Ventilator-associated events: are we losing the plot?

Hospital-acquired infections are generally considered preventable and used as a quality assessment tool in health care by regulatory bodies. Ventilator-associated pneumonia (VAP) is one of the quality indicators employed by accreditation bodies, including the National Accreditation Board for Hospitals and Healthcare Providers (NABH) in India. It is not unusual for hospital administrators and ICU staff, in particular, to dedicate considerable time and effort to ensure compliance to the satisfaction of the assessors involved with accreditation. Increasing emphasis is placed on the new definitions and surveillance methodology in the pursuit of evaluating the incidence of VAP.  

The new approach to surveillance

Let us consider the changes that have evolved over the past few years in the surveillance of VAP in critically ill patients. VAP Surveillance and public reporting commenced in the US several years ago, at the behest of the  Center for Disease Control and Prevention (CDC) and the National Healthcare Safety Network (NHSN). An inexplicable decline in the incidence of VAP was observed with the commencement of surveillance. The most likely reason for the steep decline may have arisen from biased interpretation and reporting by hospitals faced with unwelcome consequences related to a high incidence. The highly subjective criteria employed for the diagnosis of VAP may have led to bias and underreporting. Against this background, the CDC, along with the Critical Care Societies Collaborative, attempted to develop a more objective and credible definition of VAP.¹ A three-tiered algorithmic approach was introduced under the broad category of ventilator-associated events (VAE). The first step was defined as ventilator-associated conditions (VAC), followed by infection-related, ventilator-associated conditions (IVAC), and finally, possible or probable VAP(Fig. 1). Radiological confirmation of consolidation was not considered as an essential requirement for the diagnosis of VAP considering its lack of specificity. 

Problems with the new approach

The step-wise approach requires stable or decreasing F_iO₂ and PEEP levels for two calendar days. A sustained F_iO₂ increase by more than 0.2 or an increase of PEEP by more than 3 cm of H₂O for at least two consecutive days must follow the period of stability before a diagnosis of IVAC or VAP can be considered. However, a pre-defined period of stable oxygenation may not occur in patients with worsening lung disease at the outset, such as pneumonia or acute respiratory distress syndrome (ARDS). Furthermore, VAP can clearly occur without a sustained period of diminished oxygenation requiring an increase of F_iO₂ or PEEP.² Although the new definitions were intended to add objectivity to VAP surveillance, they have not been validated by clinical evidence. 

What does the evidence suggest? 

A Dutch cohort study revealed that the VAE algorithm could identify only 32% of patients with VAP, diagnosed by prospective surveillance.³ In another retrospective study that evaluated 165 episodes of VAP diagnosed according to the conventional definition, only 12.1% were identified as probable VAP and 1.2% as possible VAP based on the new diagnostic algorithm.⁴ Clearly, the new definitions are poorly sensitive to the diagnosis of VAP; besides, worsening of oxygenation is often due to non-infective conditions such as cardiogenic pulmonary edema, ARDS, and atelectasis. Furthermore, some episodes of VAP may be missed out by the exclusion of radiological findings from the VAE algorithm. Fan et al. performed a meta-analysis of 61,489 patients from 18 studies to evaluate consistency between surveillance using conventional VAP criteria and the VAE algorithm. The VAE algorithm underestimated the true incidence of VAP as diagnosed by conventional criteria, with a pooled sensitivity and positive predictive value of less than 50%.⁵

The new algorithm as a quality indicator

The creators of the VAE algorithm argue that it is meant solely for surveillance and not for clinical management of patients. However, it appears to be an imperfect screening tool and lacks sensitivity for the diagnosis of VAP based on the clinical evidence available. The new algorithm is clearly ineffective in the early identification of mechanical ventilation-related complications by focussing solely on deterioration of oxygenation. 

In India, if you seek NABH accreditation, toeing the CDC line with the VAE algorithm appears to be a key ICU quality indicator. Hospitals take great pains to furnish VAE data to the satisfaction of NABH assessors who are often far removed from the real world of bedside clinical practice. Besides, there is often an irrational expectation to seek a “root cause” for everything under the sun and corrective action that will “eliminate” the problem, with little realization that many of the common complications of clinical medicine may not be entirely preventable. 

The bottom line

• The new algorithm-based surveillance defines VAE as sustained deterioration in oxygenation after a period of stability; the new definitions were meant to add more objectivity to VAP surveillance. 
• Lack of sensitivity to diagnose VAP is one of the main drawbacks of the new algorithm; many patients who develop VAP do not experience stable oxygenation followed by sustained deterioration. 
• Absence of radiological correlation may also lead to underestimation of the true incidence of VAP.
• The validity of the new algorithm has not been established in clinical studies.
• Regulatory bodies need to be mindful of the relative lack of evidence to support the VAE algorithm-based surveillance methodology as a quality assessment tool. 

References

1.         Magill SS, Klompas M, Balk R, et al. Executive summary: Developing a new, national approach to surveillance for ventilator-associated events. Ann Am Thorac Soc. 2013;10(6):S220-223. doi:10.1513/AnnalsATS.201309-314OT

2.         Lilly CM, Landry KE, Sood RN, et al. Prevalence and test characteristics of national health safety network ventilator-associated events. Crit Care Med. 2014;42(9):2019-2028. doi:10.1097/CCM.0000000000000396

3.         Klein Klouwenberg PMC, van Mourik MSM, Ong DSY, et al. Electronic implementation of a novel surveillance paradigm for ventilator-associated events. Feasibility and validation. Am J Respir Crit Care Med. 2014;189(8):947-955. doi:10.1164/rccm.201307-1376OC

4.         Chang H-C, Chen C-M, Kung S-C, Wang C-M, Liu W-L, Lai C-C. Differences between novel and conventional surveillance paradigms of ventilator-associated pneumonia. Am J Infect Control. 2015;43(2):133-136. doi:10.1016/j.ajic.2014.10.029

5.         Fan Y, Gao F, Wu Y, Zhang J, Zhu M, Xiong L. Does ventilator-associated event surveillance detect ventilator-associated pneumonia in intensive care units? A systematic review and meta-analysis. Crit Care. 2016;20(1):338. doi:10.1186/s13054-016-1506-z