Normal Serum Sodium Range: 135-145 mEq/L
The normal serum sodium level is 135-145 mEq/L, not 154 mEq/L. A sodium level of 154 mEq/L is considered hypernatremia and is associated with significantly increased mortality risk 1.
Understanding Normal Sodium Levels
- Normal serum sodium concentration ranges from 135 to 145 mEq/L, as defined in multiple clinical guidelines 1.
- Plasma is approximately 93% aqueous with a sodium concentration in the aqueous phase of plasma of 154 mEq/L, but this is not the same as the normal serum sodium range 1.
- Hypernatremia is defined as serum sodium >145 mEq/L 1.
- Hyponatremia is defined as serum sodium <135 mEq/L 1.
Clinical Significance of Sodium Levels
Hypernatremia (>145 mEq/L)
- A sodium level of 154 mEq/L is clearly in the hypernatremic range and requires clinical attention 1.
- Hypernatremia is associated with significantly higher mortality rates compared to normal sodium levels 2.
- Research shows that patients with mild hypernatremia (145-150 mEq/L) have a 28% in-hospital mortality rate, while those with severe hypernatremia (>150 mEq/L) have a 52% in-hospital mortality rate, compared to just 5% with normal sodium levels 2.
- Even within what is traditionally considered the "normal range," mortality risk begins to rise at sodium levels above 139 mEq/L 3.
Hyponatremia (<135 mEq/L)
- Hyponatremia is the most common electrolyte abnormality in hospitalized patients, affecting approximately 15-30% of children and adults 1.
- Mild hyponatremia (125-135 mEq/L) is associated with a 9% in-hospital mortality rate, while severe hyponatremia (<125 mEq/L) has a 14% in-hospital mortality rate 2.
Special Considerations in Different Patient Populations
- In patients with acute liver failure, hyponatremia (sodium <130 mmol/L) is common and correlates with increased intracranial pressure 1.
- For patients with liver failure, some guidelines recommend targeting serum sodium levels between 140 and 145 mmol/L to help manage intracranial pressure 1.
- In pediatric patients, isotonic maintenance fluids are recommended to prevent iatrogenic hyponatremia 1.
- In dialysis patients, hyponatremia <130 mEq/L at dialysis initiation is significantly associated with increased all-cause mortality 4.
Sodium Variability and Outcomes
- Increased variability in plasma sodium levels is associated with higher mortality in critically ill patients, including burn patients 5.
- Maintaining stable sodium levels within the normal range (135-145 mEq/L) is important for optimal outcomes 5.
Common Pitfalls in Sodium Management
- Confusing the sodium concentration in the aqueous phase of plasma (154 mEq/L) with the normal serum sodium range (135-145 mEq/L) 1.
- Rapid correction of sodium abnormalities can lead to serious complications such as central pontine myelinolysis 1, 6.
- Failure to recognize that even sodium levels at the upper end of the traditional normal range (>139 mEq/L) may be associated with increased mortality risk 3.
In conclusion, the normal serum sodium range is 135-145 mEq/L, and a level of 154 mEq/L represents hypernatremia that requires clinical attention due to its association with significantly increased mortality.