SM_202a: Hyponatremia Flashcards
In a hypertonic solution, a cell will ____
In a hypertonic solution, a cell will crenate
In a hypotonic solution, a cell will ______
In a hypotonic solution, a cell will lyse
Describe isotonicity
Solutes that affect tonicity affect transmembrane water flow and are commonly known as ______
Solutes that affect tonicity affect transmembrane water flow and are commonly known as effective osmols (Na+, K+, glucose)
(trapped on one side of the cell membrane and total body water migrates to create a temporal equilibrium that forms ECF and ICF fluid compartments)
_____ and _____ are not effective osmoles
Alcohol and urea are not effective osmoles
Na+/K+ ATPase keeps most ____ in the extracellular space and most ____ in the intracellular compartment
Na+/K+ ATPase keeps most Na+ in the extracellular space and most K+ in the intracellular compartment
Tonicity only considers _____, while osmolarity considers _____ and _____
Tonicity only considers effective osmoles, while osmolarity considers effective and ineffective osmoles
Estimated serum osmolarity = ______
Estimated serum osmolarity = 2[Na+} + glucose / 18 + BUN / 2.8
Why do we measure serum [Na+]?
Why do we measure serum [Na+]?
- To determine Na+ balance
- To calculate an anion gap in an acid base disorder
- Because it is a surrogate marker of tonicity
Total body Na+ contributes to the ______
Total body Na+ contributes to the effective arterial blood volume
Baroreceptors in the _____ and _____ sense and respond to changes in EABV associated with changes in BP
Baroreceptors in the carotid bodies and aortic arch sense and respond to changes in EABV associated with changes in BP
- Adrenergic hormones: NE and E
- Aldosterone release: increase Na+ reclamation by acting on principal cells
- ADH: increase H2O reclamation by acting on principal cells
Osmoreceptors respond to _____, not _____
Osmoreceptors respond to plasma tonicity, not osmolarity
Determinant of osmoreceptor activity is the _____
Determinant of osmoreceptor activity is the degree of stretch of the osmoreceptor cell membrane
ADH synthesized in the ____ and ____ and is released from the ____
ADH synthesized in the supraoptic and paraventricular nuclei of the hypothalamus and released from the posterior pituitary
Proximal tubule is composed of _____ epithelial junctions, while the collecting duct is composed of _____ epithelial junctions
Proximal tubule is composed of leaky epithelial junctions, while the collecting duct is composed of tight epithelial junctions
- Nephron reclaims most of the filtered Na isotonically along proximal tubule and most of remaining Na by the time filtrate passes into the collecting duct, effectively separating the regulation of Na handling from H2O handling
- Presence of abscence of ADH binding to V2 receptors along collecting duct determines whether H2O is reabsorbed into the interstitium or left in filtrate for subsequent excretion as urine
- How effective ADH is in reclaiming H2O along collecting duct is dependent on integrity of concentration gradient created in the medullary interstitium
Urine is composed of a ____ fraction and _____ fraction that is _____ to plasma
Urine is composed of a free water fraction and an electrolyte fraction that is isotonic to plasma
What is the equation for electrolyte free H2O clearance?
Amount of solute excretion _____ with free water clearance
Amount of solute excretion increases with free water clearance
In presence or absence of ADH, solute excretion _____ while urine osmolality _____
In presence or absence of ADH, solute excretion increases while urine osmolality approaches isotonicity
- in presence of ADH, speed up flow rate, so equilibration time decreases
Hyponatremia has three variants: _____, _____, and _____
Hyponatremia has three variants: isotonic hyponatremia (artifactual), hypotonic hyponatremia (decreased CefH2O), and hypertonic hyponatremia (translocational)
Isotonic hyponatremia (artifactual) is characterized by ______
Isotonic hyponatremia (artifactual) is characterized by elevated solids in plasma
(can be sign of early disease)
In hypertonic hyponatremia, adding glucose ______
In hypertonic hyponatremia, adding glucose reduces serum Na+
Hypotonic hyponatremia is characterized by ______
Hypotonic hyponatremia is characterized by decreased CefH2O
Most early symptoms of hypotonic hyponatremia occurs as the serum Na+ ______
Most early symptoms of hypotonic hyponatremia occurs as the serum Na+ drops below 125 mEq/L
- Symptoms include nausea, fatigue, headache, lethargy, somnolence, coma, and seizures
- Symptoms depend on how quickly patient becomes hypotonic
- Aggressive treatment undertaken when serum Na+ is below 118 mEq/L regardless of symptoms
Why would you not want to increase serum Na+ by more than 8 mEq/L?
Do not want to increase serum Na+ by more than 8 mEq/L because water will come out of brain, and brain will shrink, which may lead to osmotic demyelination if done too quickly
Describe the key points regarding hypotonic hyponatremia
Hypotonic hyponatremia
- Hypotonicity can occur at any blood volume: volume depletion w/ orthostasis, euvolemia, volume expansion with edema
- Get hypotonic by taking in water and failing to excrete it: water intake exceeds CefH2O
- You know patient took in water, but you have to figure out why they have reduced CefH2O
- Never caused by kidney excreting more Na+ than H2O
Hypotonic hyponatremia is NEVER caused by the kidney excreting more ____ than ____
Hypotonic hyponatremia is NEVER caused by the kidney excreting more Na+ than H2O
Hypotonic hyponatremia can occur under conditions of _____, _____, and _____
Hypotonic hyponatremia can occur under conditions of volume depletion (increased water, decreased total body Na+), near euvolemia (increased water, normal total body Na+), and edema (increased water, increased total body Na+)
Describe hypotonic hyponatremia with volume depletion
Hypotonic hyponatremia with volume depletion
- Reduction of EABV stimulates Na+ and H2O reclamation
- Patient takes in hypotonic fluids increased total body water relative to available total body mOsms
Describe hypotonic hyponatremia with edema
Hypotonic hyponatremia with edema
- Perception of a reduced EABV stimulates Na+ and H2O reclamation
- Reduced EABV -> baroreceptors fire -> FR decreases
- Angiotensin II -> increased activity of Na+/H+ antiporter and Na+/K+/2Cl- and Na+/Cl- symporter
- Recapture of Na+ and water -> oliguria
- Patient takes in hypotonic fluids increased total body water relative to available total body mOsms
Describe psychogenic polydipsia
Psychogenic polydipsia
- Stand in shower and consume lots of water
- Become profoundly hypotonic because intake acutely exceeds the mechanical limits of the kidneys
- Have seizure
- Stop drinking and undergo H2O diuresis returning to isotonicity
- Cycle repeats
There is no such thing as a ____ urine volume
There is no such thing as a normal urine volume
Urine volume = _____
Urine volume = (solute excretion/day) / (average urine mOsm/L/day)
Potomania can occur when _____ or _____
Potomania can occur when person takes in a steady diet of beer or drinks water beyond thirst while on a crash diet
_____ diuretics can cause hyponatremia
Thiazide diuretics can cause hyponatremia
In syndrome in inappropriate ADH secretion (SIADH), Uosm is ____ for the Posm
In syndrome in inappropriate ADH secretion (SIADH), Uosm is inappropriate for the Posm
In syndrome in inappropriate ADH secretion (SIADH), urine Na+ will reflect _____ at euvolemia
In syndrome in inappropriate ADH secretion (SIADH), urine Na+ will reflect dietary Na+ intake at euvolemia
Describe treatment for hypotonic hyponatremia
Treatment for hypotonic hyponatremia
- Water restriction to allow for evaporation
- If volume depleted, normal saline until euvolemic
- If edema, control water intake and treat primary disease to see if CefH2O will increase
- Oral V2 receptor antagonists can raise tonicity in SIADH and heart failure but contraindicated in liver disease
- SNa should not rise faster than 8 mEq/L/day to avoid osmotic demyelination
- Acute intoxication w/ symptoms of cerebral edema may require limited administration of 3% Na+ - goal is not to get SNa to normal
- Avoid normal saline in SIADH unless coupled w/ loop diuretics because kidney will dump the Na+ and keep the H2O
In treatment of hypotonic hyponatremia, keep the rise in SNa below _____
In treatment of hypotonic hyponatremia, keep the rise in SNa below 8 mEq/L/day
