What is the effect of 0.44% Normal Saline (NS) on serum sodium levels?

Effect of 0.44% Normal Saline on Serum Sodium

0.44% normal saline (half-normal saline) is a hypotonic solution that will lower serum sodium levels, making it appropriate for treating hypernatremia but contraindicated when normal or low sodium levels are present.

Mechanism and Physiological Effect

0.44% NS contains 77 mEq/L of sodium, which is significantly hypotonic compared to plasma (normal sodium 135-145 mEq/L). When administered intravenously, this solution delivers free water in excess of sodium, resulting in:

• Dilution of serum sodium concentration through provision of hypotonic fluid 1
• Net negative sodium balance when the solution's sodium content is lower than urinary sodium losses 1
• Expansion of intravascular volume with simultaneous reduction in serum osmolality 1

Clinical Applications

Hypernatremia Treatment

0.44% NS (also called 0.45% NS or half-normal saline) is effective for correcting hypernatremia in critically ill patients:

• Studies demonstrate successful reduction of serum sodium from 156 ± 4 to 143 ± 6 mEq/L over 3-7 days when administered at approximately 1.5 L/day 1
• Total sodium intake decreases from 210 ± 153 to 156 ± 112 mEq/day during treatment 1
• The solution allows controlled correction without excessive fluid administration 1

Contraindications and Warnings

Hypotonic solutions like 0.44% NS should be avoided in specific clinical scenarios:

• Patients with severe head trauma or traumatic brain injury should not receive hypotonic solutions due to risk of fluid shift into damaged cerebral tissue and worsening cerebral edema 2
• Trauma patients with bleeding should receive isotonic crystalloids (0.9% saline or balanced crystalloids) rather than hypotonic solutions 2

Important Safety Considerations

Risk of Hemolysis

A critical safety concern with 0.44% NS is the potential for hemolysis when administered centrally:

• Plasma free hemoglobin increased from 4.9 ± 5.4 mg/dL to 8.9 ± 7.4 mg/dL after 2.6 days of continuous IV administration 1
• Hematocrit decreased from 26% ± 3% to 24% ± 2%, and hemoglobin fell from 9.1 ± 1.1 to 8.2 ± 0.8 g/dL 1
• This evidence of minor hemolysis warrants caution and further research before routine use can be recommended 1

Preferred Alternative for Hypernatremia

For hypernatremic dehydration, D5W (5% dextrose in water) is the preferred primary IV fluid rather than 0.44% NS:

• D5W delivers no renal osmotic load, allowing controlled correction without adding sodium burden 3
• 0.9% NaCl should be avoided as it paradoxically worsens hypernatremia by providing excessive osmotic load 3
• D5W provides pure free water replacement once the dextrose is metabolized 3

Comparison to Other Crystalloid Solutions

The choice of crystalloid solution significantly impacts patient outcomes:

• Buffered crystalloid solutions are recommended over 0.9% saline in most perioperative settings due to reduced risk of hyperchloremic acidosis and acute kidney injury 2
• Large volumes of 0.9% saline cause hyperchloremic acidosis, renal vasoconstriction, and increased major adverse kidney events 2
• For initial resuscitation in trauma or sepsis, isotonic solutions (0.9% saline or balanced crystalloids) are indicated, not hypotonic solutions 2

Clinical Pitfalls to Avoid

• Never use hypotonic solutions for volume resuscitation in hypotensive or shocked patients 2
• Avoid in patients with cerebral edema or traumatic brain injury due to risk of worsening intracranial pressure 2
• Monitor for signs of hemolysis (decreasing hemoglobin/hematocrit, elevated free hemoglobin) during prolonged administration 1
• Correction of hypernatremia should not exceed 8-10 mEq/L per day to prevent cerebral edema 3
• Consider D5W as the primary fluid for hypernatremia correction rather than 0.44% NS 3