Diagnostic Value of Lung Ultrasound for Ventilator-Associated Pneumonia

Prospective, Observational Study of Diagnostic Value of Lung Ultrasound for Ventilator-Associated Pneumonia

Ventilator-associated pneumonia (VAP) is the most common nosocomial infection acquired by mechanically-ventilated patients in the intensive care unit (ICU). It has significant clinical and economic consequences, as it is associated with considerable morbidity, increased mortality, and excess health care costs. Appropriate antibiotic therapy for patients with VAP significantly improves outcomes, making rapid identification of patients with VAP an important clinical goal.

This application is for support of a prospective, multi-centered study to evaluate the diagnostic value of lung ultrasound for VAP. The primary hypothesis is that the association of the Clinical Pulmonary Infection Score (CPIS) to specific lung ultrasound signs could allow for early and reliable diagnosis of bacterial VAP.

Objective 1: To evaluate the sensitivity, specificity, and diagnostic accuracy of lung ultrasound alone and in association with the CPIS.

Objective 2: To determine the frequency of specific lung ultrasound signs (subpleural consolidation, irregular B-lines) in VAP.

Objective 3: To promote development of a diagnostic pathway for VAP incorporating CPIS, lung ultrasound, and unprotected tracheal aspirate (UTA).

Patients will be enrolled within 24 hours of the point at which criteria are met for suspected VAP. Upon enrollment, the following variables will be recorded from the online medical record, and a Clinical Pulmonary Infection Score will be calculated.

• Demographics (height, weight, comorbidities)
• Ventilation parameters
• Infectious disease data during present admission (antibiotic history, culture data)
• Biochemical data (WBC count with differential, arterial blood gas)
• Microbiological data (UTA and BAL) - UTA data must have been collected within 24 hours of enrollment and BAL data within 12 hours of enrollment
• Radiological data (CXR or chest CT)

Lung ultrasound will be performed within 24 hours of the point at which criteria are met for suspected VAP. Lung ultrasound will include examination of both lungs. Each hemithorax will be divided into three regions using anterior and posterior axillary lines as landmarks. Each of these regions will be further divided into upper and lower quadrants, yielding a total of 6 quadrants per hemithorax. Examination will specifically identify the presence or absence of the following lung ultrasound findings: normal pleural A lines, non-coalescent B lines, coalescent B lines, consolidations (subpleural or lobar), and linear air bronchograms. A Lung Ultrasound Aeration Score will be calculated based on these findings. Ultrasonographic diagnosis of VAP will be defined based on the presence of subpleural consolidation, entire lobar consolidation, or air bronchogram within consolidation.

The results of microbiological data will be followed up for confirmation of culture results. Cultures will be considered positive if ≥ 100,000 bacterial colony-forming units (cfu) are isolated.

At day #28 of study enrollment, the patient's status will be documented (alive vs. deceased, inpatient vs. discharged).

Inclusion Criteria:

• Mechanical ventilation for at least 48 hours,

• New or evolving infiltrate on chest radiograph (CXR) or computed tomography (CT), and

• A minimum of two of the following clinical criteria:

  • Body temperature ≥ 38.5° C (101° F) or < 36° C (97° F)
  • White blood cell count > 10,000/ml or < 4,000/ml or > 10% immature cells
  • Partial pressure of oxygen in arterial blood < 60 mmHg or partial pressure of oxygen in arterial blood/ inspired oxygen fraction ratio < 300
  • Purulent respiratory secretions

Exclusion Criteria:

Known ongoing pneumonia

• Patient younger than 18 years old
• Mechanical ventilation <48 hours
• Contraindication to bronchoscopy