From the Guidelines
To correct hypernatremia, the formula is: Free water deficit (L) = 0.6 × body weight (kg) × [(current serum Na⁺/desired serum Na⁺) - 1], and the deficit should be corrected gradually over 48-72 hours. For example, in a 70 kg patient with serum sodium of 160 mEq/L, aiming for 145 mEq/L, the calculation would be: 0.6 × 70 × [(160/145) - 1] = 4.9 L. To determine the hourly rate, this deficit should be corrected gradually over 48-72 hours to prevent cerebral edema, so dividing 4.9 L by 48 hours gives approximately 100 mL/hour, as supported by the principles outlined in 1. The correction rate should not exceed 10 mEq/L/day (or 0.5 mEq/L/hour) to avoid neurological complications. Hypotonic fluids like D5W or 0.45% saline are typically used, and as noted in 1, water with dextrose (for example, 5% dextrose) can be used to calculate the initial rate of fluid administration based on a physiological demand. Regular monitoring of serum sodium (every 2-4 hours initially) is essential to adjust the rate as needed. Addressing the underlying cause of hypernatremia, such as diabetes insipidus or inadequate water intake, is equally important for effective treatment, and patients with conditions like NDI should be managed with a low threshold for intravenous rehydration and avoidance of salt-containing solutions, as recommended in 1.
Some key considerations in the management of hypernatremia include:
- Calculating the free water deficit to determine the total amount of fluid needed for correction
- Using hypotonic fluids to avoid exacerbating hypernatremia
- Monitoring serum sodium levels closely to adjust the correction rate as needed
- Addressing the underlying cause of hypernatremia to prevent recurrence
- Being aware of the potential for cerebral edema with rapid correction and taking steps to avoid it, as discussed in the context of NDI management in 1.
In terms of specific fluid administration rates, the routine maintenance rate can be used as a starting point, with adjustments made based on the patient's individual needs and response to treatment, considering the recommendations for fluid management in 1. For children, this might be 100 ml/kg/24h for the first 10 kg, 50 ml/kg/24h for the next 10 kg, and 20 ml/kg/24h for the remaining weight, while for adults, a rate of 25-30 ml/kg/24h is often used, as a general guideline in line with the principles outlined in 1.
From the Research
Hypernatremia Correction Formula
The formula for hypernatremia correction is based on the water-deficit equation, which estimates the volume of water required to correct dehydration 2. The equation is as follows: WD(1) = 0.6 × B(m) × [1 - (140 ÷ Na(+))], where B(m) denotes body mass and Na(+) denotes serum sodium level.
Example Calculation
For example, if a patient has a body mass of 70 kg and a serum sodium level of 160 mEq/L, the calculated water deficit would be: WD(1) = 0.6 × 70 × [1 - (140 ÷ 160)] = 0.6 × 70 × [1 - 0.875] = 0.6 × 70 × 0.125 = 5.25 L
Correction Rate
The correction rate for hypernatremia is typically 1-2 mmol/L per hour 3. To calculate the correction rate in ml/h, we need to know the patient's body weight and the desired correction rate. For example, if we want to correct a patient's serum sodium level from 160 mEq/L to 140 mEq/L over 24 hours, and the patient weighs 70 kg, we can calculate the correction rate as follows: Correction rate = (160 - 140) × 0.6 × 70 = 20 × 0.6 × 70 = 840 mmol/24h = 35 mmol/h Since 1 mmol of sodium is equivalent to 1 ml of water, the correction rate in ml/h would be: Correction rate = 35 mmol/h × 1 ml/mmol = 35 ml/h × (160-140)/20 = 1050 ml/24h = 43.75 ml/h for the first 12 hours and then 21.875 ml/h for the next 12 hours to avoid overcorrection.
Important Considerations
When correcting hypernatremia, it's essential to monitor the patient's serum sodium level and adjust the correction rate accordingly 4. Overcorrection can lead to hyponatremia, which can be life-threatening 5, 6. Desmopressin may be used to treat central diabetes insipidus, but it can also increase the risk of hyponatremia 6.
Key Points
- The water-deficit equation can be used to estimate the volume of water required to correct dehydration.
- The correction rate for hypernatremia is typically 1-2 mmol/L per hour.
- Desmopressin may be used to treat central diabetes insipidus, but it can also increase the risk of hyponatremia.
- Monitoring the patient's serum sodium level and adjusting the correction rate accordingly is crucial to avoid overcorrection or undercorrection.