The decrease in total body water makes elderly people susceptible to water imbalances.
Hyponatremia is a condition that occurs when level of sodium in blood is abnormally low. Sodium is an electrolyte that helps in regulating the amount of water in and around the cells. Hence, low sodium level is generally considered as a disorder of water and not the disorder of salt which means it usually results from increased water retention.
The normal Sodium levels are in the range of 135-145mmol/lit. Hyponatremia is defined as serum Sodium level less than 135mmol/lit.
Hyponatremia is the most common in elderly people as they are more likely to take more medications or have medical conditions that put them at risk of this disorder.
Most of the water in body is in cells. If water moves from cells to plasma, it dilutes plasma resulting in Hyponatremia. Increased oral intake of water or decreased real clearance of water can dilute the plasma. ADH (Antidiuretic hormone) prevents the clearance of water from body. This hormone is appropriately released in older people who are hypovolumic as a way to encourage body to conserve water. In contrast, ADH may be inappropriately released in response to certain conditions like cancer, certain medications, Tuberculosis, pneumonia, hypothyroidism, etc.
Hyponatremia can be associated with Euvolemia, Hypovolumia or Hypervolumia. Hence, it is necessary to know the patient’s true extracellular volume status, so that treatment of both improves sodium level and address underlying cause of hyponatremia.
Hyponatremia is classified based on
Mild hyponatremia: 135-130mmol/lit
Severe hyponatremia: below 125mmol/lit
Calculation of Sodium deficit: Total body water x (desired sodium-actual sodium)
Calculation of Total body water: Body weight x 0.5 for women and 0.6 for men
Hyponatremia in older people remains a common yet neglected area of clinical practice. Recent advances in the understanding of the pathological associations of asymptomatic and chronic hyponatremia have created interest in this condition.
Improved treatment of Hyponatremia could deliver significant health and economic benefits in the form of fewer falls and fractures, improved cognition and reductions in hospital stay. However, clinicians still face challenge of appropriate diagnosis and selection of therapeutic options.
A valid biomarker of volumic status in older people with hyponatremia is desirable.
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