SM_202a: Hyponatremia

Question 1

In a hypertonic solution, a cell will ____

Answer 1

In a hypertonic solution, a cell will crenate

Question 2

In a hypotonic solution, a cell will ______

Answer 2

In a hypotonic solution, a cell will lyse

Question 3

Describe isotonicity

Answer 3

Question 4

Solutes that affect tonicity affect transmembrane water flow and are commonly known as ______

Answer 4

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)

Question 5

_____ and _____ are not effective osmoles

Answer 5

Alcohol and urea are not effective osmoles

Question 6

Na⁺/K⁺ ATPase keeps most ____ in the extracellular space and most ____ in the intracellular compartment

Answer 6

Na⁺/K⁺ ATPase keeps most Na⁺ in the extracellular space and most K⁺ in the intracellular compartment

Question 7

Tonicity only considers _____, while osmolarity considers _____ and _____

Answer 7

Tonicity only considers effective osmoles, while osmolarity considers effective and ineffective osmoles

Question 8

Estimated serum osmolarity = ______

Answer 8

Estimated serum osmolarity = 2[Na⁺} + glucose / 18 + BUN / 2.8

Question 9

Why do we measure serum [Na⁺]?

Answer 9

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

Question 10

Total body Na⁺ contributes to the ______

Answer 10

Total body Na⁺​ contributes to the effective arterial blood volume

Question 11

Baroreceptors in the _____ and _____ sense and respond to changes in EABV associated with changes in BP

Answer 11

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

Question 12

Osmoreceptors respond to _____, not _____

Answer 12

Osmoreceptors respond to plasma tonicity, not osmolarity

Question 13

Determinant of osmoreceptor activity is the _____

Answer 13

Determinant of osmoreceptor activity is the degree of stretch of the osmoreceptor cell membrane

Question 14

ADH synthesized in the ____ and ____ and is released from the ____

Answer 14

ADH synthesized in the supraoptic and paraventricular nuclei of the hypothalamus and released from the posterior pituitary

Question 15

Proximal tubule is composed of _____ epithelial junctions, while the collecting duct is composed of _____ epithelial junctions

Answer 15

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

Question 16

Urine is composed of a ____ fraction and _____ fraction that is _____ to plasma

Answer 16

Urine is composed of a free water fraction and an electrolyte fraction that is isotonic to plasma

Question 17

What is the equation for electrolyte free H₂O clearance?

Answer 17

Question 18

Amount of solute excretion _____ with free water clearance

Answer 18

Amount of solute excretion increases with free water clearance

Question 19

In presence or absence of ADH, solute excretion _____ while urine osmolality _____

Answer 19

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

Question 20

Hyponatremia has three variants: _____, _____, and _____

Answer 20

Hyponatremia has three variants: isotonic hyponatremia (artifactual), hypotonic hyponatremia (decreased C^efH₂O), and hypertonic hyponatremia (translocational)

Question 21

Isotonic hyponatremia (artifactual) is characterized by ______

Answer 21

Isotonic hyponatremia (artifactual) is characterized by elevated solids in plasma

(can be sign of early disease)

Question 22

In hypertonic hyponatremia, adding glucose ______

Answer 22

In hypertonic hyponatremia, adding glucose reduces serum Na⁺

Question 23

Hypotonic hyponatremia is characterized by ______

Answer 23

Hypotonic hyponatremia is characterized by decreased C^efH₂O

Question 24

Most early symptoms of hypotonic hyponatremia occurs as the serum Na⁺ ______

Answer 24

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

Question 25

Why would you not want to increase serum Na⁺ by more than 8 mEq/L?

Answer 25

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

Question 26

Describe the key points regarding hypotonic hyponatremia

Answer 26

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 C^efH₂O
• You know patient took in water, but you have to figure out why they have reduced C^efH₂O
• Never caused by kidney excreting more Na⁺ than H₂O

Question 27

Hypotonic hyponatremia is NEVER caused by the kidney excreting more ____ than ____

Answer 27

Hypotonic hyponatremia is NEVER caused by the kidney excreting more Na⁺ than H₂O

Question 28

Hypotonic hyponatremia can occur under conditions of _____, _____, and _____

Answer 28

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⁺)

Question 29

Describe hypotonic hyponatremia with volume depletion

Answer 29

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

Question 30

Describe hypotonic hyponatremia with edema

Answer 30

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

Question 31

Describe psychogenic polydipsia

Answer 31

Psychogenic polydipsia

1. Stand in shower and consume lots of water
2. Become profoundly hypotonic because intake acutely exceeds the mechanical limits of the kidneys
3. Have seizure
4. Stop drinking and undergo H₂O diuresis returning to isotonicity
5. Cycle repeats

Question 32

There is no such thing as a ____ urine volume

Answer 32

There is no such thing as a normal urine volume

Question 33

Urine volume = _____

Answer 33

Urine volume = (solute excretion/day) / (average urine mOsm/L/day)

Question 34

Potomania can occur when _____ or _____

Answer 34

Potomania can occur when person takes in a steady diet of beer or drinks water beyond thirst while on a crash diet

Question 35

_____ diuretics can cause hyponatremia

Answer 35

Thiazide diuretics can cause hyponatremia

Question 36

In syndrome in inappropriate ADH secretion (SIADH), Uosm is ____ for the Posm

Answer 36

In syndrome in inappropriate ADH secretion (SIADH), Uosm is inappropriate for the Posm

Question 37

In syndrome in inappropriate ADH secretion (SIADH), urine Na⁺ will reflect _____ at euvolemia

Answer 37

In syndrome in inappropriate ADH secretion (SIADH), urine Na⁺ will reflect dietary Na⁺ intake at euvolemia

Question 38

Describe treatment for hypotonic hyponatremia

Answer 38

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 C^efH₂O 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

Question 39

In treatment of hypotonic hyponatremia, keep the rise in SNa below _____

Answer 39

In treatment of hypotonic hyponatremia, keep the rise in SNa below 8 mEq/L/day