The influence of mini-BAL cultures on patient outcomes: implications for the antibiotic management of ventilator-associated pneumonia.

STUDY OBJECTIVE: To determine the influence of mini-BAL culture results on subsequent changes in antibiotic therapy and patient outcomes.

DESIGN: Prospective, single-center, cohort study.

SETTING: Medical ICU of Barnes-Jewish Hospital, St. Louis, a university-affiliated teaching hospital.

PATIENTS: One hundred thirty mechanically ventilated patients undergoing mini-BAL for suspected ventilator-associated pneumonia (VAP).

INTERVENTIONS: Mini-BAL, prospective patient surveillance, and data collection.

MEASUREMENTS AND RESULTS: Sixty (46.2%) patients had mini-BAL cultures that yielded at least one pathogen potentially accounting for the clinically suspected episode of VAP (64 bacterial, 3 viral, 2 fungal). Among the 60 patients with microbiologically positive mini-BAL cultures, 44 (73.3%) were classified as receiving inadequate antibiotic therapy (ie, identification of a microorganism resistant to the prescribed antibiotic regimen). Prior antibiotic administration or its absence remained unchanged in 51 (39.2%) patients based on the mini-BAL culture results, while in another 51 (39.2%) patients, antibiotic therapy was either begun (n=7) or the existing antibiotic regimen was changed (n=44), and in the remaining 28 (21.6%) patients, antibiotic therapy was discontinued altogether. The hospital mortality rates of these three groups were statistically different: 33.3%, 60.8%, and 14.3%, respectively (p<0.001). The most common pattern of antibiotic resistance resulting in an antibiotic change following mini-BAL was the identification of a Gram-negative bacteria resistant to a prescribed third-generation cephalosporin in 23 of 44 (52.3%) patients. Twenty-one of these 23 patients (91.3%) received prior therapy with a cephalosporin class antibiotic during the same hospitalization. Having an immunocompromised state (adjusted odds ratio [OR]=2.45; 95% confidence interval, 1.56 to 3.85; p=0.047) and the presence of a pathogen in the mini-BAL culture resistant to the empirically prescribed antibiotic regimen (adjusted OR=3.28; 95% confidence interval, 2.12 to 5.06; p=0.006) were identified as risk factors independently associated with hospital mortality by logistic regression analysis.

CONCLUSIONS: These data suggest that antibiotic selection prior to obtaining the results of lower airway cultures is an important determinant of outcome for patients with suspected VAP. A delay in initiating adequate antibiotic therapy was associated with a greater mortality. Therefore, the initial selection of antibiotics for the empiric treatment of VAP should be broad enough to cover all likely pathogens, including antibiotic-resistant bacteria. This appears to be especially important in patients having received prior antibiotics.