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Disorders of water and sodium homeostasis 

Disorders of water and sodium homeostasis
Disorders of water and sodium homeostasis

Michael L. Moritz

and Juan Carlos Ayus



Prevention of hospital-acquired hyponatraemias—recommendation that use of hypotonic intravenous fluids should be restricted to patients with hypernatraemia (Na >145 mmol/L) or those with ongoing urinary or extrarenal free water losses.

Treatment of suspected hyponatraemic encephalopathy—recommendation of a 2 ml/kg intravenous bolus of 3% sodium chloride to maximum of 100 ml to produce a controlled and immediate rise in serum sodium with little or no risk of inadvertent over-correction. Discussion of management guidelines to prevent overcorrection of hyponatraemia.

Chronic hyponatraemia—increased recognition that this is associated with significant morbidity, particularly falls and bone fractures in the elderly. Use of vasopressin receptor antagonists discussed.

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date: 27 September 2021

Water intake and the excretion of water are tightly regulated processes that are able to maintain a near-constant serum osmolality. Sodium disorders (dysnatraemias—hyponatraemia or hypernatraemia) are almost always due to an imbalance between water intake and water excretion.

Understanding the aetiology of sodium disorders depends on understanding the concept of electrolyte-free water clearance—this is a conceptual amount of water that represents the volume that would need to be subtracted (if electrolyte-free water clearance is positive) or added (if negative) to the measured urinary volume to make the electrolytes contained within the urine have the same tonicity as the plasma electrolytes. It is the concentration of the electrolytes in the urine, not the osmolality of the urine, which ultimately determines the net excretion of water....

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