Definitions & Incidence
- Defined as serum potassium < 3.5 mEq/L.
- Classification: Mild 3-3.4, Moderate 2.5-2.9, Severe < 2.5 mEq/L.
- Prevalence: 16% in adolescents hospitalized for eating disorders. 40.2% in pediatric intensive care admissions.
- Distribution: 98% of total body K is intracellular (150 mEq/L), 2% is extracellular (4 mEq/L). Na/K-ATPase maintains gradient.
- Fecal wastage usually small (10 mEq/day) but drastically increases in diarrhea (30-60 mmol/L in stool).
Diagnostic Approach
- Check Urine K Fraction (<40% vs >40%), K/Cr ratio, and TTKG.
- Renal wasting (TTKG > 4): Assess acid-base status.
- With Metabolic Acidosis: Check anion gap. High gap = DKA. Normal gap = RTA or acetazolamide.
- With Metabolic Alkalosis: Check Urine Chloride. If <10 mmol/L = Vomiting / CF. If >20 mmol/L (Normotensive) = Bartter / Gitelman / Diuretics.
- If >20 mmol/L + Hypertensive: Check Renin & Aldosterone. Normal Re/Aldo = Cushing. Low Re/Aldo = Liddle / CAH / Licorice. High Re/Aldo = Renal artery stenosis. Low Re/High Aldo = Primary hyperaldosteronism.
- Transcellular Shift Causes: Alkalosis, beta-2 agonists (albuterol), insulin, xanthines, hypothermia, barium/cesium toxicity.
Clinical Presentation
- Symptoms: Muscle cramps, fasciculations, weakness, rhabdomyolysis, polyuria, polydipsia, constipation (smooth muscle ileus).
- Severe (<2.5): Paralysis, respiratory failure, myocardial necrosis.
- ECG Findings: T-wave decrease/inversion, ST depression, Prominent U-waves (fusion of T and U), prolonged PR/QT.
Management & Guidelines
- Check/Replace Magnesium: Treatment is fundamentally refractory if hypomagnesemia is not corrected. Use MgSO4 25-50 mg/kg IV every 4-6 hrs.
- Dietary: White beans, spinach, potatoes, apricots, bananas, avocados.
- Oral Route (Preferred if stable): 1-2 mEq/kg every few hours. Max single dose 40 mEq, max day 100 mEq.
- IV Route (Severe/Arrhythmias): Potassium Chloride. Dose 1 mEq/kg (max 40mEq for peripheral line) over 1-2 hours.
- Rate Limit: Target to raise serum K by 0.3-0.5 mEq/L/hour. Strict max peripheral concentration is 40 mEq/L to prevent extreme phlebitis.
- Caution: NEVER give IV Potassium in a Dextrose solution (stimulates insulin, drives K further into cells).
Diagnostic & Management Algorithm
- Hypokalemia Replacement: [START] Serum K < 3.0 -> [DECISION] Arrhythmias present? -> [YES] IV KCl 0.5-1.0 mEq/kg over 1 hour (monitor ECG) -> [NO] Oral KCl or increase TPN K
References for this guideline are being added; see the methodology for our source hierarchy.
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