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Patient Safety Definitions

A medical error is defined as the "failure of a planned action to be completed as intended or the use of a wrong plan to achieve an aim (1)." Most medical errors do not result in medical injury, although some do, and these are termed preventable adverse events. An adverse event is defined as "an injury caused by medical management rather than by the underlying disease or condition of the patient (1)." An ameliorable adverse event is defined as "an injury whose severity could have been substantially reduced if different actions or procedures had been performed or followed (2)." Many adverse events are neither preventable nor ameliorable. For example, an unavoidable adverse event can occur from an unknown drug reaction in a patient who has received the appropriate administration of a particular drug for the first time. However, if a drug reaction occurred in a patient who knowingly had a previous allergic reaction to that particular drug, the adverse event would be considered preventable and might be considered negligent (3). Negligence is considered present when the care provided failed to meet the standard of care reasonably expected of an average physician qualified to take care of the patient in question (4). An adverse event can also result from an error of omission, if a necessary procedure or intervention failed to be performed, leading to morbidity or mortality to the patient involved (5).

The fear of discipline or retribution from organizations providing employment and privileges prevents clinicians from acknowledging and managing errors in which they have been involved (6). Conclusions have been reached that most errors result from a complex interrelationship that involves multiple factors (7, 8). Rarely are errors due to negligence or misconduct of individual clinicians (7). The evidence overwhelmingly suggests that error in medicine is due primarily to systemic and organizational failures (7-9). Therefore, efforts should avoid punishing individual clinicians and focus on designing a system that would encourage detection and reporting of errors. Such a system would allow clinicians to learn from the mistakes of others and prevent them from repeating similar mistakes.


  1. Kohn L.T., Corrigan J.M., Donaldson M.S. (eds.): To Err is Human: Building a Safer Health System. Washington, DC: National Academy Press, 2000.
  2. Forster A.J., et al.: The incidence and severity of adverse events affecting patients after discharge from the hospital. Ann Intern Med138:161-167, Feb. 4, 2003.
  3. Leape L.L., et al.: The nature of adverse events in hospitalized patients. Results of the Harvard Medical Practice Study II. N Engl J Med324:377-384, Feb. 7, 1991.
  4. Brennan T.A., et al.: The nature of adverse events in hospitalized patients: Results of the Harvard Medical Practice Study I. N Engl J Med324:370-376, Feb. 7, 1991.
  5. Justiniani F.R.: Iatrogenic disease: An overview. Mt Sinai J Med51:210-214, Apr. 1984.
  6. Kapp MB. Medical mistakes and older patients: admitting errors and improving care. J Am Geriatr Soc. 2001;049:1361-1365.
  7. Leape LL. Can we make health care safe? In: Reducing Medical Errors and Improving Patient Safety: Success Stories From the Frontlines of Medicine. Accelerating Change Today (ACT) for America's Health. Washington, DC: National Coalition on Health Care and Boston: Institute for Healthcare Improvement; 2000:2-3.
  8. Wears RL, Leape LL. Human error in emergency medicine. Ann Emerg Med. 1999;34:370-372.
  9. Leape LL. Error in medicine. JAMA. 1994;272:1851-1857.