9 - Dyskalemias Flashcards
largest store of ICF potassium is in
muscle
clinical scenarios in which ICF potassium floods ECF
crush injuries
rhabdomyolysis
acute liver failure
hemolysis
3 short term causes of K uptake by cells
insulin
epi (beta 2)
alkalosis (less important)
beta blockers have what effect on serum K
higher after ingesting K load
urinary K is from filtered, secreted, or both?
secreted
2 factors regulating renal K secretion by principal cells
aldosterone
distal Na delivery
results of aldosterone action
lumen negativity in CCD
K and H secretion, Na reabsorption
hypokalemic periodic paralysis
intermittent acute attacks of muscle weakness w/ hypokalemia
triggered by large carb meals, rest post exercise
2 forms - AD mutation in DHP sensitive Ca channel OR thyrotoxicosis
3 possibilities for hypokalemia w/ metab alkalosis and high urine Cl
loop/thiazide diuretics
bartter’s syndrome
gitelman’s syndrome
Bartter’s syndrome
mutation in transporters in TAL of LoH
phenotype is that of pt taking loop diuretic > dec fn of Na/K/2Cl channel
hypokalemia, metab alkalosis, absence of HTN, hypocalcemia
Gitelman’s syndrome
mutation in Na/Cl cotransporter in DCT - looks like pt is on thiazide diuretics
hypokalemia, metab alkalosis, no HTN, hypercalcemia
example of condition that can cause hypokalemia with metab alkalosis and low urine Cl
vomiting:
lose H from stomach > absorb bicarb in small intestine
excess plasma bicarb > overwhelms reabs in PCT > lose as NaBicarb
volume depletion > stim aldosterone > K loss, > PCT Na and Cl reabs > low urine chloride
what is the next step in evaluating a pt w/ hypokalemia and high BP?
check renin and aldosterone levels
causes of hypokalemia w/ HTN and high renin and aldosterone
renin secreting tumor
RAS > hypoperfused kidney keeps secreting renin regardless of volume status
both cause K wasting from aldosterone and high BP from NaCl retention
causes of hypokalemia w/ HTN and low renin and high aldosterone
Conn’s syndrome - aldosterone secreting tumor
bilateral adrenal gland hyperplasia
glucocorticoid remediable aldosteronism (GRA)
glucocorticoid remediable aldosteronism (GRA)
AD inheritance
crossover of aldosterone synthase and steroid 11B-hydroxylase that causes aldosterone secretion to be under control of ACTH instead of ATII
tx w/ dexamethasone to suppress ACTH
causes of hypokalemia w/ HTN and low or normal renin and aldosterone
Cushing’s syndrome
Syndrome of Apparent Mineralocorticoid Excess (SAME)
Liddle’s syndrome
SAME
syndrome of apparent mineralocorticoid excess
dysfunctional enzyme 11B-OHSDH that normally breaks down cortisol. extra cortisol in principal cell binds to mineralocorticoid receptor and acts like there is too much aldosterone > hypokalemia and HTN
licorice (glycyrrhizic acid) can cause what syndrome?
SAME
Liddle’s syndrome
mutation in Na channel (eNaC) in CD principal cell > always open
causes hypokalemia, HTN, metabolic alkalosis (looks like hyperaldosteronism)
tx: block that channel (amiloride)
clinical presentation of hypokalemia
asymptomatic until nephrogenic DI due to ADH resistance
U wave is pathognomonic for
hypokalemia
tx for hypokalemia
give K - oral is safest, IV burns small vessels
K rich foods
potatoes, beans, avocados, spinach, banana, tomato, raisin, fish
3 causes of impaired K entry into cells resulting in acute hyperkalemia
lack of insulin - hyperglycemia pulls K rich water out of cells SYNS blockade (beta blockers) inorganic acidoses
why do inorganic acidoses cause hyperkalemia but organic ones (lactic for ex) dont?
in organic, the anion can follow H in so K doesnt have to leave
in inorganic, the anion often can’t follow H in, so K is driven out
2 main causes of chronic hyperkalemia
renal failure
hypoaldosteronism (includes K sparing diuretics which block aldosterone)
2 times when you might be in a hypoaldosterone state
type 4 RTA
spironolactone
hyperkalemia clinical presentation
depolarizes cardiac muscle - peaked T waves, loss of P wave, widened QRS, basically progressing towards sine wave / Vfib
skeletal muscle weakness
hyperkalemia tx
stabilize cardiac fn w/ IV calcium (doesnt fix hyperkalemia at all)
shift K into cells (quick fix) - insulin+glucose, beta 2 agonist, NaBicarb (may not work in renal failure)
remove K from body - diuretics, cathartic or cation exchange resin (kayexalate), dialysis
why does high aldosterone cause alkalosis?
intercalated cell secretes H allowing bicarb to enter blood
how do you differentiate bartter’s from gitelman’s?
urine calcium
