POTASSIUM HOMEOSTASIS

I. Hypokalemia:

1. Causes: vomiting, diuretics, hyperaldo (liver failure, CHF, Cushing's), diarrhea, renal tubular dis.
2. Effects: U waves bigger than T's on EKG; ventr. ectopy
3. Treatment: oral K supplements (40-80mEq in divided doses), IV K (40-80mEq in 500ml D5W IV over 3-6h with cardiac monitor; max. 0.5 mEq/kg/h up to 30mEq/h in adults, ?given as max 40mEq/l unless in central line?)

II. Hyperkalemia:

1. Causes:

1. Reduced kaliuresis

1. Reduced GFR: Acute or Chronic RF of any cause
2. Reduced tubular K secr.: Addison's & other hypoaldo states, K-sparing diuretics

2. Shifts between fluid compartments

1. Acidosis
2. Cell destruction (tumor lysis, burns, hemolysis)
3. Hypoinsulinemia, esp. with hyperglycemia

3. Exogenous K admin. with decr. ability to excrete

1. Straight K admin
2. Transfusion

4. Digitalis

2. Effects:

1. Cardiac: Peaked T's @ 6.5mEq/l; Inc. PR intvl @ 7-8, then lost P & wide QRS; asystole @ 8-10

3. Management options

1. Calcium gluconate--counters cardiac effects; May unmask Digoxin toxicity
2. Glucose + Insulin IV
3. Sodium bicarbonate IV
4. Inhaled beta-2 adrenergic agonists (?)
5. Dialysis
6. Increase potassium excretion with

1. Diuretics
2. Hemodialysis
3. Sodium polystyrene sulfonate (Kayexelate) PO or PR
   1. Can cause constipation, so often given with sorbitol, although the combination may be associate dwith colonic necrosis
   2. Can also cause sodium overload
   3. May not actually result in clinically significant reduction of serum potassium concentration (J. Am. Soc. Nephrol. 21:733, 2010-JW)