Hyperkalemia

Key Features

Essentials of Diagnosis

• Serum potassium level > 5.2 mEq/L (5.2 mmol/L)

• Check medications carefully; hyperkalemia may develop from angiotensin-converting enzyme (ACE) inhibitors, angiotensin-receptor blockers and potassium-sparing diuretics, most commonly in patients with kidney dysfunction

• ECG may be normal despite life-threatening hyperkalemia

• Rule out pseudohyperkalemia and extracellular potassium shift from cells

General Considerations

• Hyperkalemia is a rare occurrence in healthy individuals due to adaptive mechanisms designed to prevent accumulation of potassium in the extracellular fluid, mainly via rapid urinary excretion

• Persistent hyperkalemia generally requires an impairment in renal potassium excretion due to

  • Impaired secretion of or hyporesponsiveness to aldosterone

  • Impaired delivery of sodium and water to the distal nephron

  • Kidney disease (acute or chronic)

• Transient hyperkalemia suggests shift of potassium from inside cells into the extracellular fluid, which can occur in the context of

  • Tissue damage (rhabdomyolysis, tumor lysis, massive hemolysis, and trauma)

  • Metabolic acidosis

• Pseudohyperkalemia is a laboratory artifact in which there is an elevation in serum potassium levels in the absence of true electrolyte imbalance as a result of

  • Tourniquet application or fist clenching during blood draw

  • Improper transport or processing of venous samples in patients with marked thrombocytosis or leukocytosis

Clinical Findings

Symptoms and Signs

• Symptoms of hyperkalemia are a consequence of impaired neuromuscular transmission

• Potassium concentrations above 7 mEq/L may cause cardiac conduction abnormalities and neuromuscular manifestations, such as muscle weakness, which may be profound

• Hyperkalemic period paralysis

  • Rare genetic disorder

  • Characterized by episodes of painless muscle weakness precipitated by potassium ingestion, rest after heavy exercise, and cold exposure

• Hyperkalemia additionally impairs urinary ammonium excretion and may lead to metabolic acidosis

Diagnosis

Laboratory Tests

• The diagnosis should be confirmed by repeat laboratory testing to rule out spurious hyperkalemia, especially in the absence of medications that cause hyperkalemia or in patients without kidney disease

Diagnostic Procedures

• Electrocardiography is an unreliable method for detecting hyperkalemia with clinical studies showing poor correlation between serum potassium levels and cardiac manifestations

ECG Changes

• The rapidity in development of hyperkalemia may correlate with the development of ECG changes

• Typical sequential changes

  • Peaking of the T waves

  • ST-segment depression

  • Widening of the PR and QRS intervals

• As the QRS continues to widen, sine waves may develop, which are concerning for imminent ventricular fibrillation and ultimately asystole

Treatment

Medications

• Exogenous sources of potassium should be eliminated

• Medications that can impair potassium excretion should be discontinued

• Volume depletion should be corrected

• Metabolic acidosis, if present, should be improved

• Treatment of hyperkalemia is outlined in Table 21–5

• In emergency situations (cardiac toxicity, muscle weakness or potassium > 6.5 mEq/L), initial therapy ...