Ventilator-associated pneumonia (VAP) refers to pneumonia that occurs more than 48 hours after patients are intubated and treated with mechanical ventilation, and it is the second most common nosocomial infection in the United States. Despite this clinical frequency, VAP has been surprisingly difficult to diagnose as there is no single clinical criterion that is specific to VAP. In addition, there is variation in the literature as to what constitutes the clinical diagnosis of VAP. Depending upon the study reviewed, there have been varying interpretations of clinical signs and symptoms suggestive of lung infection, different definitions of colonization versus infection, and different use of antibiotics in the intensive care unit (ICU).

Consistent and timely diagnosis is no small matter as early and appropriate treatment of VAP has been directly linked to favorable patient outcomes. Conversely, late or inappropriate therapy has been found to increase risk of in-hospital mortality by as much as a factor of seven. Typically, pneumonia is suspected if the patient has a radiographic infiltrate that is new or progressive concurrent with clinical findings suggesting infection: new onset of fever, purulent sputum, leukocytosis, or a decline in oxygenation. Unfortunately, these clinical signs are nonspecific and subjective. At best, no single radiographic sign has greater than 68% diagnostic accuracy.

In an effort to enhance diagnostic sensitivity and specificity for VAP, and to provide some consistency within the literature, Pugin et al. developed the clinical pulmonary infection score (CPIS). This clinical scoring system establishes the likelihood of VAP based upon several clinical parameters that can be scored 0, 1, or 2 points (as adapted by Singh et al.) (Table 141.1).

When the total CPIS exceeds 6, there is a 93% sensitivity and a 96% specificity for the presence of pneumonia, as defined by quantitative cultures of bronchoscopic and nonbronchoscopic bronchoalveolar lavage (BAL) specimens. The sensitivity and specificity of the CPIS does vary to some degree upon the reference standard used for diagnosis of pneumonia. For instance, when compared with postmortem quantitative lung cultures as the reference standard, the CPIS has a lower sensitivity of 72% to 77% and specificity of 42% to 85%. Varying
sensitivity and specificity aside, the overall interpretation based upon these studies is that the CPIS is reasonably accurate for the clinical diagnosis of VAP. Furthermore, if the CPIS is >6 there should be suspicion of VAP and empiric antibiotics should be started.