The dangers associated with inadequate hydration or uncontrolled dehydration are not always well understood. We often hear about electrolyte imbalances or water deficiency and their consequences, but what happens when the balance between water and minerals in our bodies is disrupted? In this article, we will explore this topic. Hypernatremia , which is the consequence of an excessive concentration of sodium in the body during dehydration or poor electrolyte intake.
1. How to calculate the water deficit in hypernatremia?
Calculating your free water deficit is an indicator of how much free water we need to consume to restore the balance with sodium.
1.1 Formula for calculating the free water deficit:
The calculation is given by the following formula:
Free water deficit = (total body water ) x { ( current serum sodium/target serum sodium ) - 1 }
Total body water depends on a person's age , sex , and body fat percentage . Simply put, it represents 60% of a man's weight, 50% of a woman's, and 50% of an elderly person's. For example, a man weighing 70 kg would have a total body water of 70 x 0.6 = 42 L.
Current sodium level is actually the measured concentration of sodium in the blood plasma (in mmol/litre).
The target serum sodium level is 140 mmol/liter. Above this level, hypernatremia becomes increasingly serious and requires more intensive care.
1.2 Calculation example:
For a 70 kg man with a current serum sodium level of 155 mmol/litre:
Total body water is equal to 42 liters.
The free water deficit = 42 × 155 140 - 1 = 42 × 0.107 = 4.5 litres.
This man therefore has a free water deficit of 4.5 liters.
2. What is hypernatremia?
2.1 Relationship between hypernatremia and free water deficit
First and foremost, hypernatremia is the name given to the phenomenon that occurs when the concentration of sodium in the blood is too high. The problem is that hypernatremia (high sodium concentration in the blood) increases our plasma osmolarity (the number of active particles: sodium, potassium, sugar, for example…) and this causes intracellular dehydration .
When we tried to calculate our free water deficit, it is actually the amount of water that is needed for the sodium concentration to return to normal.
3. Causes of hypernatremia
Hypernatremia can take several forms, defined according to the resulting extracellular volume . There are three possibilities: it either decreases, remains constant, or increases.
3.1 Hypovolemic hypernatremia
Hypovolemic hypernatremia is caused by a greater loss of free water than sodium, which increases sodium concentration and decreases extracellular volume. In effect, if there is a balance between water and sodium but more water is lost than sodium, then its concentration increases, creating hypernatremia.
The main causes are: diarrhea , vomiting , excessive sweating, or diabetes.
3.2 Euvolemic hypernatremia
Secondly, we have euvolemic hypernatremia . Put simply, this occurs when only water is lost, and not sodium. This again leads to an increase in sodium concentration, but while maintaining a stable extracellular volume. It can be a consequence of excessive sweating , hyperventilation , or even kidney failure.
3.3 Hypervolemic hypernatremia
Now let's look at a third case, hypervolemic hypernatremia . This is the occurrence of excessive sodium retention relative to water, which then leads to hypernatremia. This phenomenon, caused by excessive sodium intake in the diet, increases extracellular volume .
4. Symptoms of hypernatremia
The symptoms of hypernatremia are linked to excessively high osmolarity in the blood plasma and intracellular dehydration. They are quite numerous and depend on the different types of imbalances we mentioned earlier:
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Furthermore, neurological symptoms may also appear. Thus, in addition to marked thirst, you may experience fatigue, irritability, headaches , muscle weakness, and disorientation. These symptoms tend to worsen as hypernatremia progresses.
5. Diagnosis of hypernatremia
To diagnose hypernatremia, the best approach remains clinical evaluation, including measuring plasma sodium levels to determine your sodium concentration. To give you an idea:
A concentration between 146 and 150 mmol/L corresponds to mild hypernatremia.
Between 151 and 159 mmol/L, it becomes moderate
And if it is greater than 160 mmol/L, the case is severe.
If you go to the doctor, they will take your blood pressure, examine the condition of your mucous membranes, and check for signs of edema, thus verifying the various symptoms we have discussed. A urine test may also be performed to check the sodium concentration in your body.
6. Management of hypernatremia
Hypernatremia, which corresponds to an excess of sodium in the blood, is often caused by severe dehydration . To restore balance, it is essential to drink enough water, or even slightly diluted electrolyte drinks. However, rehydration should not be done too quickly , as this can cause imbalances in the brain.
If hypernatremia is linked to an underlying condition (such as a kidney problem or a specific type of diabetes), medical monitoring is essential. Only a healthcare professional can tailor the treatment plan and offer appropriate solutions.
7. Causes and risk factors of free water deficit
Free water deficit results from an imbalance between fluid loss and fluid intake, leading to hypernatremia. Several conditions can cause it. Chronic kidney disease , hyperglycemia , diabetes insipidus , and the use of loop diuretics are factors that increase water elimination without adequate compensation, thus promoting intracellular dehydration.
More common causes can also be responsible for a free water deficit such as prolonged fever, hyperventilation, excessive sweating or repeated vomiting which will accelerate fluid loss, thus increasing the risk of hypernatremia.
Certain individuals are particularly vulnerable to this imbalance, notably the elderly and infants who are at increased risk due to their higher water requirements and less efficient thirst regulation.
Hypernatremia can develop more easily in older adults. Several factors contribute to this imbalance. A decreased sensation of thirst, medical treatments, and reduced kidney function all increase water loss and decrease water intake, leading to fluid imbalance. Furthermore, the environment also plays a role. Hot weather, for example, can cause excessive sweating, resulting in significant water loss. This can impact cardiovascular and neurological function and should not be overlooked.
8. Water deficit: Definition and differences with free water deficit
Fluid deficit refers to an overall loss of body water, which can involve both water and electrolytes , particularly sodium. This type of imbalance occurs primarily in cases of vomiting, diarrhea, or excessive fluid loss without sufficient compensatory intake. Unlike free water deficit, fluid deficit does not directly affect serum sodium levels because water and sodium are lost proportionally, thus maintaining a relatively stable plasma osmolarity.
The management of these two situations differs. In cases of fluid deficiency, it is essential to provide electrolytes in addition to water to restore a stable ionic balance. Conversely, to correct a free water deficit, the intake of pure water or hypotonic solutions is preferred, depending on the symptoms and the degree of dehydration of each individual.
In this article, we've seen how to calculate your free water deficit, as well as the consequences and symptoms associated with a fluid imbalance. Maintaining optimal hydration is important to avoid any complications. However, if any of the symptoms we've described occur, we recommend consulting a healthcare professional for a complete assessment and appropriate medical advice.
Bibliography
L Berwert, B Vogt, M Burnier - Swiss Medical Review, 2010 - revmed.ch
Diagnosis and treatment of hypernatremia Saif A. Muhsin MBChB a , David B. Mount MD (Associate Chief)
