Abstract
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,
gramnegative bacilli, and is more likely in the most severely ill patients. Systemic
manifestations of VAP should resolve in the first 1 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.
