Hyponatremia Flashcards
Osmoregulation
- Sensing plasma osmolality
- Via hypothalamic osmoreceptors
- Responds w/ ADH regulation and thirst regulation
- Acts on kidney and brain
- Modulates renal water excretion and oral water intake
Volume regulation
- Senses effective circulating volume (intravascular blood volume)
- Sensors are carotid sinus, atria, aortic arch, and JGA
- Baroreceptors
- Responds w/ RAAS, sympathetics, ANP, and ADH
- Acts on heart and vessels immediately and kidney long term
- Affects BP immediate and Na+ excretion long term
Define hyponatremia
- Low [Na+] in the plasma
- Reflects relative excess of water in relation to sodium
- Due to kidney’s altered ability to excrete ingested/infused H2O
- Usually from inability to suppress ADH release in response to decreased osmolality (can’t properly dilute urine)
Plasma Osmolality
-Ratio of plasma solutes to plasma H2O
2[Na+]+[glu]/18+[Urea]/2.8
-If difference b/t measured and calculated, then there is a gap
-Gap caused by presence of other solutes: ethanol, mannitol, or ethylene glycol are examples
Urine osmolality
-Reflects water reabsorption and level of concentration activity
Urine Na+ concentration
- Reflects renal response to perceived volume status
- Fractional excretion of Na+ (FeNa)
- fraction of filtered Na+ excreted by the kidney
- Reflects response to perceived volume status
- High percent is perceived hypervolemia
- Low percent is perceived hypovolemia
- Normal is 1%
Hyponatremia with Normal plasma osmolarity
- Isotonic hyponatremia
- Na+<135
- Osmolality 280-295mOsm/L
- Pseudohyponatremia
- Due to hyperproteinemia or hyperlipidemia
Hyponatremia with Elevated plasma osmolality
- Hypertonic Hyponatremia
- Na+295mOsm/L
- Hyperglycemia or mannitol
- For every 62mg/dL increase in glucose, Na+ decreases 1mEq/L
Hypotonic hyponatremia with hypovolemia, and elevated urine sodium
- Hypotonic Hyponatremia (Na<280mOsm/L)
- Due to renal volume Loss
- Diuretics
- RTA with increased bicarb
- Mineralocorticoid deficiency
- Salt losing nephropathy
- Cerebral salt wasting
Hypotonic Hyponatremia with hypovolemia and low urine sodium
- Urine sodium <20
- External Volume loss
- Skin or GI tract loss
- Burns or pancreatitis: 3rd space
Euvolemic hypotonic hyponatremia with Urine osmolality low
- Urine osmolality <100mOsm/L (indicates ADH properly off)
- Excess H2O intake
- Primary polydipsia
- IV fluids
Euvolemic hypotonic hyponatremia with Urine osmolality High
- Urine osmolality >100mOsm/L (ADH improperly on)
- Impaired renal urine dilution ability
- SIADH: cancer, lung disease, CNS disorder
- Reset osmostat
- Endocrine disorder: hypothyroid, adrenal insufficiency
- Stress, nausea, pain, drugs
Hypervolemic hypotonic hyponatremia with Urine osmolality high
- Urine sodium >20mOsm/L
- Renal failure
Hypervolemic hypotonic hyponatremia with Urine osmolality Low
- Urine osmolality <20mOsm/L
- Edematous state
- CHF
- Cirrhosis
- Nephrotic syndrome
