In a patient with severe hypernatremia (serum sodium 168 mEq/L) whose sodium fell to 155 mEq/L after 0.45% normal saline (0.45% sodium chloride), can I now use 0.9% normal saline (0.9% sodium chloride) to continue correction?

Can You Use 0.9% Normal Saline After Initial 0.45% Saline in Severe Hypernatremia?

No, you should not switch to 0.9% normal saline at this point—continue with hypotonic fluid (0.45% saline or D5W) to complete the correction of hypernatremia, as 0.9% saline will halt or reverse the sodium decline and risks neurological complications from inadequate correction.

Why 0.9% Saline is Inappropriate for Ongoing Hypernatremia Correction

• 0.9% normal saline contains 154 mEq/L of sodium, which is still markedly hypertonic relative to your patient's current serum sodium of 155 mEq/L. Administering this fluid will provide a net sodium load that prevents further correction or may even cause the sodium to rise again. 1

• The goal in hypernatremia treatment is to provide free water (either as hypotonic saline or D5W) to gradually lower serum sodium at a safe rate of 0.5 mEq/L per hour (maximum 10-12 mEq/L per 24 hours). Your patient has already corrected 13 mEq/L (from 168 to 155), so you need continued hypotonic fluid to reach the target range safely. 1

• Switching to isotonic saline mid-correction is a common and dangerous pitfall. It stems from the misconception that "normal saline" is appropriate for all fluid needs, but in hypernatremia it functions as a relative hypertonic solution. 2

What You Should Do Instead

• Continue 0.45% saline if you can obtain it from another source (pharmacy, transfer from another unit, or emergency supply), as this is the standard hypotonic crystalloid for hypernatremia correction. 1

• If 0.45% saline is truly unavailable, use D5W (5% dextrose in water) as your hypotonic fluid. D5W provides pure free water once the glucose is metabolized and is equally effective for correcting hypernatremia. 1

• Calculate the free water deficit to guide total volume: Free water deficit (L) = 0.6 × body weight (kg) × [(current Na ÷ 140) – 1]. Replace this deficit over 48-72 hours while monitoring sodium every 2-4 hours initially. 1

• Monitor serum sodium every 2-4 hours during active correction to ensure you are achieving the target rate of 0.5 mEq/L per hour and not correcting too rapidly (which risks cerebral edema) or too slowly (which prolongs hyperosmolar injury). 1

Why This Matters for Morbidity and Mortality

• Inadequate or stalled correction of severe hypernatremia (Na >160 mEq/L) is associated with mortality rates of 40-60%, primarily from neurological complications including seizures, intracerebral hemorrhage, and permanent cognitive impairment. 1

• Overly rapid correction (>12 mEq/L in 24 hours) can cause cerebral edema as brain cells that adapted to hyperosmolarity by losing intracellular solutes suddenly swell when extracellular osmolality drops too quickly. 1

• Using 0.9% saline in this scenario will leave your patient in a prolonged hypernatremic state, increasing the risk of thrombotic complications, rhabdomyolysis, and acute kidney injury that accompany severe hyperosmolarity. 1

Practical Algorithm for Fluid Selection in Hypernatremia

Current Sodium 155-170 mEq/L (Severe Hypernatremia)

• First choice: 0.45% saline at a rate calculated to lower sodium by 0.5 mEq/L per hour 1
• If 0.45% saline unavailable: D5W at equivalent rate 1
• Never use: 0.9% saline, as it will not correct hypernatremia 1, 2

Current Sodium 145-154 mEq/L (Mild Hypernatremia)

• First choice: 0.45% saline or D5W 1
• Alternative: 0.9% saline may be considered only if sodium is <150 mEq/L and trending down, but hypotonic fluid is still preferred 1

Current Sodium <145 mEq/L (Correction Complete)

• Switch to: Isotonic balanced crystalloid (Ringer's lactate or Plasma-Lyte) for maintenance 3, 4
• Avoid: Continued hypotonic fluids, which risk iatrogenic hyponatremia 3

Critical Pitfalls to Avoid

• Do not assume that because the patient "improved" from 168 to 155 mEq/L, you can now use "normal" saline. The patient remains severely hypernatremic and requires continued hypotonic fluid therapy. 1

• Do not use 0.9% saline for drug dilution or catheter flushes in hypernatremic patients, as even these small volumes contribute significant sodium load and can impede correction. 2

• Do not correct hypernatremia faster than 0.5 mEq/L per hour (12 mEq/L per 24 hours maximum), even if the patient is symptomatic, as overly rapid correction causes cerebral edema. 1

• Do not delay obtaining appropriate hypotonic fluid. If your facility lacks 0.45% saline, D5W is universally available and equally effective—there is no justification for using 0.9% saline. 1