//fpnotebook.com/
Hypokalemia
Aka: Hypokalemia, Hypokalemia Related EKG Changes
- See Also
- Serum Potassium
- Hypokalemia due to Renal Potassium Loss
- Hypokalemia due to Extrarenal Potassium Loss
- Hypokalemia due to Transcellular Potassium Shift
- Familial Periodic Paralysis
- Potassium Replacement
- Dietary Potassium
- Pathophysiology
- Approximate Total body Potassium = 55 meq/kg
- Serum Potassium decreased 0.3 mEq/L: 100 mEq K+ total body deficit
- Serum Potassium decreased 1 mEq/L: 350 mEq K+ total body deficit
- Serum Potassium less than 2 mEq/L: 1000 mEq K+ total body deficit
- Causes
- Hypokalemia due to Transcellular Potassium Shift
- See Transcellular Potassium Shift
- Medications (Beta-agonists, Insulin excess)
- Metabolic Alkalosis
- Hypokalemic Periodic Paralysis
- Thyrotoxicosis
- Hypokalemia due to Renal Potassium Loss
- See Renal Potassium Loss (Hyperkaluria)
- Hypertension: Obtain Plasma Renin and Aldosterone
- Renin high
- Renovascular disease, renin secreting tumor or Malignant Hypertension
- Renin normal
- Liddle's Syndrome
- Renin low
- Aldosterone High: Primary Hyperaldosteronism, Bilateral adrenal hyperplasia
- Aldosterone Low: Congenital Adrenal Hyperplasia, Cushing's Syndrome, Ectopic ACTH
- Normotensive: Obtain serum bicarbonate and Urine Chloride
- Serum Bicarbonate Low
- Renal Tubular Acidosis
- Serum Bicarbonate High
- Urine Chloride Low: Vomiting
- Urine Chloride High: Barter's Syndrome, Normotensive primary Hyperaldosteronism, Diuretic use
- Hypokalemia due to Extrarenal Potassium Loss
- See Extrarenal Potassium Loss
- Normal Acid-Base Status or Metabolic Alkalosis
- Gastrointestinal or skin losses, Hypomagnesemia, Penicillin or Aminoglycosides, Acute Leukemia
- Metabolic Acidosis
- Diabetic Ketoacidosis, Diarrhea, Laxatives
- Other causes
- Inadequate Potassium intake (typically in hospitalized patients)
- Total Parenteral Nutrition
- Anorexia or Starvation
- Dementia
- Pseudohypokalemia
- Delayed lab analysis of sample
- Severe Leukocytosis (>75,000/mm3)
- Findings: Symptoms and Signs (when Serum Potassium < 2.5 mEq/L)
- General
- Malaise
- Fatigue
- Neurologic
- Weakness
- Decreased Deep Tendon Reflexes
- Paresthesia
- Cramps
- Restless Legs Syndrome
- Rhabdomyolysis
- Paralysis
- Gastrointestinal
- Constipation
- Ileus
- Exacerbated Hepatic Encephalopathy
- Cardiovascular
- Orthostatic Hypotension
- Hypertension
- Arrhythmias (rare in otherwise healthy patients)
- Acute or recent Myocardial Infarction (5 fold increased risk of Ventricular Fibrillation if K+ <3.9 mEq/L)
- Digoxin use and Hypokalemia predisposes to Arrhythmia
- Renal
- Metabolic Alkalosis
- Polyuria, Polydipsia
- Decreased GFR
- Glucose Intolerance
- Labs
- Serum Potassium <3.5 mEq/L
- Serum Magnesium
- Confirm no Hypomagnesemia (Hypokalemia cause)
- Complete Blood Count
- Confirm no severe Leukocytosis (pseudohypokalemia)
- 24 hour Urine Potassium and Urine Sodium
- Most accurate evaluation of Urine Potassium excretion
- However, Urine Potassium-to-Creatinine ratio is typically obtained instead
- Sample should have total Urine Sodium > 100 meq
- Urine Potassium <20-30 meq/day
- See Extrarenal Potassium Loss
- Urine Potassium >20-30 meq/day
- See Renal Potassium Loss
- Urine Potassium-to-Creatinine ratio
- Ratio <=1.5 mEq/mmol: Hypokalemia due to Extrarenal Potassium Loss
- Manage underlying losses
- Ratio >1.5 mEq/mmol: Hypokalemia due to Renal Potassium Loss
- Elevated Blood Pressure or hypervolemia (mineralcorticoid excess)
- Hyperaldosteronism
- Renal Artery Stenosis
- Cushing Syndrome
- Congenital Adrenal Hyperplasia
- Metabolic Acidosis
- Type I and II Renal Tubular Acidosis
- Metabolic Alkalosis
- Diuretics
- Renal Tubular transport disorders (e.g. Bartter Syndrome)
- Diagnostics: Electrocardiogram
- Early changes
- T Waves decreased amplitude to flattened
- Later changes
- Prominent U Waves
- ST depression
- T Wave Inversion
- PR prolongation (first degree AV Block)
- QTc Prolongation
- Arrhythmias associated with Hypokalemia
- Sinus Bradycardia
- Ventricular Tachycardia or Ventricular Fibrillation
- Torsade de pointes
- Management: General
- Potassium Replacement
- Goal Serum Potassium >3.5 mEq/L (>4.0 in CAD, CHF)
- Total body Potassium deficit
- Serum Potassium: <3.5 mEq/L = 100 meq total Potassium deficit
- Serum Potassium: 3.2 mEq/L = 200 meq total Potassium deficit
- Serum Potassium: 2.9 mEq/L= 300 meq total Potassium deficit
- Serum Potassium: 2.6 mEq/L = 400 meq total Potassium deficit
- Avoid rebound Hyperkalemia (over-shooting replacement)
- Hyperkalemia with replacement is unlikely if normal Renal Function, adequate fluid intake
- Dietary Potassium (Potassium phosphate) is less efficient replacement than Potassium chloride
- Most Hypokalemia is associated with concurrent chloride depletion
- However Potassium chloride compliance is poor (Dyspepsia, Dietary Potassium tastes better)
- Half of Potassium Replacement is typically excreted by the Kidneys
- Aside from Renal Failure and dehydration, at least half of Potassium Replacement (esp. oral) is excreted
- Approximate oral replacement
- Serum Potassium < 3.0 mEq/L (total body deficit 200-300 meq)
- Start with KCl 20 meq orally every 2 hours for 4 doses and consider recheck level
- Typically continue Potassium Replacement at 20 meq twice daily for 4-5 days
- Serum Potassium: 3.0 to 3.5 mEq/L(total body deficit 100-200 meq)
- Give KCl 20 mEq orally every 2 hours for 2 doses OR KCl 40 mEq once
- Typically continue Potassium Replacement at 20 meq twice daily for 2-3 days
- Magnesium Replacement (empirically or based on lab demonstrated Hypomagnesemia)
- Especially consider empiric Magnesium Replacement in refractory Hypokalemia
- Take oral Magnesium supplement 400-500 mg tabs 1-2 daily along with Potassium supplement
- Emergent replacement indicated for serious findings or risks
- EKG changes (esp. QTc Prolongation, see above)
- Severe Hypokalemia (Serum Potassium <2.5 mEq/L)
- Rapid onset Hypokalemia
- Serious comorbidity (heart disease, Cirrhosis)
- Consider pseudohypokalemia
- Consider re-drawing lab for confirmation if delayed analysis
- Confirm no severe Leukocytosis (WBC >75,000/mm3)
- Consider Transcellular Potassium Shift
- See Transcellular Potassium Shift
- Hypokalemia from transcellular shift is typically transient
- Management: Hospital Replacement Criteria
- Hypokalemia with Serum Potassium <3.0 mEq/L AND QTc Prolongation >500 ms
- Severe Hypokalemia with Serum Potassium <2.5 mEq/L
- References
- Orman and Slovis in Herbert (2018) EM:Rap 18(8): 4-5
- Viera (2015) Am Fam Physician 92(6): 487-95 [PubMed]