Diagnosis of ventilator-associated respiratory infections (VARI): microbiologic clues for tracheobronchitis (VAT) and pneumonia (VAP)

Abstract

Intubated patients are at risk of bacterial colonization and ventilator-associated respiratory infection (VARI). VARI includes tracheobronchitis (VAT) or pneumonia (VAP). VAT and VAP caused by multidrug-resistant (MDR) pathogens are increasing in the United States and Europe. In patients with risk factors for MDR pathogens, empiric antibiotics are often initiated for 48 to 72 hours pending the availability of pathogen identification and antibiotic sensitivity data. Extensive data indicate that early, appropriate antibiotic therapy improves outcomes for patients with VAP. Recognizing and treating VARI may allow earlier appropriate therapy and improved patient outcomes.

Fig. 1

Pathogenesis of ventilator-associated respiration infections (VARI). Bacteria enter the lower respiratory tract from the oropharynx by leakage around the endotracheal tube (ETT) cuff or from intraluminal biofilm. The black arrows represent the battle between the entering bacterial pathogen(s) and host defenses. The circles correspond to either colonization or VARI, manifest as either tracheobronchitis (VAT), pneumonia (VAP), or both.

Fig. 2

Schematic view of the intubated patient with orogastric tube (OGT) and endotracheal tube (ETT). High levels of bacteria are present in the oropharyngeal secretions that may collect in the subglottic space above the ETT cuff. Bacteria-encased biofilm in the ETT lumen may colonize or embolize into the distal airways. Ventilator-associated respiratory infection (VARI) includes tracheobronchitis (VAT) or pneumonia (VAP) or both. Endotracheal aspirates (EA) examined by quantitative methods (Q-EA) or semiquantitative methods (SQ-EA) are used to distinguish infection versus colonization, and bronchoalveolar lavage (BAL) and protected specimen brush (PSB) are used to define VAP versus VAT or colonization.

Fig. 3

Clues for diagnosis of ventilator-associated respiratory infection (VARI), which includes tracheobronchitis (VAT), pneumonia (VAP), or both. Clinical clues are common to all (VARI, VAT, VAP). Radiology clues may help to discriminate VAP from VAT based on the presence or absence of a new pulmonary infiltrate. By comparison, microbiology clues differ depending on the diagnostic methodology employed. Note that the significant growth of pathogen on bronchoscopic–bronchoalveolar lavage (B-BAL≥10⁴ cfu/mL), nonbronchoscopic BAL (N-BAL>10⁴ cfu/mL), or protected specimen brush (PSB≥10³ cfu/mL) is diagnostic for VAP. Absence of significant growth (B-BAL<10⁴ cfu/mL, N-BAL<10⁴ cfu/mL, PSB<10³ cfu/mL) is consistent with VAT or colonization. When endotracheal aspirates (EAs) are used for diagnosis, it is difficult to discriminate between VAT and VAP, but they are helpful for distinguishing between colonization and infection (VARI).

Fig. 4

Chest radiograph and computerized tomographic (CT) scan of patient with acute respiratory failure and diffuse bilateral infiltrates. Radiographic findings demonstrating diffuse airspace disease are also consistent with diagnosis of acute respiratory distress syndrome (ARDS) or congestive heart failure with or without infection. Patient also displayed clinical clues of ventilator-associated respiratory infection (VARI). Due to pre-existing changes on chest radiograph, no new infiltrate could be detected to confirm a diagnosis of ventilator-associated pneumonia (VAP). The quantitative endotracheal aspirate had greater than 10⁶ colony forming units (cfu)/mL indicating ventilator-associated tracheobronchitis (VAT) or pneumonia (VAP). Bronchoalveolar lavage (BAL) could not be performed due to the severity of her ARDS.

Fig. 5

Patient “MJ” had clinical signs (fever, leukocytosis and purulent sputum) of ventilator-associated respiratory infection (VARI). Her semiquantitative endotracheal aspirate (SQ-EA) showed many/++++ bacterial growth (A), and a simultaneous Q-EA demonstrated >10⁶ cfu/mL of Pseudomonas aeruginosa on blood agar plates (B), consistent with the diagnosis of ventilator-associated tracheobronchitis (VAT) or pneumonia (VAP). Patient “YL” had clinical signs of VARI; an SQ-EA showed few/++ bacterial growth (C) and Q-EA<10⁴ cfu/mL of Escherichia coli (D), consistent with endotracheal colonization.

Fig. 6

Model for the use of quantitative (Q) and semiquantitative (SQ) endotracheal aspirates (EAs) to initiate “argeted rather than empiric antibiotic therapy. Ventilator-associated respiratory infections (VARIs) include tracheobronchitiis (VAT) and pneumonia (VAP). The goal is early targeted appropriate antibiotic therapy to improve patient outcomes in terms of reduced mortality, morbidity, and health care costs.