Electrolyte Disturbances in Critical Illness

Electrolyte disturbances are abnormalities in the plasma concentrations of sodium, potassium, calcium, magnesium, phosphate, and related ions, and they are pervasive in the critically ill. They arise from the underlying illness, from kidney dysfunction, and from the fluids, nutrition, and therapies of intensive care, and several of them — notably potassium and sodium derangements — can be immediately life-threatening.

Definition

Electrolyte disturbances in critical illness are deviations of plasma ion concentrations — including sodium, potassium, calcium, magnesium, and phosphate — from the normal range, occurring as a consequence of disease, organ dysfunction, or treatment in critically ill patients.

Scope

This topic covers the major electrolyte abnormalities seen in intensive care, the mechanisms that produce them, and why disturbances of sodium and potassium in particular carry acute risk. It is a reference-educational overview of how these disturbances arise and are understood; it does not provide correction rates, replacement doses, or patient-specific management.

Key concepts

• Hyponatraemia and hypernatraemia
• Hyperkalaemia and hypokalaemia
• Plasma sodium as a marker of water balance
• Hypocalcaemia and hypomagnesaemia
• Hypophosphataemia and refeeding
• Acid-base interactions
• Iatrogenic and dilutional contributions

Mechanisms

Plasma sodium concentration reflects the balance between water and solute rather than total body sodium, so hyponatraemia and hypernatraemia are fundamentally disorders of water handling, governed by antidiuretic hormone, thirst, and renal water excretion. Potassium homeostasis depends on both renal excretion and the shift of potassium between intracellular and extracellular compartments, which is influenced by acid-base status, insulin, and catecholamines; this is why hyperkalaemia, by altering cardiac membrane excitability, can be rapidly dangerous. Calcium, magnesium, and phosphate are disturbed by sepsis, kidney injury, nutrition, and cellular uptake (for example during refeeding). Many disturbances in the intensive care unit are compounded by the fluids, drugs, and renal support the patient receives.

Clinical relevance

Electrolyte abnormalities are among the most common laboratory derangements in critical care and several can precipitate arrhythmia, seizure, or neurological injury, so understanding how they arise is part of critical care literacy. This entry explains the mechanisms and significance of these disturbances for reference and education; the rate and manner of correcting any abnormality in an individual patient is a clinical decision outside its scope.

Epidemiology

Disturbances of sodium and potassium are detected in a large share of intensive care unit patients, and both hyponatraemia and hypernatraemia in the critically ill are associated with worse outcomes. Disturbances of magnesium, phosphate, and calcium are also frequent, often in combination.

History

The understanding that plasma sodium concentration tracks water balance rather than salt content, and that potassium shifts between body compartments under hormonal and acid-base control, developed through twentieth-century renal physiology. A persistent clinical theme has been the danger of correcting chronic hyponatraemia too rapidly, which can cause osmotic demyelination, leading to an emphasis on controlled rates of correction in the literature.

Debates

How fast should chronic hyponatraemia be corrected?

Raising plasma sodium too quickly in chronic hyponatraemia risks osmotic demyelination, while undercorrection leaves cerebral oedema unaddressed; the safe rate of correction and how to handle overcorrection remain matters of careful clinical judgement discussed in the literature.

Key figures

• Richard Sterns
• Burton Rose
• Horacio Adrogue
• Nicolaos Madias

Seminal works

• sterns-2015

Frequently asked questions

Why is plasma sodium described as a water problem rather than a salt problem?

Because plasma sodium concentration reflects the ratio of sodium to body water; hyponatraemia and hypernatraemia usually result from disordered water handling rather than from a primary excess or deficit of sodium itself.

Why is hyperkalaemia considered an emergency?

Elevated potassium alters the electrical excitability of cardiac cell membranes and can provoke dangerous arrhythmias, which is why severe hyperkalaemia is treated as an acute, life-threatening disturbance.