How clinical reasoning works

In a recent examination, students were given a scenario and then asked a few questions about it. Their answers show me how they interpreted the evidence.

A man suffers a pulmonary fat embolism and hypoxia after trauma to his legs from a motor vehicle accident. He is intubated and ventilated. His blood pressure is normal and stable. Subsequently he develops elevated levels of urea and creatinine in his blood. His serum potassium is also elevated (6.5mmol/L). His urine output is recorded as 450ml/day. His ECG shows sinus rhythm with frequent ventricular premature beats. His serum creatine phosphokinase (CPK) level in the blood is significantly elevated. His ABG shows signs of metabolic acidosis. His blood counts show a haemoglobin value of 10.5gm/dL, an elevated white cell count and a slightly low platelet count (130000/uL). His PT and PTT are normal. 

The students were asked:

What is the complication (apart from fat embolism) that is seen in him?

Some answered 'Acute myocardial infarction'.
Comment: These students got this response by looking at the ventricular ectopic beats in the ECG and the elevated CPK level in the blood. However they failed to take into account the lack of ST segment or T wave changes in the ECG. 

Some answered 'Sepsis with multi-organ failure'
Comment: These students looked at the elevated white cell count and the abnormalities in the lung and kidney to come up with this answer. They did not realise that elevated WBC count can be due to inflammation after trauma and that the lung abnormality is due to fat embolism. Sepsis is a possibility in this situation but, with the available evidence, we have no unequivocal evidence of sepsis yet. 

What is the correct way to reason and answer this question?
The rising urea and creatinine within a short period of time along with a lower than expected urine output suggests acute kidney injury. What could be the cause of the kidney injury? There is trauma and a raised CPK level. These suggest severe damage to muscles. Hence rhabdomyolysis could be a cause. It is also possible that he has hypovolemia due to loss of blood and that has contributed to the acute kidney injury but the evidence for this is not seen in the scenario. So, the answer to the question should be: The complication that he has now developed is acute kidney injury secondary to rhabdomyolysis. 

How will the ventricular ectopics be explained? The logical explanation for it will be: hypoxia from the fat embolism is the cause of the myocardial irritability.  

Evidence based medicine and Black Swans

Evidence based medicine tells us that
a) beta blockers are useful for those with atrial fibrillation (1),
b) that beta blockers are useful for those in heart failure with systolic dysfunction (2).

Can we extrapolate and say that beta blockers will therefore be useful for those suffering from atrial fibrillation and heart failure with systolic dysfunction? Will we prescribe beta blockers for those with atrial fibrillation and heart failure based on evidence? I am sure most of us will answer “yes” to both questions.

Unfortunately this view turns out to be incorrect as new evidence from a meta-analysis of beta blockers in patients with atrial fibrillation and heart failure with systolic dysfunction shows. The authors of this analysis, published in JACC Heart Failure in February 2013, say: The main finding of the present meta-analysis indicates that the effect of beta-blockers in patients with Heart Failure (HF) and Atrial Fibrillation (AF) is significantly different from the effect of these drugs in patients with HF and sinus rhythm. Indeed, beta-blockers were not found to have a favourable effect on HF hospitalizations or mortality in 1,677 AF patients who had been enrolled in placebo-controlled, randomized studies (3).

Unexpected results or events are what the author and Dean’s Professor in the Sciences of Uncertainty at the University of Massachusetts, Nasim Nicholas Taleb, calls Black Swans. The term arises from the once-held conviction that all swans are white because no one had ever seen a black swan for hundreds of years. A Black Swan, by definition, is a rare event that cannot be predicted by existing knowledge but which, when it occurs, can have tremendous impact on our lives or radically change our thinking. We make ourselves open to Black Swans when we allow our knowledge to blind us by making us believe that we know everything. Black Swans remind us that we must never be too confident that we know everything simply because we know a lot of stuff.

Evidence based medicine is a great repository of knowledge. When a form of treatment is proposed, we often ask the question: Is it evidence based? The assumption is that, if it is evidence based, we can be sure of the kind of effect the proposed treatment will have. Black Swans tell us that evidence based medicine should be used for predicting results only after being aware of variations in clinical situations between the past and the present. There is a subtle randomness about reality, and variations between individuals, that should make us aware of possible errors in extrapolating data from the past.

Intellectual humility is a mark of wisdom because it makes doctors aware that there are many things they do not know. Only through wisdom can we avoid being struck by Black Swans.

References: 
1. Rodney H. Falk. Atrial Fibrillation. N Engl J Med 2001; 344:1067-1078 
2. Wilson S. Colucci. Use of beta blockers in heart failure due to systolic dysfunction. Uptodate.
3. Rienstra M, Damman K, Mulder BA, et al. Beta-Blockers and Outcome in Heart Failure and Atrial Fibrillation: A Meta-Analysis. JCHF. 2013;1(1):21-28.