Endotracheal Aspirate Culture Used to Diagnose Ventilator-Related Pneumonia Comparison of Mini-BAL Culture
SUMMARY
The aim of this study was to compare the culture results of endotracheal aspirate (ETA) and mini-bronchoalveolar lavage (BAL) methods, which are used to quickly and accurately identify the possible cause of ventilator-associated pneumonia (VAP), especially in intensive care units. Thirty (32.2%) patients who developed VAP from 92 patients who were followed up on mechanical ventilator between June 2010 and June 2011 in our intensive care unit were included in the study. The diagnosis of VAP was made clinically and radiologically; The patients were evaluated with clinical pulmonary infection score (CPIS) scoring system and CPIS value> 6 was considered in the diagnosis. ETA and mini-BAL samples were collected before VAP patients; In addition, two blood cultures and urine cultures were obtained from the patients. Microbiological evaluation and identification were performed using conventional methods and the Phoenix 100 automated system (BD Diagnostic Systems, USA). Bacterial growth of> 10,000 cfu / ml for BAL and> 100,000 cfu / ml for ETA was considered significant in the evaluation of quantitative cultures. The mean age of patients who developed VAP (n = 30; 18 males) and non-developed (n = 62; 39 males) during mechanical ventilation; 68.23 ± 16.19 and 52.16 ± 10.41 years; the duration of mechanical ventilation was as follows; 29.57 ± 15.78 and 12.11 ± 6.01 days. When examined by multivariate logistic regression analysis; advanced age (p <0.001) and duration of mechanical ventilation (p <0.001) were independent risk factors for VAP development. There was a statistically significant difference between CPIS values of patients with and without VAP (6.8 ± 1.15 and 2.71 ± 1.06 points, respectively; p <0.001). Accordingly, the use of a CPIS score was considered useful in the diagnosis of VAP in patients with mechanical ventilators. In our study, 16 strains (six Acinetobacter baumannii , three Pseudomonas aeruginosa , one Klebsiella pneumoniae , six Staphylococcus aureus ) and 30 strains (16 A.baumannii , six P.aeruginosa , four Klebsiella ) from ETA cultures of 30 patients with VAP pneumoniae , two, Escherichia coli , six S.aureus ). Contamination rate was 27% (8/30) in ETA cultures, while no contamination was observed in mini-BAL cultures. There was no growth in 20% (6/30) of ETA cultures and 7% (2/30) of mini-BAL cultures. Pathogenic bacterial growth (six A.baumannii , one K.pneumoniae ) was detected in 7 (87.5%) of the mini-BAL cultures from eight patients with ETA contamination. Similarly, pathogenic bacteria (two E.coli , two K.pneumoniae , one P.aeruginosa ) were isolated from mini-BAL cultures of 5 (83%) of six patients who had no growth in ETA culture. No statistical correlation was found between the culture results of the samples taken by ETA and mini-BAL methods (p = 0.464). The agreement between the culture results of the samples taken by ETA and mini-BAL methods was found to be 50%. In conclusion, due to the increased risk of contamination in ETA culture methods and higher isolation rate from mini-BAL samples, it was concluded that mini-BAL sampling would be more suitable for EAP instead of ETA microorganisms.
Key words: Ventilator-associated pneumonia; bronchoalveolar lavage; mini-BAL, endotracheal aspirate; culture.
ABSTRACT
The objective of this study was to compare the results of cultures obtained by mini-bronchoalveolar lavage (BAL) and endotracheal aspiration (ETA) techniques, used for rapid and accurate determination of pathogens causing ventilator-associated pneumonia (VAP) in intensive care units. Of the 92 patients on mechanical ventilation followed by the emergency care unit of our hospital between June 2010 and June 2011, 30 (32.2%) patients were diagnosed as VAP and they were included in this study. VAP diagnosis was based on clinical and radiological findings. Clinical pulmonary infection score (CPIS) of> 6 was accepted as the clinical criteria of VAP. Initially ETA samples were collected from the patients followed by mini-BAL sampling 15 minutes later, together with urine and two blood cultures. Microbiological evaluation and identification were performed by conventional methods and Phoenix 100 (BD Diagnostic Systems, USA) automated system. In quantitative culture analysis,> 10,000 cfu / ml for BAL and> 100,000 cfu / ml for ETA were accepted as positive results. The mean ages of VAP-developed (n = 30; 18 were male) and nondeveloped (n = 62; 39 were male) patients were 68.23 ± 16.19 and 52.16 ± 10.41 years, respectively, and the mean durations of mechanical ventilation were 29.57 ± 15.78 and 12.11 ± 6.01 days, respectively. Multivariate logistic regression analysis showed that older age (p <0.001) and duration of mechanical ventilation (p <0.001) were independent risk factors for VAP development. VAP and not (6.8 ± 1.15 and 2.71 ± 1.06, respectively; p <0.001). The use of CPIS for VAP diagnosis has been found to be useful in patients on mechanical ventilation. In our study, a total of 16 strains (six A.baumannii , three P.aeruginosa , one K. pneumoniae , six S.aureus ) were isolated from ETA cultures, while 34 strains (16 A.baumannii , six P.aeruginosa , four K. pneumoniae , two E. coli , six S. aureus ) were isolated from mini-BAL cultures of 30 VAP patients. The contamination rate for ETA cultures was found as 27% (8/30), however there was no contamination in mini-BAL samples. The rates of negative cultures for ETA and mini-BAL were 20% (6/30) and 7% (2/30), respectively. Seven (87.5%) of the eight contaminated ETA samples, yielded pathogenic bacterial growth (six A.baumannii , one K. pneumoniae ) in mini-BAL samples. Similarly, of the six negative ETA samples, 5 (83%) yielded bacterial growth (two E. coli , two K. pneumoniae , one P. aeruginosa ) in mini-BAL samples. Statistical analysis with Spearman test indicated no positive correlation between the results of mini-BAL and ETA (p = 0.464), and the concordance between the results of these methods was found as 50%. It was used in the study of mini-BAL instead of ETA samples for the isolation of causative microorganisms of VAP.
Key words: Ventilator-associated pneumonia; bronchoalveolar lavage; mini-BAL; endotracheal aspirate; cultura.
Received Date: 14.11.2011 • Accepted Date: 13.03.2012
LOGIN
Ventilator-associated pneumonia (VAP) is pneumonia that develops 48 hours after intubation in a patient without invasive mechanical ventilation and without pneumonia during intubation 1 , 2 . Tracheal intubation and mechanical ventilation increase the incidence of pneumonia 7 to 21 times 3 .
The diagnosis of VAP is very difficult. Studies have shown that 50% of patients diagnosed with VAP clinically do not have VAP, whereas approximately 1/3 of patients with VAP cannot be diagnosed 4 . Diagnosis alone is not sufficient clinical evaluation, radiological methods, microscopic and microbiological examination of respiratory secretions are needed. The clinical pulmonary infection score (CPIS) may also contribute to the diagnosis of patients with VAP. In this scoring, the presence of CPIS> 6 increases the probability of pneumonia. One of the important criteria for the diagnosis of VAP is the diagnostic criteria of "Centers for Disease Control and Prevention (CDC)". In addition to all these diagnostic criteria, the diagnosis of patients with clinical suspicion of VAP should be supported by microbiological cultures. Respiratory tract samples are obtained by bronchoscopic and nonbronchoscopic methods. Today, nonbronchoscopic methods are preferred more because of its ease of use and less cost.
Microbiological examination of endotracheal aspirate (ETA) sample is the most commonly used method in the diagnosis 1 . Another method used for diagnosis is the examination of mini-bronchoalveolar lavage (BAL) sample. The most important advantage of this method is to minimize contamination with possible upper respiratory tract flora. The aim of this study was to compare the results of ETA and mini-BAL culture used to quickly and accurately identify the possible cause of VAP, especially in intensive care units.
Materials and Methods
Selection of Cases and Data Collection
Thirty patients (32.6%) diagnosed as VAP were included in this study from 92 patients who were followed up in mechanical ventilator between June 2010 and June 2011 in the internal medicine intensive care unit of our hospital. All patients who were seropositive to human immunodeficiency virus (HIV), who received immunosuppressive therapy, and who had radiotherapy and / or chemotherapy oncology, and who had mechanical ventilation for more than 48 hours were included in the study. The patients underwent a physical examination every day; Daily fever follow-up, daily leukocyte count and chest x-ray every three days. The amount and character of tracheobronchial secretion were also noted at the same time; mechanical ventilation times were recorded. Clinically diagnosed patients with VAP were evaluated with CPIS scoring system and CPIS was considered to be over 6. Antibiotic use of the patients was monitored before culture. ETA, mini-BAL, two blood cultures and urine cultures were obtained.
Clinically, VAP was defined by adding at least two of the following criteria to the newly detected infiltration or increase in existing infiltrative involvement on chest X-ray: (1) Fever (> 38.5 ° C) or hypothermia (<36 ° C), (2) Purulent tracheobronchial (3) leukocytosis (12,000 / µL) or leukopenia (4000 / µL). Pneumonia developed in the first four days in patients who underwent mechanical ventilation was defined as early-onset VAP and pneumonia developed in the fifth and subsequent days were defined as late-onset VAP.
Taking Samples
Collection of the ETA sample: Fourteen F sterile aspiration catheters ( Figure 1A ) were advanced through the endotracheal tube and further distal 2 cm. The tip of the aspiration probe was connected to the aspiration device. 5-10 ml of ETA was obtained in the aspirate tube 6 .
Picture 1
Mini-BAL removal: 10-15 minutes after ETA removal , a mini-BAL catheter (Combicath ® ) ( Figure 1B ) was advanced blindly through the endotracheal tube. When catheter progression stopped, the outer catheter was withdrawn and the inner catheter was advanced 2-3 cm further. 20 ml of saline was administered through the internal catheter. A sterile syringe was aspirated to obtain 1-3 ml of bronchoalveolar fluid.
Microbiological Methods
After the sample was vortexed for 1 minute, sheep blood agar (CCA), chocolate agar and EMB agar were added with 0.001 loop. CCA and chocolate agar were incubated for 48 hours in a CO 2 oven and EMB in an aerobic environment for 48 hours. Plates were checked after 24 hours and no growth was expected at the end of 48 hours. Gram staining was performed from the colonies. Bacteria were identified as gram-negative or gram-positive as a result of gram staining and evaluation of growth in culture plates. Species identification and antibiogram tests of the bacteria were performed using the Phoenix 100 automated system (BD Diagnostic Systems, USA). The colonies of single fallen bacteria on the blood agar were removed with sterile swabs and the McFarland was adjusted to turbidity of 0.5-0.6. Bacterial suspension prepared from gram-negative bacteria was placed into the device via the Phoenix NMIC / ID panel and gram-positive bacteria were placed into the device via the Phoenix PMIC / ID panel. Reading and evaluation procedures were performed automatically by the device.
The quantitative evaluation was performed as follows: The total number of colonies was multiplied by 1000 and the result was the number of bacteria per ml. If this number was over 10,000 for BAL and over 100,000 for ETA, the result was considered positive. The values below were evaluated as oropharyngeal contamination. In addition, Corynebacterium spp., Group A beta-hemolytic streptococcus and Neisseriae spp. As it was found in normal throat flora, it was not defined as VAP agent and was considered as contamination.
Statistical Evaluation
After the data were transferred to the computer, SPSS 15.0 package program was analyzed. Frequency, percentage, mean, standard deviation, minimum and maximum values were used as descriptive statistics. The difference between the groups with and without VIP in terms of age and duration of mechanical ventilation was compared with Student-t test and CPIS with Mann-Whitney U test. The chi-square test was used to compare the two groups in terms of gender. The effect of gender, age and duration of mechanical ventilation for VAP development was examined by multivariate logistic regression analysis. Spearman correlation was used to determine whether there was a correlation between ETA and mini-BAL in the VAP group. A p value of <0.05 was accepted for statistical significance.
RESULTS
In the intensive care unit (ICU), between June 2010 and June 2011 due to mechanical ventilation, 18 (60%) of the 30 patients who developed VAP were male and 12 (40%) were female; Of 62 patients who did not develop VAP, 39 (63%) were male and 23 (37%) were female. Table I presents the age, follow-up time and CPIS score characteristics of patients with and without VAP during mechanical ventilation.
Table I
Of the 30 patients diagnosed as VAP, 24 (80%) were mortal during the follow-up and treatment period; Six patients (20%) were discharged from the ICU after completion of their treatment. The rate of VAP development in internal ICU was 18.3 per 1000 ventilator days.
ETA and mini-BAL samples were taken in all 30 patients who developed VAP during mechanical ventilation. The reproduction results of these samples were shown in Table II . Mini-BAL cultures showed higher bacterial growth than ETA cultures; It was determined that contamination which was 27% in ETA cultures was not seen in mini-BAL cultures and Escherichia coli and more than one microorganism growth could not be detected in ETA culture in mini-BAL cultures.
Table II
Acinetobacter baumannii , Klebsiella pneumoniae growth was observed in 6 (75%), 1 (12.5%) of the mini-BAL cultures taken from eight patients whose endotracheal aspirate sample cultures were evaluated as contamination. In the ETA sample, E.coli was isolated in 2 (33%), K.pneumoniae in 2 (33%) and P. aeruginosa in 1 (17%) of six mini-BAL specimens without reproduction. In 1 (17%) sample, mini-BAL culture also showed no growth ( Table III ).
Table III
In the statistical analysis, the mean age (68.23 ± 16.19 years and 52.16 ± 10.41 years; p <0.001) and the duration of mechanical ventilation (29.57 ± 15.78 days and 12.11 ± 6.01 days, respectively; <0.001). When the effect of gender, age and mechanical ventilation duration for VAP development was examined by multivariate logistic regression analysis; It was found that gender was not a risk factor in the development of VAP, whereas mechanical ventilation time and patient age significantly increased the risk of developing VAP independently of each other and gender. OR = 1.205, 95% CI = 1.104-1.316 and p <0.001 for mechanical ventilation time, OR = 1.162, 95% CI = 1.074-1.258 and p <0.001 for age.
The results of Mann-Whitney U test revealed significant differences in CPIS scores (6.8 ± 1.15 and 2.71 ± 1.06, respectively) between the patients with and without VAP (p <0.01).
As a result of statistical evaluation with Spearman test, no significant correlation was found between the culture results of the samples taken by ETA and mini-BAL methods (p = 0.464); The agreement between the culture results of the samples taken by ETA and mini-BAL methods was found to be 50%.
DISCUSSION
VAP is the most important infection seen in patients undergoing mechanical ventilation in ICUs. According to the results of various studies, 28-85% of patients who underwent mechanical ventilation may develop VAP 2 , 7 , 8 , 9 , 10 , 11 , 12 . In our study, 30 (32.6%) of 92 patients who underwent mechanical ventilation developed VAP. This ratio was found to be compatible with other studies conducted in our country and in the world. In studies performed, 2.5-39 VAP development rate was found in 1000 ventilator days in patients who were connected to ventilator 2 , 3 , 8 , 13 , 14 . In our study, the rate of VAP development was found to be 18.3 per 1000 ventilator days, which was consistent with previous studies.
Advanced age is one of the important risk factors that increases the risk of nosocomial pneumonia 2-3 times 2 . Besides, it carries 1-3% risk increase for VAP development every day due to mechanical ventilator 15 . In the 16 studies of Gedik et al., The mean age of the patients who developed VAP was 56 years and the mean duration of mechanical ventilation was 20 days. In the study performed by Khilnani et al. 17 , mean age was 55.6 ± 16.17 years, mean mechanical ventilation time was 34.88 ± 32 days; In another study by Bacakoglu et al. 18 , the mean age was 63.9 ± 19 years and the mean duration of mechanical ventilation was 7.4 ± 6.3 days. In our study, the mean age of patients who developed VAP was 68.23 ± 16.19 years and the mean duration of mechanical ventilation was 29.57 ± 15.78 days. As a result of the multivariate logistic regression analysis of the data obtained in our study, patient age (p <0.001) and duration of mechanical ventilation (p <0.001) were determined as a risk factor for the development of VAP. a correlation was shown.
The most common cause of mortality among hospital-acquired infections is pneumonia. The rate of mortality in VAP cases varies between 24-76% 16 , 17 , 18 , 19 , 20 , 21 , 22 . In our study, the mortality rate was found to be 80% and this rate was higher than the other studies. This was thought to be due to the long mechanical ventilation periods and the advanced age of the patients. In addition, other underlying conditions, ICU stay and increased frequency of A.baumannii infection in ICU during this period may be other causes of mortality.
The major disadvantages of CPIS calculation used in the diagnosis of VAP are the differing interpretation of variables by clinicians and incorrect calculation of scoring 23 . The presence of CPIS above 6 increases the likelihood of pneumonia. In a study, the diagnosis of VAP; The sensitivity of CPIS ≥ 6 was 93% and the specificity was 100% 23 . However, some researchers have indicated that CPIS should be used in the evaluation and management of treatment 24 . Khilnani et al. 17 , mean CPIS score of patients diagnosed with VAP was 6.76 ± 1.67; Bacakoglu et al. 18 reported 7.2 ± 2.1 points. In our study, the mean CPIS score was 6.8 ± 1.15 points in patients with VAP and 2.71 ± 1.06 points in those who did not, and the difference between the two groups was significant (p <0.001). Based on these results, the use of CPIS score may be useful in the diagnosis of VAP in patients with mechanical ventilators. In a study, mini-BAL, bronchoscopic BAL, bronchoscopic brush culture results and CPIS values of CPIS ≥ 6 patients were compared; The correlation between CPIS and mini-BAL was 80%, the correlation with bronchoscopic brush was 86%, and the correlation with bronchoscopic BAL was 76% 17 . In our study, the agreement between CPIS and ETA was 60% and the agreement between mini-BAL was 80%. However, in addition to all these diagnostic criteria, the diagnosis of patients with clinically suspected VAP should be supported by microbiological cultures.
Gram-negative bacteria are most frequently isolated as VAP agents in the studies 16 , 17 , 18 , 22 , 25 , 26 , 27 . In our study, it was observed that the most frequently isolated microorganisms were gram-negative bacteria. Khilnani et al. 17 reported that 88% of pathogenic microorganisms causing VAP were grown in mini-BAL culture and 68% in ETA culture. In our study, A.baumannii , P.aeruginosa and S.aureus (methicillin resistant or susceptible) isolation rates in mini-BAL and ETA cultures were as follows; 53% and 20%, 20% and 10%, 20% and 20% respectively ( Table II ). It was thought that the high A.baumannii ratio in our study may be due to ICU flora. Therefore, it is important to carry out surveillance studies in each hospital and in each ICU in the same hospital, to detect environmental contamination in these units and to determine their resistance profiles. Thus, effective empirical antibiotic therapy for an infection with high mortality can be determined.
Quantitative culture of mini-BAL ( protected telescoping catheter (PTC)) is used instead of bronchoscopic methods for the diagnosis of VAP especially in some centers because of the low level of contamination due to upper respiratory tract flora, not an invasive method and high specificity 26 , 28 . However, the most common method used for the diagnosis of VAP in centers without bronchoscopy is the quantitative culture of ETA. The most important disadvantage of this method is the high level of contamination due to upper respiratory tract flora 29 . In our study, oropharyngeal contamination was detected in 27% of ETA samples, while no contamination was observed in mini-BAL samples. Seven out of eight patients with contamination in the ETA specimen were found to have pathogen bacterial growth in the mini-BAL specimen culture ( Table III ). In the study of Fangio et al. 30 , the sensitivity and specificity of ETA quantitative cultures were reported as 89.5% and 66.7%, respectively. In contrast, Elatrous et al. 26 , when the cut-off value was 10 4 cfu / ml, the sensitivity and specificity of ETA quantitative culture were 92% and 85%, respectively; reported that when the evaluation threshold was taken as 10 5 cfu / ml, these rates were determined as 84% and 90%, respectively. In our study, sensitivity and specificity values of ETA and mini-BAL quantitative culture methods could not be determined due to lack of control group. The clinical and radiological diagnosis of VAP in this patient group led to this limitation.
In the studies, a strong agreement (77-88%) was observed between the results obtained with mini-BAL and bronchoscopic brush methods. 17 , 31 , 32 , 33 . In contrast, Khilnani et al. 17 reported that among the methods used to obtain distal airway specimens, ETA was the most unsuccessful in obtaining the correct specimen; Bacakoglu et al. 18 reported 67% agreement between ETA and mini-BAL. In our study, the agreement between ETA and mini-BAL was found as low as 50%.
Advantages of nonbronchoscopic methods include; less invasive, requiring less experienced personnel, affecting less oxygenation, continued ventilation and respiration during the procedure, less intracranial pressure increase and arrhythmia, less risk of contamination and less expensive 17 , 23 26 , 30 . Although Mini-BAL is a blinding method, it is quite compatible with the results obtained with bronchoscopic brush. Routine application of bronchoscopic methods in ICU patients is not possible in our country and other developing countries. Therefore, evaluation of nonbronchoscopic techniques is important. As a result, in our study, there was no significant correlation between ETA and mini-BAL culture methods, increased risk of contamination in ETA culture method and higher isolation rate from mini-BAL samples. It has been considered.
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