Hypokalemia
Hypokalemia = Serum potassium (K⁺) <3.5 mEq/L,it is is less dangerous than hyperkalemia.
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Severity |
Serum K⁺ |
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Mild |
3.0–3.5 mEq/L |
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Moderate |
2.5–2.9 mEq/L |
|
Severe |
<2.5 mEq/L |
- 98% intracellular and Only 2% extracellular,Therefore serum potassium may not accurately reflect total body stores.
Potassium Homeostasis
|
Mechanism |
Site/Stimulus |
Action on Potassium |
|
Na⁺/K⁺-ATPase Pump |
Stimulated by insulin, β₂-agonists, thyroid hormone |
Moves 3 Na⁺ out and 2 K⁺ into cells, maintaining intracellular K⁺ stores |
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Renal Regulation |
Proximal Tubule |
Reabsorbs ~65% of filtered K⁺ |
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Thick Ascending Limb (TAL) |
Reabsorbs ~25% of filtered K⁺ |
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Collecting Duct (Principal Cells) |
Secretes K⁺ into tubular lumen; major site of regulated K⁺ excretion |
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Collecting Duct (Intercalated Cells) |
Reabsorbs K⁺ during potassium depletion/hypokalemia |
Causes of Hypokalemia
|
Category |
Cause |
Key Features / Mechanism |
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Reduced Intake |
StarvationAlcoholism—Eating disorders—Elderly—Prolonged NPO |
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Transcellular Shift |
Insulin / DKA treatment |
Drives K⁺ into cells; total body K⁺ usually depleted in DKA |
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Excess insulin |
Intracellular K⁺ shift |
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β₂-agonists (Salbutamol, Terbutaline, Epinephrine) |
Stimulate Na⁺/K⁺-ATPase |
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Metabolic alkalosis |
H⁺ leaves cells, K⁺ enters cells |
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Thyrotoxic periodic paralysis |
Common in Asians; sudden paralysis with intracellular K⁺ shift |
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Refeeding syndrome |
Insulin-mediated intracellular shift |
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Vitamin B12 therapy |
Increased cellular uptake during hematopoietic recovery |
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Theophylline toxicity |
β-adrenergic stimulation |
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Caffeine toxicity |
Catecholamine-mediated intracellular shift |
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Familial hypokalemic periodic paralysis |
Genetic channelopathy causing intracellular K⁺ shift |
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Extrarenal K⁺ Loss |
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Renal K⁺ Loss – Diuretics |
Loop diuretics (Furosemide, Bumetanide, Torsemide) |
Most common renal cause |
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Thiazides (Hydrochlorothiazide, Chlorthalidone) |
Increased distal sodium delivery → K⁺ wasting |
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Mineralocorticoid Excess |
Primary hyperaldosteronism (Conn syndrome, adrenal adenoma) |
↑ Aldosterone → renal K⁺ secretion |
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Secondary hyperaldosteronism |
Renal artery stenosis, CHF, cirrhosis, nephrotic syndrome |
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Cushing syndrome |
Cortisol-mediated mineralocorticoid effect |
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Ectopic ACTH syndrome |
Excess cortisol causing K⁺ wasting |
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Renal Tubular Disorders |
Bartter syndrome |
NKCC defect; hypokalemia, metabolic alkalosis, high urine Cl⁻, normal BP; mimics loop diuretics |
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Gitelman syndrome |
NCC defect; hypokalemia, hypomagnesemia, hypocalciuria; mimics thiazides |
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Liddle syndrome |
ENaC activation; hypertension, hypokalemia, low renin, low aldosterone |
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Renal Tubular Acidosis |
Type 1 (Distal RTA) |
Renal potassium wasting with metabolic acidosis |
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Type 2 (Proximal RTA) |
Potassium loss due to bicarbonaturia |
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Hypomagnesemia |
Magnesium deficiency |
Refractory hypokalemia; ↑ ROMK-mediated renal K⁺ wasting |
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Drug-Induced Renal K⁺ Loss |
Amphotericin B,Aminoglycosides Cisplatin High-dose penicillins Tenofovir Ifosfamide |
Tubular toxicity causing K⁺ wasting |
Clinical Manifestations
Severity depends on:
- Potassium level
- Speed of fall
- Presence of heart disease
Neuromuscular Manifestations
Mild
- Weakness
- Fatigue
- Myalgia
Moderate
- Muscle cramps
- Constipation
Severe
- Flaccid paralysis
- Ascending weakness
- Respiratory failure
Gastrointestinal Manifestations
- Ileus
- Constipation
- Abdominal distension
- Pseudo-obstruction
Renal Manifestations
Nephrogenic Diabetes Insipidus
- Polyuria
- Polydipsia
Metabolic Alkalosis
Increased Ammonia Production
May worsen hepatic encephalopathy.
ECG Findings
- Early—Flattened T wave
- Progressive—ST depression,T-wave inversion
- Classic—Prominent U wave
- Severe—QT prolongation (actually QU prolongation),VT,VF
- Arrhythmias Atrial—PACs,Atrial tachycardia,AF.
- Ventricular—PVCs,VT,VF,Torsades de pointes
Diagnostic Approach
No need of in-depth workup in every patient . If hypokalemia is severe or persistent, then a full evaluation SHOULD BE DONE
- Confirm TRUE Hypokalemia
Repeat potassium if unexpected. Rule out:pseudo-hypokalemia—[1] Delayed sample analysis (cells absorb potassium while the blood tube is sitting around).
[2] Markedly elevated cell counts, usually acute leukemia with WBC >100,000/uL (leukocytes take up potassium while the blood is awaiting analysis).
- Check magnesium level(Target – higher than low normal)
- Review the medication list
- Measure 24-hour Urine Potassium
<20 mEq/day→ Extrarenal loss
20 mEq/day→ Renal loss
- Spot Urine Potassium(basic test)
<15 mEq/L→ Extrarenal
>15-20 mEq/L→ Renal
- Spot Urine Potassium-Creatinine Ratio
<13 mEq/g→ Extrarenal
13 mEq/g→ Renal loss
- FEK (fractional excretion of potassium)->9.3% suggests renal potassium wasting
- Transtubular Potassium Gradient (TTKG)
Historically used but no longer routinely recommended due to physiologic limitations and poor reliability.
Approach
|
Finding |
Likely Cause |
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Metabolic alkalosis + low urine chloride |
Vomiting |
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Metabolic alkalosis + high urine chloride |
Diuretics, Bartter, Gitelman |
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Metabolic acidosis |
Diarrhea, RTA |
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Hypertension |
Hyperaldosteronism, Cushing, Liddle |
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Hypomagnesemia |
Gitelman, alcoholism, diarrhea |
Potassium Deficit Estimation
Approximate:
|
Serum K |
Estimated Deficit |
|
3.0 |
100–200 mEq |
|
2.5 |
200–400 mEq |
|
2.0 |
400–600 mEq |
Deficit estimates are rough and unreliable in acute shifts.
Management
- Nearly all patients: >3.5 mM.
- DKA with adequate renal function: >5 mM (higher because tends to drop over time while resuscitating DKA .
Oral Potassium Replacement
Not preferred in NPO status,Profound shock(absorption#) and severe hypokalemia (<2.5 mM).
Potassium Chloride (KCl)
- most commonly used formulation.it causes a non-anion-gap metabolic acidosis
- Dose:40–100 mEq/day in divided doses
- Single oral dose:Usually ≤60 mEq(large dose cause gastric irritation)
Potassium citrate
- Potassium citrate is equally effective as KCl .
- Potassium citrate is useful in patients with NAGMA (non-anion-gap metabolic acidosis). The citrate will be converted into bicarbonate, thereby improving the acidosis.
Intravenous Potassium Replacement
Indications:
- Severe hypokalemia
- NPO
- Ileus
- Symptomatic patient
- Arrhythmias
DO NOT GIVE IN Mild-moderate hypokalemia WHO CAN TAKE PER ORALLY
Formulation-Potassium chloride(most common),Potassium acetate(preferred in acidosis)
Peripheral IV
- Maximum concentration:10 mEq/100 mL
- Rate:Up to 10 mEq/hr
- Higher rates are painful and cause phlebitis.
Central Venous Line
- Typical:10-20 mEq/hr
- Life-threatening cases:40 mEq/hr (ICU with continuous ECG monitoring and hourly potassium monitoring)
Expected Rise
Approximately:10 mEq KCl→ increases serum K by ~0.1 mEq/L
Highly variable.
Choice of Potassium Salt
|
Situation |
Preferred Salt |
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Most patients |
Potassium chloride |
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Metabolic acidosis |
Potassium citrate / bicarbonate |
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Hypophosphatemia |
Potassium phosphate |
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DKA |
Potassium chloride ± phosphate |
ICU Potassium Replacement Strategy
|
Serum K |
Replacement |
|
3.3–3.5 |
20–40 mEq |
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3.0–3.2 |
40–60 mEq |
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2.6–2.9 |
60–80 mEq |
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<2.5 |
80–120+ mEq with ECG monitoring |
Recheck potassium:Every 2–4 hours during aggressive replacement.
Special Situations
DKA Do NOT start insulin if: K⁺ <3.3 mEq/L
First:Potassium replacement Then:Insulin
Digoxin Toxicity
Hypokalemia increases digoxin binding.Correct potassium carefully.
Thyrotoxic Periodic Paralysis
Treatment:
- Potassium replacement
- Nonselective β-blocker (propranolol)
- Definitive treatment of hyperthyroidism
Complications of Treatment
Hyperkalemia-Most common complication
Rebound Hyperkalemia
Occurs especially in:
- Transcellular shift disorders
- Thyrotoxic periodic paralysis
- DKA recovery
Phlebitis-From concentrated IV KCl
References
- Harrison’s Principles of Internal Medicine
- Oh’s Intensive Care Manual
- Irwin and Rippe’s Intensive Care Medicine
- Washington Manual of critical care