Chest
Volume 112, Issue 2, August 1997, Pages 445-457
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clinical investigations in critical care
The Diagnosis of Ventilator-Associated Pneumonia: A Comparison of Histologic, Microbiologic, and Clinical Criteria

https://doi.org/10.1378/chest.112.2.445Get rights and content

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 mechanical ventilation. Postmortem fiberoptic bronchoscopy (FOB) and open lung biopsy were performed with collection of specimens initiated < 1 h after death. The microbiological specimens included suction catheter aspirate of tracheal secretions, FOB-guided protected specimen brush (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 performed on all specimens, and quantitative bacteriologic study was performed on all but the suction catheter aspirate of the trachea. A biopsy specimen of peripheral lung parenchyma from the same region sampled by FOB was sent for quantitative culture and histologic analysis. The BALF was analyzed for cell population and percent of neutrophils containing intracellular organisms. The clinical criteria selected for comparison with histologic and microbiological results included a temperature ≥38.5°C during the 48 h prior to death, a WBC count ≥15,000/mm3 in the 48 h prior to death, presence of a bacterial or fungal pathogen on the last sputum culture, radiographic worsening in the week prior to death, and worsening gas 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 quantitative 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 significant correlation between qualitative and quantitative microbiological results from the distal airway/FOB-guided PSB, distal airway/BALF, and quantitative culture of the lung parenchyma. Also, suction catheter aspirate of the trachea had a sensitivity of 87% in recognizing the bacterial species simultaneously present in lung parenchyma. None of the patients with histologic pneumonia had <50% neutrophils in the BALF.

Conclusions

Neither the bacterial density from the four airway quantitative cultures, nor the bacterial density from quantitative culture 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 pneumonia. A BALF with <50% neutrophils had a 100% negative predictive value for histologic pneumonia. A BALF quantitative culture had a sensitivity of 63%, specificity of 96%, and positive predictive value of 91% in recognizing sterile lung parenchyma. Thus, BALF may have a role in excluding pneumonia/infection in the ventilated patient. Antibiotic choice for the empiric therapy of VAP can be accurately guided by the microbial population recognized through culture of a tracheal suction catheter aspirate.

Section snippets

Study Design

The study, a prospective cross-sectional study of 40 patients dying while receiving mechanical ventilation, was approved by our institutional review committee on human research.

Patient Population

The patients were recruited from the combined medical and surgical ICU of a 234-bed teaching hospital. The criteria for inclusion were as follows: (1) the patient had >24 h of mechanical ventilation prior to death; (2) the patient had been hospitalized for ≥72 h prior to death; and (3) specimen collection could be

Results

From August 1991 to October 1994, 40 patients were prospectively entered. The pathology specimen from one patient was lost in the course of the study and the related data were excluded from analysis. The study group of 39 patients consisted of 20 women and 19 men with a mean age of 66 years (range, 38 to 85 years). The duration of mechanical ventilation ranged from 1 to 134 days with a mean of 14 days and median of 8 days. Thirty-six of 39 patients had airspace disease on the chest radiograph

Discussion

The diagnosis of pneumonia in the ventilated patient remains elusive. Chastre and colleagues8 in 1984 were the first to use postmortem lung biopsy specimens for validation of the diagnosis of pneumonia, comparing histologic features with results from quantitative culture of lung parenchyma and an FOB-guided PSB of distal airway secretions. Twenty-six patients ventilated for a mean 11 days were studied, 14 of whom were receiving antibiotics. The lung biopsy specimen consisted of six 5-mm3

ACKNOWLEDGMENT

The authors gratefully acknowledge Donald E. Johnson, MT (ASCP), for performing the bacteriology, Ingrid M. Peterson, MD, for her radiologic review, Rae Wu, MD, MPH, for her statistical analysis, and Jane Lopez for her superb assistance in manuscript preparation and editing.

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    This work was funded by the Edward H. Morgan Fund for Clinical Research in Pulmonary Disease, Virginia Mason Research Center, Seattle.

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