Hypernatremia, a high sodium concentration in the blood (exceeding 145 milliequivalents per liter or mEq/L), is a serious electrolyte imbalance requiring careful medical attention. The body tightly regulates its sodium level. Correcting this imbalance is a medically supervised process focused on safely lowering the plasma sodium back to the normal range. The goal of treatment is to restore the body’s water balance without causing neurological harm, necessitating a controlled and deliberate approach.
What Hypernatremia Is and Why It Happens
Hypernatremia is fundamentally a “water problem” resulting from a deficit of total body water relative to the amount of sodium and potassium in the body. It arises from either a net loss of water or a net gain of sodium. The most common mechanism is the loss of free water that exceeds sodium loss, often due to inadequate water intake or excessive fluid loss.
This imbalance is frequently seen in individuals with an impaired thirst mechanism or restricted access to water, such as the elderly or those with altered mental status. Specific medical conditions can also drive excessive water loss, including severe diarrhea, certain kidney diseases, and Diabetes Insipidus. In rare cases, hypernatremia can be caused by a massive sodium gain, such as the accidental ingestion of salt or the administration of highly concentrated saline solutions.
The Principle of Correction: Replenishing Free Water
The core strategy for correcting hypernatremia involves calculating and replenishing the estimated free water deficit to dilute the concentrated sodium in the blood. Management begins by determining the total volume of water needed to bring the serum sodium concentration down to a safe target, typically 140 mEq/L. This calculation uses the patient’s current sodium level, total body water estimate, and the desired sodium level.
The speed of correction is the most important factor in safe management because the brain adapts to high sodium levels by generating protective solutes. If the external sodium concentration drops too rapidly, water rushes into the brain cells, causing dangerous swelling known as cerebral edema.
To prevent this, the plasma sodium concentration should be lowered by no more than 0.5 mEq/L per hour. The total reduction should not exceed 10 to 12 mEq/L over any 24-hour period, especially if the hypernatremia has been present for more than 48 hours. This controlled rate allows brain cells time to safely eliminate their protective solutes and re-equilibrate. A slower correction rate is safer for chronic cases, while a more rapid correction may be considered for acute, symptomatic hypernatremia.
Choosing the Right Fluids and Delivery Method
The fluid chosen for correction must be hypotonic to provide the necessary free water. The specific fluid and delivery method depend on the patient’s underlying volume status and the severity of the condition. For mild cases, oral water replacement is often the simplest and safest route.
For more severe cases, intravenous (IV) fluid administration is necessary, utilizing fluids like 5% dextrose in water (D5W) or 0.45% sodium chloride (half-normal saline). D5W is the most hypotonic choice, acting as pure free water once the dextrose is metabolized, making it ideal for aggressive free water replacement. Half-normal saline provides both free water and a small amount of sodium, which can be beneficial when volume losses also need to be addressed.
When a patient is hypovolemic, the initial priority is to stabilize circulation. Isotonic saline (0.9% sodium chloride) may be temporarily used to restore blood volume before transitioning to hypotonic fluids. For euvolemic hypernatremia (a pure water deficit) and hypervolemic hypernatremia (excess water and sodium), the focus shifts immediately to providing hypotonic fluids and promoting water excretion.
Preventing Complications and Treating the Underlying Cause
Safe correction of hypernatremia demands continuous monitoring to prevent overly rapid correction and neurological complications. Serum sodium levels must be checked frequently, often every two to four hours initially, to ensure the correction rate stays within the safe target. This allows clinicians to adjust the hypotonic fluid infusion rate in real-time, preventing a dangerous drop in plasma sodium.
Managing the underlying cause of the water deficit is just as important as the fluid administration itself. If the cause is a medication, such as a diuretic, that drug must be adjusted or discontinued. If the hypernatremia is due to Diabetes Insipidus (the body’s inability to conserve water), treatment may involve administering the synthetic hormone desmopressin to help the kidneys retain water. Ongoing losses, such as through fever or gastrointestinal issues, must be estimated and replaced concurrently to ensure long-term stability and prevent recurrence.