From the Guidelines
To correct hypernatremia, the initial rate of fluid administration should be calculated based on a physiological demand, with a routine maintenance rate of 100 ml/kg/24 h for the first 10 kg of body weight in children, and 25-30 ml/kg/24 h in adults, using water with dextrose (e.g., 5% dextrose) to avoid excessive renal osmotic load 1. When considering a one-time infusion rate, such as 100 ml/h, it is crucial to calculate the individual's water deficit and adjust the rate accordingly to avoid overly rapid correction. The formula to calculate the infusion rate is based on the water deficit, which can be estimated using the formula: Water deficit (L) = Current TBW × [(Current Na⁺/Desired Na⁺) - 1], where TBW is approximately 0.6 × weight in kg for men and 0.5 × weight in kg for women. For example, in a patient with severe hypernatremia, the goal is to correct the sodium level gradually, aiming to reduce it by 8-10 mEq/L per 24 hours to prevent neurological complications. Key considerations include:
- Calculating the water deficit based on the patient's current sodium level, desired sodium level, and total body water
- Using water with dextrose to minimize renal osmotic load
- Monitoring serum sodium levels regularly (every 2-4 hours initially) to adjust the infusion rate as needed
- Individualizing the infusion rate based on the patient's volume status, underlying conditions, and severity of hypernatremia, as recommended by recent expert consensus statements 1.
From the Research
Hypernatremia Correction Formula
The formula for hypernatremia correction is not directly provided in the given studies. However, the correction rate of hypernatremia is discussed in the study 2, which suggests a reduction rate not to exceed 0.5 mmol/L per hour.
Calculation of Correction Rate
To calculate the correction rate, the following formula can be used: Correction rate (mmol/L/h) = (Target sodium level - Current sodium level) / Time (hours) For example, if the current sodium level is 160 mmol/L and the target sodium level is 140 mmol/L, and the time is 24 hours, the correction rate would be: Correction rate = (140 - 160) / 24 = -0.42 mmol/L/h (which is approximately 0.42 mmol/L/h)
Fluid Administration Rate
The fluid administration rate can be calculated based on the correction rate. For example, if the correction rate is 0.5 mmol/L/h, and the patient's weight is 70 kg, the fluid administration rate can be calculated as follows: Fluid administration rate (mL/h) = (0.5 mmol/L/h x 70 kg x 0.6) / 154 mmol/L (where 0.6 is the percentage of body weight that is water, and 154 mmol/L is the sodium concentration of the fluid) Fluid administration rate = (0.5 x 70 x 0.6) / 154 = approximately 136 mL/h
Example of Fluid Administration Rate
In the study 3, the patient received an infusion of 1250 ml 5%-glucose during 2 hours, which is approximately 625 mL/h. However, this rate is not recommended for routine use, as it may cause rapid correction of hypernatremia, which can lead to cerebral edema.
Recommended Fluid Administration Rate
The recommended fluid administration rate for hypernatremia correction is not explicitly stated in the given studies. However, the study 2 suggests that a correction rate not to exceed 0.5 mmol/L per hour is recommended. Based on this, a fluid administration rate of approximately 100-150 mL/h can be used, depending on the patient's weight and the desired correction rate. For example, a rate of 100 mL/h can be used for a short period, such as 1 hour, to correct hypernatremia, but this should be done with caution and close monitoring of the patient's sodium levels and clinical status.
- Key points to consider when correcting hypernatremia:
- Correction rate should not exceed 0.5 mmol/L per hour
- Fluid administration rate should be calculated based on the correction rate and the patient's weight
- Close monitoring of the patient's sodium levels and clinical status is essential
- Rapid correction of hypernatremia can lead to cerebral edema, so caution is advised 2, 4, 5, 6