In 79 patients admitted to a university general intensive care unit with clinically suspected VAP, right- and left-lung bronchoalveolar lavage (BAL) samples were taken with separate bronchoscopes and quantitatively cultured. Primary end-point variable was microbiologic concordance rate between right- and left-lung BAL cultures. Secondary outcomes included predictors of microbiologic concordance, rates of appropriate antibiotic treatment, and diagnostic accuracy of chest x-ray.
BAL cultures were bilaterally negative in 21 (27%) of 79 patients, bilaterally positive in 36 (46%), and unilaterally positive (right in 12, left in 10) in 22 (28%). Intra-patient concordance was observed in 47 (59.5%) of 79 cases and independently associated with purulent secretions and bilateral infiltrates on chest x-ray. In simulated prescribing experiments, treatments chosen based on right or left cultures alone were as appropriate as those based on bilateral data in > 90% of cases. The presence of a radiographic infiltrate in the sampling area predicted BAL culture positivity with a positive predictive value of only 61%.
In patients with clinically suspected VAP (especially those without purulent secretions or without radiographically documented bilateral infiltrates), quantitative culture of a single BAL sample may provide an incomplete assessment of lung microbiology, without having a relevant impact on the appropriateness of antimicrobial treatment. These findings suggest that single sampling of respiratory secretions, regardless radiographic opacity, seems to be a reliable diagnostic method in the management of VAP.