Discussion

The results of the current study demonstrate the feasibility of using routinely collected electronic data to screen for AEs. A total of 1870 (1.3%) AEs were identified using the screening criteria. Although the event rate is low, the types of AEs that were identified are consistent with those reported in other settings and using different methodologies. The most common types of AEs were procedure and drug-related. Significant and clinically important differences in healthcare utilisation were identified for those patients with an AE. They were more likely to be transported to hospital by ambulance, to have a longer length of stay in the ED and to be admitted to hospital and to an intensive care unit.

Although there are several studies that have described AEs occurring as a result of care in the ED,8–10 there is limited literature describing AEs identified in the ED setting, but related to events that took place prior to an ED visit. In a retrospective chart review, Hendrie et al screened records from patients presenting to the ED in a tertiary care hospital in Australia. They determined an event rate of 5.1%, with more than half of the events occurring prior to the ED visit. The rest of the events occurred during the ED visit. Drug reactions and diagnostic issues were the most common types of events.11 ,12

Using data from the 2006 National Hospital Ambulatory Medical Care Surveys and National Hospital Discharge Surveys in the USA, Burt et al concluded that 2.3 million ED visits (2.0% of the total) were made by patients who had recently been hospitalised. Moreover, they suggested that approximately 10% of those visits were for medical or surgical complications that may have been related to the hospitalisation.13 Forster et al determined that 19% of patients discharged from hospital experience an AE soon after discharge. Adverse drug events and complications from procedures were the most common types of AE.14 In a prospective study of patients discharged from a medical service in a Canadian hospital, 23% experienced an AE within 30 days of their discharge, of whom 12% required an ED visit.15 In the current study, most of the procedure-related AEs appear to be secondary to surgical complications and are thus likely to have had their genesis during a hospital admission.

There is limited literature on AEs resulting from treatment in primary or long-term care that are identified in the ED. In the Harvard Medical Practice Study, it was concluded that the majority of AEs that occurred prior to the index hospital admission took place in physicians' offices (7.7% of all AEs), at home (2.7%) or in an ambulatory care unit (1.4%).3 There were similar findings in New Zealand with 6.4% occurring in doctor's offices, 5.3% at home and 3.8% in a nursing home.5 In these hospital-based studies of AEs, those that may have occurred prior to hospitalisation, but not identified until the patient was admitted, represent the more severe end of the spectrum. That is, the AE was serious enough to warrant hospitalisation. The current study provides more information on the full spectrum, with the majority of patients with AEs (82.7%) being discharged from the ED. Those with device-related AEs were more likely to be admitted to hospital (36.5%), and those with drug-related AEs were more likely to be admitted to an intensive care unit (5.1%).

Drug-related AEs identified and treated in the ED have received greater attention in the literature.16–20 In a prospective study conducted in the ED of a tertiary care hospital in a large Canadian city, Zed et al concluded that one in 10 visits to the ED was for a drug-related AE.16 Capuano et al17 found that 1.2% of visits to 10 EDs in Italy were due to adverse drug events. In the US, Budnitz et al estimated that 2.5% of all unintentional injury presentations to EDs were due to adverse drug events.18 In the current study, less than 1% of the visits were drug-related. The variation may be due to a number of factors including differences in study design and methods, definition of a drug-related adverse event and regional incidence. It is likely that the methodology employed in the current study underestimates the total burden of ED visits related to harm from earlier healthcare interventions. In part, this is related to the nature of assigning a diagnosis using EDIS. For example, if a patient presents to the ED because of an intracerebral haemorrhage secondary to overcoagulation from warfarin, the ED diagnosis will likely be coded by the condition (haemorrhage), not the underlying or contributing factors. In a validation study of the screening criteria, it was determined that identification of drug-related events was significantly reduced if external cause of injury codes were not used, as was the case with the current study. For this reason, it is likely that the actual number of drug-related AEs during the study period was higher than identified.7 It is possible that some of the drug-related AEs included episodes of intentional self-harm; however, the potential for misclassification was minimised by reviewing all relevant text descriptions in EDIS with respect to intent.

Despite the likely underestimation, this method has several advantages over other methods of event detection. The information is routinely collected, readily available and accessible for low cost. Most importantly, data can be obtained without any impact on clinical staff. These attributes increase the utility for ongoing system-level monitoring. Although the current study examined EDIS data retrospectively, because of its real-time data collection capabilities, data queries can be developed to create an ongoing surveillance system. This novel approach expands the potential sources for relevant information on the overall burden of AEs to the healthcare system and can be used on a regular basis to inform development and enhance evaluation of targeted interventions. Many EDs in countries around the world use some form of electronic data capture such as EDIS, thus facilitating adoption of the methods.