Hyperkalemia

*Hyperkalaemia*

For medical students2 min readUpdated 2026-10-10

Hyperkalemia is a common electrolyte disorder characterized by a serum potassium concentration exceeding 5.5 mmol/L. This condition poses a life-threatening medical emergency due to its disruptive effects on the electrophysiological properties of excitable tissues, potentially leading to fatal cardiac arrhythmias.

Diagnostic CriterionSerum potassium level rises above the normal upper limit of 5.5 mmol/L.

Cardiac RiskAt potassium concentrations exceeding 10 mEq/L (or 13 mmol/L), cardiac arrest in diastole may occur.

Renal ReserveNormally, healthy kidneys are capable of excreting up to 1000 mEq of potassium per day.

Effect of AcidosisA decrease in blood pH by 0.1 units increases plasma potassium concentration by approximately 0.6 mEq/L.

Etiology and Major Causes

There are three primary pathogenetic groups of factors leading to hyperkalemia:

Decreased Renal Excretion. Healthy kidneys excrete quantities of potassium that significantly exceed daily intake. However, in renal impairment, hyperkalemia develops even with normal or reduced potassium intake. Another cause is hypoaldosteronism (due to adrenal insufficiency or decreased tubular epithelial sensitivity in amyloidosis, renal failure, and interstitial disease). This leads to impaired $Na^+$ reabsorption in the distal tubules, which disrupts the coupled excretion of $K^+$.
Transcellular Shift (Intracellular to Extracellular). Observed during massive tissue damage and cell destruction: erythrocyte hemolysis, burns, crush injuries, ischemia, necrosis, and crush syndrome (compartment syndrome). Additionally, potassium efflux is stimulated by hypoinsulinemia (due to enhanced glycogenolysis and proteolysis) and intracellular acidosis, in which $K^+$ ions leave the cell while $Cl^-$ ions enter.
Excessive Intake. Acute or chronic dietary hyperkalemia is extremely rare because intact kidneys efficiently eliminate excesses.

Clinical Manifestations

The clinical presentation of hyperkalemia is entirely driven by disruptions in the resting membrane potential (RMP), action potential generation, and impulse transmission at neuromuscular synapses.

Neuromuscular Disturbances Patients report muscle pain and marked weakness. Objective findings include muscle hypotonia, hyporeflexia, and in severe cases, flaccid paralysis. A characteristic visceral manifestation involving internal organs is intestinal atony.

Cardiovascular Manifestations The most critical clinical sign is the progressive loss of cardiomyocyte excitability alongside a significant increase in the heart's cholinoreactive properties. This results in bradycardia and severe arrhythmias. Atrioventricular and intraventricular blocks develop. At potassium levels of 8–10 mmol/L, complete heart block may occur, and at levels above 10 mEq/L, cardiac arrest in diastole ensues.

Management of Hyperkalemia

Emergency therapy involves three main approaches:

Treat the Underlying Cause. Eliminating the primary etiological factor that triggered the electrolyte disturbance.
Promote Intracellular Shift. Stimulating the transport of $K^+$ from the extracellular fluid back into cells. Intravenous administration of calcium chloride, sodium bicarbonate (which potentiates intracellular potassium uptake), or a combination of dextrose (glucose) and insulin is utilized. Insulin stimulates the co-transport of glucose and potassium into cells, rapidly reducing hyperkalemia and cardiotoxicity.
Enhance Potassium Elimination. Treatments include hemodialysis (lowering potassium levels by half in 3–4 hours), loop diuretics (e.g., furosemide), and aldosterone analogs (deoxycorticosterone acetate). Cation-exchange resins (such as sodium polystyrene sulfonate) show high efficacy. Upon reaching the intestine—where potassium concentration is 2 to 4 times higher than in the blood—they bind and eliminate 60–100 mmol of the macroelement within the first 4–6 hours.

Mnemonic

To remember the drugs administered intravenously to shift potassium into cells, use the mnemonic BIG K: Bicarbonate (sodium), Insulin with Glucose, Kalium (Calcium chloride).

Frequently asked questions

What are the characteristic ECG changes seen in hyperkalemia?

Specific ECG changes in hyperkalemia affect waveform morphologies and time intervals, progressing as potassium concentration rises.

Changes include:

T wave — becomes tall, narrow, peaked, and symmetrical.
QT interval — shortens.
PR interval — prolongs.
P wave — widens and eventually disappears.
QRS complex — widens.

At $K^+$ concentrations of 8–9 mmol/L, the QRS complex merges with the T wave, giving the QRST complex a sine-wave appearance. At levels above 9 mmol/L, atrioventricular block, ventricular tachycardia, or ventricular fibrillation may develop.

Why does intracellular acidosis increase blood potassium levels?

During acidosis, a compensatory ion exchange occurs: hydrogen ions move into the cells, while potassium ions shift out into the extracellular fluid and blood. Simultaneously, chloride influx into cells is stimulated.

How does hypoinsulinemia affect potassium homeostasis?

Insulin deficiency leads to increased glycogenolysis and proteolysis in tissues. The breakdown of these intracellular structures is accompanied by the release of large amounts of potassium into the bloodstream.

Why does dietary potassium excess rarely cause hyperkalemia in healthy individuals?

Healthy kidneys possess a massive excretory reserve. They are normally capable of excreting up to 1000 mEq of potassium per day, which significantly exceeds standard dietary intake.

What is the mechanism of action of cation-exchange resins in treating hyperkalemia?

These medications (e.g., sodium polystyrene sulfonate) act within the intestinal lumen. Because the potassium concentration in intestinal secretions is 2 to 4 times higher than in blood serum, the resins effectively bind and eliminate it from the body.

Go deeper

Electrophysiology of excitable tissues: resting membrane potential and action potential generation
Pathogenesis of crush syndrome and its systemic consequences
The role of aldosterone in regulating sodium reabsorption and potassium secretion in the renal distal tubules
Mechanisms of intracellular acidosis and its impact on electrolyte balance
The effects of hyperkalemia on myocardial cholinoreactive properties