A 72-year-old woman on thiazide diuretics for hypertension presents with acute onset seizures. Serum sodium is 112 mEq/L. CT head is normal. She is actively seizing. What is the most appropriate immediate action?

## Clinical Diagnosis: Acute, Severe Hyponatremia with Seizures ### Critical Assessment **Key Point:** Seizures due to hyponatremia are a medical emergency. Acute hyponatremia (onset < 48 hours) with Na < 115 and neurologic symptoms (seizures, coma, altered mental status) requires immediate hypertonic saline to raise serum sodium acutely and stop seizure activity. **Warning:** Do NOT delay hypertonic saline to obtain imaging or wait for fluid restriction to work. Seizures from hyponatremia are life-threatening and demand rapid sodium correction. ### Mechanism of Hyponatremic Seizures 1. **Osmotic gradient:** Low serum osmolality causes water to shift into neurons → cerebral edema and increased intracranial pressure. 2. **Neuronal dysfunction:** Swelling of neurons impairs synaptic transmission and lowers seizure threshold. 3. **Acute vs. chronic:** Acute hyponatremia (< 48 hours) causes severe cerebral edema because the brain has not had time to adapt by losing intracellular osmolytes. Chronic hyponatremia is better tolerated. ### Management Algorithm for Symptomatic Acute Hyponatremia ```mermaid flowchart TD A[Hyponatremia Na < 115]:::outcome --> B{Symptoms: seizures,<br/>coma, altered mental status?}:::decision B -->|Yes| C[EMERGENCY]:::urgent C --> D[3% saline bolus<br/>100 mL IV over 10-20 min]:::action D --> E[Recheck Na at 20 min]:::action E --> F{Na increased by<br/>4-6 mEq/L?}:::decision F -->|Yes| G[Continue 3% infusion<br/>to raise Na by 8-10 mEq/L<br/>in first 24 hrs]:::action F -->|No| H[Repeat bolus]:::action B -->|No: asymptomatic| I[Fluid restriction or<br/>hypertonic saline slowly]:::action ``` ### Hypertonic Saline Dosing and Monitoring **High-Yield:** The goal is to raise serum sodium by **4–6 mEq/L acutely** to stop seizures, then continue slower correction (6–8 mEq/L per 24 hours total) to avoid osmotic demyelination. **Calculation for 3% saline:** $$\text{mEq of Na to add} = (\text{desired Na} - \text{current Na}) \times \text{Vd}$$ $$\text{Vd} \approx 0.6 \times \text{body weight (kg)}$$ For a 70 kg woman: - Current Na = 112 mEq/L - Desired Na (acute target) = 118 mEq/L (raise by 6 mEq/L) - mEq needed = (118 − 112) × 0.6 × 70 = 252 mEq - 3% saline contains 513 mEq/L, so ~50 mL bolus over 10–20 minutes **Clinical Pearl:** After the bolus, check serum sodium at 20 minutes to confirm response. If seizures persist and Na has not risen by 4–6 mEq/L, repeat the bolus. ### Why Fluid Restriction is Inadequate Here Fluid restriction works over hours-to-days. Seizures require immediate sodium elevation within minutes. Delaying hypertonic saline to start fluid restriction risks status epilepticus, aspiration, and death. [cite:Harrison 21e Ch 297; Robbins 10e Ch 7]