Original Research

Classification of medical errors and preventable adverse events in primary care: A synthesis of the literature

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However, we found a striking gap in the literature of an absence of discussion of the contribution of patient factors to medical errors, despite a logic suggesting these are important issues.21,22 A new model of patient safety dynamics should incorporate features of these models and add patient issues. Our proposed “Hourglass” model, derived from the classification system, incorporates 4 potential components of preventable adverse events in the primary care setting: 2 relating mainly to the primary health care system (process errors and patient safety factors) and 2 relating mainly to patients (patient risk factors for adverse events and patient-controlled patient safety factors; Figure). At the top of the hourglass, patient encounters enter like pieces of sand that flow through a health care system full of process errors that happen regularly. But, as in the Swiss Cheese model, there are barriers (patient safety factors) stopping these process errors from becoming preventable adverse events. Unfortunately, these barriers sometimes allow errors to slip through and a bad outcome results. Luckily, only a small number of patient encounters likely exits the primary health care system with a preventable adverse event, as demonstrated by the narrow part of the hourglass.

Outside the doctor’s office, factors in the patient’s milieu influence the probability of a preventable adverse event occurring. We postulate an experience analogous to that within the health care system. There are more factors increasing a patient’s likelihood of suffering a preventable adverse event,23 but there are also patient-controlled factors serving as barriers against errors and their consequences. These are not well researched24 but occur, for example, when a patient receives a blue pill from the pharmacy that had been pink in the past. The patient may prevent an adverse event by not taking the pill and double-checking with the clinician and pharmacist.

The order in which various process errors and safety factors interact with each other likely varies with each encounter and episode. Interactions within the classification suggest that, for any episode of disease or preventive care, the hourglass gets shaken and turned over numerous times as the health care system and patient factors interact with each other at multiple levels.

Future research needs

The literature review that led to our classification system and the proposed model of interaction have identified specific areas for future study. These include assessing patients’ perspectives, investigating prevalence and causality, and testing interventions designed to improve patient safety. The current medical literature based primarily on physician reports describes events that are meaningful to the physician half of the dyad between patient and physician. Patients’ opinions about what constitutes error and the role of patients as active participants in error and safety are unknown,24 although preliminary studies are currently underway.25

No published studies to date have explored the prevalence of preventable adverse events and errors in primary care. Physician self-report biases reporting toward remembered events and errors. In addition, medical error studies to date have not directly studied causal links between errors and adverse events.26,27 Observational and epidemiologic studies incorporating multiple methods may be necessary to ascertain and compare all components of the medical error equation: the amount of harm done, the preventable adverse events and near misses, the process errors, and the error-free functioning of the health care system. Although observational studies have assessed adverse events in a hospital setting28 and described primary care practices,29 they have not been used to assess preventable adverse events in the primary care setting.

This literature review and synthesis may have missed some studies that merited inclusion. Only English-language studies were included. Studies pertaining to specific diseases, diagnoses, or treatments or from non-primary care settings may have shed light on the interaction of errors, adverse events, and harm but could not have helped in defining a classification system for primary care errors. The small number of studies available and their small sample sizes also limit the depth and breadth of derived classification components.

Decreasing medical errors and increasing patient safety are important parts of quality health care.30 Currently, the research agenda aiming to identify effective error reduction strategies appears to be based more on ease of study subject or accessibility of patients than on the severity or importance of the problem.31 By categorizing process errors and preventable adverse events and studying their relations more thoroughly and by adding the patient’s perspective, interventions can be designed that address the most common and the most serious of preventable adverse events in primary care.

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