Heuristics and Medical Decision Making

Clinical Grand RoundsAug. 15, 2007Dr. Shounak Das

Medical Errors

• Classification of Medical Errors:1. Patient factors2. Outside systems3. Access: EMS, transfers4. Triage5. Human error6. Teamwork failure7. Local environment: the microsystem8. Hospital environment: the macrosystem9. Hospital administration and third party factors10. Community, society, health care policy

Medical Errors

• Human Errors: Cognitive error Skill-set error Task-based error Personal impairment

Heuristics

• Heuristics

+ve: increase efficiency

-ve: potential source of diagnostic error

(hyu’-ris-tiks)

= an aid to learning or problem solving by experimental and especially trial-and-error methods; cognitive “short cuts” or “rules of thumb”

Heuristics

• Types of heuristics:1) Representative heuristic2) Sampling heuristic3) Saliency heuristic4) Simple weighting heuristic5) Availability heuristic6) Anchoring heuristic7) Framing effect8) Blind obedience9) Premature closure

Representative Heuristic

• Representative heuristic = how well signs + symptoms fit a “representative” picture of a particular disease

• ignores pre-test probabilities – i.e. the differential diagnosis includes pneumonia which is far likelier

i.e.: a patient presents with pleuritic chest pain, dyspnea, and a low-grade fever

• diagnosis = PE

Sampling Heuristic

• Sampling heuristic = basing pre-test probabilities on personal experience i.e.: an intern who trains at a tertiary academic center sees 3 cases of granulomatous vasculitis during her medicine rotation

• a patient presents with dyspnea + wheezing

• overestimates rare disorder (gran. vasc.) and underestimates common disorder (asthma)

• diagnosis = granulomatous vasculitis!

Saliency Heuristic

• Saliency heuristic = focusing on a “striking” point, feature, or highlight recency rarity novel clinical features “burned” by missing a case

Simple Weighting Heuristic

• Simple weighting heuristic = assigning equal value to all factors

i.e.: a patient presents with chest pain, a strong +ve family history of CAD, nausea, and diaphoresis

• chest pain + strong +ve family history of CAD = ?acute coronary syndrome

• nausea + diaphoresis = ?gastroenteritis

Availability Heuristic • Availability heuristic = focusing on

diagnoses which are easily available common or recently encountered problems

• i.e.: are there more words in the English language that begin with the letter “r” or have the letter “r” as their third letter?

• people tend to think that there are more words that begin with “r” because they’re easier to “r”ecall even though the true ratio is almost 2:1 the other way

Anchoring Heuristic

• Anchoring heuristic = sticking to first impression i.e. people thinking that their arthritis

symptoms are worse when the weather’s bad ̶ this may have happened on a single occasion, but people remember it and forget the other times they’ve had symptoms on sunny days

Framing Effect

• Framing effect = coming to different conclusions depending on how the information is presented i.e. more people chose radiation

treatment over surgery for lung cancer if it was presented as giving them a 90% chance of surviving than when it was presented as giving them a 10% chance of dying

Blind Obedience

• Blind obedience = obeying another authority attending physician or consultant prior diagnoses lab or x-ray finding

Premature Closure

• Premature closure = stop thinking of alternative diagnoses or explanations (this is a type of anchoring bias) premature closure is paradoxically more

compelling when there are several choices vs. 1 choice: in one study –clinicians chose surgery over medications to treat hip pain (72% vs. 53%) when 2 alternative medications were offered as opposed to just 1 medication

*reminder to self – make a joke about orthopedic surgeons

Case Study

• Mr. Davis is a 65 year-old African American man who presented to the ER of an academic medical center with back pain, general body aches, and a sore throat. He was given a diagnosis of a “viral syndrome” and sent home on ibuprofen.

Case Study

• Availability heuristic “viral syndromes” are common, so

alternative diagnoses are not considered• Anchoring heuristic

once a diagnosis is made, other data are ignored (?back pain)

Case Study

• Mr. Davis ends up having a positive blood culture for Staph. aureus

Case Study

• Here, if the data were framed as a case of: “pharyngitis, myalgias, and a blood culture positive for Staphylococcus,” one might stick with the diagnosis of a viral syndrome and explain away the positive blood culture as a skin contaminant. This would be an example of both the framing effect, and the anchoring heuristic (consider how the differential diagnosis changes if the case is presented as “fever, back pain, and hematuria”).

Case Study

• However, Mr. Davis is called and told to come back to the ER

Case Study

• Mr. Davis is admitted to hospital and started on vancomycin. He has a normal transthoracic echocardiogram. Plain films of his cervical and lumbar spines just show degenerative changes. He has a long history of moderately severe lichen planus, and it is assumed that this is the source of his infection. The Staph. comes back methicillin-sensitive, so he is switched to nafcillin, and discharged home in 4 days. He is instructed to complete a 2-week course of dicloxacillin, and to follow-up with his PCP in 2-3 weeks.

Case Study• In this case, blind obedience to the findings of

a normal echocardiogram and negative plain films have resulted in the premature closure of both endocarditis and osteomyelitis as possible diagnoses.

• Neither test has sufficient sensitivity to completely rule out these diagnoses.

• Consider that Staph. bacteremia is unusual in a non-diabetic patient. Also, lichen planus leading to bacteremia is unusual. One also wonders why this situation has never developed previously when Mr. Davis has such a long history of lichen planus.

Case Study

• Mr. Davis sees his PCP as instructed. Since being discharged, symptoms of generalized fatigue, neck and back pain have recurred. He also reports tingling sensations in his fingers and difficulty urinating. Blood cultures are drawn, and he is sent home.

Case Study

• One of 2 surveillance blood cultures is positive for S. aureus, so Mr. Davis is readmitted to hospital.

• This time he has an MRI of the spine, and is diagnosed with osteomyelitis at C6-7 with an epidural abscess and impingement of the spinal cord. He declines surgery and is instead treated with 6 weeks of IV antibiotics.

Case Study• The PCP may have fallen trap to the following

heuristics: Blind obedience

accepting the diagnoses given to him by Mr. Davis’ physicians in the hospital

Anchoring heuristic sticking with the initial diagnosis of Staph. bacteremia

secondary to lichen planus Sampling heuristic

he may never have seen a case of spinal osteomyelitis with an epidural abscess, so he does not consider this diagnosis

Simple weighting heuristic giving fatigue equal weight with difficulty urinating in Mr.

Davis’ symptom complex

Case Study

• A traditional critique of this case might be to say: “never forget osteomyelitis”

• Looking at the case from the perspective of cognitive psychology allows for analysis of decision making, and where shortcuts can lead one down the wrong path

• A seasoned clinician can still rely on her heuristics, but awareness of them can add safeguards to the diagnostic process

Using Follow-up To Overcome Cognitive Fallibilities

• Follow-up is a feasible strategy to prevent cognitive shortcuts from causing harm

• Follow-up would give time to read up on a subject to counteract the availability heuristic

• Follow-up would also give time and distance from a case to counteract the anchoring heuristic and premature closure

• One caveat to follow-up is that delay in diagnosis of certain conditions can cause irreparable damage

Some Corrective Strategies to Counteract Heuristics

References

1. Redelmeier DA. The cognitive psychology of missed diagnoses. Ann Int Med 2005; 142: 115-120.

2. Redelmeier DA. Problems for clinical judgement: introducing cognitive psychology as one more basic science. CMAJ 2001; 164: 358-360.

3. Elstein AS. Heuristics and biases: selected errors in clinical reasoning. Acad Med 1999; 74: 791-794.

4. Kohn LT et al. eds. “To err is human: building a safer health system.” Washington, DC: National Academy Press; 1999.

5. Redelmeier DA, Shafir E. Medical decision making in situations that offer multiple alternatives. JAMA. 1995; 273: 302-5.