腎臟科Nephrology random notes 02: Hypokalemia

Hypokalemia

1. K+ pool in body: 3500 mEq l (50 mmol/Kg), extracellular only 60~80 mEq

    Daily intake: 100 mEq

2. K+ balance:

- acute internal balance: transcellular; driving force (inward) including Na/K pump, Na/H exchange, beta 2 agonist, insulin, thyroid hormone

- chronic external balance: renal secretion ; K+ secretion = [K+ ]CCD x Flow rateCCD

- GI: (metabolic acidosis)diarrhea, laxative use, villous adenoma,  (metabolic alkalosis) NG drainage, vomiting

3. Definition 

- K+ <3.5 mEq/L in blood

- does no equal low K+ in sum 

4. Etiologies:

- Uk >30 mEq/ day, >15 mEq/L, TTKG>7 --> renal loss--> check BP, acid-base, Ucl

- Uk <25 mEq/ day, <15 mEq/L, TTKG<3 -->extrarenal loss

TTKG= (urine/plasma [K+ ])/(urine/plasma osmolality)

5.  Common manifestations
- Mild to moderate= 2.5~3.5 mEq, usually asymptomatic

- Arrhythmia ( U wave, QT interval↑, PVCs, VT, VF)

- Muscle cramps and weakness

- Polyuria

- n/v, ileus

- tendon reflex↓

6. Treatment

Lin SH, Halperin ML. Hypokalemia: a practical approach to diagnosis and its genetic basis. Curr Med Chem 2007; 14: 1551-65.
Kunin AS, Surawicz B, Sim EA. Decrease in serum potassium concentrations and appearance of cardiac arrhythmias during infusion of potassium with glucose in potassium-depleted patients. N Engl J Med 1962; 266: 228-33

↓ 1 mEq= 200 mEq total body loss
K+ 2.5~3.5 mEq↓: oral slow-K 40~100 mEq/day, no more than 20 mEq in one dose
K+ 2.5 mEq↓: IV K+ supplement, do not give over 40 mmol/L or 60 mmol/hour
Peripheral line: 20 mEq/L(max 40), 10 mEq/hr
Central line: 40 mEq/L(max 100), 20 mEq/hr~40mEq/hr

IV: DO NOT mix with dextrose solution metabolic acidosis:  use KHCO3, K+ citrate
metabolic alkalosis: use KCl
low phosphorous: use K+ phosphate

Potassium sparing diuretics: 
- amiloride
- triamterene
- spironolactone #1 BID or #2 QD with loop diuretics #1?