SGIM FORUM 2011; 34(11)

CHALK TALK Thinking about Thinking: Medical Decision Making Under the Microscope Christiana Iyasere, MD, and Douglas Wright, MD, PhD

Drs. Iyasere and Wright are faculty in the Inpatient Clinician Educator Service of the Department of Medicine at Massachusetts General Hospital in Boson, MA.

ase: A 36-year-old African-Ameri- athletic—he graduated from college than 10 seconds and says “20,160” C can woman, healthy except for with a degree in physics and has before moving breezily along with treated hypothyroidism, visits you in completed several triathlons. Neil is a her coffee. Having Katrina’s input, are clinic complaining of six months of fa- veteran of the US Navy, where he you tempted to change your answer tigue and progressive shortness of served as fleet naval aviator and land- to questions 3a and 3b? Go ahead, breath with exertion. You thoroughly ing signal officer. Is Neil more likely to admit it. Aren’t you now more confi- interview and examine the patient. be: a) a librarian or b) an astronaut? dent that the correct answer is that Physical examination reveals conjunc- Question 2: Jot down a list of the product is closest to 20,000? tival pallor and dullness to percussion English words that begin with the let- Question 5: You have known one third of the way up both lung ter “r” (e.g. rooster). Next, jot down your medical school roommate Jus- fields. Something tells you to ask her a list of words that have an r in the tice for four years. You trust him ab- about skin rashes, and you learn that third position (e.g. forsake). Is the let- solutely and have confided in him she has had worsening sun sensitiv- ter r more likely to occur at the start many times. Justice is always ity for the past year. A light bulb goes of words or in the third position? smartly dressed, and he loves to on in your mind. Along with routine Question 3a: In no more than 10 shop. You are at a mall shopping with labs and a TSH, you order an antinu- seconds, estimate the product 1 x 2 Justice when you briefly notice him clear antibody test and a chest X-ray. x 3 x 4 x 5 x 6 x 7 x 8 = n, and an- down another aisle putting what You find the hematocrit to be 25%, swer quickly whether n is closer to a) looks like a belt into his knapsack. (In the TSH normal, and the ANA to be 1,000; b) 10,000; c) 20,000; or d) truth you can’t tell whether he was positive at 1:1024. The chest film 50,000. Mark your answer and move putting the belt into the knapsack or shows large bilateral pleural effu- immediately to the next question. taking it out, and if pressed you sions. You make the diagnosis of sys- Question 3b: Now, wipe your couldn’t be 100% certain that it was temic lupus erythematosis. mind’s “slate” clean, and again in a belt. You think nothing of this.) A Elementary, right? But how did no more than 10 seconds, start in few minutes later you are shocked to you arrive at this diagnosis as op- reverse order, and estimate the find two security guards interrogating posed to another? Coming to an ac- product 8 x 7 x 6 x 5 x 4 x 3 x 2 x 1 Justice, accusing him of stealing a 1 curate diagnosis is based on pattern = n. Answer quickly whether n is belt. Justice insists that the belt was recognition, algorithmic thinking, and closer to a) 1,000; b) 10,000; c) already in his bag. It seems odd that deductive reasoning—all enriched by 20,000; or d) 50,000. Resist the the belt still has the price tag on it, experience. We rely on these tools to temptation to calculate the exact but you trust Justice, assume that he parse through all the information that answer. is telling the truth, and stand by him is presented to us. Making accurate Question 4: As it happens, your in his argument with the security diagnoses with incomplete and often friend Katrina (a former Russian child guards. Thinking back, you wonder contradictory information in limited chess champion and math whiz) how Justice affords the expensive time is the playing field of the in- passes by the Starbucks lounge chair clothes that he wears, given his ternist. However, the very processes where you sit answering question 3. modest income. Later that month, that help us think are likely to incor- You like Katrina but sometimes tire of despite your appearance as a charac- rectly our thinking and cause di- the way she drops hints about her in- ter witness at his trial, Justice is con- agnostic error. In essence, our minds telligence and math prowess. (How, victed of shoplifting and ordered to are sometimes misled not only by the you wonder, did she manage to tell pay a $500 fine and to perform 40 facts themselves but also by how we you that she scored 800 on the math hours of community service. think. The often helpful but some- SAT?) It bugs you that she always Given this new and quite startling times dangerous shortcuts that we says that her undergraduate degree development, will you: take in thinking are called .1 from Princeton was in “mathemat- To explore the concept of heuris- ics.” (Why can’t she just say “math” a) Believe Justice’s denial of guilt tics, please take the following quiz. like a normal person?) And it is espe- (he is after all your good friend Question 1: Consider Neil, a 44- cially irritating that Katrina now whom you trust) and carry on as year-old man from Santa Monica, Cal- glances at the multiplication you if nothing had happened?; ifornia. He is well educated and have just tried to estimate in less continued on page 2 CHALK TALK continued from page 1

include on our differential some diag- Step running product of: running product of: noses that may be more common 1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 8 x 7 x 6 x 5 x 4 x 3 x 2 x 1 1 256than ones we have thought of but 2 6 336 are less familiar to us. For example, 3 24 1,680 when asked to list causes of 4 120 6,720 petichiae in hospitalized patients, 5 720 20,160 many physicians will include vasculi- 6 5,040 40,320 tis and endocarditis (both of these 7 40,320 40,320 causes are drilled into us during med- ical training) but forget to include b) Begin to reevaluate your one of NASA’s 62 elite astronauts. NSAID-induced platelet dysfunction, relationship with Justice, perhaps Clinical examples of the danger of which is more common. A variant of thinking twice about confiding in the representativeness the availability heuristic is called last him as you have?; or abound, and we are in daily danger case bias, in which your experience c) Jettison your friendship with of falling prey to it. Indeed, we are with a particularly memorable case Justice? sometimes encouraged to use repre- causes you to overestimate the likeli- sentativeness by the following admo- hood of the condition in subsequent Discussion of Quiz Questions nition: “If it looks like a duck, walks differential diagnoses. For example, if Question 1. The description of Neil like a duck, and quacks like a duck, you recently had a pancytopenic pa- was crafted to vaguely characterize it’s a duck.” However, if a “duck” ap- tient who turned out to have hairy an astronaut—an intelligent, athletic, pears in a part of the world where cell leukemia, which is exceedingly motivated man with a background in this would be unlikely, such as the rare, you might overestimate the like- aviation and physics. If you are like Sahara Desert, perhaps one should lihood that your next pancytopenic many smart people who have an- reconsider the label or rename the patient has hairy cell leukemia, by- swered this question, you therefore creature something more broad, like passing other more common causes chose astronaut and fell victim to “a feathered animal with wings and of pancytopenia. what is referred to as the represen- a bill, resembling a bird.” Awareness Questions 3a and 3b. How did 2 tativeness heuristic.1 In short, you ig- of the danger of representativeness your estimate of the product 1 x 2 x nored prior probability. According to has given rise to the clinical maxim 3 x 4 x 5 x 6 x 7 x 8 compare with the American Library Association “an uncommon presentation of a the same product shown in reverse (www.ala.org), there are approxi- common disease is more common order as 8 x 7 x 6 x 5 x 4 x 3 x 2 x 1? mately 122,000 US libraries, employ- than a common presentation of a If you are like most people, your esti- ing 150,000 librarians. (This does not rare disease.” mate was larger when the product count 190,000 other paid staff who Question 2. We daresay that most was presented in descending order.1 work in libraries.) According to NASA people had a harder time, worse luck, This is because when estimating a (www.jsc.nasa.gov/Bios), there are and scratched their heads more com- product expressed in descending 62 active astronauts. This means ing up with words that have the letter order, you are starting with higher that the prior probability that an indi- r in the third position than words that numbers at the beginning of your cal- vidual employed adult is an astronaut begin with r—our minds are just wired culation and you naturally estimate is 2,400 times greater than the prob- that way—even though the harsh real- higher (see table). ability that he/she is an astronaut. ity is that English words starting with r This effect is called the anchoring You argue, “But Neil is an athletic are certainly less common than those heuristic,1 and it describes how we physics major who flew jets in the having r in position three.1 This is an often estimate by choosing a starting Navy, and he doesn’t sound at all example of the availability heuristic. value and then making an adjustment like a librarian!” Even taking into ac- In medicine, when constructing a to it. The problem with this method count his demographics and back- differential diagnosis we naturally is that while the starting value might ground, given only those two have an easier time thinking of diag- be easy to imagine, we often do not choices, the odds are still greater noses that we are more familiar with. make enough of an adjustment. that he is a librarian than that he is The danger here is that we will not continued on page 3

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A clinical example of anchoring fell victim to a heuristic referred to lost consciousness—with an SaO2 might arise in the following situa- as deference to authority. Because of 50%. A “code blue” was called. tion. Imagine that you are a second- of Katrina’s ability and her breezy Luckily, the patient was kept alive year internal medicine resident and confidence, you might have allowed by bag mask ventilation and a timely that you are called for a preopera- her to change your thinking. dose of intravenous tPA, which dis- tive cardiac risk assessment of a An example of deference to au- solved the pulmonary embolism and 92-year-old man who had a myocar- thority in medicine is presented in rescued her from the brink of cer- dial infarction six weeks ago and the following story relayed to you by tain death. has diabetes (on insulin), chronic a friend and colleague who is still The experience was quite upset- kidney disease (creatinine 2.1), con- shaken by her experience. A 31- ting to your friend. To her great gestive heart failure, atrial fibrillation year-old woman who was on oral credit, she decided to learn from her and a history of ventricular ectopy, contraceptives and smoked ciga- error. With a little research, she critical aortic stenosis, and a history rettes returned from a trip to Africa found that the sensitivity for PE-pro- of a prior stroke. The patient is on a direct flight from Nairobi to tocol CTA for detecting PE in sub- scheduled for urgent exploratory la- Newark and over the next two days segmental vessels can be quite parotomy for suspected intestinal started feeling short of breath and low.4 She realized that she had re- perforation. Although new to preop- right calf pain. On the third day she lied too heavily on the “authority” of erative risk stratification, you are fa- began to feel sharp pain near her the CTA and had ignored the very miliar with the Revised Cardiac Risk right diaphragm each time she took high pretest probability of pulmonary Index2 (RCRI) and are aware that a deep breath. Your friend saw her embolism, which should have the probability of untoward cardiac in the emergency department, prompted her to start anticoagula- events in the highest risk patients in where the patient had a heart rate tion and to pursue the diagnosis of the RCRI is about 10%. On review- of 105 beats per minute and a respi- pulmonary embolism further. “Au- ing the RCRI you decide that your ratory rate of 22 breaths per minute thorities” that we commonly defer patient has more comorbid illnesses with obvious splinting on deep inspi- to in medicine are experts, diagnos- and is older than the patients in the ration. There was pitting edema of tic tests, “UpToDate”, textbooks, 3 RCRI, so you decide to take the the right calf and foot, and deep pal- and medical literature—much of the 10% figure and revise it upward to pation of the right calf caused the time these authorities steer us in 20%. Although this might seem like patient to wince. She ordered a the right direction. The problem is a generous estimate, the actual car- pregnancy test (negative) and a PA that authorities are not always diac risk in this patient is far higher and lateral chest X-ray, which correct. than 20% (using the original Multi- showed a small area of consolida- Question 5. There is of course factorial Index of Cardiac Risk in tion or atelectasis in the right lower no right answer to question 5. It is Noncardiac Surgical Procedures,3 lobe. Concerned about pulmonary meant to illustrate premature clo- the risk would be 78%), but be- embolism (PE), your colleague also sure—a term that describes sticking cause you started (“anchored”) at a ordered a D-dimer, which came back by a conclusion that we have made low number, your final estimate elevated (Don’t they always?) and a despite evidence that the conclu- was too low. PE-protocol CT-angiogram (CTA) of sion is wrong. Initially, our tendency Question 4. By now you have the chest, which was negative for might have been to stick by Justice probably realized that Katrina the PE. Relieved that the CTA was neg- and to believe his version of the math whiz was wrong about the ative, your friend started antibiotics story, despite the fact that he was product in question 3, which is actu- for community-acquired pneumonia caught red handed shoplifting and ally closest to 50,000, not 20,000. (It and tried her best to convince the that we saw him do it. Premature is 40,320.) If she did in fact influ- patient to give up smoking. While closure, a type of anchoring heuris- ence you, it is because we gave her finishing up the discharge paper- tic, deserves special mention be- a semblance of authority in math (or work, your colleague was alerted cause it has been cited as the in “mathematics”) and perhaps led that the patient was in respiratory single most common cause of diag- you to think that we agreed with her distress. Indeed she was—the pa- nostic error in internal medicine.5 In conclusion. If you took the bait, you tient rapidly became grey-blue and continued on page 4

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medicine, attachment to a diagnosis 4. Do I understand the sensitivity References can lead us to ignore information and specificity of the test results 1. Tversky A, Kahneman D. that does not fit that diagnosis. We that have helped me establish Judgment under uncertainty: can prematurely conclude that we this diagnosis? heuristics and . Science have the right answer, essentially 5. Have I revisited my original 1974; 185:1124. forcing a round peg into a square diagnosis and weighted all of the 2. Lee TH, et al. Derivation and hole. subsequent information since that prospective validation of a simple So how do we avoid falling into time? After doing so, do I still feel index for prediction of cardiac risk the thinking pitfalls outlined above? confident in my diagnosis? of major noncardiac surgery. At present, the best method seems 6. When thinking about a diagnostic Circulation 1999; 100:1043. to be maintaining awareness that possibility, do I start by realistically 3. Goldman L, et al. Multifactorial your mind may be playing tricks on assessing the prior probability of index of cardiac risk in noncardiac you. Here are six questions to ask the disease or condition? surgical procedures. N Engl J yourself that may help you avoid Med 1977; 297:845. falling prey to your own cognitive Thinking about how we think as 4. Stein PD, Henry JW. Prevalence biases: physicians is an important compo- of acute pulmonary embolism in nent of enriching our mental models central and subsegmental 1. Is a singular previous clinical about disease processes. It is inte- pulmonary arteries and relation to experience, either positive or gral to becoming a better physician probability interpretation of negative, influencing my decision? and is something to be revisited ventilation-perfusion lung scans. 2. Am I emotionally vested in my every time we choose one diagnosis Chest 1997; 111:1246. diagnosis being correct? over another. Ultimately it can be a 5. Graber ML, et al. Diagnostic error 3. Have I considered more than two fun and enriching exercise. Sharpen in internal medicine. Arch Intern to three alternative diagnoses? your senses, and get to work! Med 2005; 165:1493. SGIM

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SGIM FORUM 2011; 34(11)