What is the definition of ventilator-acquired pneumonia (VAP)?

Definition of Ventilator-Acquired Pneumonia (VAP)

Ventilator-associated pneumonia is defined as pneumonia occurring more than 48 hours after patients have been intubated and received mechanical ventilation. 1

Diagnostic Criteria

VAP diagnosis requires a combination of clinical, radiographic, and microbiological findings:

Primary Diagnostic Elements

• New or progressive radiographic infiltrate on chest imaging
• Onset after 48-72 hours of mechanical ventilation
• Clinical evidence of infection

Clinical Criteria

VAP is suspected when a patient develops:

• New or progressive infiltrate on chest radiograph
• Plus at least one of:
  • Fever (≥38.3°C) or hypothermia (≤36°C)
  • Leukocytosis (≥12 × 10⁹/ml) or leukopenia (≤5 × 10⁹/ml)
• Plus at least one of:
  • Purulent tracheobronchial secretions
  • Cough/dyspnea
  • Declining oxygenation 2

Diagnostic Challenges

The accuracy of clinical criteria alone is limited:

• When all three clinical variables (infiltrate, fever, and leukocytosis) are required, sensitivity is only 23%
• Using a single variable results in poor specificity (33%)
• A combination of new/persistent infiltrate plus two clinical criteria has sensitivity of 69% and specificity of 75% 1

Special Considerations in ARDS

• Diagnosis is particularly challenging in ARDS patients
• False-negative rate of 46% for clinical diagnosis of VAP in ARDS patients
• Higher suspicion is warranted in ARDS patients with even one clinical criterion, unexplained hemodynamic instability, or deteriorating gas exchange 1

Clinical Significance

VAP has significant clinical implications:

• Second most common nosocomial infection in critically ill patients
• Affects 27% of all critically ill patients
• 86% of nosocomial pneumonias are associated with mechanical ventilation
• Incidence: 5-10 cases per 1,000 hospital admissions
• Attributable mortality: 0-50% (varies by population and adequacy of initial therapy)
• Higher mortality with certain pathogens (Pseudomonas aeruginosa, Acinetobacter spp., Stenotrophomonas maltophilia)
• Increases ICU length of stay by 4-13 days
• Additional costs: $5,000-$20,000 per case 1

Recommended Diagnostic Approach

1. Maintain high clinical suspicion in ventilated patients
2. Obtain chest imaging to identify new/progressive infiltrates
3. Evaluate for systemic signs of infection (fever, leukocytosis)
4. Assess respiratory secretions for purulence
5. Obtain microbiological samples before initiating antibiotics
6. Consider reasonable clinical criteria: new/persistent (48-h) or progressive radiographic infiltrate plus two of: temperature of ≥38°C or ≤36°C, blood leukocyte count of ≥10,000 cells/ml or ≤5,000 cells/ml, purulent tracheal secretions, and gas exchange degradation 1

Early diagnosis and appropriate management are essential to reduce the significant morbidity and mortality associated with VAP.