Which fluids should be avoided in hyponatremia?

Fluids to Avoid in Hyponatremia

Hypotonic fluids (such as 0.45% saline, 0.2% saline, and D5W) should be strictly avoided in patients with hyponatremia, as they worsen sodium dilution and can cause life-threatening hyponatremic encephalopathy. 1

Primary Fluids to Avoid

Hypotonic Solutions - The Main Culprit

• 0.45% saline (half-normal saline)
• 0.2% saline (quarter-normal saline)
• D5W (5% dextrose in water)
• Any solution with sodium content <130 mEq/L

The 2018 American Academy of Pediatrics guidelines explicitly state that hypotonic maintenance fluids have caused "increasing reports of the deleterious effect of hyponatremia in the acute care setting" and are associated with "acute or permanent neurologic impairment" 1. These fluids provide free water that cannot be excreted in patients with elevated antidiuretic hormone (ADH/vasopressin), which is common in hospitalized patients due to pain, nausea, stress, surgery, infections, and numerous medications 1, 2.

The Counterintuitive Danger: 0.9% Normal Saline in SIADH

In patients with syndrome of inappropriate antidiuresis (SIADH), even 0.9% normal saline should be avoided because it paradoxically worsens hyponatremia 3. Here's why:

• In SIADH, urine osmolality is inappropriately elevated (>100 mOsm/L) with high urine sodium
• When 0.9% saline (154 mEq/L sodium) is given to a patient whose urine sodium exceeds 154 mEq/L, the kidneys excrete the sodium but retain the free water
• This creates a net gain of free water, worsening the hyponatremia 3
• Additionally, 0.9% saline causes rapid fluctuations in sodium levels—initial correction during infusion followed by post-infusion worsening—increasing risk of osmotic demyelination syndrome 3

Context-Specific Fluid Restrictions

In Cirrhosis with Hypervolemic Hyponatremia

The 2025 AGA guidelines specify additional restrictions 4:

• Limit total fluid intake to 1-1.5 L daily for mild asymptomatic hyponatremia (sodium >120 mEq/L)
• Restrict fluids to less than urine output for severe or symptomatic cases
• Avoid excessive free water from any source, including oral intake and IV medications containing free water 1, 4

In Edematous States

Patients with heart failure, cirrhosis, or nephrotic syndrome have impaired ability to excrete both sodium and free water 1:

• Avoid isotonic saline at typical maintenance rates—this risks volume overload
• Fluids should be restricted with close monitoring 1

Additional Sources of Free Water to Avoid

Beyond IV fluids, be vigilant about 1:

• IV medications diluted in free water or hypotonic solutions
• Excessive oral free water intake
• Excessive laxative use (can cause free water loss leading to compensatory ADH release) 4

The Evidence Base

Multiple prospective randomized trials demonstrate that hypotonic fluids significantly increase hyponatremia risk compared to isotonic solutions 1, 5. A 2010 study showed plasma sodium fell in both hypotonic groups regardless of infusion rate, with 30% developing hyponatremia versus only 10% in isotonic groups (P=0.02) 5. Critically, fluid type, not rate, determined hyponatremia risk on multivariate analysis 5.

The literature contains "multiple reports of death or permanent neurological impairment" from hospital-acquired hyponatremia, and "virtually all neurological morbidity resulting from hospital-acquired hyponatremia has been associated with administration of hypotonic fluids" 2. In contrast, there is "not a single report in the literature of neurological complications resulting from the use of 0.9% NaCl in non-neurosurgical patients" 2.

Common Pitfalls

1. Assuming all patients need hypotonic fluids for "free water"—this outdated practice from the 1950s ignores that most hospitalized patients have elevated ADH and cannot excrete free water 1, 2

2. Using 0.9% saline reflexively in SIADH—check urine sodium and osmolality first; if urine sodium >154 mEq/L, normal saline will worsen hyponatremia 3

3. Forgetting about hidden free water sources—IV medications, oral intake, and excessive laxatives can all contribute 1, 4

4. Not recognizing high-risk medications—desmopressin, carbamazepine, cyclophosphamide, and vincristine all increase hyponatremia risk 1