Management of Hypernatremia with 0.45 % NaCl Infusion

Fluid Selection Strategy

In patients with isolated hypernatremia (serum sodium ≈ 153 mmol/L), the preferred initial therapy is 0.45 % NaCl administered at 4–14 ml kg⁻¹ h⁻¹ to avoid further sodium excess. 1
When hypernatremia occurs in the setting of a hyperglycemic crisis, give isotonic saline (0.9 % NaCl) at 15–20 ml kg⁻¹ h⁻¹ during the first hour to restore intravascular volume and renal perfusion, then switch to 0.45 % NaCl at 4–14 ml kg⁻¹ h⁻¹ once volume is repleted. 1
Potassium should be added to the infusion (20–30 mEq L⁻¹, composed of ~2/3 KCl and 1/3 KPO₄) once adequate renal function is confirmed. 1

The change in plasma osmolality must not exceed 3 mOsm kg⁻¹ h⁻¹ during correction, which corresponds to a serum sodium reduction of roughly 0.5–0.6 mmol L⁻¹ h⁻¹ (12–14.4 mmol L⁻¹ day⁻¹). 1
Fluid replacement should correct the estimated total sodium deficit within 24 hours while staying within the 3 mOsm kg⁻¹ h⁻¹ limit. 1

Continuous hemodynamic monitoring (blood pressure, fluid input/output, bedside examination) is essential to gauge response and detect overload. 1
Serial electrolyte panels—including serum sodium, osmolality, and renal function—should be obtained at regular intervals during resuscitation. 1
Ongoing mental‑status assessment is required to identify early signs of cerebral edema or other neurologic complications. 2

Using 0.9 % NaCl when the corrected serum sodium is normal or elevated can aggravate hypernatremia and should be avoided. 1
Aggressive fluid administration in patients with underlying renal or cardiac disease can precipitate iatrogenic fluid overload; therefore, frequent cardiac, renal, and neurologic assessments, close osmolality monitoring, and rate adjustments are mandatory. 1

The allowable infusion range of 0.45 % NaCl is 218–764 ml h⁻¹ (4–14 ml kg⁻¹ h⁻¹). 3
A common starting point is 4–6 ml kg⁻¹ h⁻¹, equating to 218–327 ml h⁻¹ for a 54.6‑kg individual. 4
Subsequent rate adjustments should be guided by clinical response, serum sodium measurements every 2–4 hours, and observed changes in plasma osmolality. 5

In patients with isolated hypernatremia, isotonic saline (0.9 % NaCl) should be avoided because its high tonicity (~300 mOsm/kg H₂O) can impose a large renal osmotic load that may worsen hypernatremia rather than correct it. 6

The dextrose component of D5 0.45 % NaCl provides no renal osmotic load, permitting a gradual reduction in plasma osmolality without additional sodium accumulation. 6

In patients with very low body‑mass index, clinicians should evaluate for inadequate oral intake, diabetes insipidus, or other mechanisms of free‑water loss as potential contributors to hypernatremia. 6