An elderly woman with ‘heart failure’: Cognitive biases and diagnostic error

CASE CONTINUED: NO IMPROVEMENT OVER 3 DAYS

The night float resident, who has six other admissions this night, cannot ask the resident who evaluated this patient in the emergency department for further information because the shift has ended. The patient’s son left at the time of admission and is not available when the patient arrives on the medical ward.

The night float resident quickly examines the patient, enters admission orders, and signs the patient out to the intern and resident who will be caring for her during her hospitalization. The verbal handoff notes that the history was limited due to a language barrier. The initial problem list includes heart failure without a differential diagnosis, but notes that an elevated pro-BNP and chest radiograph confirm heart failure as the likely diagnosis.

Several hours after the night float resident has left, the resident presents this history to the attending physician, and together they decide to order her regular at-home medications, as well as deep vein thrombosis prophylaxis and echocardiography. In writing the orders, subcutaneous heparin once daily is erroneously entered instead of low-molecular-weight heparin daily, as this is the default in the medical record system. The tired resident fails to recognize this, and the pharmacist does not question it.

Over the next 2 days, the patient’s cough and shortness of breath persist.

After the attending physician dismisses their concerns, the residents do not bring up their idea again

On hospital day 3, two junior residents on the team (who finished their internship 2 weeks ago) review the attending radiologist’s interpretation of the chest radiograph. Unflagged, it confirms the resident’s interpretation but notes ill-defined, scattered, faint opacities. The residents believe that an interstitial pattern may be present and suggest that the patient may not have heart failure but rather a primary pulmonary disease. They bring this to the attention of their attending physician, who dismisses their concerns and comments that heart failure is a clinical diagnosis. The residents do not bring this idea up again to the attending physician.

That night, the float team is called by the nursing staff because of worsening oxygenation and cough. They add an intravenous corticosteroid, a broad-spectrum antibiotic, and an inhaled bronchodilator to the patient’s drug regimen.

How do cognitive errors predispose physicians to diagnostic errors?

When errors in diagnosis are reviewed retrospectively, cognitive or “thinking” errors are generally found, especially in nonprocedural or primary care specialties such as internal medicine, pediatrics, and emergency medicine.^16,17

A widely accepted theory on how humans make decisions was described by the psychologists Tversky and Kahneman in 1974¹⁸ and has been applied more recently to physicians’ diagnostic processes.¹⁹ Their dual process model theory states that persons with a requisite level of expertise use either the intuitive “system 1” process of thinking, based on pattern-recognition and heuristics, or the slower, more analytical “system 2” process.²⁰ Experts disagree as to whether in medicine these processes represent a binary either-or model or a continuum²¹ with relative contributions of each process determined by the physician and the task.

What are some common types of cognitive error?

Experts agree that many diagnostic errors in medicine stem from decisions arrived at by inappropriate system 1 thinking due to biases. These biases have been identified and described as they relate to medicine, most notably by Croskerry.²²

Several cognitive biases are illustrated in our clinical scenario:

The framing effect occurred when the emergency department resident listed the patient’s admitting diagnosis as heart failure during the clinical handoff of care.

Anchoring bias, as defined by Croskerry,²² is the tendency to lock onto salient features of the case too early in the diagnostic process and then to fail to adjust this initial diagnostic impression. This bias affected the admitting night float resident, primary intern, resident, and attending physician.

Diagnostic momentum, in turn, is a well-described phenomenon that clinical providers are especially vulnerable to in today’s environment of “copy-and-paste” medical records and numerous handovers of care as a consequence of residency duty-hour restrictions.²³

Availability bias refers to commonly seen diagnoses like heart failure or recently seen diagnoses, which are more “available” to the human memory. These diagnoses, which spring to mind quickly, often trick providers into thinking that because they are more easily recalled, they are also more common or more likely.

Confirmation bias. The initial working diagnosis of heart failure may have led the medical team to place greater emphasis on the elevated pro-BNP and the chest radiograph to support the initial impression while ignoring findings such as weight loss that do not support this impression.

Blind obedience. Although the residents recognized the possibility of a primary pulmonary disease, they did not investigate this further. And when the attending physician dismissed their suggestion, they thus deferred to the person in authority or with a reputation of expertise.

Overconfidence bias. Despite minimal improvement in the patient’s clinical status after effective diuresis and the suggestion of alternative diagnoses by the residents, the attending physician remained confident—perhaps overconfident—in the diagnosis of heart failure and would not consider alternatives. Overconfidence bias has been well described and occurs when a medical provider believes too strongly in his or her ability to be correct and therefore fails to consider alternative diagnoses.²⁴

Despite succumbing to overconfidence bias, the attending physician was able to overcome base-rate neglect, ie, failure to consider the prevalence of potential diagnoses in diagnostic reasoning.

Each of these biases, and others not mentioned, can lead to premature closure, which is the unfortunate root cause of many diagnostic errors and delays. We have illustrated several biases in our case scenario that led several physicians on the medical team to prematurely “close” on the diagnosis of heart failure (Table 1).

CASE CONTINUED: SURPRISES AND REASSESSMENT

On hospital day 4, the patient’s medication lists from her previous hospitalizations arrive, and the team is surprised to discover that she has been receiving infliximab for the past 3 to 4 months for her rheumatoid arthritis.

Additionally, an echocardiogram that was ordered on hospital day 1 but was lost in the cardiologist’s reading queue comes in and shows a normal ejection fraction with no evidence of elevated filling pressures.

Computed tomography of the chest reveals a reticular pattern with innumerable, tiny, 1- to 2-mm pulmonary nodules. The differential diagnosis is expanded to include hypersensitivity pneumonitis, lymphoma, fungal infection, and miliary tuberculosis.

How do faulty systems contribute to diagnostic error?

It is increasingly recognized that diagnostic errors can occur as a result of cognitive error, systems-based error, or quite commonly, both. Graber et al¹⁷ analyzed 100 cases of diagnostic error and determined that while cognitive errors did occur in most of them, nearly half the time both cognitive and systems-based errors contributed simultaneously.¹⁷ Observers have further delineated the importance of the systems context and how it affects our thinking.²⁵

In this case, the language barrier, lack of availability of family, and inability to promptly utilize interpreter services contributed to early problems in acquiring a detailed history and a complete medication list that included the immunosuppressant infliximab. Later, a systems error led to a delay in the interpretation of an echocardiogram. Each of these factors, if prevented, would have presumably resulted in expansion of the differential diagnosis and earlier arrival at the correct diagnosis.

CASE CONTINUED: THE PATIENT DIES OF TUBERCULOSIS

The patient is moved to a negative pressure room, and the pulmonary consultants recommend bronchoscopy. During the procedure, the patient suffers acute respiratory failure, is intubated, and is transferred to the medical intensive care unit, where a saddle pulmonary embolism is diagnosed by computed tomographic angiography.

One day later, the sputum culture from the bronchoscopy returns as positive for acid-fast bacilli. A four-drug regimen for tuberculosis is started. The patient continues to have a downward course and expires 2 weeks later. Autopsy reveals miliary tuberculosis.

What is the frequency of diagnostic error in medicine?

Diagnostic error is estimated to have a frequency of 10% to 20%.²⁴ Rates of diagnostic error are similar irrespective of method of determination, eg, from autopsy,³ standardized patients (ie, actors presenting with scripted scenarios),²⁶ or case reviews.²⁷ Patient surveys report patient-perceived harm from diagnostic error at a rate of 35% to 42%.^28,29 The landmark Harvard Medical Practice Study found that 17% of all adverse events were attributable to diagnostic error.³⁰

Diagnostic error is the most common type of medical error in nonprocedural medical fields.³¹ It causes a disproportionately large amount of morbidity and death.

Diagnostic error is the most common cause of malpractice claims in the United States. In inpatient and outpatient settings, for both medical and surgical patients, it accounted for 45.9% of all outpatient malpractice claims in 2009, making it the most common reason for medical malpractice litigation.³² A 2013 study indicated that diagnostic error is more common, more expensive, and two times more likely to result in death than any other category of error.³³