Medical Errors

Definitions and Concepts

Key definitions and concepts-many adapted from systems-based research on error prevention in other industries-underlie the current efforts to understand and prevent medical errors. An error is defined by the IOM as either the failure of a planned action to be completed as intended or the use of a wrong plan to achieve an aim. The former is referred to as an error of execution and the latter as an error of planning. This formulation is based on the work of James Reason and others who extensively studied accidents in aviation and other industries.

Errors of execution are due either to slips or lapses. A slip is an observable error of execution, such as when a surgeon inadvertently cuts the wrong tissue. A lapse is unobservable, as when an internist forgets to order antibiotics for a patient with pneumonia after intending to do so. In both cases the physician knew what the right thing was to do and intended to do it. In contrast, errors of planning are mistakes in that the actions proceeded as planned but the plan was wrong.

Errors may be classified as biomedical or contextual, the former occurring because of inattention to processes occurring within the boundary of the skin and the latter from inattention to processes expressed outside that boundary-that is, processes that form the context of a patient's illness. Failing to prescribe a medication that effectively treats a serious condition is a biomedical error. Prescribing a medication that a patient cannot afford when a less costly effective medication is available is a contextual error. In both instances, the patient does not obtain the necessary therapy: in the first, from a failure to attend correctly to the patient's disease and, in the second, from inattention to the context surrounding the disease.

Fortunately, not all errors result in an adverse event, the term for an injury that is caused by medical mismanagement. Neglecting to wash one's [Page 731]hands prior to examining a postsurgical wound is an error, for instance, but in most cases this does not result in a wound infection because of the patients' inherent capacity to fight off infection. Conversely, adverse events may occur despite flawless care: A patient's surgical wound may become infected despite excellent sterile technique. Harm that is specifically attributable to error is termed a preventable adverse event.

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