What is the appropriate rate of running Normal Saline (N/S) in hyponatremia?

Appropriate Rate of Normal Saline in Hyponatremia

Normal saline (0.9% NaCl) should NOT be used for severe hyponatremia, as it may worsen hyponatremia in SIADH and is only appropriate for hypovolemic hyponatremia with careful monitoring.

Assessment of Hyponatremia Type

• First determine the type of hyponatremia based on volume status assessment 1:
  • Hypovolemic: Signs of dehydration, low urine sodium (<30 mmol/L)
  • Euvolemic: Normal volume status, high urine sodium (>20 mEq/L), high urine osmolality (>500 mosm/kg)
  • Hypervolemic: Edema, ascites, signs of fluid overload

Treatment Based on Volume Status

For Hypovolemic Hyponatremia:

• Discontinue diuretics and administer isotonic saline (0.9% NaCl) for volume repletion 1
• Monitor serum sodium levels every 4 hours initially 1
• Maximum correction rate: 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 2
• For patients with liver disease or malnutrition: more conservative correction (4-6 mmol/L per day) 1

For Euvolemic Hyponatremia (SIADH):

• Do not use normal saline as it may worsen hyponatremia 1, 3
• Implement fluid restriction to 1 L/day as first-line treatment 1, 3
• For severe symptoms: use 3% hypertonic saline with goal to correct 6 mmol/L over 6 hours or until symptoms resolve 2, 3

For Hypervolemic Hyponatremia (e.g., cirrhosis, heart failure):

• Do not use normal saline as it will worsen fluid overload 1
• Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L 4, 1
• Consider albumin infusion for patients with cirrhosis 1

Correction Rate Guidelines

• Maximum correction: 8 mmol/L in 24 hours for most patients 1, 2, 3
• For severe symptoms: Initial correction of 6 mmol/L over 6 hours or until symptoms resolve 2, 3
• After initial correction, limit to only 2 mmol/L in the following 18 hours 2
• For patients with advanced liver disease, alcoholism, or malnutrition: 4-6 mmol/L per day 1

Monitoring During Treatment

• For severe symptoms: Monitor serum sodium every 2 hours initially 3
• After resolution of severe symptoms: Monitor every 4 hours 2
• Calculate sodium deficit using formula: Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 1

Common Pitfalls to Avoid

• Using normal saline in SIADH can worsen hyponatremia 1
• Overly rapid correction (>8 mmol/L in 24 hours) can lead to osmotic demyelination syndrome 1, 5
• Inadequate monitoring during active correction 1
• Using fluid restriction in cerebral salt wasting (CSW) can worsen outcomes 1
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1

Special Considerations for Cirrhotic Patients

• Hyponatremia in cirrhosis is mostly hypervolemic due to non-osmotic hypersecretion of vasopressin and enhanced proximal nephron sodium reabsorption 4
• Fluid restriction to 1-1.5 L/day is recommended for severe hyponatremia (serum sodium <125 mmol/L) 4
• Fluid restriction may prevent further decrease in serum sodium but rarely improves it significantly 4
• It is sodium restriction, not fluid restriction, that results in weight loss as fluid passively follows sodium 4
• Temporarily discontinue diuretics if sodium <125 mmol/L 4

Remember that the rate of correction should be determined by symptom severity and onset timing, with careful monitoring to prevent osmotic demyelination syndrome, which is a rare but severe neurological condition 1, 6.