. There are several clearly defined risk factors for VAP, and awareness of these can facilitate early diagnosis and hence treatment. In this article, we discuss the risk factors, strategies for prevention, approaches to diagnosis and management plan for the patient with VAP.

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.

Microscopic examination of intracellular organisms in protected bronchoalveolar mini-lavage fluid for the diagnosis of ventilator-associated pneumonia

STUDY OBJECTIVES

To assess the cutoff percentage of cells containing intracellular organisms (ICOs) in the microscopic examination of mini-lavage fluid for the diagnosis of ventilator-associated pneumonia (VAP), and to study the accuracy of this diagnostic procedure on patients who have received previous antibiotic therapy (AT).

DESIGN

Prospective clinical investigation.

SETTING

The medico-surgical ICU of a university hospital.

PATIENTS

Eighty-two patients who fulfilled the clinical criteria of first episode of VAP.

INTERVENTIONS

Lower airway secretion samples were obtained by a nonbronchoscopic protected bronchoalveolar mini-lavage (mini-PBAL).

MEASUREMENTS AND RESULTS

A total of 82 mini-PBALs were performed. The fluid obtained was divided into two samples. The first sample underwent direct microscopic examination using centrifugal cytology and Giemsa stain in order to determine the percentage of cells containing ICOs. The second sample was processed for Gram stain and quantitative cultures. VAP was the final diagnosis in 65 patients based on the mini-PBAL results obtained in the quantitative cultures. At least one bacterial species grew in a significant concentration (> or = 10(3) cfu/mL). The mini-PBAL was performed on 42 patients during AT (> or = 24 h of effective AT at the time of diagnostic procedure) and on another 40 patients with no AT (No AT). The results of the quantitative cultures were compared with the percentage of cells containing ICOs using a receiver operator characteristic (ROC) curve. The cutoff point of > or = 2% of cells containing ICOs had the highest sensitivity (80%) and specificity (82%) in the studied population (area under the ROC curve [AUC], 0.83; 95% confidence interval [CI], 0.70 to 0.90). In patients receiving AT, the sensitivity was 70% and specificity was 75% (AUC, 0.73; 95% CI, 0.58 to 0.90); and in No AT-group patients sensitivity was 88% and specificity was 100% (AUC, 0.92; 95% CI, 0.84 to 1.0). The comparative analysis of both ROC curves was statistically significant (p = 0.04).

CONCLUSIONS

The cutoff point of > or = 2% of cells containing ICOs has the highest sensitivity and specificity in the microscopic examination of mini-lavage fluid for the diagnosis of VAP. However, sensitivity is too low to be clinically useful. The direct examination of mini-PBAL fluid is less accurate when previous AT has been administered.

Correlation of intracellular organisms with quantitative endotracheal aspirate

BACKGROUND

The presence of intracellular organisms (ICOs) in polymorphonuclear cells obtained from respiratory secretions is a possible method for rapid diagnosis of ventilator-associated pneumonia. We correlated ICOs with quantitative endotracheal aspirate (QA) in intubated patients.

METHODS

Consecutive intubated patients in the surgical intensive care unit had respiratory samples obtained every 2 days until extubation. Two thresholds for ICOs and quantitative culture were examined. Sensitivity, specificity, and positive and negative predictive values were calculated using QA as reference.

RESULTS

One hundred one samples were obtained from 35 patients. Colony counts >or= 100,000 were found in 34 samples; 60 samples had colony counts >or= 10,000. Antibiotic use did not affect the sensitivity or specificity of ICOs. Sensitivity of ICOs was 39% to 85%, and specificity was 82% to 97%. Positive predictive value was 70% to 96%, and negative predictive value was 50% to 91%.

CONCLUSION

ICOs provide a quick method for establishing the presence of a significant bacterial load in the respiratory tract. Accuracy of ICOs in predicting a positive QA is not affected by concurrent antibiotics.

Diagnosis and management of pneumonia in the intensive care unit

Ventilator-associated pneumonia is a significant contributor to excess morbidity and mortality in the ICU. Alteration of physical defenses, bacterial flora, and immune response contribute to the susceptibility of the critically ill ventilated patient. Controversies regarding its definition continue to complicate the understanding of the extent of the disease and evaluation of the outcome of therapies. Traditional parameters, such as clinical suspicion with standard tracheal aspirates, are associated with overuse of antibiotics, a prime risk factor for development of resistant organisms and increased mortality. Global emergence of resistance is also a major concern. Whether invasive methods have any substantial clinical benefit either through improved patient outcomes or lower rates of resistance remains to be proved. In patients who fail to respond to therapy, a search for nonpulmonary infections and noninfectious causes of pulmonary infiltrates is essential. Finally, preventative measures offer additional areas of investigation that could favorably impact on the incidence of infection.

Controversies in the diagnosis of ventilator-acquired pneumonia

The appropriate investigation of patients with suspected VAP is controversial. Because it is unlikely that any new diagnostic technique will become available in the near future with better performance characteristics than those currently available, physicians need to tailor their diagnostic approach depending on individual patients and clinical scenarios. The most crucial factor in deciding which diagnostic approach to take is the influence that any test result would have on management. If preliminary screening tests, including Gram stain, are used to determine whether to start antibiotic therapy, invasive diagnostic techniques have an advantage over ETA. Quantitative cultures of respiratory specimens have a higher specificity than qualitative cultures and should be used if there is any possibility that a negative culture result would result in the discontinuation of antibiotic therapy. Physicians are caught between the need to treat VAP promptly with appropriate antibiotics and the undeniable problems of multidrug-resistant bacteria and their association with inappropriate antibiotic use. When clinically possible, a diagnostic strategy should be chosen that maximizes the possibility of limiting broad-spectrum antibiotic use. To give physicians greater comfort in the ability to withhold or discontinue antibiotics safely, further research is needed into the appropriate diagnostic strategies in different clinical settings that make this possible. The studies by Fagon et al and Singh et al are important steps in this direction.

Flexible bronchoscopy in nosocomial pneumonia

In this article, an overview on the diagnostic performances of bronchoscopic techniques for the diagnosis of nosocomial pneumonia is given with special emphasis on the inherent problems of the methodology of validation applied to different studies. The current evidence about the importance of bronchoscopic techniques for the outcome is reviewed. It is outlined that future prospects of bronchoscopic investigations mainly include the evaluation of its role in the reassessment of the patient with pneumonia not responding to the initial antimicrobial treatment.

Value of gram stain examination of lower respiratory tract secretions for early diagnosis of nosocomial pneumonia

Except for bronchoalveolar lavage, the value of the Gram stain examination of respiratory tract samples for the diagnosis of hospital-acquired pneumonia (HAP) and their potential impact on empiric antibiotic treatment have rarely been assessed. During a 14-mo period, both plugged telescoping catheter (PTC) and endotracheal aspirate (EA) were performed when an HAP was suspected in mechanically ventilated patients. The results of Gram stain examinations and cultures and previous and subsequent antibiotic treatment were prospectively recorded. Two criteria for pneumonia were considered: (1) clinically diagnosed pneumonia, according to attending physicians, based on clinical and radiological evolution and the PTC culture results, and (2) microbiologically proven pneumonia (solely based on the result of quantitative PTC culture). Of 91 episodes of suspected HAP in 51 patients, 27 (30%) episodes were clinically diagnosed as pneumonia. When considering clinically diagnosed pneumonia, the sensitivity and specificity of Gram stain examination were similar (respectively, 89% and 62% for EA and 67% and 95% for PTC). When considering microbiologically proven pneumonia, the sensitivity and specificity of Gram stain examination were, respectively, 91% and 64% for EA and 70% and 96% for PTC. The negative predictive value of Gram stain examination of EA and the positive predictive value of Gram stain examination of PTC were high. Our results suggest that the combination of Gram stain examination of paired PTC and EA may contribute to the early diagnosis of HAP in about two-thirds of mechanically ventilated patients, and guide the empiric therapy when needed. In the remaining one-third of patients, the Gram stain examination is not helpful in predicting HAP.

Protected specimen brush or bronchoalveolar lavage to diagnose bacterial nosocomial pneumonia in ventilated adults: a meta-analysis

OBJECTIVE

We conducted a meta-analysis by using summary receiver operating characteristic curves to compare the diagnostic value for bacterial nosocomial pneumonia of the following: a) quantitative culture (colony-forming units per milliliter or CFU/mL) of respiratory secretions collected with a bronchoscopic protected specimen brush (PSB); b) quantitative culture of a bronchoscopic bronchoalveolar lavage (BAL); and c) the percentage of infected cells (IC) in BAL.

DATA SOURCES

All studies published in the English or the French language, through January 1, 1995, on the evaluation of PSB or BAL for the diagnosis of pneumonia were considered for analysis. The relevant literature was identified through computer and reference searching and by experts in the field.

STUDY SELECTION

A study was included if at least two of three independent readers regarded its purpose as the evaluation of CFU-PSB, CFU-BAL, or IC-BAL for the diagnosis in human beings of bacterial nosocomial pneumonia in ventilated adults and if the study was prospective and published in a peer-reviewed journal.

DATA EXTRACTION

Three readers reviewed all published articles and decided whether to include each study; consensus was defined as agreement by at least two readers. The authors of each original article included in the meta-analysis were asked to complete a questionnaire in which they were asked to check and to correct the data extracted by one of the independent readers.

DATA SYNTHESIS

Summary receiver operating characteristic curves were used to compare the efficacy of three diagnostic tests. Eighteen studies on CFU-PSB (795 patients) were included, as well as 11 studies on CFU-BAL (435 patients) and 11 on IC-BAL (766 patients). The accuracy of these tests was not different. However, it seems that administration of previous antibiotics markedly decreased accuracy of CFU-PSB (p = .0002) but not the accuracy of CFU-BAL and that of IC-BAL.

CONCLUSION

Both PSB and BAL are reliable to diagnose bacterial nosocomial pneumonia. Because CFU-BAL and IC-BAL seemed more resistant to the effects of antibiotics, we recommend BAL rather than PSB if the patient is already receiving antibiotics.

Detection of non-infectious conditions mimicking pneumonia in the intensive care setting: usefulness of bronchoalveolar fluid cytology

The present study investigated the usefulness of bronchoalveolar (BAL) fluid cytology in the identification of non-infectious pulmonary conditions in patients hospitalized in the intensive care unit (ICU) and suspected of pneumonia. A total of 182 BAL fluid samples obtained during a 27-month period from 130 ICU patients with suspected pneumonia were quantitatively cultured and investigated for opportunistic pathogens. Cytocentrifuged preparations stained with the May-Grünwald Giemsa and Perls's methods were reviewed. A non-infectious aetiology was considered when cultures yielded micro-organisms in quantities < 10(3) colony-forming units (CFU) per ml, in the absence of any other pathogen and in conjunction with one or more of the following cytological findings: > 20% haemosiderin macrophages, > 10% lymphocytes, the presence of activated lymphocytes, plasma cells, > 5% eosinophils, a preponderance of foamy macrophages, reactive type II pneumocytes or malignant cells. Patients' clinical records were reviewed to identify a clinical diagnosis for these episodes. In thirty-five (19.2%) BAL fluid samples from 26 patients, the cytological findings pointed to a non-infectious origin. An alternative diagnosis was ascertained in 20 of 26 patients. Diagnoses included: drug-induced pneumonitis (n = 7), aspiration of gastric contents (n = 2), pulmonary emboli (n = 3), adult respiratory distress syndrome (n = 4), lung contusion (n = 1), cardiogenic pulmonary oedema (n = 1), and carcinomatous lymphangitis (n = 2). The BAL fluid cytological findings were readily discernable and proved to be useful in the diagnostic work-up of samples obtained from ICU patients with suspected pneumonia.

Test characteristics of acridine orange, Gram, and May-Grünwald-Giemsa stains for enumeration of intracellular organisms in bronchoalveolar lavage fluid

For enumeration of intracellular organisms (ICO) in bronchoalveolar lavage fluid samples, the May-Grünwald-Giemsa (MGG) stain displayed higher interobserver agreement than the acridine orange and Gram stains. The MGG stain offered a reliable enumeration of ICO when 200 cells were counted by one observer.

Diagnosis of ventilator-associated pneumonia

The diagnosis of ventilator-associated pneumonia (VAP) is problematic despite numerous attempts at defining acceptable diagnostic criteria and the optimal technique for routine respiratory sampling. Clinical criteria have imperfect diagnostic reliability in ventilated patients, but remain crucial for defining those patients who may require respiratory sampling. Quantitative clinical scoring systems may improve the accuracy of clinical diagnosis in some ventilated patients. Review of published studies suggest that fibreoptic bronchoscopic techniques have greater diagnostic reliability than qualitative endotracheal aspirates, despite inconsistent results when comparing the same techniques in different centres. However, the cost and invasive nature of bronchoscopic methods precludes their use as first-line techniques in VAP. Non-bronchoscopic, non-directed techniques are cheaper, safer and more widely available alternatives to fibreoptic bronchoscopy techniques and have comparable accuracy. Quantitation of respiratory tract cultures is useful in excluding VAP in patients with equivocal signs of pneumonia. The diagnostic threshold of bacterial load that defines the presence of VAP should vary according to the pre-test probability of pneumonia, length of ventilation, antibiotic administration and immunocompetence of the patient.

[Diagnostic characteristics of acquired pneumonia in patients under mechanical respiration]

Ventilator-associated pneumonias (VAP) are the most frequent nosocomial lung infections. Histological diagnosis is the standard for reference. A diagnosis of VAP can be considered in presence of fever or hypothermia, hyperleucocytosis or leucopenia, worsening of blood gases, and new radiological infiltrate. Their diagnostical value is dependent on the number of included manifestations. A clinical pulmonary infection score (CPIS) has been produced and compared with histological data. Bacteriological data are essential for an adapted antibiotherapy. The blind non-protected specimen brush is inexpensive and reliable at levels of 10(4) and 10(6) CFU.mL-1, the sensitivity and specificity reach 60%. The double-protected catheter is a sensitive and specific test at the level of 10(3) CFU.mL-1. At present its accuracy has only been compared with bronchial brushing. The culture of a 20 mL mini-broncho-alveolar lavage (same material) is specific (50%) but not sensitive enough (< 70%) at the level of 10(3) CFU.mL-1. The culture of the protected telescopic brush is the most expensive test. It does not carry a risk of contamination, but does not detect a significant amount of VAP even at a level below 10(3) CFU.mL-1. Due to its high specificity it is used as the reference test in numerous studies. The endoscopic broncho-alveolar lavage provides a rapid diagnosis. Although not protected, it carries a low risk of false positives. It also allows the diagnosis of non-bacterial or atypical bacterial lung infections. The diagnosis can also be obtained with lung biopsy which however carries a risk in case of mechanical ventilation, whatever the technique. Except for the protected double catheter, a direct examination has been advocated, for the differentiation between infection and colonization and the improvement of the performances of the simple culture of the broncho-alveolar lavage (search for intra-cellular bacteria).

Diagnostic accuracy of protected specimen brush and bronchoalveolar lavage in nosocomial pneumonia: impact of previous antimicrobial treatments

OBJECTIVE

To determine whether the diagnostic accuracy of bronchoscopy samples in patients with suspected ventilator-associated pneumonia is affected by prior antibiotic treatment given for a previous infection, and/or by antibiotic treatment recently started to treat suspected ventilator-associated pneumonia.

DESIGN

Study of critically ill patients.

SETTING

Intensive care unit in a university hospital.

PATIENTS

Sixty-three episodes of suspected ventilator-associated pneumonia were prospectively evaluated. Based on prior antibiotic treatment, three groups were defined: no antibiotic group (no previous antibiotic treatments), n = 12; current antibiotic group (antibiotic treatment initiated >72 hrs earlier), n = 31; and recent antibiotic group (new antibiotic treatment class started within the last 24 hrs), n = 20.

INTERVENTIONS

Fiberoptic bronchoscopy with quantitative protected specimen brush cultures, bronchoalveolar lavage cultures, and intracellular organism counts of bronchoalveolar lavage cells.

MEASUREMENTS AND MAIN RESULTS

The diagnosis of ventilator-associated pneumonia was made in 35 cases, based on histology (n = 2), cavitation (n = 2), blood cultures (n = 4), or outcome under appropriate antibiotic treatment (n = 27). The discriminative value of the tests, based on the area under the receiver operating characteristic curve, was high (> or =0.85) in both current antibiotic treatment and recent antibiotic treatment patients. Sensitivities for a 5% intracellular organism count of bronchoalveolar lavage cells, a protected specimen brush culture threshold of 10(3) colony-forming units (cfu)/mL, and a bronchoalveolar lavage culture threshold of 10(5) cfu/mL were as follows, respectively, in the three groups: 0.71, 0.88, and 0.71 (no antibiotic treatment group); 0.5, 0.77, and 0.83 (current antibiotic group); and 0.67, 0.40, and 0.38 (recent antibiotic group). Specificity was consistently > or =0.9. In the recent antibiotic group, protected specimen brush and bronchoalveolar lavage cultures had lower sensitivities (p < .05), and the best threshold values for these two tests were 10(2) cfu/mL and 10(3) cfu/mL, respectively.

CONCLUSIONS

After recent introduction of an antibiotic treatment for suspected ventilator-associated pneumonia, protected specimen brush and bronchoalveolar lavage culture thresholds must be decreased to maintain good accuracy. In contrast, current antibiotic treatment prescribed for a prior infectious disease does not modify the diagnostic accuracy of protected specimen brush or bronchoalveolar lavage.

Nosocomial pneumonia in the critical care unit

Nosocomial pneumonia poses a major threat to the recovery of patients receiving mechanical ventilation. In addition, nosocomial pneumonia is often difficult to diagnose. This article examines the extent of the threat and some of the difficulties facing the critical care physician when diagnosing nosocomial pneumonia.

Early diagnosis of ventilator-associated pneumonia. Is it possible to define a cutoff value of infected cells in BAL fluid?

STUDY OBJECTIVE

To assess the usefulness of quantification of infected cells (ICs) in BAL fluid for the diagnosis of ventilator-associated pneumonia (VAP).

DESIGN

A prospective study.

SETTING

A medico-surgical ICU in a tertiary health-care institution.

PATIENTS

One hundred thirty-two patients (mean age, 52 +/- 19 years). The suspicion of nosocomial pneumonia was strong in these patients: all had fever (> or = 38.5 degrees C), purulent tracheal aspirates, leukocytosis (> or = 10,000 cells per cubic millimeter), and new or persistent radiographic lung infiltrates.

INTERVENTIONS

One hundred sixty-three samples (BAL and protected specimen brushes [PSB]) were obtained.

RESULTS

VAP was present in 56 cases. The diagnosis was excluded in the remaining 107 cases. The IC count was performed on 100 cells in BAL fluid. The percentage of IC was significantly higher (12.6 +/- 12.4 vs 1.14 +/- 3.39; p < 0.0001) in patients with pneumonia: the area under the receiver operating characteristic (ROC) curve was 0.888 and a threshold of 2% of IC corresponded to a sensitivity of 84%, a specificity of 80%, a positive predictive value of 69%, and a negative predictive value of 90%.

CONCLUSIONS

It is possible to define a threshold of IC in BAL fluid with a good reliability by using an ROC curve. This technique is useful for the early diagnosis (< 2 h) of nosocomial bacterial pneumonia in mechanically ventilated patients and allows a rapid and appropriate treatment of most of the patients with suspected VAP.

Diagnosis and treatment of ventilator-associated pneumonia--impact on survival. A decision analysis

STUDY OBJECTIVE

To determine the impact of antibiotic treatment of ventilator-associated pneumonia (VAP) on survival.

DESIGN

Decision analysis.

PATIENTS

A hypothetical cohort of immunocompetent patients receiving mechanical ventilation who have suspected bacterial pneumonia. The analysis was performed separately for the following diagnostic techniques: clinical criteria, bronchoscopic protected specimen brush (PSB), and nonbronchoscopic protected BAL (pBAL). Additional factors accounted for in the analysis included the presence or absence of prior antibiotic use, mortality of antibiotic-treated and untreated pneumonia, mortality attributable to VAP, development of antibiotic resistance, and mortality due to adverse drug reactions.

MEASUREMENTS AND RESULTS

The overall survival of patients who receive antibiotic therapy was compared to survival if antibiotic therapy had been withheld. Antibiotic treatment of clinically diagnosed VAP was associated with lower overall survival than withholding treatment. Antibiotic treatment of VAP diagnosed by invasive (PSB) or semi-invasive (pBAL) techniques was associated with better survival than withholding treatment, although withholding antibiotic therapy was favored as the mortality rate of antibiotic-treated VAP approached 70%.

CONCLUSIONS

Invasive or semi-invasive diagnostic techniques should be used to diagnose VAP, guide therapy, and thereby potentially improve survival. A prospective, randomized trial assessing outcome according to diagnostic technique is needed.

Value of intracellular bacteria detection in the diagnosis of ventilator associated pneumonia

BACKGROUND

Markers of ventilator associated pneumonia are of interest for confirming the diagnosis and for guiding the initial management of this frequent complication of mechanical ventilation. The detection of intracellular organisms in the polymorphonuclear leucocytes (PMNLs) and/or macrophages of bronchoalveolar lavage (BAL) fluid has been suggested as a specific test for the early indication of an infectious pulmonary process.

METHODS

The diagnostic value of detecting intracellular organisms in two types of BAL fluid--protected (P-BAL) and conventional (C-BAL)--in 25 patients who died in one unit was prospectively studied. Immediately after death both P-BAL and C-BAL were performed bilaterally. Through a minithoracotomy on both sides of the chest bilateral bronchoscopically guided open lung biopsy samples were obtained from the same area, and an average of eight open lung blind biopsy samples (not bronchoscopically guided) were taken from each lung for histological examination. BAL fluid was examined for quantitative cultures (threshold 10(4) cfu/ml) and for the presence of intracellular organisms and extracellular organisms, and differential cell counts were also performed.

RESULTS

Using the histopathology of the bronchoscopically guided open lung biopsies as the gold standard, detection of intracellular organisms in P-BAL (> or = 5%) and C-BAL (> or = 5%) fluids yielded 75% and 57% positive predictive values, and 83% negative predictive values, respectively. Prior treatment with antibiotics decreased the positive and negative predictive values of intracellular organism detection for both types of BAL fluid. The presence of intracellular organisms was correlated with the quantitative cultures of P-BAL and C-BAL samples. Quantitative cultures from P-BAL fluid were less sensitive (22% versus 45%) and more specific (100% versus 55%) than those from C-BAL samples. The percentage of extracellular organisms and the differential cell count in P-BAL and C-BAL samples could not discriminate between the presence or absence of pneumonia.

CONCLUSIONS

The presence of > or = 5% intracellular organisms infecting PMNLs or macrophages in P-BAL or C-BAL fluids is a specific marker of ventilator associated pneumonia.

Diagnostic value of direct examination of protected specimen brush samples in nosocomial pneumonia

The value of direct examination of Giemsa and Gram stains of cytospin preparations of protected specimen brush samples was compared to that of quantitative culture. Sixty-one samples from patients suspected to have nosocomial pneumonia were analysed. Twenty-five samples were positive by quantitative culture, 21 of which contained microorganisms seen by direct examination. The presence of leucocytes was not specific for a positive culture, but in their absence, a positive culture was unlikely. The presence of intracellular organisms always correlated with a positive culture, but was not very sensitive.

The role of bronchoalveolar lavage in the diagnosis of bacterial pneumonia

Bronchoalveolar lavage (BAL) has become an invaluable diagnostic tool with important clinical implications in both opportunistic infections and the pulmonary pathology of immunologic disease. Until recently, the use of BAL was limited primarily to two areas: the study of interstitial lung diseases and the diagnosis of lung infections by opportunistic microorganisms in severely immunocompromised patients with lung infiltrates. Over the past decade, the use of BAL has been expanded to include the conventional diagnosis of bacterial pneumonia in non-immunocompromised patients. In the past, different clinical studies proposed using BAL to quantify cultures in the sample obtained as a means of increasing the tool's effectiveness. Recent developments have led to a number of newer applications of BAL, such as bronchoscopic BAL, non-bronchoscopic BAL and protected BAL. The most important use of BAL in the non-immunocompromised patient is the diagnosis of pneumonia in the mechanically ventilated patient.

Use of elastin fibre detection in the diagnosis of ventilator associated pneumonia

BACKGROUND

Elastin fibre detection could be a simple and reliable marker of ventilator associated pneumonia. To confirm this, a prospective study was undertaken to evaluate the diagnostic yield of elastin fibre detection in the diagnosis of ventilator associated pneumonia.

METHODS

Seventy eight mechanically ventilated patients were evaluated by examining endotracheal aspirates for the presence of elastin fibres. All patients were previously treated with antibiotics. Quantitative bacterial cultures of endotracheal aspirates and protected specimen brush samples were also performed. Patients were classified into three diagnostic categories: group 1, definite pneumonia (n = 25); group 2, probable pneumonia (n = 35); and group 3, controls (n = 18).

RESULTS

Patients with definite and probable pneumonia were grouped together. The presence of elastin fibres in endotracheal aspirate samples was more frequent in groups 1 and 2, being found in 19 of the 60 patients compared with five of the control group. Although the presence of elastin fibres had a low sensitivity (32%), it was a reasonably specific marker (72%) of pneumonia. This specificity increased to 86% and 81% respectively when only Gram negative bacilli and Pseudomonas aeruginosa pneumonia were considered. Again, calculated sensitivity was 43% and 44% when analysing cases infected by Gram negative bacilli and Ps aeruginosa, respectively. The negative predictive value of the detection of elastin fibres in pneumonia caused by Ps aeruginosa was 81%. Detection was more frequent with infection by Gram negative bacilli (14/19), particularly with Ps aeruginosa (8/14). By contrast, pneumonia due to Gram positive cocci or non-bacterial agents uncommonly resulted in positive elastin fibre preparations (4/19, 21%). When analysing patients with and without chronic obstructive pulmonary disease, the diagnostic value of elastin fibre detection did not change.

CONCLUSIONS

Potassium hydroxide preparation of elastin fibres is a rapid and simple specific marker of ventilator associated pneumonia and may be a useful technique to help diagnose pulmonary infections in mechanically ventilated patients, although this assessment is at present limited to patients without adult respiratory distress syndrome.

Diagnosing ventilator-associated pneumonia: the role of bronchoscopy

OBJECTIVE

To discuss the two diagnostic procedures used most frequently to obtain uncontaminated lower airway secretions during bronchoscopy.

DESIGN

This article reviews the contributing risk factors of ventilator-associated pneumonia (VAP) and the recent studies that have assessed the usefulness of the protected specimen brush (PSB) and bronchoalveolar lavage (BAL) in the nonimmunocompromised host.

RESULTS

A prompt, accurate diagnosis of VAP, including specific identification of the bacterial pathogen, remains a common challenge in the intensive-care unit. Standard clinical criteria are of suboptimal specificity for making decisions, including selecting antibiotic therapy. Bronchoscopic techniques of lung secretion sampling can be used in the intensive-care unit in an effort to overcome the effects of oropharyngeal contamination. The PSB and BAL, used appropriately, can help intensive-care clinicians formulate specific antimicrobial therapy. Evaluation of intracellular bacteria obtained by BAL has been reported to be useful in guiding empiric antibiotic therapy while the final results of cultures obtained with the PSB are pending. Prior antibiotic therapy, however, may confound the interpretation and clinical utility of results.

CONCLUSION

Currently, for a patient taking antibiotic therapy, no reliable technique nor quantitative culture threshold exists to help in diagnosing suspected VAP or in guiding antibiotic therapy. If the clinical situation allows, antibiotic therapy should be discontinued for 48 hours; then, the PSB, BAL, protected BAL, or endobronchial aspiration should be used. These contemporary modalities, however, necessitate further clinical trials before widespread use is warranted.

New approaches in the diagnosis of nosocomial pneumonia

We have presented a review of the present literature on new modalities to diagnose nosocomial pneumonia. Procedures are now available that, when correctly used, can establish a diagnosis of pneumonia with a high degree of reliability. In our institution, reliance on bronchoscopic modalities has simplified management of patients with suspected VAP, by eliminating confusion and rationalizing antibiotic treatment. Invasive procedures, however, should be performed only if the results of cultures are consistently applied to treatment. As this field rapidly evolves, we hope that this review will provide the reader with a foundation to understand new developments.

Usefulness of microscopic examination of intracellular organisms in lavage fluid in ventilator-associated pneumonia

STUDY OBJECTIVE

To assess the usefulness of quantification of bronchoalveolar lavage (BAL) cells containing intracellular organisms (ICO) in the diagnosis of ventilator-associated pneumonia.

DESIGN

The reliability of cytologic analysis in comparison with the protected specimen brush (PSB) and BAL quantitative cultures has been assessed in a prospective study.

SETTING

An intensive care unit of a tertiary-referral teaching hospital.

PATIENTS

A total of 33 ventilated patients with suspected pneumonia based on clinical grounds and radiographic findings.

INTERVENTIONS

All patients underwent fiberoptic bronchoscopy within the first 24 h after clinical suspicion of pneumonia. Specimens were obtained by PSB and BAL and were processed for quantitative cultures using standard methods. Two 0.5-ml samples of resuspended original BAL fluid were centrifuged and stained with Gram and modified May-Grünwald-Giemsa for differential cell counts and percentage of cells with ICO.

RESULTS

Pneumonia was the final diagnosis in 16 (49 percent) of the 33 patients. In 14 (42 percent) patients, pneumonia was excluded and in the remaining 3 the diagnosis was uncertain. Twelve of the 16 patients with pneumonia had their conditions diagnosed by PSB, 14 by BAL, and 10 by quantification of ICO. Only one patient's condition was diagnosed exclusively by cytologic examination. There were no false-positive results with any of the diagnostic techniques.

CONCLUSIONS

Microscopic identification of ICO in cells recovered by BAL allows early and accurate diagnosis of pneumonia in mechanically ventilated patients. However, the sensitivity of this technique is lower than with either PSB or BAL.

[Value of the cytology of bronchoalveolar lavage in the early diagnosis of nosocomial lung infections in patients with thoracic injuries]

Mechanically ventilated patients, especially those with thorax trauma, suffer commonly from nosocomial pneumonia. In these patients, conventional diagnostic criteria for bacterial pneumonia may not be completely reliable, as an accurate interpretation of the chest radiograph is too difficult. The invasive means for the diagnosis of pneumonia (protected specimen brush, bronchoalveolar lavage), require 24-48 hours to obtain the results of cultures. Therefore no information is available to guide the initial choice of antimicrobial therapy. For some authors, the quantification of intracellular bacteria, present in cytocentrifuged preparations made from lavage fluid, may provide rapid identification of patients with pneumonia. We evaluated the benefit of this type of analysis in thorax trauma patients. In 36 patients, 48 samples were taken. With a threshold value of 10% of cells containing intracellular organisms, microscopic examination had a sensitivity and a specificity of 83%. We conclude that this technique may be useful for the early diagnosis of nosocomial pneumonia in ventilated thorax trauma patients.

Cardiopulmonary effects of bronchoalveolar lavage in critically ill patients

Bronchoalveolar lavage (BAL) has been proposed as a useful procedure for bacteriologic diagnosis of lower respiratory tract infection in mechanically ventilated patients. To determine the cardiopulmonary effects of this procedure and to identify the patients at risk of poor tolerance, 30 critically ill ventilated patients suspected of having pneumonia were studied. Hemodynamic and gas exchange parameters were continuously recorded using an arterial catheter, a Swan-Ganz catheter with SvO2 display, and a pulse oximeter. In addition to the basal sedation required by these patients, midazolam, 0.1 mg/kg intravenously, was administered 5 min prior to bronchoscopy. A moderate increase (10 percent from basal values) in heart rate, mean arterial pressure, and cardiac index was recorded at each measurement during the procedure. A marked decrease in PaO2 was observed during bronchoscopy associated with an increase in oxygen consumption. Maximal changes in SaO2 and SvO2 were recorded at the end of BAL. Two hours after the end of BAL, PaO2 values were still 20 percent lower than pre-BAL values in 40 percent of the patients. We conclude that BAL can be performed safely in most critically ill ventilated patients who have stable hemodynamic and ventilatory parameters. However, none of the recorded parameters allows identification of the patients at risk of poor tolerance of the procedure.

Diagnostic efficiency of endotracheal aspirates with quantitative bacterial cultures in intubated patients with suspected pneumonia. Comparison with the protected specimen brush

The objectives of the study were to determine the agreement between the protected specimen brush technique (PSB) with quantitative cultures and endotracheal aspirates (EA) with quantitative cultures when using increasing interpretative cutoff points and to investigate the respective operating characteristics for the diagnosis of pneumonia of PSB and EA when using quantitative cultures. Consecutive sampling of respiratory secretions using these two techniques was conducted in the respiratory intensive care units in 52 mechanically ventilated patients with clinical and radiologic suspicion of pneumonia. Quantitative bacterial cultures of PSB and EA samples were obtained. The 10(6) cfu/ml cutoff point was the most accurate diagnostic threshold for the EA technique. When using this threshold, there was a high level of agreement (84.6%) between PSB and EA results. Among the few discrepancies, the EA result was always indicative of pneumonia, whereas the PSB result was nonindicative, thus permitting us to classify correctly five patients in whom pneumonia would have been erroneously excluded on the basis of the sole result of PSB. Conversely, there was no case where the PSB result was indicative of pneumonia when the EA result (at the 10(6) cfu/ml level) was not. The operating characteristics of the PSB technique for the diagnosis of pneumonia were in accordance with previously published studies. The operating characteristics of the EA technique (when taking the 10(6) cfu/ml of respiratory secretions as the interpretative cutoff point) compared favorably with those of the PSB technique. Diagnostic accuracy rates were similar. The specificity of EA was somewhat lower (83 versus 96%), but the sensitivity was higher (82 versus 64%).(ABSTRACT TRUNCATED AT 250 WORDS)

Specificity of endotracheal aspiration, protected specimen brush, and bronchoalveolar lavage in mechanically ventilated patients

The specificity of the different techniques used to diagnose ventilator-associated pneumonia is still a matter of controversy. To investigate the specificity of endotracheal aspiration (EA), protected specimen brush (PSB), and bronchoalveolar lavage (BAL) quantitative cultures, we studied 27 consecutive mechanically ventilated (MV) patients (> 72 h) without clinical or radiographic evidence of pulmonary infection. Comparing different thresholds for quantitative cultures (from 10(3) through 10(6) CFU/ml), the lowest rate of false positive results was obtained using 10(6) for EA, 10(5) for PSB, and 10(6) for BAL. Using 10(6) CFU/ml for EA, 10(4) CFU/ml for PSB, and 10(5) CFU/ml for BAL as cutoff points, we obtained the following specificities: 85, 85, and 78% for the three techniques, respectively. A bacterial index of 8 was the best threshold to get a low percentage of false positive results for all techniques except for EA (0% for PSB and 12% for BAL). There were reasonable qualitative agreements (PSB versus EA = 58%; BAL versus EA = 69%; and PSB versus BAL = 62%) and poor quantitative correlations between concomitantly isolated microorganisms from the three types of samples. Quantitative cultures of EA, PSB, and BAL may show a considerable percentage of false positive results at the respective cutoff points usually accepted. Increasing the thresholds for quantitative cultures, albeit loosing sensitivity, may rule out better the absence of pulmonary infection in MV patients.

The effect of antibiotic therapy on recovery of intracellular bacteria from bronchoalveolar lavage in suspected ventilator-associated nosocomial pneumonia

Intracellular bacteria (ICB) within recovered cells (> 7 percent) obtained via bronchoalveolar lavage (BAL) have been described as predictive of subsequent positive quantitative protected specimen brush (PSB) cultures in patients not receiving antibiotics. To determine the effect of prior or current antibiotic therapy on ICB relative to subsequent PSB culture, we prospectively evaluated 49 consecutive episodes of clinically suspected ventilator-associated pneumonia in 36 patients. Three patient groups were defined based on antibiotic administration: group 1 (current antibiotics), n = 31, samples obtained from patients currently receiving antibiotics; group 2 (recent antibiotics), n = 5, samples obtained from patients who received antibiotics > 48 h but < 72 h prior to sampling; and group 3 (no antibiotics), n = 13, samples from patients receiving no previous antibiotics within 7 days prior to sampling. Overall, PSB cultures (> or = 10(3) cfu/ml) were positive in 14 of 49 (29 percent) samples. In group 1, 2 of 31 (6 percent) samples were positive while 5 of 5 (100 percent) samples in group 2, and 7 of 13 (54 percent) in group 3 were positive. The presence or absence of ICB accurately predicted both positive and negative PSB cultures in 43 of 49 episodes. Of 43 correct predictions, 34 were negative predictions (negative ICB, negative PSB culture). The vast majority of these (29) were obtained from group 1, patients currently receiving antibiotics. In contrast, of nine positive predictions (+ICB, +PSB) virtually all (seven) occurred in group 3, patients receiving no antibiotics. In group 3, 13 of 13 PSB cultures were accurately predicted, either positive or negative, by the presence or absence of ICB. Of seven positive PSB cultures in groups 1 and 2, only 2 (28 percent) were accurately predicted by ICB. From both samples, the cultured organism was resistant to all administered antibiotics. These data suggest both prior and current antibiotic therapy reduces recovery of ICB from BAL and reduces predictive accuracy of ICB for subsequent positive PSB cultures. However, negative prediction by ICB for subsequent negative PSB cultures was good. In contrast, ICB obtained from patients not receiving antibiotics are highly predictive of subsequent PSB culture results, both positive and negative. We do not recommend BAL for evaluation of ICB in patients currently receiving antibiotics or with a recent history of antibiotic use.

Management of bacterial pneumonia in ventilated patients. Protected bronchoalveolar lavage as a diagnostic tool

We conducted a prospective study to determine the effectiveness of protected bronchoalveolar lavage (PBAL) in diagnosing pneumonia in ventilated patients and the usefulness of bronchoscopic data in treating ventilated patients. Entrance criteria were (1) fever and a new or progressive infiltrate on chest roentgenogram with either leukocytosis or a macroscopically purulent tracheal aspirate, and (2) no antibiotic therapy for at least 48 h before bronchoscopy. Twenty-five ventilated patients met entrance criteria for the study and completed the protocol. PBAL was effective in retrieving distal airway secretions with a minimal degree of contamination as indicated by a specificity and a negative predictive value of 100 percent. Bacterial isolates grew in all patients with pneumonia at a concentration greater than or equal to 100,000 cfu/ml, with a median growth of 500,000 cfu/ml. The presence of a two-log difference between the highest quantitative culture count in patients without pneumonia and the lowest quantitative culture count in patients with pneumonia allowed a clearer determination of a patient's status, with regard to pneumonia, compared with the significant overlap in unprotected BAL. Gram and Giemsa stains of the PBAL were positive in all patients with pneumonia and negative in those without pneumonia. All but one patient with pneumonia received narrow-spectrum antibiotic therapy. All patients without infection had no antibiotic administered. Clinical and roentgenographic criteria could not discriminate between patients with and without pneumonia, confirming the findings of previous investigations. The results of microscopic and culture analyses of the PBAL effluent proved useful in directing antibiotic treatment in patients with pneumonia and in avoiding unnecessary antibiotic use in those patients without pneumonia.