Hyponatremia Case Study

What are the two major body fluid compartments and their primary ions?

ICF - K+

ECF - Na+ and Cl-

What causes weight gain in dilutional hyponatremia?

When fluid intake exceed fluid loss

Which compartment is diluted in dilutional hyponatremia?

The ECF is primarily diluted, though both ECF and ICF eventually have lower osmolarities due to osmotic equilibrium

How do you estimate body osmolarity using plasma Na+ concentration?

Double the plasma Na+ concentration. Normal range is 270-290 mOsm/L. In

Why is the brain the most concerning organ in dilutional hyponatremia?

The brain is confined within the rigid skull, so when cells swell it can’t expand like other tissues, leading to increased intracranial pressure and potentially severe neurological symptoms

What are the typical symptoms of hyponatremia?

• Nausea

• Headache

• Fatigue

• Confusion

• Loss of coordination

How does water movement occur in hyponatremia?

Water moves from the hypotonic extracellular space into the cells due to osmotic gradient, causing cellular swelling

What happens to vasopressin in dilutional hyponatremia?

Vasopressin (ADH) secretion decreases because the body detects excess water and doesn’t need to conserve more

What happens to aldosterone in dilutional hyponatremia?

Aldosterone secretion typically decreases to allow the kidneys to excrete excess water and help restore normal sodium concentrations

How is acute dilutional hyponatremia treated?

• Slow IV drip of 3% saline

• Restriction of oral fluid intake

• Monitor until plasma Na+ returns to normal levels

What factors affect sweating rate and composition during excercise?

• Individual variation

• Heat acclimatisation

• Sweat rate can range from 0.6L/h to 2.5L/h

• Sweat Na+ can range from 20 mEq/L to 90 mEq/L

What indicates someone is a “salty sweater”?

White salt crystals visible on skin and clothing after exercise, indicating high sodium content in sweat

What is the relationship between mEq and mmol for sodium?

For sodium (Na+), which has a valence of +1, 1 mEq equals 1 mmol

How do you calculate total fluid intake during excercise?

Total fluid intake = fluid retained + fluid lost through sweat

E.g. 2L (weight gain) + 16L (sweat loss) = 18L total intake

What hormones regulate fluid and sodium balance during exercise?

• Aldosterone: promotes Na+ retention

• Vasopressin: promotes water retention

Both are increased during normal exercise due to sympathetic output

What are the dangers of excessive water intake during endurance events?

• Dilution of blood sodium levels

• Cellular swelling

• Brain swelling

• Neurological symptoms

• Potential life-threatening complications

What are key preventative measures for exercise-associated hyponatremia?

• Balanced fluid intake

• Proper electrolyte water consumption

• Monitoring body weight changes

• Paying attention to thirst cues

What lab values indicate hyponatremia?

Plasma Na+ below 135 mEq/L

Severe: below 125 mEq/L