The Canadian Adverse Events Study: the incidence of adverse events among hospital patients in Canada

We read with interest the study by Baker et al. characterizing adverse events (AEs) in Canadian hospitals.(1) We applaud the investigators for performing this study and attempting to address the impact of AEs in institutional practice. However, despite the use of a methodology which has been used in other countries to characterize this problem, we feel the use of this methodology has underestimated the impact of adverse drug events in Canadian hospitals.

First, based on the 18 predefined criteria used in stage 1, adverse drug reaction (ADR) was the only unique criterion used to screen patients with possible drug-related adverse events. Using the pharmaceutical care model established by Hepler and Strand and practiced by many clinical pharmacists in the hospital setting, ADRs represents only one of eight possible drug-related problems (DRPs) that may constitute an AE.(2) Others DRPs such as too much/little drug, wrong drug, drug with no indication, untreated indication, non-compliance and drug interaction would not have been captured using initial screening criterion utilized in stage 1. As a result many patients, who may have been experiencing AEs secondary to medications for reasons other than ADRs, would not have been reviewed in stage 2, and not captured in the final data. We appreciate that some of the above DRPs may have been identified in stage 2, but the absence of clearly established a priori screening criteria for identifying patients with drug-related AEs other than ADRs may underestimate the incidence of drug-related AEs in Canadian hospitals.

Second, the impact of AEs in the emergency department (ED) was also not evaluated in this study, despite the substantial impact of drug- related ED visits.(3) In a well designed prospective trial, Tafeshi et al. estimated that 28% of all ED visits were drug-related of which 70% were deemed preventable.(4) Although we appreciate that the Canadian Adverse Events Study attempted to characterize the impact of AEs in hospitalized patients, the omission of a highly acute and heterogeneous patient population in the ED will contribute to underestimation of this problem in Canada. With the ongoing issues of ED overcrowding and longer wait times in our country, one can only postulate that the impact of AEs in the ED may be higher than ever and needs to be further evaluated.(5)

As the investigators clearly outline, this study is just the starting point for understanding the incidence of AEs and the burden of injury resulting from AEs in Canadian acute care hospitals. Further prospective research is clearly needed to more accurately characterize this problem and provide more accurate estimates on AEs in all patient care areas of Canadian hospitals. This will better enable us to efficiently establish systems and allocate key resources to reduce AEs for Canadian patients.

References

1. Baker GR, Norton PG, Flintoft V, Blaise R, Brown A, Cox J, et al. The Canadian Adverse Events Study: the incidence of adverse events among hospital patients in Canada. CMAJ 2004;170:1678-86.
2. Hepler CD, Strand LM. Opportunities and responsibilities in pharmaceutical care. Am J Hosp Pharm 1990;47:533-43.
3. Patel P, Zed PJ. Drug-related visits to the emergency department: how big is the problem? Pharmacotherapy 2002;22:915-23.
4. Tafreshi MJ, Melby MJ, Kaback KR, Nord TC. Medication-related visits to the emergency department: a prospective study. Ann Pharmacother 1999;33:1252-7.
5. Canadian Association of Emergency Physicians, National Emergency Nurses Affiliation. Joint position statement on emergency department overcrowding. Can J Emerg Med 2001;3:82-4

Conflict of Interest:

None declared

In a recent CMAJ study (1) there was a contrast of the rate of adverse events in Canada with those seen in other countries. Interestingly, the rate was lower in the United States and higher in Canada, Britain, Australia and New Zealand (1).

However, the differences between countries may be due more to differences in medical systems rather than in the actual quality of patient care. The US has a very different medical environment, partially because of the highly litigious nature of US culture (2). The fear of being sued may reduce the incidence of hindsight bias (3) in studies based in the United States since physicians may order more tests than are strictly necessary making it more difficult to “second guess” their decisions.

It is also the case that people of lower socioeconomic status consume more medical resources than the wealthy (4). It may be that economically disadvantaged people with complex ailments cannot obtain care in the US. As these people are more likely than average to be at risk of an adverse event, this difference might reduce the apparent AE rate in the US because these people never receive care at all.

So we should be cautious in doing comparisons between AE rates in the US and Canada. These differences could be partially explained by differences in the medical culture and may not be well captured by these types of studies.

J A Chris Delaney, MSc, Statistician, Department of Clinical Epidemiology, Royal Victoria Hospital, Montreal, Que

Mark Palko, MSc, Statistician, Atlanta, GA, USA

Andrei SP Brennan, MA, Research Ethics Quality Assurance Officer, Research Institute of the McGill University Health Centre, Montréal, Que

1. Baker GR, Norton PG, Flintoft V, Blais R, Brown A, Cox J, Etchells E, Ghali WA, Hebert P, Majumdar SR, O'Beirne M, Palacios-Derflingher L, Reid RJ, Sheps S and Tamblyn R. The Canadian Adverse Events Study: the incidence of adverse events among hospital patients in Canada. CMAJ. 2004;170(11):1678-86.

2.Abood S and Tehan T. Medical malpractice crisis. Am J Nurs. 2003 ;103(5):29.

3. Hebert PC, Levin AV and Robertson G. Bioethics for clinicians: 23. Disclosure of medical error. CMAJ. 2001;164(4):509-13.

4. Roos NP, Forget E, Walld R and MacWilliam L. Does universal comprehensive insurance encourage unnecessary use? Evidence from Manitoba says "no". CMAJ. 2004;170(2):209-14.

Conflict of Interest:

None declared