Respiratory infection in the chronically critically ill patient. Ventilator-associated pneumonia and tracheobronchitis.

The long-term ventilated patient is at high risk for developing nosocomial pneumonia or tracheobronchitis. In general, the frequency of infection increases with the duration of mechanical ventilation, but the risk appears to be greatest in the first week of intubation. Although these types of infection are common and may have morbidity and mortality impact, the daily risk is less in the long-term ventilated patient than in the acutely ill intubated patient. This reduced daily risk may reflect a "survivor effect," with less healthy patients dying early in the hospital stay and not surviving long enough to undergo tracheostomy and long-term ventilation. A number of factors predispose these patients to infection, including host defense impairment and exposure to large numbers of bacteria. This exposure can occur through the airway, and proper care of respiratory therapy devices is essential to minimize the risk for infection. Most infections of the lower respiratory tract are preceded by airway colonization with EGN bacteria and, with improvement in host defenses and nutrition, infection in the face of colonization is less likely. In some patients, colonization can be eliminated. When the long-term ventilated patient does develop infection, it generally involves highly resistant gram-negative or gram-positive organisms and therapy should be prompt and appropriate. Not all such patients respond to systemic antibiotics, and the use of adjunctive aerosol therapy may have benefit for those with either tracheobronchitis or pneumonia, especially if highly resistant pathogens are present.