From our anonymous insider..
We finished respiratory physiology with a lecture on arterial blood gases. Breathing allows the infusion of oxygen into the bloodstream and the removal of carbon dioxide produced by cellular metabolism. The respiratory rate is normally regulated by the amount of carbon dioxide in the blood, not by the amount of oxygen. CO2 is tightly regulated because carbon dioxide determines the pH of the blood. Remember that soda contains carbonic acid. When the can is cracked, carbonic acid is converted into CO2 and water, i.e., fizzy water. The reverse process, of CO2 in the blood turning into carbonic acid, results in acidic blood. The body tries to maintain a slightly basic blood pH of 7.4.
My favorite trauma surgeon used some of her patient experiences as case studies to describe the different permutations of arterial blood gas states. In one example, a drunk 18-year old falls three-stories. He is found unconscious, not breathing, with O2 saturation (sat) levels severely depressed at 60%, and CO2 levels severely elevated. The patient is suffering from respiratory acidosis. As the patient is transported to the hospital in an ambulance, his O2 sat rises to 80%, but CO2 has dropped below normal. The high-school-age EMT raised the patient’s oxygen saturation levels with the breathing bag, but was squeezing it too quickly, causing increased expiration of CO2 and respiratory alkalosis.
The patient case was “John,” a 40-year old male suffering from life-threatening asthma since the age of four. Growing up, his condition was successfully managed by the family pediatrician. John’s father was a teacher and John emphasized how this doctor had tailored the treatment and medications to his family’s modest budget, e.g., by finding low-cost alternative medications and free samples. In college, the asthma spiraled out of control. “I saw a PCP [primary care provider] at college once. The guy immediately insulted my pediatrician saying the way I was managing my asthma was terrible.” The PCP scoffed when John said the treatments were working well for him. John never went back and lost touch with the medical system. As his uncontrolled asthma began to worsen (John now admits the college PCP might have been right), he used home remedies. When he was having an asthma attack at night, he would brew a large pot of coffee and sit outside on the porch in the middle of the freezing night drinking cups of coffee with his plump pug (caffeine would relax his bronchioles). “I probably should have gone to the ED many times,” John said, “but I would push the limits. Also, I knew how much it would cost me so I gulped that coffee.”
John’s asthma said that his asthma improved after he “moved and started a new job,” enabling him to see the pulmonologist sitting next to him. It turned out that the “new job” was a cardiology fellowship and the pulmonologist was his attending. She joked that her fellow/patient was non-compliant and John admitted that it was difficult to find time to take care of himself. He sees patients as part of the fellowship, has two toddlers at home, and moonlights at the VA to support his family (a fellow earns about $60,000 per year). John noted some additional financial pressure from a recent regulation requiring eliminating Ozone-depleting chlorofluorocarbons from the inhalers’ ejection mechanism. Although the drug itself was the same, this slight tweak to the mechanism allowed pharmaceutical companies to re-patent medications that formerly had generic competition. Prices soared from single digits to hundreds of dollars per inhaler. John said his insurance now covers most of it, but many patients have to pay out-of-pocket due to high deductibles. John noted that for some patients the inhalers can cost more than their mortgage payment, leading to abandonment of the optimal medications. John emphasized the need to listen to patients: “If they say something is working, don’t brush it aside like the college PCP.”
Anatomy lab was incredible, by far the most fascinating day thus far in medical school. After an early morning excursion with Jane to pick up pastries at our favorite breakfast place, we entered the cadaver lab where a fresh pig’s heart from the local butcher awaited each student. The human hearts we removed last week were preserved for a later date once we can appreciate pathological conditions. We were quite timid at first. The surgeons and cardiologists went over and gave us a little instruction about where to make the first scalpel stroke, then said “just enjoy exploring wherever your heart desires.” As soon as we opened the hearts, which we’re told are almost identical to a human’s, we saw an unfamiliar environment. Tendinous fibers, also known as heart strings, criss-crossed in the ventricular chambers connecting the atrioventricular valves to papillary muscles on the heart chamber wall. We rubbed the translucent leaflets of the heart valves in between our fingers. I saw and felt the beautiful tree-like muscular protrusions of the ventricular wall that help guide the flow to their destination, shattering my vision of the interior heart as a smooth surface.
Afterwards my favorite trauma surgeon gave a lecture on the aging heart. She described how the current generation of physicians were all trained on a younger population. Now, when physicians apply this standard of “normal” to older patients, many normal aging processes are diagnosed as pathological. For example, during aging the whole long axis of the heart begins to shorten. This is often misconstrued and overdiagnosed as a pathological state. She cautioned, “Get used to this. You are going to be dealing with an older population.”
Last week’s ear infection patient and I now share something: fleas. I have decamped to Jane’s house until the fumigators can come. The physician with whom I saw the toddler calmly said, “It happens sometimes. Downside of seeing kids.”
Statistics for the week… Study: 12 hours. Sleep: 7 hours/night, fleas kept me up one night; Fun: no downtown outings. Example fun: movie night with Jane bedtime 9:00 pm.
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