What’s New in the Patient Safety World

February 2014

Medicare Adverse Event Trends



In the last couple decades during which the patient safety movement has gained momentum, we have struggled to demonstrate that outcomes have improved as a result of our efforts.


In our January 2011 What’s New in the Patient Safety World column “No Improvement in Patient Safety: Why Not?” we noted a study (Landrigan 2010) that showed there has been little improvement in hospital adverse events overall over a long time frame. That study, done on data from 10 North Carolina hospitals, used IHI’s Global Trigger Tool to estimate rates of patient harm and preventable harm over a 6-year period. They found essentially no reduction in harm over that period. They had chosen North Carolina because many hospitals there had participated in patient safety collaboratives and North Carolina had a much higher percentage of hospitals participating in IHI’s patient safety programs.


In our May 2011 What’s New in the Patient Safety World column “Just How Frequent Are Hospital Medical Errors? we noted another study (Classen 2011), using IHI’s Global Trigger Tool to identify hospital adverse events, found that the numbers may be 10-fold higher than what was noted in the 1999 IOM report “To Err is Human…”. Potentially avoidable adverse events occurred in a third of hospital admissions. In addition to the human cost of iatrogenic adverse events, the financial costs are huge.


The IHI Global Trigger Tool clearly identifies more adverse events than are found either via voluntary reporting or using administrative data tools like AHRQ’s PSI indicators.


Now a new study has attempted to track and trend adverse events in the hospitalized Medicare population over time using yet a different methodology (Wang 2014). Wang and colleagues looked at data from the Medicare Patient Safety Monitoring System (MPSMS) from 2005 to 2011. This system contains data abstracted from the medical records of a random sample of hospitalized Medicare patients, with 21 adverse events currently measured. Though the MPSMS was established in 2002, data on all the current 21 adverse events became available in 2005. The authors analyzed the trends in those adverse events for patients with four diagnoses: acute MI, CHF, pneumonia, and conditions requiring surgery. They used 3 separate measures of adverse events (rate of adverse events per patient at risk for such events, rate of patients with one or more adverse events, and rate of adverse events per 1000 hospitalizations). Generally, but not always, those 3 measures trended the same direction. Their results showed that adverse events rates for patients with acute MI and CHF declined significantly over the study period. However, for patients with pneumonia or conditions requiring surgery the rate of adverse events did not change. The authors conclude “Although this suggests that national efforts focused on patient safety have made some inroads, the lack of reductions across the board is disappointing.”


Frankly, while the study was done by respected researchers from places like Hopkins, Harvard and Yale and under the auspices of AHRQ, we’re really not sure what it means!


First, you can’t compare total adverse events rates across the four conditions because the individual events are not the same for all the conditions, though that may not matter as much if we are simply looking for trends. Secondly, it is difficult to understand differences in some adverse event rates without taking into account the context, which may influence adverse event rates (for example, the indications for anticoagulants may differ across the four condition categories). Third, it’s not clear whether some adverse events are double counted in conditions requiring surgery. For example, CAUTI’s appear as adverse events under events associated with knee and hip replacements and under a separate category.


But the study does raise some interesting questions. For example, why was there a statistically significant decrease in inpatient falls for patients with AMI but not the other conditions? Why were there significant decreases in adverse events associated with IV heparin and events associated with LMW heparin or factor Xa inhibitors for those with AMI but not with any of the other conditions?


The study did confirm previous observations that patients experiencing adverse events are more likely to die during the hospitalization and to have longer lengths of stay.



The bottom line: there are simply too many questions about this methodology and this study to come to any really useful conclusions. Nevertheless, it does add to our frustration that so many patient safety efforts are not leading to measurable improvements in patient care.







Landrigan CP, Parry GJ, Bones CB, et al. Temporal Trends in Rates of Patient Harm Resulting from Medical Care. N Engl J Med 2010; 363: 2124-2134




Classen D, Resar R, Griffin F, et al. ‘Global Trigger Tool’ Shows That Adverse Events In Hospitals May Be Ten Times Greater Than Previously Measured. Health Affairs 2011; 30(4): 581-589




Wang Y, Eldridge N, Metersky ML, et al. National Trends in Patient Safety for Four Common Conditions, 2005–2011. N Engl J Med 2014; 370: 341-351







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