THE DIAGNOSIS OF VENTILATOR-ASSOCIATED PNEUMONIA - A COMPARISON OF HISTOLOGIC, MICROBIOLOGIC, AND CLINICAL-CRITERIA

Study objective: To evaluate histologic, microbiological, and clinical criteria in the recognition of ventilator-associated pneumonia (VAP) in patients who died while mechanically ventilated. Methods: The study group consisted of 39 patients who died after a mean of 14 days of me chanical ventilation. Postmortem fiberoptic bronchoscopy (FOB) and ope n lung biopsy were performed with collection of specimens initiated < 1 h after death. The microbiological specimens included suction cathet er aspirate of tracheal secretions, FOB-guided protected specimen brus h (PSB) of tracheal secretions, blindly placed PSB in a distal airway, FOB-guided PSB in a distal airway, and FOB-guided BAL fluid (BALF) in a distal airway. Qualitative bacteriologic study was pet-formed on al l specimens, and quantitative bacteriologic study was performed on all but the suction catheter aspirate of the trachea. A biopsy specimen o f peripheral lung parenchyma from the same region sampled by FOB was s ent for quantitative culture and histologic analysis. The BALF was ana lyzed for cell population and percent of neutrophils containing intrac ellular organisms. The clinical criteria selected for comparison with histologic and microbiological results included a temperature greater than or equal to 38.5 degrees C during the 48 h prior to death, a WBC count greater than or equal to 15,000/mm(3) in the 48 h prior to death , presence of a bacterial or fungal pathogen on the last sputum cultur e, radiographic worsening in the week prior to death, and worsening ga s exchange defined as a 15% decrease in the PaO2/fraction of inspired oxygen ratio in the 72 h prior to death. Results: None of the quantita tive cultures had a reliable positive predictive value for histologic pneumonia. None of the five clinical criteria tested showed agreement with the presence or absence of histologic pneumonia. There was a sign ificant correlation between qualitative and quantitative microbiologic al results from the distal airway/FOB-guided PSB, distal airway/BALF, and quantitative culture of the lung parenchyma. Also, suction cathete r aspirate of the trachea had a sensitivity of 87% in recognizing the bacterial species simultaneously present in lung parenchyma. None of t he patients with histologic pneumonia had < 50% neutrophils in the BAL F. Conclusions: Neither the bacterial density from the four airway qua ntitative cultures, nor the bacterial density from quantitative cultur e of lung parenchyma accurately separated the histologic pneumonia and nonpneumonia groups. No clinical criteria or combination of clinical criteria correlated with the presence or absence of histologic pneumon ia. A BALF with < 50% neutrophils had a 100% negative predictive value for histologic pneumonia. A BALF quantitative culture had a sensitivi ty of 63%, specificity of 96%, and positive predictive value of 91% in recognizing sterile lung parenchyma. Thus, BALF may have a role in ex cluding pneumonia/infection in the ventilated patient. Antibiotic choi ce for the empiric therapy of VAP can be accurately guided by the micr obial population recognized through culture of a tracheal suction cath eter aspirate.