Ventilator Associated Pneumonia (VAP)
Ventilator Associated Events (VAE)
The generally accepted definition of Ventilator Associated Pneumonia (VAP) refers to a parenchymal lung infection that arises more than 48 hours after endotracheal intubation. However, this definition is inadequate because diagnosing VAP requires high clinical suspicion combined with bedside examination, radiographic examination, and microbiologic analysis of respiratory secretions.
Aggressive surveillance is vital in understanding local factors leading to VAP and the microbiologic milieu of a given intensive care unit. Unfortunately, accepted clinical criteria for pneumonia are of limited diagnostic value in definitively establishing the presence of VAP. In a postmortem study by Fabregas et al., when findings on histologic analysis and cultures of lung samples obtained immediately after death were used as references, a new and persistent (>48-h) infiltrate on chest radiograph plus two or more of the three criteria – (i) temperature >38.3°C, (ii) leukocytosis >12 × 109/mL, and/or (iii) purulent tracheobronchial secretions –- had a sensitivity of 69% and a specificity of 75% for establishing the diagnosis of VAP. When all three clinical variables were required for the diagnosis, the sensitivity declined further (23%); the use of a single variable resulted in a decrease in specificity (33%).
The poor accuracy of clinical criteria in the diagnosis of VAP should not be surprising considering that purulent tracheobronchial secretions are invariably present in patients receiving prolonged mechanical ventilation and are seldom caused by pneumonia. In addition, the systemic signs of pneumonia, such as fever, tachycardia, and leukocytosis, are nonspecific; they can be caused by any condition that releases the cytokines interleukin-1, interleukin-6, tumor necrosis factor-alpha, and gamma interferon. Examples of such conditions include trauma, surgery, and the fibroproliferative phase of acute respiratory distress syndrome, deep vein thrombosis, pulmonary embolism, and pulmonary infarction.
Pneumonia is the second most common nosocomial infection in the United States and is a leading cause of death due to hospital-acquired infections. VAP is a form of nosocomial pneumonia that occurs in patients receiving mechanical ventilation for longer than 48 hours. The incidence of VAP is estimated to be 22.8% in patients receiving mechanical ventilation, and patients receiving ventilator support account for 86% of the cases of nosocomial pneumonia. Furthermore, the risk for pneumonia increases three- to ten-fold in patients receiving mechanical ventilation. VAP is associated with increases in morbidity and mortality, hospital length of stay, and costs. The mortality rate attributable to VAP is 27% and has been as high as 43% when the causative agent was antibiotic resistant. Length of stay in the intensive care unit is increased 5 to 7 days and hospital length of stay two- to three-fold in patients with VAP. The cost of VAP is estimated to be an additional $40,000 per hospital admission per patient and an estimated at $1.2 billion per year in the United States.
In 2009 the CCSC began discussions with the Department of Health and Human Services (HHS) [including the Centers for Disease Control and Prevention (CDC), Centers for Medicare and Medicaid Services (CMS), and the Agency for Healthcare Research and Quality (AHRQ)] to address this vexing problem. Key CCSC leaders held a meeting at CDC Headquarters on September 19, 2011 to consider the issues of the ventilated patient and reduce the overall incidence of VAP and associated conditions. A joint CDC-CCSC task force was formed to work on this vexing problem.
The task force recognized that there is currently no gold standard, valid, reliable definition for VAP. Even the most widely-used VAP definitions are neither sensitive nor specific for VAP. Therefore, the task force decided to pursue a different approach-development of a surveillance definition algorithm for detection of ventilator-associated events (VAEs). This algorithm will detect a broad range of conditions or complications occurring in mechanically-ventilated adult patients.
Because the reliability of HAI definitions has become particularly important in recent years, the task force focused on definition criteria that use objective, clinical data that are expected to be readily available across the spectrum of mechanically-ventilated patients, intensive care units and facilities-in other words, criteria that are less likely to be influenced by variability in resources, subjectivity, and clinical practices—and that are potentially amenable to electronic data capture.
The task force proposed a new surveillance definition algorithm to detect VAEs in adult patients. It is not designed for use in the clinical care of patients. The task force anticipates that the new definition algorithm will continue to be refined, based on the results of field experience and additional research. The definition algorithm refinement process is, and will continue to be iterative, and will require the ongoing engagement of the critical care, infection prevention, infectious diseases and healthcare epidemiology communities.
In 2013 the report entitled, “Developing a New, National Approach to Surveillance for Ventilator-Associated Events” appeared in Critical Care Medicine (SCCM). The CCSC continues to monitor develops in this area and may recommend changes to the definition. These may include: Possible narrowing of the list of antimicrobial agenda applicable to possible/probably VAP, change to ‘purulent sputum’ criterion, because of wide variability between labs in how sputum gram stains are reported, and a move to location-based reporting, rather than age-based reporting. A number of educational presentations at a wide range of conferences have occurred and are ongoing to keep clinicians abreast of the latest develops on this topic.