-
total body potassium
about 3500 mEq(50-55 mEq/kg), potassium is the primary intracellular cation
-
intracellular concentration of pot
120-150 mEq/L
-
extracellular conc of pot
3.5-5 mEq/L
-
function of potassium
ratio of intra and extra K determinant of resting membrane potential, regulate protein and glycogen syn
-
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
-
average daily req of K
50 mEq/day, most get 50-150mEq
-
Na-K-ATPase pump
promotes K into cells, and Na transport out of cells
-
effect of insulin on N-K-ATPase pump
increase pump activity, increase K into cells
-
effect of catecholamines(EPI) on na-k-atpase pump
dual mechanism, increase pump activity and stimulate blood glucose, increases insulin
-
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)
-
primary site of potassium regulation
collecting duct, secreted via na-k-atpase pump. reabsorbed via h-k-atpase
-
aldosterone effect on na-k-atpase pump
activatesin collecting duct, secretion of k into the tubules in exchange for Na
-
high sodium diet effect on potassium
enhances sodium reabsoprtion and increases potassium secretion
-
distal flow rate effect on potassium
increased, potassium secretion increases, and reabsoprtion decreases, seen with polyuria and diuretics
-
Gi and potassium
increases 3-4 x's with decreased renal fxn, potassium secreted into sm int and colon in response to aldosterone
-
mild hypokalemia
3.0-3.5 mEq/L
-
moderate hypokalemia
2.5-3.0 mEq/L
-
severe hypokalemia
<2.5 mEq/L
-
relationship to total body deficit
every decrease in 0.3mEq/L K, 100 mEq total body K deficit
-
increased entry into cells-hypokalemia
increased avail of insulin, elevated B2 adrenergic activity, metabolic alk, anabolic states, refeeding syn, treatment of pernicious anemia
-
increased renal losses-hypokalemia
MC excess, increased distal sodium delivery, increased flow to the distal nephron
-
hypomagnesemia related to hypokalemia
correct both or it will be hard to correct hypokalemia
-
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)
-
NM manifestations of hypokalemia
muscle weakness, muscle cramps, paresthesia, impairment of respiratory muscle fxn
-
cardiac toxicity related to hypokal
arr, St segment depression, T wave depression, U-wave elevation
-
first tx for hypokal
treat underlying cause
-
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
-
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
-
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
-
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
-
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
-
monitoring for replacement of potassium
check serum potassium q 40 mEq of potassium replaced
-
dose for repletion of potassium
40-100 mEq/d
-
dose for prevention(i.e. diuretic induced) of potassium
20 mEq/day
-
target serum potassium for replacement or prevention
normal: 3.5-5, 4-4.5 mEq/l in pts with CVD disease
-
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)
-
mild hyperkalemia
5.0-6.0 mEq/L
-
moderate hyperkalemia
6.1-6.9mEq/L
-
severe hyperkalemia
>7mEq/L
-
increased intake of potassium
salt substitutes, enteral nutrition, dietary supplements, K repletion, metamucil effervescent
-
movement from cells into extracellular fluid-hyperkalemia
pseduohyperkalemia(hemolysis of RBC), metabolic acidosis, insuin deficiency(diabetic ketoacidosis), tissue catabolism(trauma, tumor lysis syn, rhabdomyolysis)
-
decreased urinary excretion-hyperkalemia
hypoaldosteronism(addison's, retaining more K), decreased sodium delivery, renal failure
-
drug inducers of hyperkalemia
ACE/ARBs(hypoaldosteronism), potassium-sparing diuretics(ami, triam, spirono, eplerenone)(impaired potassium excretion), dig toxicity(decreased Na-k-atpase activity_
-
clinical manifestations of hyperkalemia
muscle weakness (K>7 mEq/L)-more common with hypokalemia
-
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)
-
treatment of hyperkalemia(3 things)
antagonize action on heart with calcium, redistribute K inside cells (insuline and albu) remove excess potassium(diuretics, SPS, hemodialysis)
-
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
-
acute hyperkalemia, above or equal to 6 or symptomatic or ECG changes,
antagonize action on cardiac muscle, redistribute potassium
-
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)
-
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
-
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)
-
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
|
|