Frequency and Impact of Adverse Events in Inpatients: A Nationwide Analysis of Episodes between 2000 and 2015.

Despite being a potential cause of morbidity and economic costs, adverse events remain insufficiently studied. Therefore, we aimed to assess the frequency and impact of adverse events among inpatients. We analysed an administrative database containing a registration of all hospitalisations occurring in Portuguese public hospitals between 2000 and 2015. We identified all episodes with a registration of adverse events, and classified them into three categories, namely (1) misadventures of surgical and medical care, (2) complications of surgical or medical procedures, and (3) adverse drug events (including adverse drug reactions, poisoning events, and late effects). These episodes were compared over their length of stay, in-hospital mortality, and hospital costs with an equal number of hospitalisations matched for patients' and episodes' characteristics. Between 2000 and 2015, 5.8% (n = 861,372) of all Portuguese hospitalisations had a registration of at least one adverse event. Hospitalisations with registration of adverse events had a median length of stay of 8 days, median hospitalisation costs of 3060.7 Euro, and an in-hospital mortality of 6.7%. Hospitalisations with registration of misadventures of care, complications of procedures and adverse drug reactions had significantly higher lengths of stay and hospitalisation costs than their matched controls. In-hospital mortality was significantly higher for episodes of misadventures of care and complications of procedures, but lower for adverse drug events hospitalisations. Therefore, adverse events are common among inpatients, and have an important clinical and economic impact. Administrative databases may be useful in their epidemiological assessment.