Nearly a quarter of inpatient admissions experienced an adverse event in 2018, Massachusetts hospital study finds

Nearly a quarter of stays among an 11-hospital sample of roughly 2,800 admissions included at least one adverse event, and about 7% of admissions included an adverse event that could have been prevented, according to data published last week in The New England Journal of Medicine.

The analysis of hospital stays during 2018 found a total of 978 adverse events, roughly a third of which were deemed to be serious or worse.

Twenty-nine admissions (1%) involved a serious adverse or worse event that was judged to be preventable, researchers wrote. The sample included seven deaths related to adverse events, one of which researchers said could have been prevented.  

The findings are roughly in line with a 2022 report from the Department of Health and Human Services' Office of Inspector General (OIG), which found that a quarter of Medicare patients treated in acute care hospitals during October 2018 experienced patient harm, 43% of which was likely preventable.

The researchers wrote that these data also fall under the legacy of 1991’s landmark Harvard Medical Practice Study (HMPS). That early look at patient harm attributed 28% of identified adverse events to provider negligence, though it only reported adverse events during 3.7% of admissions due to narrower criteria.

“Three decades after the HMPS drew attention to the issue of healthcare-associated patient harm, in-hospital adverse events continue to be common, and although only approximately one-fourth of the adverse events identified in this study were deemed to be preventable, all adverse events negatively affect medical care and outcomes,” they wrote in the journal. “Despite stunning advances in medical science, we still have important gaps in patient safety.”

The researchers’ retrospective cohort study included 11 Massachusetts hospitals of varying sizes across three health systems.

Nurse reviewers looked over sampled admission records to spot possible adverse events, defined as “unintended physical injury resulting from or contributed to by medical care that requires additional monitoring, treatment or hospitalization, or that results in death.” Physicians subsequently reviewed the flagged reviews to classify the type of adverse event and assess whether patient harm was preventable.

Adverse drug events were most common, making up 39% of the 978 identified adverse events, according to the study. Surgical or other procedural events represented 30.4% of events, nursing care-associated events (such as falls or pressure ulcers) 15% and healthcare-associated infections 11.9%.

Admissions with at least one adverse event occurred more frequently among older patients as well as among men. The proportion was lower among Asian patients compared to Black or White patients and was lower among Hispanic patients than non-Hispanic patients. A lower percentage of admitted patients who used Medicaid as their primary insurance had an adverse event than those using Medicare or private insurance.

Similarly, preventable events occurred during a higher percentage of admissions of older patients, men, Black or white patients compared to Asian patients, non-Hispanic patients and Medicare, according to the study.

The researchers noted that the criteria used in various adverse event studies can vary. Their decision to exclude events that were present upon hospital admission “may have resulted in conservative estimates of event rates.”

On the other hand, the most recent study also adopted a more “inclusive” definition of an adverse event compared to some prior studies by counting “temporary patient harm” alongside more severe events such as disability at discharge. The researchers also mentioned the addition of several new types of adverse events and new infection detection capabilities over the last few decades may have expanded the count compared to HMPS and subsequent reviews.

With the clear room for improvement, the researchers highlighted the potential of longitudinal electronic patient records, enhanced surveillance and cross-facility collaboration on interventions to better tackle patient harm.

“There is considerable variability among hospitals in adverse event rates, with larger sites having rates of approximately 40% or higher; this finding suggests that if hospitals had data that were more reliable and more routinely collected, it is possible that monitoring could be improved, adverse event rates could be reduced, and improvement strategies could be shared through careful study of interventions,” they wrote.

“Our findings are an urgent reminder to all health care professionals of the need for continuing improvement in the safety of the care we deliver.”