Cognitive bias and diagnostic error (November 2015)

TO THE EDITOR: I appreciated the article on cognitive biases and diagnostic error by Mull et al in the November 2015 issue.¹ They presented an excellent description of the pitfalls of diagnosis as reflected in a case of a patient misdiagnosed with heart failure who ultimately died of pulmonary tuberculosis complicated by pulmonary embolism (the latter possibly from using the wrong form of heparin). To the points they raised, I would like to add a few of my own about diagnosis in general and heart failure in particular.

First, any initial diagnosis not confirmed objectively within the first 24 hours should be questioned, and other possibilities should be investigated. I have found this to be essential for every day’s stay in the hospital and for every outpatient visit. The authors mention checklists as part of the solution to the problem of misdiagnosis, and I would suggest that confirmation of initial diagnoses be built into these checklists.

In the case of a presumptive diagnosis of an acute exacerbation of heart failure treated empirically with diuretics, the diagnosis should be confirmed by the next day’s response to the diuretics, ie, increased urine output, a lower respiratory rate, and a fall in the pro-B-type natriuretic peptide level. Moreover, a change in the radiographic appearance should be seen, and respiratory and pulmonary function should improve after the first 24 hours on oxygen supplementation plus diuretics. Daily patient weights are also critical in determining response to a diuretic, and are rarely done accurately. I order weights and review them daily for patients like this.

Second, it is good to look at things yourself, including the patient, medication lists, laboratory values, and radiographic films. The attending physician should look at the radiographs together with a senior radiologist. Seeing no improvement or change on the second hospital day, or seeing signs incompatible with heart failure, one could order computed tomography of the chest and begin to entertain pulmonary diagnoses.

Even vital signs can be questionable. For example, in the case presented here, with a temperature of 99°F, a heart rate of 105, and a pulse oxygenation saturation of 89%, a respiratory rate of 24 seems unbelievably low. In my experience, the respiratory rate is recorded erroneously most of the time unless it is recorded electronically or checked at the bedside by the physician using a timepiece with a sweep second-hand.

Additionally, I have found that ordering several days’ laboratory tests (eg, complete blood cell counts, chemistry panels) in advance, in many cases, risks missing important findings and wastes time, energy, and the patient’s blood. I have learned to evaluate each patient daily and to order the most pertinent laboratory tests. With electronic medical records, I can check laboratory results as soon as they are available.

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