From the Guidelines
In hyponatremia with dehydration, the serum osmolality is typically high (hyperosmolar), usually greater than 295 mOsm/kg, as evidenced by the most recent study 1. This condition occurs because dehydration leads to water loss, which should theoretically increase sodium concentration. However, in this scenario, sodium is lost in greater proportion than water, resulting in hyponatremia despite the overall dehydrated state. Some key points to consider in the management of hyponatremia with dehydration include:
- The high osmolality reflects the presence of effective osmoles other than sodium (like glucose or mannitol) in the bloodstream, as noted in 2.
- Treatment focuses on addressing the underlying cause while carefully correcting both the fluid deficit and sodium imbalance, typically with isotonic or hypertonic saline depending on the severity and clinical presentation, as recommended in 3 and 4.
- It is essential to avoid rapid correction of serum sodium concentration to prevent central pontine myelinolysis, as warned in 3 and 4.
- The use of hypertonic sodium chloride administration should be limited to severely symptomatic hyponatremia, as stated in 4.
- In patients with liver cirrhosis, hypovolemic hyponatremia caused by excessive diuretic use is common, and withdrawal of diuretics or correction of other possible cause of dehydration should be considered, as mentioned in 3.
From the Research
Osmolality in Hyponatremia with Dehydration
- In patients with hyponatremia and dehydration, the osmolality is typically low, as hyponatremia is characterized by a serum sodium level of less than 135 mEq/L 5.
- The treatment of hyponatremia with dehydration depends on the severity of symptoms and the underlying cause of the condition 6, 7.
- In cases of hypovolemic hyponatremia, the use of half normal saline may be more appropriate than normal saline to avoid rapid correction of serum sodium levels and reduce the risk of central pontine myelinolysis (CPM) 8.
- The goal of treatment is to correct the serum sodium level at a rate that is safe and effective, typically 4-6 mmol/L in the first few hours, and then 8 mmol/L over 24 hours 7.
- The osmolality of the treatment fluid can affect the rate of correction of serum sodium levels, with hypertonic saline being used in cases of severe symptomatic hyponatremia 5, 6.
- It is essential to monitor serum sodium levels and osmolality closely during treatment to avoid overly rapid correction and minimize the risk of complications such as osmotic demyelination 5, 7.