Clinical Scenario:  A 66-year-old male with a past medical history of traumatic brain injury and frequent urinary tract infections sent from his nursing home with hypernatremia. On a routine blood draw he was found to have hypernatremia to 160. His mental status is unchanged. How do you correct his hypernatremia?

Hypernatremia is caused by

  1. Excessive water loss: gastrointestinal tract (vomiting or diarrhea), sweating, or urination, renal, third spacing (loss of hypotonic fluid)
    • Signs: dry mucous membranes, decreased skin turgor, orthostatic changes
  2. Hypertonic sodium gain (iatrogenic)
    • Often causes acute hypernatremia

Steps to correct

STEP 1: Calculate water deficit

  • TBW = lean body weight x %
    • Young: 60% male or 50% female
    • Elderly: 50% male or 45% female
  • Calculate water deficit

free-water-deficit

STEP 2: Choose rate of correction

    • Acute hypernatremia (<48 hours)
      • Goal to lower acutely to 145mmol/L within 24 hours
    • Chronic hypernatremia (>48 hours)
      • Goal lower maximum 10mEq/L in 24 hours (0.5mEq/L/hour)
      • The rate should not exceed this to avoid cerebral edema
      • Re-check sodium every 2 hours

Step 3: Calculate Fluid Repletion

  • Acute (< 48 hours)
    • Hourly infusion rate (mL/hour) > water deficit in mL/24 hours
  • Chronic (> 48 hours)

1. Pick infusate based on volume status. More hypotonic solutions require less volume.

  • Free water via oral or peg tube if mentating well
  • D5, 1/4 NS, or 1/2 NS if unable to take by mouth
  • Only use normal saline if the patient is hypotensive, orthostatic, or with frank hemodynamic compromise.

2. Calculate change in serum sodium

Figure from: Adrogue HJ, Madias NE. Hypernatremia. N Engl J Med. 2000;342(20):1493-1499.
Figure from: Adrogue HJ, Madias NE. Hypernatremia. N Engl J Med. 2000;342(20):1493-1499.

3.  Calculate the infusion rate

  • Infusion rate (L/d) = Target change in serum Na / Calculated change in serum Na = 10mEq/L / Calculated change in serum Na
  • Account for insensible losses by adding 1 L/day and you get the infusion volume/day

infusion-sodium

Back to the case… this was CHRONIC hypernatremia

Step 1:

  • TBW = lean body weight x 50% = 70kg x 50% = 35kg
  • Water deficit = TBW x (Serum [Na]/140 – 1) = 35 x (160/140 – 1) = 5 L

Step 2:

  • Goal: 0.5mEq/L/hour or 10mEq/L/day

Step 3: In this case we will use 0.45% NaCl as the patient is moderately hypovolemic

  • Change in serum Na = (infusate Na – serum Na)/(TBW +1) = (77-160)/35 + 1) = -2.3 mmol
  • 1/2NS infusion rate = 10mEq/L / 2.3 mEq = (4.34 L + 1L)/24 hours = 220 mL/hour

Or… alternatively you can use MDCalc …Free Water Deficit or Sodium Correction

References/Additional resources (Accessed 12/30/16)

  1. Adrogue HJ, Madias NE. Hypernatremia. N Engl J Med. 2000;342(20):1493-1499.
  2. If you prefer podcast form http://emcrit.org/podcasts/hypernatremia/
  3. Free water deficit calculator http://www.mdcalc.com/free-water-deficit-hypernatremia/
  4. Sodium correction in hyper/hyponatremia http://www.mdcalc.com/sodium-correction-rate-hyponatremia-hypernatremia/