renal-exam 1-potassium

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renal-exam 1-potassium
2010-03-02 22:34:29

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  1. total body potassium
    about 3500 mEq(50-55 mEq/kg), potassium is the primary intracellular cation
  2. intracellular concentration of pot
    120-150 mEq/L
  3. extracellular conc of pot
    3.5-5 mEq/L
  4. function of potassium
    ratio of intra and extra K determinant of resting membrane potential, regulate protein and glycogen syn
  5. beneficial effects of potassium
    decrease: BP, risk of stroke, risk of ventricular arr, inhbiit free radical form, vascular smooth muscle proliferation and arterial thrombosis, strong bones
  6. average daily req of K
    50 mEq/day, most get 50-150mEq
  7. Na-K-ATPase pump
    promotes K into cells, and Na transport out of cells
  8. effect of insulin on N-K-ATPase pump
    increase pump activity, increase K into cells
  9. effect of catecholamines(EPI) on na-k-atpase pump
    dual mechanism, increase pump activity and stimulate blood glucose, increases insulin
  10. H-K-ATPase pump
    to maintain electroneutrality, metabolic acidosis(increase H in blood, pump increases H into cells and K out of cells, increase in serum K), metabolic alkalosis(decrease H in blood, pump increases H into blood and increases K into cells, decreases serum potassium)
  11. primary site of potassium regulation
    collecting duct, secreted via na-k-atpase pump. reabsorbed via h-k-atpase
  12. aldosterone effect on na-k-atpase pump
    activatesin collecting duct, secretion of k into the tubules in exchange for Na
  13. high sodium diet effect on potassium
    enhances sodium reabsoprtion and increases potassium secretion
  14. distal flow rate effect on potassium
    increased, potassium secretion increases, and reabsoprtion decreases, seen with polyuria and diuretics
  15. Gi and potassium
    increases 3-4 x's with decreased renal fxn, potassium secreted into sm int and colon in response to aldosterone
  16. mild hypokalemia
    3.0-3.5 mEq/L
  17. moderate hypokalemia
    2.5-3.0 mEq/L
  18. severe hypokalemia
    <2.5 mEq/L
  19. relationship to total body deficit
    every decrease in 0.3mEq/L K, 100 mEq total body K deficit
  20. increased entry into cells-hypokalemia
    increased avail of insulin, elevated B2 adrenergic activity, metabolic alk, anabolic states, refeeding syn, treatment of pernicious anemia
  21. increased renal losses-hypokalemia
    MC excess, increased distal sodium delivery, increased flow to the distal nephron
  22. hypomagnesemia related to hypokalemia
    correct both or it will be hard to correct hypokalemia
  23. drug induced hypokalemia
    B2 agonists, theophylline, caffeine, insulin overdose, GM-CSF, diuretics, MCs, high dose GCs, high dose IV PCN abxs, drugs assoc with Mg depletion(AGs, cis, amp B, foscarnet)
  24. NM manifestations of hypokalemia
    muscle weakness, muscle cramps, paresthesia, impairment of respiratory muscle fxn
  25. cardiac toxicity related to hypokal
    arr, St segment depression, T wave depression, U-wave elevation
  26. first tx for hypokal
    treat underlying cause
  27. potassium formulations
    Wax matrix capsules-higher incidence of GI ulceratin, microencapsulateed-can be dissolved in H20 or sprinkled on applesauce, effervescent tablets, liquids and powders-tastes bad, Gi irritation, NV, IV-phlebitis can occur
  28. salt forms of potassium
    • chloride-use in presence of chloride depletion or metabolic alkalosis
    • bicarbonate, citrate, acetate(precursors to bicarbonate, use if metabolic acidosis, gluconate
  29. route of potassium for hypokalemia
    oral is preferred(less risk of tx-induced hyperkal, no phlebitis), IV-severe hypo <2.5, pts with EKG changes, pts unable to tolerate oral formulation, precautions
  30. Concentration issues related to potassium infusion
    needs to be diluted, peripheral more irritation than central(less volume), invert bag and squeeze, can add lidocaine 10-30mg/L, can also burn, central line 100-400 mEq/L, periph 10-100mEq/L
  31. rate of administration (NO BOLUS) of potassium
    adult: max(no EKG)-10 mEq/hr, (with EKG)-20mEq/hr unless life threatening arr present, then up to 40 mEq/hr

    Child: max(no EKG)-0.5 mEq/kg/hr up to a max of 10 mEq/hr, with EKG-1 mEq/kg/hr up to a max of 20 mEq/hr
  32. monitoring for replacement of potassium
    check serum potassium q 40 mEq of potassium replaced
  33. dose for repletion of potassium
    40-100 mEq/d
  34. dose for prevention(i.e. diuretic induced) of potassium
    20 mEq/day
  35. target serum potassium for replacement or prevention
    normal: 3.5-5, 4-4.5 mEq/l in pts with CVD disease
  36. other options to supplement potassium
    salt substitutes (10 mEq K/gm about 200 mEq/tablespoon or potassium containing food-usually coupled with phos or citrate, less likely to correct hypokalemica assoc with calcium depletion(diuretic induced), hypokal assoc with hypomag-magnesium oxide (mag ox 400 qid) po or magnesium chloride (slow-mag qid)
  37. mild hyperkalemia
    5.0-6.0 mEq/L
  38. moderate hyperkalemia
  39. severe hyperkalemia
  40. increased intake of potassium
    salt substitutes, enteral nutrition, dietary supplements, K repletion, metamucil effervescent
  41. movement from cells into extracellular fluid-hyperkalemia
    pseduohyperkalemia(hemolysis of RBC), metabolic acidosis, insuin deficiency(diabetic ketoacidosis), tissue catabolism(trauma, tumor lysis syn, rhabdomyolysis)
  42. decreased urinary excretion-hyperkalemia
    hypoaldosteronism(addison's, retaining more K), decreased sodium delivery, renal failure
  43. drug inducers of hyperkalemia
    ACE/ARBs(hypoaldosteronism), potassium-sparing diuretics(ami, triam, spirono, eplerenone)(impaired potassium excretion), dig toxicity(decreased Na-k-atpase activity_
  44. clinical manifestations of hyperkalemia
    muscle weakness (K>7 mEq/L)-more common with hypokalemia
  45. cardiac signs and symptoms of hyperkalemia(more commonly seen but not everyone experiences)
    palpitations, peaked T wave (>5.5-6), prolonged PR interval and widening of QRS (6-7), slowed cardiac conduction (7-8), ventricular fibrillation (9-10_ asystole (10-12)
  46. treatment of hyperkalemia(3 things)
    antagonize action on heart with calcium, redistribute K inside cells (insuline and albu) remove excess potassium(diuretics, SPS, hemodialysis)
  47. acute hyperkalemia <6mEq/L, asymptomatic, and no changes on ECG
    decrease intake, d/c offending agents, diuretics(furo 20-40 mg po or IV (over 5 min)q 4-6 hr prn
  48. acute hyperkalemia, above or equal to 6 or symptomatic or ECG changes,
    antagonize action on cardiac muscle, redistribute potassium
  49. acute hyperkalemia, above or equal to 6 or symptomatic or ECG changes,antagonize action of potassium
    with ca gluc (or chloride-3 x's more ca bad with extrav) 1 gm over 5-10 min(slow IV push), onset 1-2 min, dur:30 min, may repeat if no effect in 5-10 min(short-term, will only buy time)
  50. acute hyperkalemia, above or equal to 6 or symptomatic or ECG changes, redistribute potassium
    insulin 10 units plus or minus glucose 50 gm over 5 minutes, onset 10-20 min, duration 4-6 hours(drives K into cells) or albu 10-20 mg nebulized, onset-30 min, duration-2 hours
  51. chronic hyperkalemia associated with decreased renal fxn
    1. diuretics 2. SPS-4-6 hours for onseet, use in caution with CHF risk of volume overload, exchanges 1 mEq potassium for 1 mEq/sodium/gm of resin, PO-15-60 gm in 60-240 mL of 20% sorbitol, rectal dose 30-60 gm + 150 ml water, 3. hemodialysis(most effective, but takes awhile to set up)
  52. chronic hyperkalemia associated with normal renal fxn
    if decrease aldosterone level-fludrocortisone 0.1 mg PO d to TIW, if increased aldosterone level and increase BP-diuretic, if above efforts fail, low potassium diet plus or minus kayexalate...after measuring aldosterone levels