Internal Medicine

0521779407-09 CUNY1086/Karliner 0 521 77940 7 June 13, 2007 7:54

786 Hypokalemia

Hypokalemia.......................................

BIFF F. PALMER, MD

history & physical

■clinical setting often helpful in determining etiology

■does patient have significant leukocytosis (>100,000)

■recurrent sudden weakness precipitated by high carbohydrate meal

or exercise, symptoms of hyperthyroidism in Asian or Mexican

patient

■chronic alcoholic, anorexia nervosa

■diarrhea, laxative abuse

■vomiting/nasogastric suction, diuretic use

■presence or absence of hypertension

tests

■measure 24 hour urinary K excretion to determine renal versus

extrarenal loss

■if urine K <20 mEq/24h, check stool phenolphthalein to screen for

surreptitious laxative abuse

■if hypertensive measure plasma renin and aldosterone

■measure plasma HCO3, Mg++

differential diagnosis

■pseudohypokalemia (WBC >100,000)

■redistribution (can account for transient not chronic hypokalemia)

➣insulin use

➣alkalosis (can only explain minimal declines in plasma K)

➣beta-2 adrenergic stimulants (epinephrine, albuterol inhaler)

➣post-vitamin B(12) for megaloblastic anemia

➣hypothermia

➣familial hypokalemic periodic paralysis (mutation in voltage acti-

vated Ca channel)

➣Acquired hypokalemic periodic paralysis with thyrotoxicosis

■extrarenal loss

➣diarrhea, surreptitious laxative use, villous adenoma, excessive

sweating (unusual)

■renal loss

➣primary increase in distal Na delivery (normal or low EABV) (UNa

>20 mEq/L)

increased serum HCO3, increased urine Cl (>20 mEq/L)