Ventilator-associated pneumonia (VAP) is the commonest and most serious hospital acquired infection in ITU patients with the mortality reaching 50%. The problem regards up to 20% of patients mechanically ventilated for longer than 24 h [1].

It has been demonstrated that the effectiveness of VAP treatment markedly depends on early institution of antibiotics according to the Surviving Sepsis Campaign Guidelines [2]. The initiation of treatment before the microbiological results are available improves the therapy outcome. Although essential to determine the drug susceptibility of bacteria, the qualitative findings of examinations of the bronchial tree material are obtained with delay due to technical limitations of the method. The quantitative results are obtainable quickly; they are an important diagnostic criterion of pneumonia and may serve for monitoring the treatment efficacy. There are various methods of collecting the bronchial tree material. The most useful method is broncho-alveolar lavage (BAL) and protected specimen brush (PBS). However, due to its simplicity and low costs, an endotracheal aspiration (EA) is commonly used, particularly in the countries with low medical care expenditure.

The aim of the study was to compare the effectiveness of EA with BAL and PSB in patients with VAP. 

METHODS

The study was conducted with the approval of the Bioethics Committee. Since all the patients received sedatives and analgesics, which alter the consciousness, it was not possible to obtain their informed consent.

The study included 61 patients with VAP, mechanically ventilated for longer than 24 h. VAP was diagnosed based on the criteria of the Centre for Disease Control/National Healthcare Safety Network [3] (Table 1). No exclusion criteria were used. All the patients were ventilated with the Puritan Bennett 7200. The FIO2 values necessary to obtain proper oxygenation of arterial blood ranged from 0.6 to 0.8. The material for bacteriological tests was collected on VAP diagnosis and immediately sent to the microbiological laboratory.

The collection methods were as follows:

• ST – a standard endotracheal tube. A sterile catheter was blindly inserted to the airway through the standard tube and the secretion aspirated. Once the catheter was removed its distal end was cut off and placed in the sterile microbiological medium;

• IT– interior of the endotracheal tube. After the removal of the endotracheal tube, the material was collected from its interior. The material was placed in the sterile microbiological medium;

• NT – a new endotracheal tube. The endotracheal tube was replaced with a new one, through which the sterile catheter was introduced. After the aspiration, the distal end was removed and placed in the sterile microbiological medium. Each time before the replacement, the patient’s oral cavity was thoroughly cleansed to prevent the transfer of secretion to the lower respiratory tract. The replacement was carried out extremely efficiently. No episodes of saturation drops were observed; SpO2 was higher than 90% in all patients;

• PSB – protected specimen brush. A bronchofibrescope was introduced to the segmental bronchus with radiologically detected inflammatory changes through a new, sterile endotracheal tube. The material was collected using protected specimen brush (Mill-Rose Laboratories, Inc., USA) and placed in the transport medium;

• BAL – broncho-alveolar lavage. After inserting the bronchofibrescope tip in the segmental bronchus, 20-50 mL of 0.9% NaCl solution was administered to the total volume of 150-200 mL. Each volume of fluid administered was immediately removed from the bronchial tree and placed in the sterile container.

The collected material was placed on the McConkey and agar medium with the addition of 5% equine blood. The bacterial strains were identified and their susceptibility assessed using the VITEK2 (bioMérieux, France) and identification charts.

The conformity of diagnoses (cultures) was compared for all potential pairs of collection methods. The Cohen κ coefficient measuring the agreement of two classification systems and calculated on the basis of symmetrical cross tabulations, was used for statistical deductions; κ <0.2 was considered extremely low conformity; 0.2-0.4 low; 0.4-0.6 moderate; 0.6-0.8 high; and >0.8 extremely high conformity.

The zero hypothesis: κ=0 was verified using the t-test. At p <0.05 the zero hypothesis was rejected; 95% confidence interval for κ was estimated based on the coefficient value, standard deviation and sample size.

RESULTS

The study encompassed 61 patients of different age, gender and clinical condition (Table 2). Positive microbiological results were found in 39 (63.9%) cases. Irrespective of the collection method, the most commonly isolated strains were Acinetobacter baumannii, followed by Staphylococcus aureus MRSA, Enterococcus faecalis and Pseudomonas aeruginosa (Table 3).

The ST vs BAL methods were characterized by an extremely high conformity of κ (0.817). High conformity was found for ST vs PBS (0.677) and IT vs BAL (0.639) (Table 4). The detailed data regarding κ for individual methods of material collection were presented in Table 5.

DISCUSSION

The ventilator-associated pneumonia is diagnosed based on the clinical guidelines of CDC/NHSN, Clinical Pulmonary Infection Score (CPIS) and microbiological criteria. The laboratory results may be quantitative (the value of units forming colonies) or qualitative (type of bacteria and their susceptibility to antibiotics).

According to the recommendations of the European Respiratory Society, European Society of Clinical Microbiology and Infectious Diseases and European Society of Intensive Care Medicine [4], pneumonia is diagnosed when the inflammatory lesions are present in the lungs and one of the following symptoms is observed: purulent secretion in the bronchi, body temperature >38°C, leucocytosis or leucopoenia. The above-mentioned recommendations are similar to the CDC/NHSN guidelines, thus the diagnosis in all study patients was established according to the current state of knowledge. The quantitative bacteriological analyses, which increase the reliability of VAP diagnosis, were not performed as all the patients received broad-spectrum antibiotics before the study, which makes such analyses poorly reliable [5].

The antibacterial treatment, started before the VAP diagnosis, resulted in positive microbiological results only in 63.9% of cases; the remaining specimens were negative, which confirms the observations of other authors that patients receiving antibiotics have lower numbers of bacteria in quantitative tests [5]. This may be used to assess the efficacy of antibacterial treatment in VAP patients. 

Numerous publications compared the usefulness of various methods of material collection for VAP diagnosis, yet their findings were not explicit [6]. Some observations demonstrate that identification of bacteria in the BAL material confirms the diagnosis of VAP with the frequency comparable to the CDC/NHSN criteria [7].

The originality of our method is the analysis of bacterial flora of the bronchial tree secretion through a new, sterile endotracheal tube (NT), which prevents the contamination with microorganisms resident on its internal surface, on the catheter or bronchofibrescope.

Broncho-alveolar lavage is considered the best and referential method of material collection. Our findings demonstrate extremely high conformity of ST and BAL and high conformity of PBS and BAL as well as BAL and IT, which confirms significant usefulness of simple endotracheal aspiration. Based on the results of 44 patients with hospital-acquired pneumonia, Clec’h and colleagues [8] suggested that endotracheal aspiration may be used for pneumonia diagnosis as an alternative to reference methods (BAL and PSB). The Canadian Critical Care Trials Group study carried out in 780 patients with a suspicion of hospital-acquired pneumonia, treated in 28 ITUs, did not show significant differences between BAL and endotracheal aspiration regarding 28-day mortality, duration of treatment, type of antibiotic therapy and organ failure scores [9].

The same bacterial strains were isolated in 89% of samples collected using endotracheal aspiration or broncho-alveolar lavage; in 95% of cases the choice of antibiotic therapy based on these methods was proper [10]. It has not been demonstrated, however, that routine BAL for the diagnosis of pneumonia in patients with burns does not affect the outcome of treatment nor antibiotic therapy administered [11].

However, broncho-alveolar lavage has its limitations, i.e. the availability of a bronchofibrescope, appropriate skills to use it and decreased saturation of arterial blood observed during pouring the fluid into the bronchi. In patients requiring high concentrations of oxygen in the respiratory mixture such a situation may be potentially difficult, although some studies did not confirm these concerns [12, 13].

The findings of meta-analyses indicate that in half of cases the results of tests of the material collected from the airway using a bronchoscope resulted in management-related changes; however, the outcomes of treatment were not affected [6].

The beneficial effect of routine, every-week collection of biological material from the trachea on the selection of antibiotic therapy was demonstrated in patients with hospital-acquired pneumonia.

The results of microbiological tests of the material obtained using endotracheal aspiration or broncho-alveolar lavage were consistent in 772% of cases; moreover, the strategy of antibacterial treatment, based on endotracheal aspiration performed before the VAP diagnosis, was proper in 85% of cases, i.e. significantly more often compared with to the data of the American Thoracic Society [14].

In the group of 1089 patients treated in 27 ITUs in Europe, VAP and extra-hospital pneumonia were diagnosed in 75.9% and 24.1% of cases, respectively. Microbiological specimens were collected by endotracheal aspiration in 74.8% and by bronchofibrescopy in 23.2% of cases. The most common bronchoscopic method was BAL (78.8%) [15]. In Australia and New Zealand, bronchoscopic methods of collection of bronchial tree material were used only in 29.7% of cases [16].

During routine airway toilet by aspiration, bacteria colonizing the internal surface of the endotracheal tube may detach from it, which is believed to be one of the potential factors leading to the development of ventilator-associated pneumonia [17]. Early institution of treatment with broad-spectrum antibiotics is essential for the management of severe infections, including VAP. The treatment should involve Gram-positive and Gram-negative bacteria as well as fungi in some cases. The empirical treatment of VAP is effective in 80-90% of cases. Due to technical limitations, the results of microbiological examinations are obtained with delay; nonetheless, they are an important element modifying the broad-spectrum antibiotic therapy to targeted management.

CONCLUSIONS

1. There is a high positive correlation between simple endotracheal aspiration and broncho-alveolar lavage as well as PSB.

2. Endotracheal catheter aspiration may be considered a simple, screening method of collecting the material for bacterial flora culturing.

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REFERENCES

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8.    Clec’h C, Jauréguy F, Hamza L, Karoubi P, Fosse JP, Hamdi A, Vincent F, Gonzalez F, Cohen Y: Agreement between quantitative cultures of postintubation tracheal aspiration and plugged telescoping catheter, protected specimen brush, or BAL for the diagnosis of nosocomial pneumonia. Chest 2006; 130: 956-961.

9.    The Canadian Critical Care Trials Group: A randomized trial of diagnostic techniques for ventilator-associated pneumonia. N Engl J Med 2006; 355: 2619-2630.

10.    Michel F, Franceschini B, Berger P, Arnal J-M, Gainnier M, Sainty J-M, Papazian L: Early antibiotic treatment for BAL-confirmed ventilator-associated pneumonia: a role for routine endotracheal aspirate cultures. Chest 2005; 127: 589-597.

11.    Wahl WL, Franklin GA, Brandt MM, Sturm L, Ahrns KS, Hemmila MR, Arbabi S: Does bronchoalveolar lavage enhance our ability to treat ventilator-associated pneumonia in a trauma-burn intensive care unit? J Trauma 2003; 54: 633-638; discussion 638-639.

12.    Bauer TT, Torres A, Ewig S, Hernández C, Sanchez-Nieto JM, Xaubet A, Agustí C, Rodriguez-Roisin R: Effects of bronchoalveolar lavage volume on arterial oxygenation in mechanically ventilated patients with pneumonia. Intensive Care Med 2001; 27: 384-393.

13.    Hertz MI, Woodward ME, Gross CR, Swart M, Marcy TW, Bitterman PB: Safety of bronchoalveolar lavage in the critically ill, mechanically ventilated patient. Crit Care Med 1991; 19: 1526-1532.

14.    JungB, Sebbane M, Chanques G, Courouble P, Verzilli D, Perrigault PF, Jean-Pierre H, Eledjam JJ, Jaber S: Previous endotracheal aspirate allows guiding the initial treatment of ventilator-associated pneumonia. Intensive Care Med 2009; 35: 101-107.

15.    Koulenti D, Lisboa T, Brun-Buisson C, Krueger W, Macor A, Sole-Violan J, Diaz E, Topeli A, DeWaele J, Carneiro A, Martin-Loeches I, Armaganidis A, Rello J: EU-VAP/CAP Study Group. Spectrum of practice in the diagnosis of nosocomial pneumonia in patients requiring mechanical ventilation in European intensive care units. Crit Care Med 2009; 37: 2360-2368.

16.    Boots RJ, Lipman J, Bellomo R, Stephens D, Heller RE: The spectrum of practice in the diagnosis and management of pneumonia in patients requiring mechanical ventilation. Australian and New Zealand practice in intensive care (ANZPIC II). Anaesth Intensive Care 2005; 33: 87-100.

17.    Ewig S: Diagnosis of ventilator-associated pneumonia: non routine tools for routine practice. Eur Respir J 1996; 9: 1339-1341.

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address:

*Wojciech Kowalczyk
Klinika Anestezjologii I Intensywnej Terapii
Wojskowy Instytut Medyczny w Warszawie
ul. Szaserów 128, 04-141 Warszawa
tel.: 22 810 80 89

received: 05.09.2010
accepted: 17.02.2011