Implementation of a standard admission order set at our medical center was associated with a small increase in overall VTEP use. This increase, however, appeared to be driven by pre-implementation secular trends in all groups (which unexpectedly terminated after the order set, including, unfortunately, in the likely benefit group) and a transient increase in VTEP at the moment of implementation in patients with potential harm from it. Further, despite the intervention, rates of in-hospital hemorrhage and perhaps of in-hospital VTE both increased over time.
The transient increase in VTEP use in patients potentially harmed by it may have resulted from the following. First, institutional mandates to standardize care and pressure to improve VTEP rates, coupled with the new VTEP module, may have created the impression that VTEP prescription should be the default decision, overwhelming any module-based caveats or alternatives. Second, this impression may have had the maximum impact on patients with potential harm, because in these patients VTEP use was initially appropriately rare. Thankfully, VTEP use among this population quickly returned to baseline, indicating that perhaps early misuse was recognized and corrected. To our knowledge, at our hospital, there were no other specific interventions to explain this decline. Given that our intervention was explicitly modeled after successful decision support strategies,15
that our absolute increase in VTEP (7%) falls within the range seen in other studies (3.3%25
), and that our proportion of patients with a contraindication to VTEP due to potential harm (13%) is similar to that of other administrative data sets (20%26
), similar increases in potential misuse may well exist elsewhere and deserve urgent exploration.
Our study is the first, to our knowledge, to explicitly recognize VTEP use among patients with potential harm from it—potential misuse—as an important endpoint for quality improvement interventions. This proceeded from our observations that such misuse may serve as an early warning of unintended consequences and that many quality improvement initiatives do not currently report it.7
While the Society of Hospital Medicine comprehensive VTEP quality improvement toolkit does suggest risk-stratifying patients and measuring outcomes such as heparin-induced thrombocytopenia or hemorrhage, they also recommend omitting patients with contraindications from consideration within the initiative.27
As a result, potential VTEP misuse in this group might never be discovered.
Our study supports the importance of measuring adverse events, as we saw a secular increase in in-hospital hemorrhage (and perhaps even in VTE) after implementation despite a raw increase in VTEP after the intervention. In-hospital hemorrhage and VTE would be the ideal efficacy endpoints for any VTEP intervention. However, they are very rare (approximately 0.5–1.0% each for our patients, similar to that seen in meta-analyses of VTEP efficacy28
) and should be measured in conjunction with, not as substitutes for, potentially beneficial and harmful use. Most single institutions will be underpowered to detect even clinically meaningful differences in actual benefit or harm.
Our study had important limitations. We used billing and diagnosis-code administrative data to identify patient groups, events, and VTEP use. ICD9 codes often describe severity of illness (e.g. degree of respiratory disease, gastrointestinal hemorrhage, or thrombocytopenia) or even category of illness poorly,29
though our chart reviews suggest that our data are accurate for these uses. Though we were able to examine the effect of admission to a medical or a surgical service before, during, and after the order form, we were unable to identify individual providers who may have been more or less affected by it. We were unable to account for admission to the ICU (though we used mechanical ventilation as a proxy) as an ACCP criterion for likely benefit, and for impending surgical procedures as a criterion for potential harm (because there was no way to distinguish the hour of either VTEP or of surgery). We were forced to impute presence on admission for several diagnoses, a process that can introduce both imprecision and bias, especially if the imputation models are not optimized. However, our chart review indicated excellent calibration of the imputed data sets for VTE, we demonstrated that VTEP use increased in the potential harm group regardless of how potential harm was characterized, our imputed data sets were very similar to one another, and the trend (and change in trend) for each outcome was robust. The use of first prescription of VTEP is likely less specific for benefit and harm than overall time receiving VTEP, though we focused on the former because our order set centered on the admission. Information regarding pneumatic compression device use was also unavailable from our administrative data set, as was expectation of early patient mobility. The finding that increasing VTEP did not correlate with decreasing VTE is at odds with a recent review.30
However, our study may have been different for two reasons. First, we were examining administrative data and thus clinical VTE events rather than radiological VTE events, which were the outcome of the reviewed studies. Second, while VTEP indisputably reduces VTE in a high-risk population, it may not be as effective in a more general population such as ours, which also appears to be at slightly higher risk of bleeding. Finally, the use of typewritten order sets and computerized ones may not correspond perfectly since handwriting and typewriting are different cognitive processes.31
It is unclear how our findings will generalize to the era of computerized physician order entry.
In conclusion, a standard admission order set at our institution was associated with a transient increase in VTEP use among patients with potential harm from it and increased in-hospital hemorrhage and potentially VTE as well. Quality improvement initiative assessment should measure targeted intervention use in all patients to ensure overuse and misuse are not overlooked, especially as drivers of overall use. This approach will provide a deeper understanding of the effects of these interventions and help us to avoid those in which the overall increase in use occurs primarily in the group most likely to be harmed by it.