Active Error (or Active Failure)
The terms active and latent as applied to errors were coined by Reason. Active errors occur at the point of contact between a human and some aspect of a larger system (e.g., a human–machine interface). They are generally readily apparent (e.g., pushing an incorrect button, ignoring a warning light) and almost always involve someone at the frontline. Active failures are sometimes referred to as errors at the sharp end, figuratively referring to a scalpel. In other words, errors at the sharp end are noticed first because they are committed by the person closest to the patient. This person may literally be holding a scalpel (e.g., an orthopedist operating on the wrong leg) or figuratively be administering any kind of therapy (e.g., a nurse programming an intravenous pump) or performing any aspect of care. Latent errors (or latent conditions), in contrast, refer to less apparent failures of organization or design that contributed to the occurrence of errors or allowed them to cause harm to patients. To complete the metaphor, latent errors are those at the other end of the scalpel—the blunt end—referring to the many layers of the health care system that affect the person "holding" the scalpel.

Adverse Drug Event (ADE)
An adverse event (i.e., injury resulting from medical care) involving medication use.

  • anaphylaxis to penicillin
  • major hemorrhage from heparin
  • aminoglycoside-induced renal failure
  • agranulocytosis from chloramphenicol
As with the more general term adverse event, the occurrence of an ADE does not necessarily indicate an error or poor quality of care. ADEs that involve an element of error (either of omission or commission) are often referred to as preventable ADEs. Medication errors that reached the patient but by good fortune did not cause any harm are often called potential ADEs. For instance, a serious allergic reaction to penicillin in a patient with no prior such history is an ADE, but so is the same reaction in a patient who has a known allergy history but receives penicillin due to a prescribing oversight. The former occurrence would count as an adverse drug reaction or non-preventable ADE, while the latter would represent a preventable ADE. If a patient with a documented serious penicillin allergy received a penicillin-like antibiotic but happened not to react to it, this event would be characterized as a potential ADE.

An ameliorable ADE is one in which the patient experienced harm from a medication that, while not completely preventable, could have been mitigated. For instance, a patient taking a cholesterol-lowering agent (statin) may develop muscle pains and eventually progress to a more serious condition called rhabdomyolysis. Failure to periodically check a blood test that assesses muscle damage or failure to recognize this possible diagnosis in a patient taking statins who subsequently develops rhabdomyolysis would make this event an ameliorable ADE: harm from medical care that could have been lessened with earlier, appropriate management. Again, the initial development of some problem was not preventable, but the eventual harm that occurred need not have been so severe, hence the term ameliorable ADE.

Adverse Drug Reaction
Adverse effect produced by the use of a medication in the recommended manner—i.e., a drug side effect. These effects range from nuisance effects (e.g., dry mouth with anticholinergic medications) to severe reactions, such as anaphylaxis to penicillin. Adverse drug reactions represent a subset of the broad category of adverse drug events—specifically, they are non-preventable ADEs.

Adverse Event
Any injury caused by medical care.

  • pneumothorax from central venous catheter placement
  • anaphylaxis to penicillin
  • postoperative wound infection
  • hospital-acquired delirium (or "sundowning") in elderly patients
Identifying something as an adverse event does not imply "error," "negligence," or poor quality care. It simply indicates that an undesirable clinical outcome resulted from some aspect of diagnosis or therapy, not an underlying disease process. Thus, pneumothorax from central venous catheter placement counts as an adverse event regardless of insertion technique. Similarly, postoperative wound infections count as adverse events even if the operation proceeded with optimal adherence to sterile procedures, the patient received appropriate antibiotic prophylaxis in the perioperative setting, and so on. (See also iatrogenic).

View Patient Safety Primer
Adverse Events after Hospital Discharge
See Primer. Being discharged from the hospital can be dangerous for patients. Nearly 20% of patients experience an adverse event in the first 3 weeks after discharge, including medication errors, health care–associated infections, and procedural complications.

Anchoring Error (or Bias)
Refers to the common cognitive trap of allowing first impressions to exert undue influence on the diagnostic process. Clinicians often latch on to features of a patient's presentation that suggest a specific diagnosis. Often, this initial diagnostic impression will prove correct, hence the use of the phrase anchoring heuristic in some contexts, as it can be a useful rule of thumb to "always trust your first impressions." However, in some cases, subsequent developments in the patient's course will prove inconsistent with the first impression. Anchoring bias refers to the tendency to hold on to the initial diagnosis, even in the face of disconfirming evidence.

The Acute Physiologic and Chronic Health Evaluation (APACHE) scoring system has been widely used in the United States. APACHE II is the most widely studied version of this instrument (a more recent version, APACHE III, is proprietary, whereas APACHE II is publicly available); it derives a severity score from such factors as underlying disease and chronic health status.(1,2) Other points are added for 12 physiologic variables (ie, hematocrit, creatinine, Glasgow Coma Score, mean arterial pressure) measured within 24 hours of admission to the ICU. The APACHE II score has been validated in several studies involving tens of thousands of ICU patients.

1. Knaus WA, Draper EA, Wagner DP, Zimmerman JE. APACHE II: a severity of disease classification system. Crit Care Med. 1985;13:818-29.[ go to PubMed ]

2. Knaus WA, Wagner DP, Zimmerman JE, Draper EA. Variations in mortality and length of stay in intensive care units. Ann Intern Med. 1993;118:753-61.[ go to PubMed ]

Authority Gradient
Refers to the balance of decision-making power or the steepness of command hierarchy in a given situation. Members of a crew or organization with a domineering, overbearing, or dictatorial team leader experience a steep authority gradient. Expressing concerns, questioning, or even simply clarifying instructions would require considerable determination on the part of team members who perceive their input as devalued or frankly unwelcome. Most teams require some degree of authority gradient; otherwise roles are blurred and decisions cannot be made in a timely fashion. However, effective team leaders consciously establish a command hierarchy appropriate to the training and experience of team members. Authority gradients may occur even when the notion of a team is less well defined. For instance, a pharmacist calling a physician to clarify an order may encounter a steep authority gradient, based on the tone of the physician's voice or a lack of openness to input from the pharmacist. A confident, experienced pharmacist may nonetheless continue to raise legitimate concerns about an order, but other pharmacists might not.

Availability Bias (or Heuristic)
Refers to the tendency to assume, when judging probabilities or predicting outcomes, that the first possibility that comes to mind (i.e., the most cognitively "available" possibility) is also the most likely possibility. For instance, suppose a patient presents with intermittent episodes of very high blood pressure. Because episodic hypertension resembles textbook descriptions of pheochromocytoma, a memorable but uncommon endocrinologic tumor, this diagnosis may immediately come to mind. A clinician who infers from this immediate association that pheochromocytoma is the most likely diagnosis would be exhibiting availability bias. In addition to resemblance to classic descriptions of disease, personal experience can also trigger availability bias, as when the diagnosis underlying a recent patient's presentation immediately comes to mind when any subsequent patient presents with similar symptoms. Particularly memorable cases may similarly exert undue influence in shaping diagnostic impressions.

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