Definition of Ventilator-Associated Pneumonia
Ventilator-associated pneumonia (VAP) is pneumonia that occurs more than 48 hours after patients have been intubated and placed on mechanical ventilation. 1, 2
Core Diagnostic Requirements
VAP diagnosis requires three integrated components working together 1, 2:
- Temporal criterion: The infection must develop after 48 hours of mechanical ventilation, not before 1, 3
- Clinical assessment: Bedside examination revealing signs of infection 1, 2
- Radiographic evidence: New or progressive infiltrate on chest radiograph 1, 2
- Microbiologic confirmation: Analysis of respiratory secretions 1, 2
Clinical Diagnostic Criteria
A reasonable clinical suspicion for VAP includes a new and persistent (48-hour) or progressive radiographic infiltrate plus at least two of the following findings 1, 2:
- Temperature >38°C or <36°C 1
- Blood leukocyte count >10,000 cells/ml or <5,000 cells/ml 1
- Purulent tracheal secretions 1, 2
- Gas exchange degradation or declining oxygenation 1, 2
Important Diagnostic Limitations
Clinical criteria alone have significant limitations that clinicians must recognize 1:
- Sensitivity is only 69% and specificity 75% when using radiographic infiltrate plus two clinical criteria 1
- Purulent secretions are nearly always present in prolonged mechanical ventilation regardless of pneumonia 1
- Systemic signs (fever, leukocytosis, tachycardia) are nonspecific and can result from trauma, surgery, ARDS, deep vein thrombosis, or pulmonary embolism 1
Special Considerations in ARDS
In patients with ARDS, maintain an extremely high index of suspicion as clinical criteria perform even worse 1:
- False-negative rate reaches 46% in ARDS patients 1
- Even a single clinical criterion, unexplained hemodynamic instability, or unexplained arterial blood gas deterioration should prompt further diagnostic evaluation 1, 2
- New infiltrates may be difficult to detect on chest radiograph in the setting of existing ARDS 1
Epidemiologic Impact
VAP represents a major burden in critical care 1, 2:
- Affects 27% of all critically ill patients, with 86% of nosocomial pneumonias associated with mechanical ventilation 1, 2
- Incidence of 5-10 cases per 1,000 hospital admissions 1, 2
- Attributable mortality ranges from 0-50%, with higher rates for resistant organisms like Pseudomonas aeruginosa, Acinetobacter species, and Stenotrophomonas maltophilia 1, 2
- Increases ICU length of stay by 4-13 days 1, 2
- Adds $5,000-$20,000 in incremental costs per diagnosis 1, 2
Distinction from Nosocomial Tracheobronchitis
When purulent sputum, positive cultures, fever, and leukocytosis occur without a new lung infiltrate, consider nosocomial tracheobronchitis instead of VAP 1: