Initial Efforts to Modify VAP Surveillance in the NHSN
In response to concerns of the healthcare epidemiology, infection prevention, and critical care communities, and to the charge from the NQF, the CDC initiated efforts in early 2009 to revise its approach to VAP surveillance. Several guiding principles were considered in this process:
CDC healthcare-associated event surveillance definitions are not intended to be used in the clinical management of patients.
CDC healthcare-associated event surveillance definitions should be appropriate for use in every healthcare facility, regardless of the availability of specialized diagnostic testing, with minimal burden on infection prevention and other facility personnel.
This surveillance does not seek to recommend diagnostic testing or procedures by including selected criteria in its healthcare-associated event surveillance definitions. The surveillance definitions are updated periodically in an attempt to reflect changes in medical practice; they are not updated to drive changes in medical practice.
The CDC is not a regulatory agency, and does not have the authority or ability to require that facilities adhere to particular diagnostic testing standards to meet criteria in its healthcare-associated event surveillance definitions.
Input from subject matter experts initially indicated that the PNEU definitions should be revised to achieve even greater specificity, through the requirement of microbiological evidence of infection in addition to radiographic and clinical evidence. The NQF VAP Technical Advisory Panel also urged the CDC to consider "development of an outcome measure based on a definition that requires laboratory results (e.g., histopathological exams, semi-quantitative and quantitative cultures), clinical criteria, and radiology results consistent with VAP" (20, p. 16). The difficulties with introducing a requirement for microbiological evidence were four-fold: 1) ample evidence suggests that microbiological findings do not increase the accuracy of VAP diagnosis, compared to a histopathological "gold standard"; 2) lung biopsies are rarely obtained in critically ill and frequently unstable patients suspected of having VAP; 3) considerable debate and uncertainty remains regarding the optimal approach to sampling the lower respiratory tract in patients suspected of having VAP; and 4) significant variability exists in lower respiratory tract sampling practices, microbiology laboratory specimen processing, and reporting practices among intensive care units (ICUs) and healthcare facilities.
Similarly, although chest radiographs remain integral to the clinical diagnosis of pneumonia, including VAP, they pose specific challenges when utilized in a surveillance definition: 1) chest radiographic findings lack specificity for VAP; 2) interobserver variability in detecting pneumonia on chest radiographs is substantial; and 3) infection preventionists, who are the hospital personnel typically responsible for VAP surveillance, often lack the expertise to independently assess chest radiographs and reports for the presence of findings that meet the VAP definition criteria.
In 2009–2010, with the potential for public reporting, interfacility comparisons of VAP rates, and use of VAP in federal pay-for-reporting and pay-for-performance programs on the horizon, it was rapidly becoming apparent that reliability—the ability to ensure that the definition could be used in a standard way across all ICUs and healthcare facilities—was a critical consideration in making any modifications to the VAP surveillance approach. At the same time, it was unclear if any specific modifications to the VAP definitions would increase their accuracy in identifying patients with bona fide VAP. The lack of a widely accepted, objective approach to VAP diagnosis has been a fundamental challenge in efforts to improve surveillance. Other VAP definitions do exist, such as the Clinical Pulmonary Infection Score, the criteria of Johanson and colleagues, and the European VAP surveillance definitions, but they are no more reliable than the CDC PNEU definitions.
With this in mind, the CDC decided to focus its efforts on enhancing the reliability and usability of the VAP surveillance definitions, and began evaluating new definitions based on research done by Klompas and colleagues in the CDC Prevention Epicenters Program. The Epicenters work, which began as an effort to enhance the objectivity and usability of the PNEU/VAP definitions, evolved to focus more generally on potentially preventable complications of mechanical ventilation rather than VAP alone. This allows for a simpler and more objective approach to surveillance and encourages a broader view of prevention in mechanically ventilated patients. Epicenters investigators utilized a definition of "ventilator-associated complications," based on sustained increases in the daily minimum fraction of inspired oxygen (FIO2) or positive end-expiratory pressure (PEEP) after ≥2 days of stable or decreasing daily minimum FIO2 or PEEP. In a retrospective study in which the ventilator-associated complications definition was applied to medical record data from approximately 600 patients, those who met the definition had longer durations of mechanical ventilation, length of ICU, and hospital stay, and increased mortality rates, compared to patients who did not meet the definition. Identification of cases using the ventilator-associated complications definition took significantly less time than using the PNEU/VAP definitions. Other evaluations conducted by the CDC Prevention Epicenters, the CDC, and other collaborators using similar objective definitions have supported these findings.