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.

Specious Ideas: Trending Troponins and Chasing Lactates

I want to use this post to discuss an article in this week's JAMA called Lactate in Sepsis, which I think is fatally flawed and misleading.  But first...

Several years ago on the Medical Evidence Blog I talked about cardiac troponins and how their use is often misguided.  Not long after this post a young woman e-mailed me to describe a diagnostic and therapeutic misadventure that ensued after an abnormal troponin was "discovered" during work-up for a urological problem.  This led to transfer to another facility via ambulance for a cardiac catheterization with multiple complications including stroke.  It was a sad and unfortunate tale, but I fear it is not too uncommon.

Troponin, like all tests, needs to be ordered on the basis of a clinical suspicion (prior probability) that, when combined with the likelihood ratio of the test using Bayes Theorem (see calculator on the right of the blog), results in a posterior probability of disease that crosses a decision threshold.  (Because of the woeful inadequacy of medical education in regards to basic decision theory, I would not be surprised if the majority of physicians cannot correctly describe priors, Bayes, posteriors, or decision thresholds.  But this is old news, and beyond the scope of this post.)  The low prior probability of acute coronary syndromes in critically ill patients with non-cardiac primary diagnoses (PE, AECOPD, sepsis, etc.) leads me to list "non-specific troponin increase in the setting of critical illness" as a problem (an artificially begotten one) in my assessments after colleagues regretfully order tests that should never have been ordered.  And I will defer discussion of all those d-dimers and the needless CT angiograms they engender, lest I descend into unmitigated belligerence.

The Slave, the Master, Captain Obvious, and Insatiable Searching

I'm going to use some cheeky analogies to prove some points in today's quick post.

Imagine that while you are away, your fire alarm goes off, and the fire trucks come, sirens ablaze.  After an investigation, the brave men in blue determine that there is no emergency, every thing is in order, no fire.  They return to their station and not long later your alarm sounds again.  And again.  And again.  Should they douse your home with water just in case they're missing something?  Or should you disable your alarm?

Recently, I was consulted to assist with "vent management".  A patient was "fighting the vent" and was not ventilating well, with a pH of 7.03.  I arrive and find her deeply sedated on propofol and fentanyl (attempts to kill the fight in her) and breathing slowly at a rate of 8 (hence the low pH and high pCO2.)  Every ventilator mode has been tried, but she "breath stacks" or otherwise "fights the vent" without heavy sedation, which itself depresses respiratory drive so much that she gets a respiratory acidosis.  Turn up the rate, and she's back to "breath stacking."  But alas, she was not fighting the vent at all, she was fighting its alarms and it was fighting her.  A post-operative patient, she had low respiratory system compliance (her chest was stiff) and she was also not relaxing after the initial breath delivery, setting off the alarm and the inspiratory delivery, not exhaling, then taking another breath on top of the prior incomplete one.  Raising the peak pressure limit alarm to 60 stopped this and allowed discontinuation of most of the sedatives.  Now she accepts the breath, albeit at a higher peak pressure.  So was solved the problem that never existed, but was created by the alarm settings and the misguided responses to them. One should always ask oneself as regards ventilator alarms "Who is the slave and who is the master?"

The police are sometimes accused of settling prematurely on a suspect, at the exclusion of other possibilities, thereby leaving the real perpetrator free to commit other crimes.  In medicine we would call this premature closure, or search satisficing.  But the opposite of that may be delayed closure or insatiable searching.  Imagine that we have a prime suspect with a motive, and have video evidence of the crime - we can see whodunnit, and there is no evidence of accomplices or other conspiracies.  What police chief would allow his detectives to waste resources going out trying to find other possible suspects in this case?

Now, suppose a previously healthy young woman is exanguinating and goes into shock and multisystem organ failure during her resuscitation and massive transfusion.  Her LFTs (Liver Function Tests) go through the roof, as is seen in shock causing "shock liver".  Why on Earth would a provider order a viral hepatitis panel and an autoimmune panel in this patient?  What are the chances that this exanguinating trauma patient coincidentally has viral hepatitis instead of or on top shock liver?

A young patient with normal renal function develops post-operative shock and renal failure.  Should you order a renal ultrasound to check for obstruction?  What are the chances this patient has a predictable complication and spontaneous urinary obstruction or obstruction instead of the usual complications from shock?

A patient has a witnessed aspiration, say, from overdose.  There are bilateral infiltrates on CXR.  "But we should get a CT, maybe he has PE (pulmonary embolism), too."  And maybe he's gestating an alien fetus in his cecum.

Sometimes Captain Obvious needs to come rescue us from insatiable searching.

Underperforming the Market: Why Researchers are Worse than Professional Stock Pickers and A Way Out

Here's an occasional cross post from the Medical Evidence Blog.  It's a bit more technical than what is usually posted on Status Iatrogenicus, but it gives a summary description of a pervasive problem with "evidence based medicine" that is so widely applicable to practice that I think it deserves some recognition here.

Underperforming the Market: Why Researchers are Worse than Professional Stock Pickers and A Way Out

Worshiping Relics of the Past: The Physical Examination

It seems like every year or so, an article such as this one is published in just about every medical journal either lamenting the withering importance of the physical examination (PE), bemoaning contemporary physicians' indifference to it, inventing creative perspectives to enshrine and hallow it, or just harkening back to the "good 'ol days" when that was "all we had."

The whole state of affairs is ironic and silly, for several reasons.  I would be shocked if the same doctors who hanker after the good 'ol days of Valsalva and Mueller maneuvers, Austin-Flint murmurs and Cannon A-waves don't carry around iPhones, iPads, Up-to-Date Apps, and every other manner of advanced electronic device, aid, and tool.  (They are probably also vocal proponents of EMRs.)  They don't dust off an old EKG machine from the 1960s once a week and teach medical students how to use it just in case they find themselves on a medical mission in Cuba one day.   They use computers and statistical programs to perform calculations for their epidemiological studies, not slide rules and Z-score tables.  If they have a mortar and pestle, or an old microscope, it is on a shelf under various diplomas, testaments to the past and nothing more.  So why all the fuss over the slow but inexorable obsolescence of the PE?

Reflexes are for Knees! Geez! Why do you need so many ABGs? (An introduction to Bayesian Clinical Decision Making.)

I wasn't always like this.  Ask co-interns and they will tell you I was the most notorious minutiae-obsessed physiology manipulator west of the Mississippi. 

What changed?  Well, I grew up and realized that micromanaging physiology is most often a fool's errand.  Evolution was indeed a brilliant chemist (Max Perutz), and I recognize my impotence in one-upping him.  I can order zero ABGs or a dozen ABGs in a week and little changes but the volume of blood that is flushed down the drain.

So, using an example from earlier in the day, I'll lead you through a stream of consciousness explanation of why I can most often do without an ABG.

A man in his 30s is admitted for alcohol withdrawal (WD) for the sixth time in 12 months.  About half of these times, his WD has been severe and he has required ICU admission.  Overnight, during the administration of benzodiazepines for his WD symptoms, he has become progressively tachycardic and tachypneic and his oxygen needs have been steadily increasing.  His saturation on the monitor displays a good tracing at 95%.  BIPAP is applied.  I can hear his respiratory rate at about 25, and based on the flow I hear from the BIPAP machine, I can guess that his minute ventilation is about 15 liters per minute (these guesses could be confirmed with RT).   Knowing nothing else about his case, I am asked if an ABG should be ordered to assess his respiratory status.  Should it?