Hyperkalemia

Definition & Normal Range

Serum potassium > 5.0–5.5 mEq/L (normal 3.5–5.0 mEq/L). Levels ≥ 6.0 mEq/L are potentially dangerous; ≥ 7.0 mEq/L is a medical emergency.

Hyperkalemia is rare in healthy individuals (<1% of normal adults), underscoring the kidney's potent capacity for K⁺ excretion. Its presence in a non-acutely ill patient should prompt a search for impaired renal K⁺ handling.

Etiology

Causes are classified into three mechanisms:

1. Pseudohyperkalemia

Artifactual K⁺ release after phlebotomy — not true hyperkalemia.

Hemolysis (most common — check plasma sample for pink discoloration)
Prolonged tourniquet time or limb exercise with tourniquet
Severe leukocytosis (WBC >70,000/mm³) or thrombocytosis (platelets 500–1000 × 10⁹/L — ~1/3 develop pseudohyperkalemia)
Diagnose: serum [K⁺] > 0.3 mmol/L higher than simultaneous plasma [K⁺]

2. Transcellular Shift (ICF → ECF)

Insulin deficiency / DKA — both hyperosmolarity and insulin deficiency drive K⁺ out of cells
Metabolic acidosis — H⁺ exchange for intracellular K⁺
Hyperosmolarity (e.g., mannitol, hyperglycemia)
β-blockers — block β₂-mediated cellular K⁺ uptake
Digoxin toxicity — blocks Na⁺/K⁺-ATPase
Succinylcholine — depolarizing relaxant causes K⁺ efflux (dangerous in burns, denervation, rhabdomyolysis)
Massive tissue necrosis / rhabdomyolysis — release of intracellular K⁺

3. Impaired Renal K⁺ Excretion (most common cause of chronic hyperkalemia)

Category	Examples
CKD/ESKD	Reduced functioning nephrons → reduced distal K⁺ delivery and secretion
AKI (oliguric)	Reduced tubular flow
Hypoaldosteronism	Addison's, hyporeninemic hypoaldosteronism (type 4 RTA — DM, elderly, CKD)
Drugs	ACEi, ARBs, renin inhibitors, MR blockers (spironolactone, eplerenone, finerenone), K⁺-sparing diuretics (amiloride, triamterene), NSAIDs, heparin, calcineurin inhibitors (tacrolimus, cyclosporine), TMP-SMX
Hereditary	Pseudohypoaldosteronism type I (loss-of-function ENaC or MR mutations), PHA type II (WNK1/WNK4 mutations)
Tubulointerstitial disease	Amyloidosis, sickle cell, obstructive uropathy
Excessive intake	K⁺ supplements, salt substitutes (10–13 mmol K/g), enteral nutrition

NSAIDs cause hyperkalemia by suppressing the renin-aldosterone axis and reducing GFR; COX-2-selective agents carry equal or greater risk. — Brenner & Rector's The Kidney

Clinical Manifestations

Hyperkalemia is often clinically silent until cardiac arrhythmia or arrest occurs — therefore every patient at risk must have an ECG.

Cardiac (primary danger)

ECG changes progress sequentially with rising K⁺ (Harrison's, 2025):

Serum K⁺ (mEq/L)	ECG Finding
5.5–6.5	Peaked (tented) T waves, shortened QT interval
6.5–7.5	PR prolongation, P-wave flattening/loss
7.0–8.0	Widened QRS complex
> 8.0–9.0	Loss of R-wave amplitude, ST depression
> 9.0	Sine wave pattern → ventricular fibrillation → asystole

ECG progression of hyperkalemia: normal → peaked T waves → widened QRS → sine wave pattern

Contractility may be relatively preserved until late. Hypocalcemia, hyponatremia, and acidosis accentuate cardiac effects. ECG changes may be completely absent even when hyperkalemia is severe — a normal ECG does not exclude dangerous K⁺ elevation.

Neuromuscular

Generalized skeletal muscle weakness (usually K⁺ > 8 mEq/L)
Diaphragmatic weakness → respiratory failure in severe cases
Ascending paralysis (rare)

Workup

Evaluation of Hyperkalemia diagnostic flowchart

Key investigations:

Repeat K⁺ in plasma (not serum) if hemolysis suspected
ECG — immediately for any K⁺ ≥ 5.5 or clinical suspicion
BMP: creatinine, BUN, glucose, bicarbonate, pH
Urine K⁺, urine Cr, urine osmolality → calculate TTKG (transtubular K⁺ gradient)
- TTKG > 10 with hyperkalemia → extrarenal cause
- TTKG < 5–7 → aldosterone deficiency or resistance
Aldosterone and plasma renin activity (PRA) if hypoaldosteronism suspected
CBC (leukocytosis/thrombocytosis?)

Treatment

Treatment strategy follows three parallel goals:

1. Membrane Stabilization (immediate, minutes)

Calcium — antagonizes K⁺ effects on cardiac membrane directly; onset within 1–3 minutes, duration ~30–60 min.

Calcium gluconate 10 mL of 10% IV over 2–3 minutes (or 5–10 mL); can repeat in 5 min if ECG unchanged
Calcium chloride 3–5 mL of 10% IV (provides ~3× the calcium, use via central line)
⚠️ Caution in digoxin toxicity — calcium potentiates digoxin cardiotoxicity

2. Intracellular Shift (temporary — minutes to 1 hour)

Agent	Dose	Onset	Duration	Notes
Insulin + glucose	10 units regular IV + 25–50 g glucose (unless hyperglycemic)	15–30 min	4–6 h	Peak effect up to 1 h; monitor for hypoglycemia closely
Sodium bicarbonate	1–2 mEq/kg IV	15 min	1–2 h	Most effective when metabolic acidosis present
β₂-agonists	Albuterol 10–20 mg nebulized (2–8× the bronchodilator dose!) or IV	15–30 min	2–4 h	~25% non-responders; causes tachycardia

Low-dose epinephrine infusion rapidly lowers K⁺ and provides inotropic support in severe/unstable cases (e.g., post-massive transfusion).

3. K⁺ Elimination (definitive)

Method	When to use	Notes
Loop diuretics (furosemide)	Adequate renal function, no hypovolemia	Large doses may be needed in CKD
Potassium-binding resins	Chronic hyperkalemia, stable patients
— Sodium polystyrene sulfonate (SPS/Kayexalate)	Oral or rectal	Safety and efficacy questioned; colonic necrosis risk
— Patiromer	Oral (preferred)	Better tolerated; 2025 meta-analysis supports use in CKD/HF to maintain RAAS inhibitor therapy
— Sodium zirconium cyclosilicate (ZS-9)	Oral, rapid onset	Acts within 1 hour
Dialysis	Life-threatening hyperkalemia, impaired renal function	Definitive; indicated when above measures fail or K⁺ > 6.5 with ECG changes

4. Address the Underlying Cause

Discontinue offending drugs (ACEi/ARB, K⁺-sparing diuretics, NSAIDs) if benefits don't outweigh risks
Treat metabolic acidosis, obstructive uropathy
Fludrocortisone for hypoaldosteronism
Dietary K⁺ restriction counseling

Special Situations

DKA: Serum K⁺ is often elevated at presentation despite total body K⁺ depletion — once insulin is started and acidosis corrects, K⁺ will drop rapidly. If K⁺ is already normal at presentation, defer insulin until K⁺ replacement is underway.
CKD patients: Even modest K⁺ loads or drugs like β-blockers and ACEi can precipitate dangerous hyperkalemia. Any CKD patient in cardiac arrest should be presumed hyperkalemic.
Succinylcholine: Potentially dangerous in pre-existing hyperkalemia (CKD, burns, denervation injury, rhabdomyolysis).
RAAS inhibitors: Novel K⁺ binders (patiromer, ZS-9) now allow continuation of prognostically beneficial ACEi/ARB/MRB therapy in CKD/HF patients — a 2025 systematic review (PMID 40542996) confirms their efficacy in reducing hyperkalemia while optimizing RAAS inhibitor use.

Sources:

Comprehensive Clinical Nephrology, 7th Ed., Ch. 10
Harrison's Principles of Internal Medicine, 22E (2025)
Morgan & Mikhail's Clinical Anesthesiology, 7e, Ch. 49
ROSEN's Emergency Medicine, Ch. 83 & 114
Brenner & Rector's The Kidney, 2-Volume Set, Ch. 13

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