Linda S. Costanzo, PhD

Medical Teacher, 2018 (http://doi.or/10.1080/0142159X.2018.1445832)

Acid-Base and Me

When first-year medical student Pete Q apprehended me in the stairwell after my physiology lecture on acid-base, I knew I was about to be stumped—again. “Your explanation of contraction alkalosis doesn’t make sense in terms of basic chemistry,” he said, breathless from having chased me up three flights of stairs.

Pete’s last question, several weeks prior, was about how the Bernoulli principle from physics applied in physiology. He’d caught me off-guard, since Bernoulli is about the potential energy of fluids—not usual medical school fare. Now here we were again, blocking traffic to discuss fundamentals.

What flaw had he found? Contraction alkalosis is shorthand for a common acid-base disturbance that every physician will encounter in their career. While the phenomenon was well known in 1987, when Pete posed his question, the underlying mechanism would not be solved until years later. Nonetheless, textbooks at the time provided a simple explanation, which I taught and which he saw through.

Busted! In order to teach a fuzzy concept to the first-years, I imagined the prototypical middle-of-the-class student who wanted to know just enough and nothing more. By waving hands over the then-mysterious contraction alkalosis, I could satisfy most students and then move quickly to the next point, where I would be on firmer ground. I was brand new to the business, a first-year teacher hanging on by her fingernails.

§

Acid-base was my first teaching assignment as a junior faculty member at the Medical College of Virginia. I was eager to teach medical students, having taken a stab at it as a postdoc, and acid-base was available because of the poor evaluations of my predecessor. Such openings are rare, so I said yes, without pausing to consider that those previous evaluations might forecast trouble for me. Never mind that acid-base terrified me.  

In my own student days, I had found acid-base to be a wasteland of confusion. Something big simply did not connect. While things started pleasantly enough in the halcyon days of childhood acid-base—color-changing pH strips in junior chemistry kits¾by high school, burettes and titration curves made appearances, and there were rumblings of trouble in acid-base-land. By college, acid-base had fully reared its ugly head, spewing cruel terms like “negative base excess.” (Is a negative excess even possible?)

College chemistry is replete with other stomach-churning terms like buffer lines, isobars, Henderson-Hasselbalch, and—the student’s worst nightmare—the “p’s”: pH and pK.  Those p’s look innocent enough; but trust me, they’re not. They were at the heart of my confusion (and, it turns out, the confusion of my future students). Those p’s signify negative logarithms. The inescapable truth at the heart of acid-base was that there would be no getting around the logarithm (math’s bad boy), the antilogarithm (the bad boy’s evil twin), or the minus sign that means when things are high we say they’re low, and when things are low we say they’re high.

There is an official explanation for the origins of acid-base phobia from the biggest names in the field. Cohen and Kassirer, in the preface of their landmark textbook, Acid/Base, explain that the near-universal dread among students is “rooted in mysterious concepts rendered doubly obscure by a confusing terminology.” There you have it from the people who should know—small wonder that generations of college and medical students have acid-base phobia because of “concepts rendered doubly obscure.” As if singly obscure wasn’t bad enough!

Last year I surveyed our medical students anonymously, asking about their prior experience with acid-base. One wrote, “I managed to ace general chemistry without understanding a lick of acid-base. Please help!” Another wrote, “For me, acid-base is PTSD, like a nightmare I can’t wake up from.”

One reason acid-base is so difficult is that some critical links are missing. How we would love to implore an expert in study group or a professor in a help session: Please explain this! If only we knew what “this” is. Not only are our questions vague, but the further we get in our education, the more humiliating they are to ask. Imagine a graduate student confessing in front of all: “I don’t get pH, and I really don’t get pK!”  Acid-base is one of those classic areas where students will say, “I don’t even know what my question is!”

So the charade lives on and grows into the big lie. Grade averaging (noted by the general chemistry-acing student) and hand-waving (noted by me) smooth over the details and allow the lie to grow.

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Because I wanted to avoid further stairwell embarrassment (and mostly because my students deserved better), I needed to plug the gaping holes in my acid-base firmament.

So I set out to teach myself. I sought lessons written for beginning students. If a resource glossed over elusive concepts or omitted steps in thinking, I dropped it. I was looking for someone—anyone—who could fill my gaps and anticipate my unasked questions.

Once I committed to teaching myself so that I could teach others, the logjam started to break. Slowly, I pieced together a logical story for myself. As sometimes happens with difficult topics, they are best learned backward through examples. I read case descriptions written for medical students and then puzzled out the underlying acid-base physiology from the clinical examples. If there was a gap in my logic, I acknowledged it and worked through it.

For teaching, this step has been critical, because my gaps were the same ones my students would bring in their “I don’t even know what my question is” questions. Addressing these gaps has been one of the secrets to ridding students of their acid-base baggage.

I now begin teaching acid-base with bold proclamations: By the time we are finished, you will have fallen hopelessly in love. You’ll be the Rocky of pH calculations and Henderson-Hasselbalch. You’ll be the hero of your acid-base dreams. I see skepticism on their faces, but also hope.

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Yet I look back fondly on the days when my own understanding was razor thin, even on my near misses, when the slightest deviation from plan could derail me. On more than one occasion my own “aha” moment came in real time, in the midst of addressing a student’s confusion. In the early years, I counted on students’ busyness to keep them from probing too deeply. Shabby survival techniques, for sure, and had this stage lasted much longer than it did, I would have faded into teaching oblivion.

My worst near-miss came during a guest-teaching stint at NYU School of Medicine in 1999. NYU was in a bind for teaching kidney and acid-base physiology, and they invited me to teach it to their first-year medical students.

I was comfortable with the material by then, but there was a new fly in the ointment: This was the year that our revised understanding of the “ammonia mechanism” made it into textbooks. Due to different course timing, I was to debut the new mechanism at NYU instead of at home. The ammonia mechanism is one way that the kidney preserves acid-base balance. Old ammonia had been simple, direct, fun to teach, and easy to learn. New ammonia involved—at a minimum—three kidney parts and four major steps.

I prepared handouts and practiced my diagrams and explanations. The morning of new ammonia, I was up early, going through my usual mental rehearsal. The shower is the perfect place to rehearse, as the warm water releases the neural circuits. As I reviewed the steps of new ammonia, it occurred to me to count the number of hydrogens and bicarbonates. The ammonia mechanism involves the kidney dumping hydrogen from the body at the same time it absorbs bicarbonate. For every hydrogen dumped, one bicarbonate had to be absorbed, as dictated by the law of electroneutrality. (In science, as the cliché goes, a law is a law, not just a good idea.)

I counted. For each cycle of the mechanism, I was missing a hydrogen! I recounted. Impossible. It was still missing, and the clock was running out.

In full panic mode, I bargained with the physiology gods, who rescued me in the blessing of a three-block walk down First Avenue from the faculty apartments to the medical school. Walking is as therapeutic for those mental circuits as a warm shower. I continued to count, on the chance of a last-minute reprieve. At the same time, I planned for the worst-case scenario.

Three blocks was only enough time to weigh my two (very different) options: In Option One, I would breeze over the counting, trusting students’ oblivion at 8 a.m. to not notice until I was safely back home in Virginia. In Option Two, I would pre-emptively point out the missing hydrogen, fess up that I’d just realized it, and promise to get back to them as soon as I figured out where it had gone.

Option Two was mature. Option Two acknowledged the limits of my knowledge and modeled professional behavior. Option Two was beautiful.

Yet . . . Option One was more tempting than it should have been.

Unbelievably, as I entered the back of the lecture hall, it came to me! The hydrogen was not missing at all. It had been there all along, hiding in the complexity of the three kidney parts and four steps.

My heart was still pounding as I exchanged breezy pleasantries with the arriving students. Little did they know how close I’d come to reliving my personal acid-base nightmare.

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These days the teaching of new ammonia is in good shape. The counting exercise from NYU is behind me. Still, when I come to that point in the explanation, I cannot help but alert the students to “a possible missing hydrogen” that may occur to them in the middle of the night and lead them to obsessive recounting. I cannot help but preempt their worries by telling them where to find it.

Perhaps I shouldn’t. Perhaps I should let them go through the process, lose sleep, and then stop me for an urgent Pete Q–style stairwell question. But given my own near miss, which seems like yesterday, I would feel dishonest not coming clean from the beginning.

Perhaps one day, if there are a few extra minutes on new ammonia day, I’ll even tell them the whole story.