Monday, November 20, 2017

Sunk Kidney Bias: A Lethal Form of Sunk Cost Bias

Hal Arkes
The heuristics and biases program of Kahneman and Tversky, once an obscure niche of cognitive psychology, became recognized among lay persons with Kahneman's Nobel prize in economics in 2002.  The popularity of the program surged with Kahneman's book Thinking Fast and Slow several years ago and several among the scores of related books about behavioral economics became best-sellers.  This year, Richard Thaler was the Nobel laureate in economics for his work in behavioral economics.   I became aware of heuristics and biases just before Kahneman's Nobel and started looking for them in medicine in 2003.  We (Aberegg, Haponik, and Terry, Chest, 2005) indeed found evidence for omission bias, and have discovered other biases along the way, some which are very intriguing but we aren't even sure what to name them (Aberegg, Arkes, and Terry, Medical Decision Making, 2006).  My point here is that these biases are useful but difficult to identify as patterns systematically operating within medical practice in predictable ways - they pop up here and there only to recede and reappear years later, if they are recognized at all.

Then there are biases about the biases.  Highly cited expositions of biases in clinical care, such as those of the insightful emergency physician Pat Croskerry (Academic Medicine, 2003), among many others) very often surmise the presence of biases in clinical care, without the kind of empirical evidence that established the biases in the first place.  Sometimes, new and probably useful biases are proposed (such as "search satisfycing"), without any empirical evidence, at all in any domain, for their existence.  They are merely postulates.  (Granted, empirical evidence is very difficult to generate, this the reason I don't do this kind of research anymore.)  Finally, the descriptions of the biases applied to medicine are often strained, or just plain wrong.  My favorite is the bastardization of "anchoring and adjustment" into a description of any time a physician seizes upon a diagnosis and discounts disconfirming evidence or fails to consider alternatives.  This is not anchoring and adjustment.  Anchoring refers to a numerical anchor, and failure to adjust away from it when providing numerical estimates.  Here is a summary of the original descriptions, from the wikipedia entry on anchoring and adjustment:

Tuesday, October 31, 2017

Applied Respiratory Physiology Vlog. Parts 1,2,3,4: Respiratory Failure Explained as Workload Imbalance

The following embedded videos are parts 1-4 of a 5 part talk I've been giving and refining on Applied Respiratory Physiology for about 10 years now.  (It is split into 5 parts because of youtube size limitations and for digestible 10-15 minute segments.)  The principles herein derive from many sources, but special credit must go to Nunn's Textbook of Applied Respiratory Physiology and The University of Chicago critical care text edited by Hall, Schmidt, and Wood.  For the majority of the ideas and applied principles herein, I have never seen them discussed in any lecture in 20 years of attending pulmonary conferences, didactics, etc.  My interest in applied physiology and Nunn's textbook indeed originated because of my frustration with the esoterica of the basic and advanced physiology that I was taught from medical school through fellowship -  I determined that much or most of it was not applicable at the bedside.  This lecture series, I hope, will be far more clinically applicable, intuitively appealing, memorable, and useful than what has been traditionally taught.  Real life examples highlighting the extremes of human respiratory performance should, I hope, make this a memorable lecture seeries.  I welcome comments and criticisms below.  Enjoy!



Tuesday, September 26, 2017

DIPSHIS: Diprivan Induced Pseudo-Shock & Hypoxic Illness Syndrome

This would be a very informative case report (and it's true and unexaggerated), but I anticipate staunch editorial resistance (even sans puns), so I'll describe it here and have some fun with it.

Background:  The author has anecdotally observed for many years that so-called "septic shock" follows rather than precedes intubation and sedation.  This raises the possibility that some proportion of what we call septic (or other) shock is iatrogenic and induced by sedative agents rather than progression of the underlying disease process.

Methods:  Use of a case report as a counterfactual to the common presumption that shock occurring after intubation and sedation is consequent to the underlying disease process rather than associated medical interventions.

Results:  A 20-something man was admitted with pharyngitis, multilobar pneumonia (presumed bacterial) and pneumomediastinum (presumed from coughing).  He met criteria for sepsis with RR=40, HR=120, T=39, BP 130/70.  He was treated with antibiotics and supportive care but remained markedly tachypneic with rapid shallow respirations, despite absence of subjective respiratory distress.  A dialectic between a trainee and the attending sought to predict whether he was "tiring out" and/or "going into ARDS", but yielded equipoise/a stalemate.  A decision was made to intubate the patient and re-evaluate the following day.  After intubation, he required high doses of propofol (Diprivan) for severe agitation, and soon had a wide pulse pressure hypotension, which led to administration of several liters of fluids and initiation of a noradrenaline infusion overnight.  He was said to have "gone into shock" and "progressed to ARDS", as his oxygen requirements doubled to 80% from 40% and PEEP had been increased from 8 to 16.  The next morning, out of concern that "shock" and "ARDS" were iatrogenic complications given considerations of temporality to other interventions, sedation and vasopressors were abruptly discontinued, diuresis of 2 liters achieved, and the patient was successfully extubated and discharged from the ICU a day later.

Conclusions:  This case provides anecdotal "proof of concept" for the counterfactual that is often unseen:  Patients "go into shock" and "progress to ARDS" not in spite of treatment, but because of it.  The author terms this syndrome, in the context of Diprivan (propofol) in the ICU setting, "DIPSHIS".  The incidence of DIPSHIS is unknown and many be underestimated because of difficulty in detection fostered by cultural biases in the care of critically ill medical patients.  Anesthesiologists have long recognized DIPSHIS but have not needed to name it, because they do not label as "shock" anesthetic-induced hypotension in the operating theater - they just give some ephedrine until the patient recovers.  DIPSHIS has implications for the epidemiological and therapeutic study of "septic shock" as well as for hospital coding and billing.

Sunday, August 27, 2017

The Number Needed Not To Treat To Harm (NNNTTTH): A Heuristic for Evaluating Trade-offs in Medical Decisions

A frequent conundrum of decision making that arises in medicine is when there is a generally indicated therapy, say, anticoagulation for atrial fibrillation, that poses unique risks in a particular patient.  CHADS2 and HAS-BLED scores are calculated, but don't quiet the hemming and hawing or quell the hand-wringing.  What is usually a simple dichotomous decision is now one laden with probabilities, risks and benefits, and compromise between competing objectives.  (See:  The Therapeutic Paradox:  What's Right for the Population May Not Be Right for the Patient.)  In order to restore nuance to the decision, we need to try to estimate the numerical values of the risks and benefits to determine if the net utility of anticoagulation is positive or negative, something the aforementioned calculators are intended to do in a semi-quantitative way.  But what if you opine that your patient has a specially enhanced risk of side effects and you're worried about falls or bleeding but ambivalent because of a concurrent fear of denying him of the benefit of stroke prophylaxis?  What if you think that he would have never been included in a trial of stroke prophylaxis and the results of those trials may have limited generalizability to him?  What if you think he has only a year to live?

The number needed not to treat to harm (NNNTTTH) is the number of patients whom you have to not treat with something beneficial in order to cause one harm from your omission.  It is numerically equivalent to the number needed to treat (NNT), but it reframes the decision from action to omission and from benefit to harm.  Ignoring bleeding altogether (because making relative utilities for bleeding and stroke is a fraught endeavor), you could ask yourself "how many patients can I withhold stroke prophylaxis from for one year before I statistically cause (or allow to happen, if you are prone to omission bias) a stroke?"  For most patients, withholding stroke prophylaxis has a NNNTTTH of about 25-30 per year (check the corresponding NNT from CHADS2 for a more "precise" estimate).  Reframing the question into "how much am I asking the patient to pay, in terms of statistical likelihood of stroke, to avoid anticoagulation and the particular side effects that cause me concern in his case?" can often provide some reassurance for the clinician and the patient alike.

Wednesday, July 19, 2017

Screening in Disguise: You Can't "Unknow" that Troponin, But You Can Dismiss It After Careful Thought

During MICU rounds last month, there were a lot of troponins ordered, and most of them should not have been.  Invariably when abnormal troponin values are reported on rounds, there is no mention of whether the patient had anginal chest pain, whether there were ischemic EKG changes, or whether this information was sought at the time the troponin was drawn.  This is because troponins are being used as a screening test, rather than as a diagnostic test.  "Not so!" exclaims the resident, eager to convince me that he has not engaged in the kind of mindless testing he knows I loathe.  I am told that because the first troponin was mildly elevated in a little old lady with cirrhosis, overdose, right heart failure and urinary tract infection, that we need to follow it to see where it "peaks".

Saturday, August 13, 2016

The Enemy of Good is Better: Maximizing versus Satisficing in Clinical Medicine

Herbert Simon, Nobel Laureate
Recently I was called to admit a little old lady with a digoxin overdose who had symptomatic bradycardia.  She was in her 70s, had Alzheimer's disease (AD) and a medication list that would not print on one page.  I immediately thought, what benefit does digoxin have that justifies even the occasional admission for toxicity?  That's a good question in its own right, but consider a partial list of her other medications:

  1. pantoprazole
  2. lisinopril
  3. gabapentin
  4. raloxifene
  5. estradiol
  6. donepezil
  7. labetolol
  8. furosemide
  9. glipizide
  10. fenofibrate
  11. memantine
  12. sitagliptin
  13. spironolactone
  14. amlodipine
  15. alprazolam
  16. aspirin
One certainly must wonder what goals her providers are trying to achieve with these and indubitably some other medications which aren't listed.  Her husband was frustrated when I told him that many of the medications she is taking are not really doing her any good.  "They why do they have her taking them?" was a question I could not answer, because it doesn't make sense to me either.  Exasperated, he offered a great analogy:  "Suppose you hire me as a contractor to build you a home, and I tell you that you need to build a 14 foot high retaining wall in the back yard, two feet thick, reinforced with rebar and containing 20 yards of concrete.  Would that be responsible unless it were absolutely necessary?  What kind of contractor would recommend something you didn't really need?"

"A physician contractor," came the ready answer in both of our minds, and we simultaneously nodded in understanding.

Thursday, August 11, 2016

Medical Decision Making as a "Patient": Pregnancy Leads to A Trip Down The Rabbit Hole - A Personal Story

My wife is pregnant.  Wanting to be a supportive spouse, I attended the first prenatal visit to see one member of her team of midwives.  (Being a "minimalist" I was, like my wife, fond of the idea of not unnecessarily "medicalizing" the [usually] natural act of labor and birth.)  I realized during that first visit that understanding the intricacies of medical decision making can be a double-edged sword when dealing with practitioners, especially outside of one's specialty.  If ignorance is bliss, 'tis folly to be wise, it is said.  I've come to wonder which is better for you when you get entangled in US healthcare, wisdom or bliss.

During the first visit, we were offered, with an air of agnosticism, a referral for genetic counseling +/- non-invasive prenatal testing (NIPT).  "How accurate is it," I naturally inquired, trying to avoid technical terms such as sensitivity and specificity.  "Something like 99%" came the reply.  So we were given the referral.  But I quickly realized that this was a classic problem of base rates.  The likelihood of a chromosomal abnormality is so low given my wife's age, that even extremely high sensitivities and specificities are inadequate to guide our decision - that is, the test is rendered practically useless because of the low base rates in our case.  And this despite the fact that the sensitivities and specificities of prenatal blood testing are inflated by the way they were derived.  But think of the decision we would have faced had we blindly proceeded with testing without this consideration - given the low base rate, the posterior probability of a chromosomal abnormality such as Down's Syndrome given a "positive" test result would be around 33%.  How would we act on this information?  Is that threshold high enough that we would consider an elective abortion (if we were morally disposed towards that as an option)?  Or would we ignore the information and proceed to term?  And if we were not ethically accepting of elective abortion as a possibility, what other remedy would we have that would justify the information from the testing?  Why would we talk about getting prenatal genetic testing before talking about the choices we may have to face after we receive the results?  Why would not a discussion of remedies, specifically abortion, precede consideration of the testing?  How many couples dive into the rabbit hole only to wonder how they got there and how they can get out?  In this case, we decided that ignorance was indeed bliss, and deferred NIPT.

At that same visit, blood was ordered to be drawn.  I had difficulty understanding why you would need to draw blood from a perfectly healthy woman at 12 weeks gestation.  Blood types and anemia and all that I guessed.  But I was particularly caught by the thyroid testing.  Why are we screening an asymptomatic woman for thyroid disease?  Is that justified by the prior probabilities?  It takes only a google search to learn that ACOG (the American College of Obstetrics and Gynecology) and an endocrine society do not recommend universal testing.  But my questioning why we were doing this was off-putting and frankly unanswerable for the midwife - she was just following the usual routine, whatever her supervisors and mentors had told her to do, without understanding....well without understanding any of this Bayesian mumbo jumbo that I was hinting at.  Alas, thyroid testing, like NIPT, was deferred.  But not for long.