electrolyte 1 - hypokalemia (↓K+)

normal sodium (Na⁺) range

135-145 mEq/L

normal chloride (Cl^-) range

98-107 mEq/L

normal potassium (K⁺) range

3.5 - 5.0 mEq/L

normal phosphorus (PO₄^-) range

2.7-4.5 mg/dL

normal calcium (Ca²⁺) range

8.4-10.2 mg/dL

normal magnesium (Mg²⁺) range

1.6-2.4 mg/dL

total body water (TBW)

distributed primarily into 2 compartments:

1. the intracellular compartment (ICF; 60% of TBW)

2. the extracellular compartment or extracellular fluid (ECF; 40% of TBW)

intracellular compartment (ICF)

ICF osmolality is primarily determined by the concentration of potassium and its accompanying anions (mostly organic and inorganic phosphates)

extracellular compartment/extracellualr fluid (ECF)

sodium and its accompanying anions (chloride and bicarbonate) comprise more than 90% of the total osmolality of the ECF

describe the compartmentalization of potassium

• potassium is the most abundant cation in the body, with estimated total-body stores of 3,000 to 4,000 mEq (3,000 to 4,000 mmol)

• the sodium-potassium-adenosine triphosphatase (Na⁺-K⁺-ATPase) pump located int eh cell membrane is responsible for the compartmentalization of potassium

  • this pump is an active transport system that maintains increased intracellular stores of potassium by transporting sodium out of the cell and potassium into the cell at a ration of 3:2

which drugs cause hypokalemia through intracellular shift?

• beta receptor agonists and catecholamines:

  • epinephrine, albuterol, terbutaline, pseudoephedrine

• insulin

• alkalosis — sodium bicarbonate*

  (also causes hypokalemia through renal loss)

which drugs cause hypokalemia through renal loss?

• thiazides

• loop diuretics

• penicillin

• alkalosis — sodium bicarbonate*

  (also causes hypokalemia through intracellular shift)

which drugs cause hypokalemia through GI loss

• laxatives

  • sorbitol, sodium polystyrene sulfonate

functions of potassium

• cellular metabolism & growth

• protein & glycogen synthesis

• regulation electoral gradient across myocardium

  • cardiac conduction

symptoms associated with mild hypokalemia

• 3.1 - 3.49 mEq/L

• may be asymptomatic

• N/V

• muscle weakness

symptoms associated with moderate and severe hypokalemia

• mild = 2.5 - 3.0 mEq/L

• severe = < 2.5 mEq/L

• paralysis

• respiratory compromise

• EKG changes

• cardiac arrhythmias

• death

underlying causes of hypokalemia

• refeeding syndrome:

  • can occur when severely malnourished pts (ie nutrition depleted for 7-10 days) receive aggressive nutritional supplementation —> causes severe/rapid:

    • ↓ serum phosphate

    • ↓ serum potassium

    • ↓ serum magnesium

• medications

• metabolic alkalosis (pH ↑, K⁺↓)

  • for every 0.1 ↑ in pH, [K⁺] ↓ by < 0.4

• hemodialysis

• magnesium deficiency

  • renal outer medullar potassium (ROMK) channel

hypokalemia management if pt needs to be on diuretic therapy

consider using a potassium sparing diuretic:

• aldosterone antagonists:

  • spironolactone

  • eplerenone

• sodium channel blockers:

  • amiloride

  • triamterene

potassium sparing diuretics MOA

in the collecting duct and distal tubule:

1. aldosterone antagonism (spironolactone and eplerenone)

   • inhibits aldosterone —> ↓ Na⁺ reabsorption and ↑ K⁺ sparing

2. inhibition of aldosterone sensitive sodium channels (amiloride and triamterene)

non-pharmacologic treatment for hypokalemia

diet — high potassium content foods

consensus guidelines on pharmacological treatment of hypokalemia

• usual dose to prevent hypokalemia = 20 mEq/day

• usual dose to treat hypokalemia = 40-100 mEq

• K⁺ repletion therapy is best administered orally in divided doses over several days to achieve full repletion

• K⁺ repletion therapy is recommended for pts who are:

  • sodium-senstive

  • hypertensive

  • subject to vomiting or diarrhea

  • taking diuretics

  • subject to laxative abuse

potassium repletion in pts with renal dysfunction

caution in repleting potassium in patients with renal dysfunction

• reduce by ~50% in renal insufficiency

when is PO preferred and when is IV preferred?

oral route is preferred if patient can tolerate PO and is asymptomatic

• if pt has severe hypokalemia, might need both PO and iV

• if pt is in the ICU, IV may be preferred

• if pt is NPO, IV route is preferred

which do you replete first if the pt has concomitant hypomagnesemia and hypokalemia?

replete magnesium first if it is low

oral treatment for hypokalemia

most to least % of potassium:

• Potassium Chloride

  • Rx

  • both PO and IV

• Potassium Bicarbonate

  • OTC/Rx

  • PO

• Potassium Citrate

  • OTC/Rx

  • PO

• Potassium Gluconate

  • OTC

  • PO

• Potassium Phosphate

  • Rx

  • both PO and IV

K-Phos products

• used for pts with BOTH hypophosphatemia AND hypokalemia

• different products contain SAME amount of phosphorus and VARIABLE amounts of potassium (and sodium)

• to minimize GI damage, dissolve tablets in 6-8 oz water for at least 2-5 min (can crush tablet particles that remained undissolved. stir vigorously)

• most to least K+ content:

  • Phos-NaK (*max is TID dosing)

  • K-Phos No. 2

  • Phospha 250 Neutra

  • K-Phos Neutral

oral K+ products ADEs

common:

• GI side effects (e.g. N/V, diarrhea, flatulence)

  • if dose > 40 mEq, it should be give in divided dose

    • ex. if the pt needs 60 mEq, give 30 mEq PO BID

serious:

• abdominal pain, GI ulcer

• cardiac arrest, arrhythmias

• hyperkalemia

compare the different formulations of potassium supplements

IV K⁺ products

• potassium chloride — most common, most efficient (i.e., raises serum [K⁺] at a faster rate)

  • for every ~10 mEq of K⁺ administered, serum K⁺ will ↑ by 0.1 mEq/L

• potassium phosphate — use if pt also has hypophosphatemia

• potassium acetate — use if pt has metabolic acidosis

IV K⁺ products ADEs

common:

• phlebitis (inflammation of the vein)

• injection site pain (burning)

• extravasation (can lead to tissue necrosis)

serious:

• cardiac arrest, arrhythmias

• hyperkalemia

IV potassium administration

IV potassium monitoring

• cardiac function (tele monitoring, ECGs)

• K⁺ levels

  • within 2-8 hours after replacement (sooner if symptomatic)

  • daily with morning labs

• signs of phlebitis, extravasation

IV push vs IV piggyback (IVPB)

• IV piggyback (IVPB) = administered as an infusion

• IV push = administered via syringe

• NEVER give K⁺ as an IV push —> will cause cardiac arrest

compartmentalizationof potassium (concept map)

• the normal concentration range for potassium is 3.5-5 mEq/L

• the intracellular potassium concentration is usually approximately 150 mEq/L

• the Na⁺-K⁺-ATPase is responsible for the compartmentalization

different formulations of potassium supplement GI intolerance (concept map)

wax-matrix extended-release tablets > controlled release micro-encapsulated tabletsrimp

primary causes of hypokalemia (concept map)

• loop and thiazide diuretic administration

• excessive loss of potasisum-rich GI fluid as a result of diarrhea and/or vomiting

drug induced hypokalemia

• beta2 agonsits

• insulin overdose

• high dose of penicillins