Accurate and timely diagnosis of VAP in critically injured trauma patients is of utmost importance for preventing associated morbidity and death [22
]. Common clinical indicators of VAP are difficult to interpret in this patient population, and invasive means of sampling the lower respiratory tract have been found to be more sensitive and specific than noninvasive diagnostic studies [24
]. At our institution, BAL is the primary invasive means for diagnosing VAP. However, bronchoscopy requires advanced training and special equipment and is not readily available at some centers. Recently, equipment capable of obtaining samples from the lower respiratory tract without direct vision or localization has been marketed [14
]. In addition, some investigators have attempted directed invasive measures for the side of suspected pneumonia to simplify diagnosis by decreasing intervention time and simplifying microbiologic analysis [21
Our data demonstrate that bilateral sampling of the lower respiratory tract with BAL increases the likelihood of obtaining positive BAL specimens compared with unilateral sampling. This is particularly important, as our study and others have shown that the presence or absence of infiltrates on chest radiograph have no correlation with BAL culture results [6
]. Bronchoscopic unilateral-directed BAL directed at the site of pneumonia suspected radiographically therefore results in missed diagnoses of VAP, as well as potentially incomplete antibiotic therapy. This is evident when looking at the breakdown of positive bilateral BAL culture results in our study showing 16 of the 62 positive cultures having only one side positive with an additional 7 cases resulting in different bacteria isolated from either side. Unilateral sampling via noninvasive technique likely results in similar decreases in accuracy and inappropriate therapy. Additionally, bilateral BAL in our study resulted in a higher percentage of monomicrobial growth, likely reflecting more accurate diagnosis than unilateral BAL.
Clinical indicators and scores are notoriously poor predictors of a positive VAP diagnosis in trauma patients [5
]. In our study, we demonstrated that in regard to CXRs, the presence of an infiltrate did not predict a positive BAL culture; on the other hand, the absence of infiltrate did not predict a negative BAL culture. This lack of predictive value is likely attributable to the presence of pulmonary contusion in trauma patients, as well as the systemic inflammatory response to trauma that can result in indirect pulmonary inflammation. The other clinical parameter investigated in this study, WBC, also was shown to have no predictive value for the diagnosis of VAP. Again, the systemic inflammatory response to trauma can result in elevated WBC, and the presence of other infectious or inflammatory events can cloud the picture further [27
Finally, we confirmed the results of several previous studies illustrating that the causative organisms of VAP shift from predominantly gram-positive to gram-negative bacteria as the duration of ventilation increases [28
There are several limiting factors to our study. We did not measure duration of ventilation or VAP resolution for these patients and do not know if the increased sensitivity of bilateral BAL resulted in a decrease in morbidity, antibiotic use, or pneumonia recurrence. Additionally, we used fever, leukocytosis, and absence of another obvious infection site as clinical indicators of potential pneumonia. Finally, only one staff member performed unilateral-directed BAL, whereas the other trauma staff performed the bilateral BALs. This may have resulted in differences in technique affecting our results. However, the importance in our results rests in the differences between sides in the bilateral BAL group and the potential for missed or inaccurate BAL cultures.
Whereas no gold standard for the diagnosis of VAP has been established, invasive sampling of the lower respiratory tract under conditions of suspected VAP is considered the most sensitive and specific [30
]. A BAL is a common invasive modality associated with a low rate of complications. Despite the retrospective data in this study of critically ill trauma patients, we contend that bilateral BAL sampling results in a higher diagnostic accuracy than unilateral sampling when using BAL as a tool to institute or avoid antibiotic treatment. We agree with others that classical clinical criteria of chest radiography, fever, and WBC count are less desirable. Unilateral BAL directed at the site of suspected pneumonia as well as diagnostic modalities fail to sample both lungs and are therefore likely less to be accurate for this patient population. These results and recommendations may be applicable to other critically ill ventilated patients as well.