Assessing response to therapy

Assessing the response of ventilator-associated pneumonia (VAP) to antibiotic therapy is crucial to management. It is a naive assumption by clinicians, whether they use invasive quantitative cultures or clinical diagnosis, that an accurate diagnosis and antibiotic prescription based on sensitivity testing universally leads to cure of pneumonia. Failure of antibiotic therapy for VAP may be as common as 30 to 40% of initial courses. Failure is more common with certain organisms, mainly nonfermenting, gram- negative bacilli, and is more likely in the most severely ill patients. Systemic manifestations of VAP should resolve in the first I to 2 days. Of the systemic manifestations, persistence of fever and a persistent respiratory alkalosis are the most sensitive indicators of uncontrolled local infection. Persistent leukocytosis may be a delayed marker of inadequate response to antibiotics but is not helpful in the first few days of therapy. Improved oxygenation and a decrease in minute ventilation suggest local control of infection while chest radiographs and purulent secretions are insensitive. While tracheal aspirate cultures are generally not helpful in assessing response to therapy, serial quantitative cultures may reliably detect antibiotic failure, even before it is clinically apparent.