Dollars, denominators, and risk adjustment

Because not everyone who reads this blog reads the comments, I wanted to highlight these particularly insightful observations about Mike’s post on denominators for CLABSI (emphasis mine):

"The thought experiment works with the assumption these two ICUs are indistinguishable except for the frequency of CVC use. Historically, I think the justification for comparative rates using CVC denominators was a no-brainer. These devices were critical to saving lives, and the variations in device utilization probably reflected differences in patient populations, even within similar types of locations. Accounting for the overwhelming primary risk (the CVC) made sense, since these devices were critical to care. The problem you’re outlining now is very real -- as the clinical environment has proven that a lot of the variations in CVC use may in fact be personal preference. Just like the argument with CAUTIs (where foley use is deemed less critical to care) to use a patient-day denominator is strong, we may be at a time where the CLABSI argument is as strong. Improving the classification of ICU types, by more objective criteria than currently used in NHSN (i.e. the 80% rule), would really advance the comparative metric substantially, and likely provide more valid risk adjustment with patient-day denominators than we currently have with these archaic classification schemes (e.g., "med-surg icu"). Advancing the use of composite administrative data to classify patient locations to a more objective, reliable, and granular level, based on fractions of patient-days that have key underlying diagnosis, procedures, etc. is greatly needed."

Given the millions of dollars that are now at stake based upon a hospital’s performance on healthcare-associated infection (HAI) metrics, it’s hard to overemphasize the pressure that is now being placed on the NHSN definitions, and the importance of ensuring that the definitions keep pace with evolving approaches to patient care. When I was a medical resident (yes, way back then), the presence of a CVC was a good indicator of severity of illness and likely served well as built-in risk adjustment for the broad categories of ICU. The same cannot be said now; the device utilization ratios (and percentile ranks compared across NHSN units) vary markedly between different ICU types in our hospital, and do not correlate well with illness severity. And as we’ve learned with CAUTI, the device days that are most amenable to reduction (the “low hanging fruit”) are always the lowest risk device days.