How rapidly should electrolyte free water be administered for hypernatremia

How rapidly should electrolyte free water be administered for hypernatremia?

Most cases of hypernatremia develop slowly over several days. Recommendations for treatment of chronic hypernatremia are not as well established as for chronic hyponatremia. Some authorities recommend that for hypernatremia developing over an interval longer than 48 hours, the rate of serum sodium concentration reduction should be limited to 10 mEq/L per day to minimize the theoretical risk for cerebral edema. A common strategy entails replenishing half of a patient’s electrolyte-free water deficit in the first 24 hours and the remaining half in the following 24 to 48 hours. If hypernatremia developed in less than 48 hours, it can be corrected faster. A patient’s free water deficit can be estimated with the following equation:

Total body water can be estimated by multiplying the patient’s weight in kilograms by 0.5 in the case of women or 0.6 in men. These fractions are further reduced in the obese and elderly. Using this equation, the electrolyte-free water deficit in an intubated 60 kg woman with a serum sodium of 167 mEq/L is approximately 4.8 L of water (60 × 0.5 × [1 – 140/167] = 4.8 L). Half of this deficit can be replaced in the first 24 hours by administering 300 mL of water via orogastric tube every 3 hours, followed by 150 mL of water every 3 hours in the subsequent 48 hours. Of note, if her electrolyte-free water deficit is corrected with intravenous 0.45% saline, she would require double this volume, as this fluid is only half electrolyte-free water by volume. This formula is only an approximation, so careful monitoring of the serum sodium concentration during the correction period is required. Finally, the formula does not take into account electrolyte-free water losses that are still ongoing. The fluid prescription should be augmented to match any such losses. Returning to our example above, if we assume our patient produces 1600 mL of urine daily, half of which is electrolyte-free water, 400 mL of water via orogastric tube every 3 hours in the first 24 hours (3200 mL) would match the ongoing urinary loss of electrolyte-free water (800 mL) and replenish half (2400 mL) of her free water deficit. In the ensuing 48 hours, 250 mL of water every 3 hours should be given to correct for ongoing urinary water excretion and address the remainder of her free water deficit. If the patient has 3 L/day urine output, an additional 700 mL of water administration would be required each day if the assumption that electrolyte-free water output is half of urine output remains valid. Particularly at high urine output rates and in patients with DI, the urine sodium and potassium should be measured to allow a more precise estimate of urinary electrolyte-free water loss. Since diarrheal fluid is hypotonic, additional electrolyte-free water will also be needed in patients with copious ongoing diarrhea, as with Clostridium difficile colitis.

15585

Sign up to receive the trending updates and tons of Health Tips

Join SeekhealthZ and never miss the latest health information

15856