Hypokalemia: Difference between revisions

(Major update: severity-based replacement protocol, IV rates/concentrations, magnesium correction requirement, DKA K thresholds, ECG changes, digoxin interaction, references with PMIDs)
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==Background==
==Background==
*Serum potassium '''<3.5 mEq/L'''
*Serum potassium <3.5 mEq/L
*'''Most common electrolyte abnormality''' encountered in clinical practice
*Most common electrolyte abnormality encountered in clinical practice
*Severity:
*Severity:
**Mild: 3.0-3.5 mEq/L
**Mild: 3.0-3.5 mEq/L
**Moderate: 2.5-3.0 mEq/L
**Moderate: 2.5-3.0 mEq/L
**'''Severe: <2.5 mEq/L''' (risk of arrhythmia, respiratory failure)
**Severe: <2.5 mEq/L (risk of arrhythmia, respiratory failure)
*'''Every 1 mEq/L decrease in serum K represents ~200-400 mEq total body deficit'''
*Every 1 mEq/L decrease in serum K represents ~200-400 mEq total body deficit


===Causes===
===Causes===
*'''Decreased intake''': malnutrition, anorexia, alcoholism
*Decreased intake: malnutrition, anorexia, alcoholism
*'''GI losses''' (most common):
*GI losses (most common):
**Vomiting (metabolic alkalosis → renal K wasting)
**Vomiting (metabolic alkalosis → renal K wasting)
**Diarrhea (direct K loss)
**Diarrhea (direct K loss)
**NG suction, laxative abuse
**NG suction, laxative abuse
*'''Renal losses''':
*Renal losses:
**'''Diuretics''' (loops, thiazides — most common medication cause)
**Diuretics (loops, thiazides — most common medication cause)
**Hyperaldosteronism (primary or secondary)
**Hyperaldosteronism (primary or secondary)
**[[Renal tubular acidosis]] (types 1 and 2)
**[[Renal tubular acidosis]] (types 1 and 2)
**Hypomagnesemia (impairs renal K conservation)
**Hypomagnesemia (impairs renal K conservation)
**Osmotic diuresis ([[DKA]])
**Osmotic diuresis ([[DKA]])
*'''Transcellular shift''' (K moves into cells):
*Transcellular shift (K moves into cells):
**'''Insulin''' (therapeutic or endogenous)
**Insulin (therapeutic or endogenous)
**'''Beta-2 agonists''' (albuterol)
**Beta-2 agonists (albuterol)
**Alkalosis
**Alkalosis
**Catecholamine surge, thyrotoxicosis
**Catecholamine surge, thyrotoxicosis
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==Clinical Features==
==Clinical Features==
*Often '''asymptomatic''' with mild hypokalemia
*Often asymptomatic with mild hypokalemia
*'''Muscle weakness''' (proximal > distal), cramps, myalgia
*Muscle weakness (proximal > distal), cramps, myalgia
*Ileus, constipation, nausea/vomiting
*Ileus, constipation, nausea/vomiting
*'''Rhabdomyolysis''' (severe hypokalemia)
*Rhabdomyolysis (severe hypokalemia)
*'''Cardiac arrhythmias''':
*Cardiac arrhythmias:
**PACs, PVCs → atrial or ventricular [[tachycardia]] → '''torsades de pointes''' → VF
**PACs, PVCs → atrial or ventricular [[tachycardia]] → torsades de pointes → VF
**'''Potentiates [[digoxin toxicity]]'''
**Potentiates [[digoxin toxicity]]


===ECG Changes===
===ECG Changes===
*'''Flattened T waves''' (earliest)
*Flattened T waves (earliest)
*'''Prominent U waves''' (after T wave)
*Prominent U waves (after T wave)
*'''ST depression'''
*ST depression
*Prolonged QT interval
*Prolonged QT interval
*'''T-U fusion''' (severe)
*T-U fusion (severe)


==Differential Diagnosis==
==Differential Diagnosis==
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==Evaluation==
==Evaluation==
*'''ECG''' (look for U waves, flattened T waves, prolonged QT)
*ECG (look for U waves, flattened T waves, prolonged QT)
*'''BMP''': K level, bicarbonate (alkalosis?), glucose, creatinine
*BMP: K level, bicarbonate (alkalosis?), glucose, creatinine
*'''Magnesium level''' ('''hypokalemia refractory to replacement if Mg not corrected''')
*Magnesium level (hypokalemia refractory to replacement if Mg not corrected)
*'''Calcium level''' (concurrent abnormalities)
*Calcium level (concurrent abnormalities)
*Consider: urine K (spot urine K/Cr ratio or 24h K), urine chloride, TSH, cortisol/aldosterone if unexplained
*Consider: urine K (spot urine K/Cr ratio or 24h K), urine chloride, TSH, cortisol/aldosterone if unexplained
*'''Digoxin level''' if on digoxin (hypokalemia increases digoxin sensitivity)
*Digoxin level if on digoxin (hypokalemia increases digoxin sensitivity)


==Management==
==Management==
===Guiding Principles===
===Guiding Principles===
*'''Always check and replace magnesium first''' — hypokalemia is refractory to correction with concurrent hypomagnesemia
*Always check and replace magnesium first — hypokalemia is refractory to correction with concurrent hypomagnesemia
*Oral replacement preferred when possible (better tolerated, less risky)
*Oral replacement preferred when possible (better tolerated, less risky)
*IV replacement for severe hypokalemia, ECG changes, or NPO patients
*IV replacement for severe hypokalemia, ECG changes, or NPO patients


===Mild Hypokalemia (3.0-3.5 mEq/L)===
===Mild Hypokalemia (3.0-3.5 mEq/L)===
*'''Oral KCl 20-40 mEq PO''' q2-4h (typical total dose 40-100 mEq/day)
*Oral KCl 20-40 mEq PO q2-4h (typical total dose 40-100 mEq/day)
*Increase dietary potassium
*Increase dietary potassium


===Moderate Hypokalemia (2.5-3.0 mEq/L)===
===Moderate Hypokalemia (2.5-3.0 mEq/L)===
*'''KCl 10-20 mEq/hr IV''' via peripheral line (max '''40 mEq/L concentration''' peripherally)
*KCl 10-20 mEq/hr IV via peripheral line (max 40 mEq/L concentration peripherally)
**Higher concentrations require '''central line'''
**Higher concentrations require central line
*'''Max infusion rate: 10-20 mEq/hr''' (peripheral); up to '''40 mEq/hr''' via central line with cardiac monitoring
*Max infusion rate: 10-20 mEq/hr (peripheral); up to 40 mEq/hr via central line with cardiac monitoring
*Concurrent oral supplementation
*Concurrent oral supplementation


===Severe Hypokalemia (<2.5 mEq/L or ECG Changes)===
===Severe Hypokalemia (<2.5 mEq/L or ECG Changes)===
*'''Continuous cardiac monitoring'''
*Continuous cardiac monitoring
*'''KCl 20-40 mEq/hr IV via central line'''
*KCl 20-40 mEq/hr IV via central line
*'''Magnesium sulfate 2g IV''' (if Mg not checked yet, give empirically)
*Magnesium sulfate 2g IV (if Mg not checked yet, give empirically)
*Recheck K every 1-2 hours
*Recheck K every 1-2 hours
*May require '''200+ mEq total replacement'''
*May require 200+ mEq total replacement


===Special Situations===
===Special Situations===
*'''[[DKA]]''': K may be normal or elevated on presentation but total body stores are depleted
*[[DKA]]: K may be normal or elevated on presentation but total body stores are depleted
**Replace K ''before or concurrent with insulin'' when K <5.3
**Replace K ''before or concurrent with insulin'' when K <5.3
**'''Do NOT start insulin if K <3.3''' — replace K to >3.3 first
**'''Do NOT start insulin if K <3.3''' — replace K to >3.3 first
*'''[[Digoxin toxicity]]''': maintain K >4.0 mEq/L
*[[Digoxin toxicity]]: maintain K >4.0 mEq/L
*'''Refractory hypokalemia''': check and replace magnesium; consider amiloride or spironolactone
*Refractory hypokalemia: check and replace magnesium<ref>Huang CL, Kuo E. Mechanism of hypokalemia in magnesium deficiency. J Am Soc Nephrol. 2007;18(10):2649-2652. PMID 17804670</ref>; consider amiloride or spironolactone


==Disposition==
==Disposition==
*'''Admit''' if K <2.5, symptomatic, ECG changes, arrhythmia, or ongoing losses
*Admit if K <2.5, symptomatic, ECG changes, arrhythmia, or ongoing losses
*'''Continuous telemetry''' for K <3.0 or ECG changes
*Continuous telemetry for K <3.0 or ECG changes
*'''Discharge''' if mild (3.0-3.5), asymptomatic, clear correctable cause, tolerated PO replacement, normal ECG
*Discharge if mild (3.0-3.5), asymptomatic, clear correctable cause, tolerated PO replacement, normal ECG
*Close follow-up with recheck in 24-48 hours
*Close follow-up with recheck in 24-48 hours


Latest revision as of 10:06, 22 March 2026

Background

  • Serum potassium <3.5 mEq/L
  • Most common electrolyte abnormality encountered in clinical practice
  • Severity:
    • Mild: 3.0-3.5 mEq/L
    • Moderate: 2.5-3.0 mEq/L
    • Severe: <2.5 mEq/L (risk of arrhythmia, respiratory failure)
  • Every 1 mEq/L decrease in serum K represents ~200-400 mEq total body deficit

Causes

  • Decreased intake: malnutrition, anorexia, alcoholism
  • GI losses (most common):
    • Vomiting (metabolic alkalosis → renal K wasting)
    • Diarrhea (direct K loss)
    • NG suction, laxative abuse
  • Renal losses:
    • Diuretics (loops, thiazides — most common medication cause)
    • Hyperaldosteronism (primary or secondary)
    • Renal tubular acidosis (types 1 and 2)
    • Hypomagnesemia (impairs renal K conservation)
    • Osmotic diuresis (DKA)
  • Transcellular shift (K moves into cells):
    • Insulin (therapeutic or endogenous)
    • Beta-2 agonists (albuterol)
    • Alkalosis
    • Catecholamine surge, thyrotoxicosis
    • Hypothermia (shifts K intracellularly)

Clinical Features

  • Often asymptomatic with mild hypokalemia
  • Muscle weakness (proximal > distal), cramps, myalgia
  • Ileus, constipation, nausea/vomiting
  • Rhabdomyolysis (severe hypokalemia)
  • Cardiac arrhythmias:

ECG Changes

  • Flattened T waves (earliest)
  • Prominent U waves (after T wave)
  • ST depression
  • Prolonged QT interval
  • T-U fusion (severe)

Differential Diagnosis

  • Medication-induced (diuretics, insulin, albuterol)
  • GI losses (vomiting, diarrhea)
  • Diabetic ketoacidosis (total body K depleted despite possible normal level)
  • Hyperaldosteronism
  • Renal tubular acidosis
  • Hypomagnesemia
  • Bartter/Gitelman syndrome
  • Thyrotoxic periodic paralysis

Evaluation

  • ECG (look for U waves, flattened T waves, prolonged QT)
  • BMP: K level, bicarbonate (alkalosis?), glucose, creatinine
  • Magnesium level (hypokalemia refractory to replacement if Mg not corrected)
  • Calcium level (concurrent abnormalities)
  • Consider: urine K (spot urine K/Cr ratio or 24h K), urine chloride, TSH, cortisol/aldosterone if unexplained
  • Digoxin level if on digoxin (hypokalemia increases digoxin sensitivity)

Management

Guiding Principles

  • Always check and replace magnesium first — hypokalemia is refractory to correction with concurrent hypomagnesemia
  • Oral replacement preferred when possible (better tolerated, less risky)
  • IV replacement for severe hypokalemia, ECG changes, or NPO patients

Mild Hypokalemia (3.0-3.5 mEq/L)

  • Oral KCl 20-40 mEq PO q2-4h (typical total dose 40-100 mEq/day)
  • Increase dietary potassium

Moderate Hypokalemia (2.5-3.0 mEq/L)

  • KCl 10-20 mEq/hr IV via peripheral line (max 40 mEq/L concentration peripherally)
    • Higher concentrations require central line
  • Max infusion rate: 10-20 mEq/hr (peripheral); up to 40 mEq/hr via central line with cardiac monitoring
  • Concurrent oral supplementation

Severe Hypokalemia (<2.5 mEq/L or ECG Changes)

  • Continuous cardiac monitoring
  • KCl 20-40 mEq/hr IV via central line
  • Magnesium sulfate 2g IV (if Mg not checked yet, give empirically)
  • Recheck K every 1-2 hours
  • May require 200+ mEq total replacement

Special Situations

  • DKA: K may be normal or elevated on presentation but total body stores are depleted
    • Replace K before or concurrent with insulin when K <5.3
    • Do NOT start insulin if K <3.3 — replace K to >3.3 first
  • Digoxin toxicity: maintain K >4.0 mEq/L
  • Refractory hypokalemia: check and replace magnesium[1]; consider amiloride or spironolactone

Disposition

  • Admit if K <2.5, symptomatic, ECG changes, arrhythmia, or ongoing losses
  • Continuous telemetry for K <3.0 or ECG changes
  • Discharge if mild (3.0-3.5), asymptomatic, clear correctable cause, tolerated PO replacement, normal ECG
  • Close follow-up with recheck in 24-48 hours

See Also

References

  • Kardalas E, et al. Hypokalemia: a clinical update. Endocr Connect. 2018;7(4):R135-R146. PMID 29540487
  • Gennari FJ. Hypokalemia. N Engl J Med. 1998;339(7):451-458. PMID 9700180
  • Viera AJ, Wouk N. Potassium disorders: hypokalemia and hyperkalemia. Am Fam Physician. 2015;92(6):487-495. PMID 26371733
  • Crop MJ, et al. Role of magnesium in hypokalemia. Crit Care. 2012;16(1):229. PMID 22866973
  1. ↑ Huang CL, Kuo E. Mechanism of hypokalemia in magnesium deficiency. J Am Soc Nephrol. 2007;18(10):2649-2652. PMID 17804670
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