D5W Dosing for Hypernatremia Correction in a 70-kg Adult
To reduce serum sodium by 10 mmol/L in a 70-kg adult with hypernatremia, administer approximately 3.5 liters of D5W, delivered over 48–72 hours to maintain a safe correction rate of ≤8–10 mmol/L per day.
Calculation Method
Free Water Deficit Formula
The standard approach uses the Adrogue-Madias formula to estimate the free water deficit 1:
Free Water Deficit (L) = Total Body Water × [(Current Na / Target Na) - 1]
Where:
- Total Body Water = 0.5 × body weight (kg) for adult males 1
- For a 70-kg male: TBW = 0.5 × 70 = 35 liters
Practical Example
For a patient with serum sodium of 160 mmol/L targeting 150 mmol/L:
- Free water deficit = 35 × [(160/150) - 1] = 35 × 0.067 = 2.3 liters
However, this formula estimates only the static deficit and does not account for ongoing losses 1. In clinical practice, patients with hypernatremia often have continuing free water losses (especially in diabetes insipidus or osmotic diuresis), requiring 30–50% additional volume beyond the calculated deficit 1, 2.
Adjusted Volume for 10 mmol/L Reduction
- Calculated deficit for 10 mmol/L drop: approximately 2.3–2.5 liters
- Add 30–50% for ongoing losses: 3.0–3.8 liters total
- Practical recommendation: 3.5 liters D5W over 48–72 hours
Why D5W Is the Correct Fluid
Mechanism of Action
D5W delivers pure free water because the dextrose is rapidly metabolized upon infusion, leaving only water behind 1. The effective tonicity of D5W is zero after dextrose metabolism, providing no renal osmotic load 1. This is critical because salt-containing solutions like normal saline (osmolarity ~300 mOsm/kg H₂O) would worsen hypernatremia rather than correct it 1.
Contraindicated Alternatives
- Never use isotonic saline (0.9% NaCl) to treat hypernatremia, as it will worsen the condition by providing additional sodium load that exceeds the patient's ability to excrete it 1
- Half-normal saline (0.45% NaCl) is less effective than D5W because it still contains sodium and may not provide adequate free water 1
Administration Protocol
Infusion Rate and Monitoring
- Correction rate must not exceed 8–10 mmol/L per day for chronic hypernatremia (>48 hours duration) to prevent cerebral edema 3
- Serum osmolality change should not exceed 3 mOsm/kg H₂O per hour 1
- For 3.5 liters over 48 hours: infusion rate = 73 mL/hour
- For 3.5 liters over 72 hours: infusion rate = 49 mL/hour (safer for chronic hypernatremia)
Laboratory Monitoring
Check serum sodium every 2–4 hours initially during active correction 1. Once the rate of decline is established and stable, monitoring can be reduced to every 4–6 hours 1. Adjust the D5W infusion rate based on the observed sodium decline to maintain the target correction rate 1.
Special Clinical Scenarios
Hyperglycemic Crises (DKA/HHS) with Hypernatremia
In patients with diabetic ketoacidosis or hyperglycemic hyperosmolar state:
- Once serum glucose reaches 250–300 mg/dL, change fluids to D5W with appropriate electrolytes to prevent worsening hypernatremia while continuing insulin therapy 1, 2
- Add 20–30 mEq/L potassium to D5W (as 2/3 KCl and 1/3 KPO₄) once serum potassium is <5.5 mEq/L and adequate urine output (≥0.5 mL/kg/hour) is established 1
- Maintain serum osmolality change ≤3 mOsm/kg H₂O per hour during correction 1
Nephrogenic Diabetes Insipidus
In nephrogenic diabetes insipidus with hypernatremic dehydration, D5W is the recommended fluid because these patients cannot concentrate urine and will worsen with isotonic fluids 1. These patients may require desmopressin and free water administration via nasogastric tube in addition to IV D5W to improve free water deficit 2.
Acute vs. Chronic Hypernatremia
- Acute hypernatremia (<24 hours): Can be corrected more rapidly; hemodialysis is an effective option to rapidly normalize serum sodium levels 3
- Chronic hypernatremia (>48 hours): Must be corrected slowly over 48–72 hours to avoid cerebral edema 4, 3
Comparative Effectiveness: Enteral vs. Parenteral
A recent retrospective cohort study found that parenteral D5W was slightly more effective than enteral free water for lowering serum sodium in ICU-acquired hypernatremia 5:
- D5W: mean decrease of 2.25 mmol/L per liter of fluid 5
- Enteral free water: mean decrease of 1.91 mmol/L per liter of fluid 5
However, both routes are effective, and the choice depends on patient factors such as gastrointestinal function and volume status 5.
Critical Pitfalls to Avoid
Too-Rapid Correction
Too rapid correction of hypernatremia can lead to cerebral edema and neurological deterioration 4. The brain adapts to chronic hypernatremia by generating idiogenic osmoles; rapid correction causes water to shift into brain cells, resulting in cerebral edema 3.
Inadequate Volume Calculation
The calculated free water deficit represents only the static deficit. Failure to account for ongoing losses (especially in diabetes insipidus, osmotic diuresis, or fever) will result in inadequate correction 1, 2. Add 30–50% to the calculated deficit to account for these losses 1.
Potassium Depletion
Do not administer potassium without verifying adequate urine output first, as this can precipitate life-threatening hyperkalemia 1. In hyperglycemic crises, potassium should be added to D5W once serum potassium is confirmed <5.5 mEq/L and urine output is ≥0.5 mL/kg/hour 1.
Salt Intoxication Cases
In cases of salt intoxication (rare), diuretics must be given in addition to slow water replacement to avoid the development of pulmonary edema 4.
Monitoring for Complications
Electrocardiographic Changes
Extreme hypernatremia (sodium >190 mmol/L) can cause diffuse QT prolongation leading to fatal ventricular tachycardia 6. Continuous cardiac monitoring is recommended for severe hypernatremia, and electrolytes (potassium, calcium, magnesium) should be maintained in the normal range 6.
Volume Status Assessment
Close monitoring of volume status is essential. In cases of hypovolemic hypernatremia, initial resuscitation with isotonic fluids may be necessary before transitioning to D5W 1. However, once hemodynamic stability is achieved, switch to D5W for definitive correction of hypernatremia 1.