- On an average, healthy people aged between 30-40 years old have a total body water content of 55-60%
- By the age of 75-80 years, the total body water content declines by 50%
- The thirst mechanism also diminishes with age. There is an increased risk for dehydration.
- Age related decrease in maximal urinary concentration ability due to decreased renal mass, cortical blood flow and GFR
- This contributes to frequent occurrences of Hyponatremia in elderly
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.
Background of Hyponatremia in Elderly
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.
Possible Conditions & Life Style Factors that can lead to Hyponatremia in Elderly
- Certain medications such as diuretics, anti-depressants, pain medications
- Congestive heart failure, chronic kidney disease, liver disease can cause fluids to accumulate in body, which dilutes sodium levels, and lowering its overall level
- SIADH: Syndrome of Inappropriate Antidiuretic Hormone secretion. In this condition, high levels of ADH are produced causing the body to retain water instead of excreting it in urine.
- Chronic and severe vomiting or Diarrhea: This causes the body to lose fluids and electrolytes.
- Dehydration: Taking too little fluid can also be a problem.
- Hormonal Changes: Adrenal gland insufficiency (Addisons Disease) affects adrenal glands ability to produce hormones that help in maintaining sodium and water balance. Low levels of thyroid can cause low sodium levels too.
Signs and Symptoms
- Altered sensorium, lethargy and confusion.
- Severe hyponatremia can cause seizures, coma and even death.
Hyponatremia is classified based on
- Volume status
- Serum osmolality
- ADH levels
Mild hyponatremia: 135-130mmol/lit
Severe hyponatremia: below 125mmol/lit
Goals of Correction
- 5-2 meq/l/hr for 3-4 hours until symptoms resolve
- Increase by no more than 10 meq/l in first 24 hours
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
Sodium concentration in IVFluids
- 9% NS: 154 meq/l
- 3% Nacl: 513meq/l
What happens if sodium levels increase rapidly
- Central pontine myelenosis which is a form of osmotic demyelination.
- Symptoms occur 2-6 days after sodium elevation which include quadriperesis,coma and seizures
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.