From the Guidelines
To calculate the water deficit for a patient with hypernatremia of 153 mEq/L, you need to administer approximately 2-3 liters of free water orally, with the goal of correcting the deficit gradually over 48-72 hours to prevent cerebral edema, as recommended by recent guidelines 1. The formula to determine the water deficit is: Water deficit = Total body water × [(current sodium/desired sodium) - 1]. For an average adult, total body water is roughly 60% of body weight. Assuming a 70 kg patient and a target sodium of 140 mEq/L, the deficit would be approximately 42 kg × [(153/140) - 1] = 3.9 liters. However, the most recent and highest quality study, published in 2025 in Nature Reviews Nephrology 1, suggests that patients who are old enough and capable of self-regulating their fluid intake should have ad libitum access to fluid to prevent dehydration, hypernatraemia, growth failure, and constipation. The study also recommends that the determination of the optimal amount of fluid is best left to the patient’s own thirst sensation, as it tends to be more sensitive and accurate than any medical calculation 1. In cases where patients cannot self-regulate their fluid intake, water should be offered frequently on top of their regular fluid intake, and if patients need to fast for prolonged periods, intravenous water administration should be provided 1. It is crucial to monitor sodium levels every 4-6 hours during correction and adjust the rate of administration and fluid composition accordingly, to prevent hypernatraemic dehydration and its associated complications 1. The use of salt-containing solutions, especially NaCl 0.9% solutions, should be avoided due to their large renal osmotic load, and instead, water with dextrose (for example, 5% dextrose) should be used to calculate the initial rate of fluid administration based on a physiological demand 1. Overall, the goal is to correct the water deficit gradually and safely, while preventing cerebral edema and other complications associated with hypernatremia, and recent guidelines support the use of oral rehydration as the preferred method of treatment, when possible 1.
From the Research
Hypernatremia Correction
To calculate the water deficit in a patient with hypernatremia, we need to consider the severity of the condition and the desired rate of correction.
- The goal of treatment is to restore plasma tonicity, and the rate of correction depends on the duration of hypernatremia 2.
- For acute hypernatremia, rapid correction may be necessary to prevent cellular dehydration, while for chronic hypernatremia, a slower correction rate (no more than 0.4 mmol/L/h) is recommended 2.
- The total body water deficit can be estimated using the following formula: Total body water deficit (liters) = 0.4 x body weight (kg) x ((current sodium / 140) - 1) 3.
Oral Water Intake
For patients with hypernatremia, oral water intake can be an effective way to correct the condition, especially if the patient is able to drink and has a functional gastrointestinal tract.
- The amount of water required to correct hypernatremia can be calculated based on the estimated total body water deficit.
- It is essential to monitor the patient's serum sodium levels and adjust the water intake accordingly to avoid overcorrection or undercorrection 3.
Desmopressin Therapy
In some cases, desmopressin therapy may be used to treat hypernatremia, especially in patients with central diabetes insipidus or essential hypernatremia.