Ventilator-Associated Pneumonia
Accuracy of clinical definitions of ventilator-associated pneumonia: Comparison with autopsy findings

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Abstract

Methods

We studied patients requiring mechanical ventilation for more than 48 hours who died in the intensive care unit and whose bodies were autopsied. We evaluated 3 clinical definitions of ventilator-associated pneumonia: loose definition, defined as chest radiograph infiltrates and 2 of 3 clinical criteria (leukocytosis, fever, purulent respiratory secretions); rigorous definition, defined as chest radiograph infiltrates and all of the clinical criteria; and a clinical pulmonary infection score higher than 6 points. Sensitivity, specificity, and likelihood ratios were calculated by using pathology pattern as criterion standard.

Results

One hundred forty-two (56%) of the 253 patients included had histological criteria of pneumonia. Patients who met the clinical criteria of ventilator-associated pneumonia were 163 (64%) for the loose definition, 32 (13%) for the rigorous definition, and 109 (43%) for the clinical pulmonary infection score. The operative indexes (sensitivity and specificity) of each definition were as follows: loose definition, 64.8% and 36%; rigorous definition, 91% and 15.5%; and clinical pulmonary infection score higher than 6, 45.8% and 60.4%. The addition of microbiological data to the clinical definitions increased the specificity and decreased the sensitivity but not significantly.

Conclusions

Accuracy of 3 commonly used clinical definitions of ventilator-associated pneumonia was poor taking the autopsy findings as reference standard.

Introduction

Ventilator-associated pneumonia is a leading cause of sepsis in patients with acute respiratory failure and a significant contributor to morbidity and mortality. Moreover, ventilator-associated pneumonia represents a major diagnostic challenge because of the low yield of clinical criteria and because it is often difficult to distinguish clinically from other processes that affect patients receiving mechanical ventilation [1].

Clinical criteria for the suspicion of ventilator-associated pneumonia, such as intubation for 48 hours or more with fever, leukocytosis, purulent secretions, and pulmonary infiltrates, continue to form the starting point of diagnostic evaluation.

Postmortem lung histological studies have evaluated the usefulness of clinical and radiographic signs to predict ventilator-associated pneumonia with disappointing results. Most of them have demonstrated that these clinical and radiographic parameters present a high inaccuracy rate in identifying intubated patients with nosocomial pneumonia. These studies using histological examination of lung tissue samples vary in sample size, and most studies examined a single-lung biopsy sample, which may frequently underdiagnose pneumonia [2], [3], [4], [5], [6], [7].

The objective of our study is to determine the reliability and accuracy of 3 clinical commonly used definitions of ventilator-associated pneumonia using autopsy findings as the reference standard.

Section snippets

Patients

This is a retrospective study of all patients requiring mechanical ventilation for more than 48 hours. We included all patients requiring mechanical ventilation for more than 48 hours between June 1991 and December 2004 who died in the intensive care unit of the Hospital Universitario de Getafe and whose relatives were given written permission to perform postmortem analysis. We approached the families of all patients who died, except those who became organ donors and those whose autopsies were

Patients

During the study period, 9906 patients were admitted to the intensive care unit and 1633 patients (16.5%) died. We subsequently excluded 120 organ donors and 101 patients with legally mandated autopsies. We obtained consent and performed a clinical autopsy in 497 (35%) of the remaining patients. Thirty (6%) of these patients were excluded from the analysis because the information needed to determine clinical definition was unavailable. A total of 253 patients required mechanical ventilation for

Discussion

Main finding of our study is that the accuracy of 3 different clinical definitions of ventilator-associated pneumonia was poor when they are compared with the histological findings.

The diagnosis of ventilator-associated pneumonia is usually based on 2 or 3 components: systemic signs of infection and new or worsening infiltrates seen on the chest roentgenogram, and, sometimes, bacteriologic evidence of pulmonary parenchymal infection. Several studies have evaluated the diagnostic accuracy of

References (17)

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