2. Overview of Adverse Events

In this lesson, we look at the prevalence of adverse events in the Canadian healthcare system, and try to understand the reasons they happen. We also consider the impact adverse events can have on patients, their families, and on healthcare providers.

(To read along click here.)


  • Adverse event: an incident of harm that occurs during the course of care which is not related to a patient’s underlying medical condition. Adverse events are typically referred to as either preventable or unpreventable.
  • Medical error: an act that, given the information available and the patient’s condition at the time, was performed incorrectly or wrongly in those circumstances, resulting in an adverse event or near miss.
  • Near miss: an event with the potential for harm, but because it did not reach the patient due to intervention or good fortune, no harm was done.

According to the Canadian Medical Protective Association (CMPA), adverse events are sometimes referred to as “medical errors,” but the two terms are quite different. “‘Error’ carries with it a sense of blame or fault that may be inappropriate, especially before all circumstances and facts about a case are known.” Because of this, both the CMPA and the Canadian Patient Safety Institute (CPSI) suggest avoiding the term “error.

Prevalence of Adverse Events in Canada

A great deal of research into the prevalence of adverse events has been conducted worldwide. In Canada, The Canadian Adverse Events Study, conducted by Ross Baker and Peter Norton, looked at patients who received hospital care in the year 2000. The study found that adverse events occurred in 7.5 per cent of every one hundred hospital admissions. In other words, out of over 2.5 million hospital admissions, 185,000 adverse events occurred, and close to 70,000 of them were classified as preventable. Because the Baker and Norton study did not include adverse events occurring in the fields of obstetrical care, mental health care and outpatient care, these numbers are thought to be lower than the reality.

Why Adverse Events Happen

Quite often, the public tends to assume that adverse events occur because individual healthcare providers make mistakes. In fact, these types of errors are very rare, accounting for only one per cent of all adverse events. The majority of adverse events occur, not because of one person’s error, but because of a complex healthcare system with many moving parts.

One way to understand how system-led adverse events occur is with the help of psychologist James Reason’s “Swiss cheese model of system accidents.” In his study Human error: models and management, Reason explains that organizations put defences, or barriers, in place to prevent harm from occurring. Usually, these defences succeed. But each defence is imperfect, containing many holes, like a slice of Swiss cheese. The presence of holes in any one slice does not usually result in a bad outcome. But when the holes in a number of slices line up, that’s when harm can occur.

Patients and their families are particularly vulnerable to harm during transfers of care. Even during a short period of care a patient may be treated by several different healthcare providers in a variety of settings. The chances of safety “holes” lining up increases considerably.

Impact on Patients

Because patients and their families expect safe, effective care, an adverse event can destroy their sense of trust in the healthcare providers who treated them, and in the healthcare system. Patients often deal with:

  • anger and anxiety
  • a need to clearly understand what happened
  • a need to know how they will be affected moving forward
  • a need to know what will be done to help them

Their families may deal with the same range of emotions, along with a sense of guilt about not having prevented the adverse event from occurring.

Tom Delbanco and Sigall Bell describe the emotional response of patients in their article Guilty, Afraid, and Alone—Struggling with Medical Error:

“In interviews that our group conducted for a documentary film, patients and families that had been affected by medical error illuminated a number of themes. Three of these themes have been all but absent from the literature. First, though it is well recognized that clinicians feel guilty after medical mistakes, family members often have similar or even stronger feelings of guilt. Second, patients and their families may fear further harm, including retribution from health care workers, if they express their feelings or even ask about mistakes they perceive. And third, clinicians may turn away from patients who have been harmed, isolating them just when they are most in need.”

Impact on Healthcare Providers

The emotional impact that adverse events can have on healthcare providers is beginning to be better understood and documented. In his paper Medical error, incident investigation and the second victim: doing better but feeling worse? Albert Wu describes healthcare providers involved in medical errors as “second victims” and suggests that they go through symptoms similar to the “first victims,” patients and their families.

He writes, “Signs and symptoms are similar to those in acute stress disorder, including initial numbness, detachment, and even depersonalisation, confusion, anxiety, grief and depression, withdrawal or agitation, and re-experiencing of the event. Added symptoms related to medical errors include shame, guilt, anger and self-doubt. Lack of concentration and poor memory are also common, and the affected person may be significantly impaired in performing usual roles. These symptoms may last days to weeks. A few go on to suffer long-term consequences, similar to post-traumatic stress disorder, that include re-experiencing the original trauma through flashbacks and nightmares, avoidance of situations associated with the trauma, increased arousal including sleep disturbance and irritability. These symptoms often result in significant functional impairment. Some healthcare workers leave their profession and a few even commit suicide because of the experience.”

Wu points out that healthcare providers can be affected:

  • by the adverse event itself
  • by the reactions of the patient or family
  • by the reactions of other medical colleagues—either sympathetic or unsympathetic

After an adverse event, Wu says, health professionals need to be supported both professionally and personally.

Connect to Save Progress

You are not currently logged in. Create an account to keep track of your progress.

If you already have an account, please .