How to manage hyponatremia (low sodium levels) caused by preeclampsia?

Management of Hyponatremia in Preeclampsia

The definitive management of hyponatremia in preeclampsia requires fluid restriction as the primary intervention, with hypertonic saline reserved for severe cases, and delivery of the fetus when clinically indicated, as this leads to resolution of hyponatremia in most cases within 48-72 hours. 1, 2

Pathophysiology and Prevalence

Hyponatremia is not uncommon in preeclampsia, affecting approximately 14-34% of patients 2, 3. The exact pathophysiology remains unclear, but potential mechanisms include:

• Syndrome of inappropriate antidiuretic hormone secretion (SIADH)
• Combined effect of preeclampsia and nephrotic syndrome
• Fluid retention and hypervolemia

Importantly, hyponatremia in preeclampsia is strongly correlated with severe features and adverse maternal and neonatal outcomes 3.

Diagnostic Approach

While current guidelines do not recommend routine sodium monitoring in all preeclamptic patients 4, serum sodium levels should be measured in:

• All patients with preeclampsia with severe features
• Patients with neurological symptoms (as symptoms of hyponatremia can overlap with cerebral symptoms of preeclampsia) 5
• Patients with pulmonary edema or signs of fluid overload

Management Algorithm

1. Initial Assessment and Monitoring

• Monitor sodium levels at least twice weekly along with other laboratory parameters in preeclampsia 4
• Assess volume status clinically
• Monitor for neurological symptoms that could indicate worsening hyponatremia or preeclampsia

2. Treatment Based on Severity

Mild to Moderate Hyponatremia (Na 125-134 mEq/L):

• Fluid restriction (primary intervention) 1, 2
• Continue standard preeclampsia management including:
  • Blood pressure control using recommended antihypertensives (oral nifedipine, IV labetalol, or IV hydralazine) 4
  • Magnesium sulfate for seizure prophylaxis if indicated 4
  • Consider adjusting magnesium sulfate infusion components to reduce free water intake 5

Severe Hyponatremia (Na <125 mEq/L):

• Fluid restriction
• Hypertonic (3%) saline administration 6, 2
  • Administer through a large vein for rapid dilution
  • Monitor closely for complications including fluid overload
  • Use caution in patients with preeclampsia due to risk of sodium retention 6
• ICU monitoring is necessary 1
• Avoid rapid correction (risk of serious neurologic complications) 6

3. Definitive Management

• Delivery of the fetus is the definitive treatment 4, 1
• Indications for immediate delivery include:
  • Gestational age ≥37 weeks
  • Severe hyponatremia not responding to medical management
  • Other indications for delivery in preeclampsia as per guidelines 4

4. Post-delivery Management

• Continue monitoring sodium levels until normalization
• Most cases resolve within 48-72 hours after delivery 1, 2
• Monitor blood pressure every 4-6 hours for at least 3 days postpartum 7

Special Considerations

Magnesium Sulfate Administration

• When administering magnesium sulfate for seizure prophylaxis in preeclamptic patients with hyponatremia:
  • Consider adjusting the solution to minimize free water administration 5
  • Monitor for potential interaction between calcium channel blockers and magnesium sulfate 4

Neonatal Implications

• Alert neonatologists about maternal hyponatremia as neonates may have low sodium levels (reported range: 118-128 mmol/L) 2

Pitfalls and Caveats

1. Avoid rapid correction of hyponatremia due to risk of osmotic demyelination syndrome 6

2. Recognize the potential for cardiopulmonary arrest in severe cases of hyponatremia in preeclampsia 8

3. Consider hyponatremia as a marker of preeclampsia severity - even in patients without other severe features, hyponatremia correlates with less favorable outcomes 3

4. Be cautious with fluid management - preeclamptic patients are at risk for both pulmonary edema from fluid overload and complications from hyponatremia 6

5. Monitor for overlapping symptoms - neurological symptoms may be due to either hyponatremia or worsening preeclampsia 5