Saturday, February 21, 2015

WILTIMS #257-260: To pee or not to pee

TuesdayIL: Although antinuclear antibody (ANA) is very sensitive for lupus, it's not even remotely specific. Biostats translation: If this test is negative, you definitely don't have lupus; if it's positive, you have something, but it may or may not be lupus. Anti-double stranded DNA and anti-Sm tests are much more specific, but less sensitive (if positive, you definitely have lupus, but if negative, you may or may not).

Wednesday: Today we started one of our less intensive courses, Medical Ethics II. Ethics I, which we took last year, consisted mostly of us debating hypothetical medical dilemmas and learning about the balance between concepts like autonomy, justice, beneficence, and nonmaleficence. This year is simpler in that there is only one topic and yet more complicated in that it's death. Ought to be fun!

WednesdayIL: Rheumatoid arthritis is diagnosed by a complicated scoring algorithm involving counting the the number of affected joints, positive blood tests, and the duration of the symptoms.

ThursdayIL: Urine is usually darker when it's more concentrated, the excepting being in diabetes, where the urine is extremely clear but absolutely full of sugar.

Without having other data with which to compare, there is no normal urine pH. But it's still an incredibly useful number. For the chemistry buffs out there: since there is no good pH indicator that covers the broad range of pHs urine can be found at, they actually use a mix of two pH indicators to test urine pH. A problem with this is that one of the indicators also responds to protein content (which is normally not present in urine). So, if a patient has proteinuria, you cannot rely on the normal indicator blend to determine pH.

Can you match the crystals with their descriptions of the left?
The yellow panel is uric acid, which I did not mention because it's boring.
Urine can precipitate many types of crystals. Triple phosphate (aka struvite) crystals have a coffin lid appearance. Cysteine crystals are hexagonal. Calcium oxalate crystals are bipyramidal or "envelope-like", depending on if you think in 3 or 2 dimensions.

FridayIL: Secreting acid in the urine is hard. We have pumps in the collecting ducts of the kidney that can directly excrete hydrogen ions, the problem with this is that it very quickly acidifies the urine to a pH similar to your stomach acid. You would quite literally digest your kidney.

So how do you excrete acid without making the urine too acidic? Buffers! Phosphate combines with hydrogen ions to form phosphoric acid*, which is far less acidic than the hydrochloric acid that would otherwise be formed. The phosphate is largely derived from the bones, which is why long term acidosis can cause osteoporosis. Ammonia is also used as a conjugate base to form ammonium, another weak acid.

*This is all way more complicated thanks to phosphoric acid being triprotic. For the chemistry sticklers out there: various conjugates (HPO4-2, H2PO4-1) are used as the phosphate ion moves through different pH environments.

Tuesday, February 17, 2015

WILTIMS #253-6: I kidney you not

Heart -check, lungs -check, brain -check! On to the next organ: kidneys! Compared with the previous three, the poor kidneys get no respect. But when things go wrong for your determined little blood filterers, you'll notice ...and/or die. 

Tuesday: I had a preceptor visit today where I had my first experience with an interpreter. I'm actually amazed that it took this long! Last year, the doctors I worked with were both fluent in a several languages and mostly cherry-picked the english-speaking patients for me, so they wouldn't have to play both doctor and interpreter.

Today's patient was a ~80 year old woman who came in with her grandson. The patient spoke no english at all but her grandson was extremely well spoken. I quickly saw, as we were warned in our FCM class, that a using a family member as an interpreter could be dangerous if you don't trust the interpretation or motives. Even something as innocuous as "I'm sure what she means is..." can dramatically change the narrative you're hearing from a patient and the clinical picture you base medical decisions on.

This particular interview went surprisingly well and I think I was able to get nearly all the information I wanted. Figuring out the type of pain being felt was particularly difficult. It wasn't sharp, dull, stabbing... and whatever the word was she saying didn't quite translate. We eventually settled on "tingling," which matched the our physical exam findings of nerve-associated dysfunction.

TuesdayIL: There are two broad syndromes of renal dysfunction and they are super-helpfully named: nephritic and nephrotic syndromes. Nephritic patients will have blood in the urine (hematuria), protein in the urine (proteinuria), high blood pressure, and a low urine volume. Nephrotic syndrome, by comparison, is markedly more severe proteinuria, low blood albumin levels (hypoalbuminemia), generalized swelling (edema), and high blood lipid levels (hyperlipidemia). Simple, right? And these are just broad categories that each specific renal disease shares some combination of features with.

WednesdayIL: Red blood cells should never be in the urine, but their morphology, when present, can hint at where the bleeding is happening. Crinkly red blood cells in the urine typically come from the upper urinary tract or kidney. This is might relate to the multiple changes in concentration and/or just being in the urine for a longer time. Normal looking red blood cells generally come from lower, in the ureters, bladder or urethra.

ThursdayIL: Foamy urine is indicative of severe proteinuria.

FridayIL: The indications for dialysis can be remembered by the mnemonic AEIOU:
Acidosis (low blood pH)
Electrolytes (ion imbalances)
Intoxication/Ingestion (toxic substances)
Overload of fluid
Uremia (severe blood loss through the urine)

Thursday, February 5, 2015

WILTIMS #249-252: Neuro wrap-up

Sorry again for the dearth of posts. The first exams of the new term are on Monday (barring a fantastically well-timed potential snowstorm), so learning took precedent over writing about learning. So, without further ado:

FridayIL: Morphine has the same high potential for abuse as other strong opiod medications like oxycodone. The reason you don't hear about rampant morphine addiction is that morphine undergoes extensive first pass metabolism in the liver. If a drug is taken orally, it's absorbed in the GI tract and passes through the liver en route to the rest of the body. The liver detoxifies our blood and if its enzymes are able to breakdown a drug, the amount of drug available to have an effect on the body is dramatically reduced. So, though morphine is the active ingredient in opium and is the breakdown product of other drugs like codeine, it isn't typically abused itself since it can't be effectively given orally.

Monday: SNOW DAY!

TuesdayIL: Ketamine is a N-methyl-D-aspartate (NMDA) receptor antagonist used as a chemical restraint. It is part of a class of drugs called dissociative anesthetics because people under their effects are "dissociated" from the world.

WednesdayIL: Louis Pasteur created the first rabies vaccine by blending up the spinal cord of rabbits infected with rabies.

Osmotic demyelination syndrome (aka central pontine myelinolysis) sucks. This is a form of brain damage caused by too rapidly correcting hyponatremia (low sodium). This scenario usually unfolds as an ER doctor treating a chronic alcoholic and accidentally causing permanent paralysis, locked-in syndrome or death.

Marchiafava-Bignami disease is necrosis of the central third of the corpus callosum caused by drinking crappy red wine. It's probably not actually due to the wine (which was noted in the first described cases in Italy) but the associated vitamin deficiencies seen in chronic alcoholics. So always drink in moderation and, just to be safe, drink good wine. (Not quite) doctor's orders!

Germinal matrix hemorrhage is a common brain injury found in severely premature infants. The brain is normally very good at regulating the volume of blood in its vessels. If the brain vasculature is not fully developed, the sudden increase in blood pressure when the placenta is cut off (no pun intended) from the peripheral circulation can cause the brain blood vessels to burst.

TIL: ...a wonderfully inappropriate mnemonic (aren't all the best ones?) for the structures of the cerebellum:
Lovers can't cum? Don't fret! Try prayer, U novice.
Cerebellar structures: Lingula, culmen, cline, decline, folium, trigone, pulvinar, uvula, nodulus.