🧠 Hyponatremia in Hospitalized Patients: A High-Yield Electrolyte Disturbance for the USMLE

Hyponatremia is more than a lab value—it’s a common hospital complication that can cause serious neurologic symptoms. Whether it’s from SIADH, excess fluid administration, or chronic disease, understanding the mechanisms and management is key for both USMLE success and real-world application.

🔍 Pathophysiology Recap

• Serum Sodium <135 mEq/L

• Reflects excess water retention, not total body sodium loss

• In SIADH, ADH is secreted inappropriately → water reabsorption ↑

• Plasma becomes dilute → osmotic imbalance → cerebral edema risk

📊 High-Yield Lab Findings

Parameter	Finding
Serum Sodium	↓ (<135 mEq/L)
Plasma Osmolality	↓ (<280 mOsm/kg)
Urine Osmolality	↑ in SIADH
Urine Sodium	↑ in euvolemic states

👩‍⚕️ Clinical Signs to Watch

• Headache

• Nausea

• Confusion or disorientation

• Seizures (in severe/acute cases)

• Older adults: may present with subtle changes in mental status

🧪 USMLE Key Testing Points

Step 1:

• Regulation of ADH

• Role of hypothalamus and posterior pituitary

• Osmoreceptors and aquaporins

Step 2/3:

• Scenario-based management

• Distinguishing volume status (hypo/eu/hypervolemia)

• When to use hypertonic saline (and how to avoid osmotic demyelination)

💡 First-Line Management Overview

Type of Hyponatremia	First-Line Management
Hypovolemic	Normal saline (NS)
Euvolemic (e.g., SIADH)	Fluid restriction, demeclocycline
Hypervolemic	Fluid + salt restriction, diuretics

🎮 KOTC Feature: Turn Mastery into a Game

With King of the Curve’s Adaptive Q-Bank, you’ll face clinical questions just like this one:

A 72-year-old post-op patient develops confusion. Sodium is 122 mEq/L. Urine osmolality is high. What’s the diagnosis and next best step?

That’s the power of long-term learning made effortless—and even fun.

✅ Call to Action

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