Ventilator Associated Tracheobronchitis Pathophysiology Antibiotic treatment, timing to start antimicrobial and route of administration when a patients is affected by a VAT is a subject of ongoing controversy 4,5,13 .There is little doubt to 

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... endotracheal tube and an absence of new radiographic infiltrates, but always after having ruled out other possible foci of infection. However, this case scenario is not uncommon in critically ill patients and the mere fact of making a diagnosis of VAT may be associated with an unnecessary antibiotic treatment resulting in selection pressure on pathogens. Additional information may help to accurate the diagnosis of VAT. With the use of a bronchoscopy, the characteristics of secretions might be evaluated and also by obtaining a deeper sample is a relatively simple procedure that can help in diagnosis 13 . If during the procedure purulent secretions come from the deep portions of the lung, the possibility of VAT diagnosis is increased 13 . Obtaining a sample of respiratory secretions for subsequent quantitative culture is mandatory in all patients with suspected VAT. Performing a Gram stain technique in respiratory sample allows assessing the degree of inflammation based on the number of PML and quickly guiding the antibiotic therapy used. The discovery of a potentially pathogenic microorganism in number of 10 5 , 10 4 or 10 3 CFU for BAS, BAL and protected brush respectively can also help in minimizing antibiotic overtreatment. According to some authors 4,5,6,11,14 ,infection can be differentiated from airway colonization and therefore stop antibiotic therapy initiated if microbial growth is below the cut-off points mentioned. However, due to the complexity of the mechanically ventilated critical patients, it is often difficult to distinguish clearly to whom antimicrobial therapy may be discontinued based on the cutoff points and a more comprehensive therapeutic approach is needed in order to evaluate whether to continue antibiotic treatment. Inflammatory biomarkers such as C-reactive protein (CRP) and procalcitonin (PCT) have been used for the diagnosis of VAP 20,21,22 and may also help in the diagnosis of VAT. Sierra et al 15 showed that CRP may be a good indicator of infection in patients with inflammatory response syndrome. In addition, while Lisboa et al. 16 showed a good correlation between bacterial load measured as CFU/ml on quantitative culture of respiratory secretions and serum CRP, Povoa et al 17 showed that the evolution of serum CRP could be related to the recognition and development of VAP. Finally, despite of there is a lack of evidence for VAT diagnosis based on CRP, high levels of PCT and CRP (> 30 U / L) probably suggest a high bacterial load and a greater inflammatory response secondary more evident when a VAP is present. Whereas VAP and VAT present similar clinical features, VAT does not involve lung parenchyma manifested by thoracic infiltrates in X-ray, therefore to make a differential diagnosis remains difficult in critically ill patients. The VAT may represent an intermediate process between the colonization of the lower airway and the VAP and should probably be interpreted as a continuum and dynamic process between bronchitis and pulmonary parenchymal infection 5,13 . Figure 1. It Therefore, VAT might be considered as "a particular clinical entity" that in certain patients may require specific treatment, rather than requiring a rigid and uniform definition. In an attempt to prevent bacterial colonization several strategies might be taken into account. Coated ETTs induced a nonsignificant reduction of the tracheal colonization, reduced bacterial colonization of the ETT and ventilator circuits, and prevented lung bacterial colonization 23 . In addition the role of tracheostomy in mechanically ventilated patients remains controversial. A patient who has a colonized airway and who undergoes percutaneous tracheotomy has an increased risk of VAP in the week following the procedure 24,7 . The presence of a plastic device always causes a low grade of local mucocutaneous inflammation. Microorganisms show an affinity for the tracheotomy rather than the oropharynx as the site of acquisition. In addition, introduction of microorganisms directly into the lower airways via the tracheotomy as a result of repeated suctioning and manipulation of the trachea represents an important exogenous pathway. Recently, Nseir et al 25 reported that tracheotomy was independently associated with a decreased risk of VAP due to the fact that liberation of the vocal cords, resulting in a reduced risk of aspiration of contaminated oropharyngeal secretions into the lung and the reduction in bacterial biofilm formation associated with regular changing of the tracheotomy cannula, but rates of tracheobronchitis were not reported. The role of tracheostomy in development of tracheobronchitis has not been studied and future research should be performed. Prevention of lower respiratory infection in patients under MV is cornerstone in preventing the development of VAT. Different prevention strategies may also help to avoid the development of VAT and VAP subsequently which must be implemented systematically in every patient (Figure 2). ATB had a lower incidence of VAP, faster weaning and less use of systemic ATB. These results should be interpreted with caution, since the administration of systemic ATB was not standardized and based on the attending physician. Moreover, quantitative culture of respiratory secretions was not performed. In the other hand, Nseir et al 14 conducted a prospective, multicenter randomized study in intubated patients based on surveillance quantitative culture of tracheal aspirates obtained after intubation. Patients were randomized to receive or not intravenous ATB for 8 days after performing the diagnosis of VAT by a quantitative culture of bronchial secretions with> 10 6 CFU / ml and a growth of a new pathogen not present on admission. The main findings were that the group treated with ATB had a lower mortality rate, more VM free-days and lower incidence of VAP. While these results are interesting, some important limitations of this study make to consider the findings very carefully. The study included only 34 patients after 2 years of study but had to be interrupted by the low recruitment and showed lower mortality in the interim analysis with a non pre-defined number of patients. In addition, the increased mortality in the untreated group might be due to higher incidence of Pseudomonas aeruginosa VAP and not directly related to the VAT. The results of these prospective studies, although inconclusive, are attractive and open the debate regarding when patients affected by VAT should be treated or not with ATB. In our opinion, if the patient has clinical signs of VAT with fever, leukocytosis, and purulent secretions, a short course of ATB (5-7 days) should be initiated after obtaining a respiratory specimen for culture. The administration of aerosolized ATB / nebulized in patients with uncomplicated VAT is also a attractive idea, but new well-designed prospective studies are warranted in order to implement future therapeutic decisions VAT is a relatively common entity in ventilated patients admitted to an ICU. Differential diagnosis with VAP is difficult and might require additional information based on biomarkers such as CRP or PCT. The development of VAT seems to be associated with an increase development of VAP, a longer time under MV, longer hospital stay and possibly increased mortality with probably. Recent studies seem to suggest that ATB treatment of VAT is associated with lower mortality and a reduction of days of mechanical ventilation. Nevertheless and based on the limitations suggested for previous studies conducted, the indication to start antibiotic therapy as well as the most effective route of administration should be defined by future RCT. Until these results are published, the most appropriate behavior in a patient with symptoms of VAT seems to correspond to the administration of a short course of systemic ...