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Renal > SM 202 Hyponatremia > Flashcards

SM 202 Hyponatremia Flashcards

1
Q

What is tonicity?

A

A term that refers to the volume behavior of cells in a solution, such as expansion in hypotonic and contraction in hypertonic solutions

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2
Q

What is the requirement for a solute to be an effective osmol?

A

Solutes that are effective osmols are trapped on one side of the cell and therefore effect transmembrane water flow

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3
Q

What are common effective osmoles?

A

Na + K due to the Na/K ATPase

Glucose because it gets trapped inside of cells via phosphorylation

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4
Q

What common solutes are not effective osmols?

A

Urea and Ethanol because they can cross the membrane

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5
Q

What is the utility of serum Sodium?

A

Serum Sodium is a surrogate marker of tonicity

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6
Q

How rapidly is the response to changes in tonicity?

A

Changes in tonicity rapidly cause changes in cell shape which lead to cell toxicity

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7
Q

What cell type is resistant to changes in tonicity?

A

Neurons - because they can export or import ions to compensate for changes in ions/tonicity

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8
Q

What is the difference between tonicity and serum osmolarity?

A

Tonicity is “guessed” at while serum osmolarity is measured

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9
Q

What are the units on serum osmolarity?

A

mMol/L or mOsm/L or mEq/L

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10
Q

How do ineffective mOsms effect osmolarity?

A

Can’t get rid of the ineffective mOsms so they raise Osmolarity

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11
Q

What causes hypertonicity and hypernatremia, broadly speaking?

A

Low water such as from dehydration raises effective Sodium concentration

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12
Q

What causes hypotonicity and hyponatremia, broadly speaking?

A

Excessive water such as from H2O intoxication

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13
Q

How does total body Na related to Effective Arterial Blood Volume?

A

Total blood Na contributes to EABV, with 15% on the baroreceptor side

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14
Q

What happens in response to a true decrease in EABV?

A

Volume depletion such as orthostasis

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15
Q

What happens in response to a perceived decrease in EABV?

A

Edema, perceived EABV as low despite a normal EABV

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16
Q

What neurosignaling effects EABV?

A 
Adrenergic signaling (norepi and epi)
Aldosterone release (Na reclamation from principal cells)
ADH (Water reclamation from principal cells)
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17
Q

What do osmoreceptors respond to?

A

Osmoreceptors respond to changes in plasma tonicity due to stretch deformations

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18
Q

Describe the neural pathway for ADH release?

A

Brain osmoreceptors and AngII receptors in the third ventricle detect changes tonicity
The OVLT and SFO in the 3rd cerebral ventricle signal the MnPO and Hypothalamus to release ADH from the Posterior Pituitary

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19
Q

Why is the Third Ventricle the site for osmoreceptors?

A

The third ventricle has a more permeable BBB which allows it to sample blood and determine tonicity

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20
Q

Do osmotic or non-osmotic stimuli release ADH?

A

Both! Osmotic stimuli drive ADH release primarily but severe volume depletion can also stimulate ADH

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21
Q

How is it that Na reabsorption is separate from water handling?

A

Most of the Sodium is absorbed iso-osmotically in the PCT, while the water is absorbed or released into the urine at the collecting duct

22
Q

What determines whether or not water is absorbed in the collecting tubule?

A

ADH binding to the V2R inserts Aquaporins into the Collecting Duct to determine whether or not it gets absorbed

23
Q

What is required for ADH to reclaim H2O in the collecting duct?

A

ADH requires the medullary concentration gradient setup by NKKC in the TALH to reabsorb water and draw it out of the urine

24
Q

What are insensible losses and how do they effect the kidney?

A

Insensible losses are losses of water due to respiration and sweating, which force to kidney to retain some water

25
Q

What is the equation for electrolyte-free H2O clearance?

A

Solute Excretion/Urine Osmolarity * (1 - (UrineNa + UrineK)/SerumNa)

26
Q

How do the Clearance of Electrolytes and Clearance of Free-H2O relate to Urine Volume?

A

Urine Volume = Electrolyte-free H2O Clearance + Electrolyte Clearance

27
Q

How does Electrolyte free clearance vary with urine osmolarity?

A

Electrolyte free clearance decreases with urine osmolarity

More of the urine output contains solute and less contains free water, because the urine is more concentrated at higher osmolarity

28
Q

How does urine concentration vary with solute excretion?

A

At higher solute excretions, urine concentration increases

29
Q

What are the 3 broad categories of hyponatremia?

A

Isotonic Hyponatremia
Hypotonic Hyponatremia
Hypertonic Hyponatremia

30
Q

Which form of hyponatremia is fake?

A

Isotonic Hyponatremia, aka artificial hyponatremia

31
Q

What conditions can cause Isotonic Hyponatremia?

A

Elevated proteins or fatty acids

32
Q

Why is Isotonic Hyponatremia fake?

A

In Isotonic Hyponatremia, the protein/lipid fraction of blood goes up so the portion of blood composed of water goes down, lowering the concentration of sodium measured in the tube, even if the body sodium concentration is normal; hence, fake hyponatremia

33
Q

What causes Hypotonic Hyponatremia?

A

Decreased water excretion leading to more water retention and lower effective sodium concentration = hyponatremia

34
Q

What causes Hypertonic Hyponatremia?

A

Adding impermeable solutes to the ECF, where Sodium is found, draws water into the ECF, lowering the effective concentration of Sodium = hyponatremia

35
Q

What symptoms accompany hyponatremia and why?

A

Seizures, nasuea, fatigue all due to cell swelling in the setting of hyponatremia

36
Q

What determines the severity of symptoms in hyponatremia?

A

Symptom severity is determined by how rapidly the hyponatremia sets in, with more rapid onset causing more severe symptoms

37
Q

How does the brain respond to hyponatremia?

A

Hyponatremia = less sodium in the ECF which lowers osmolarity and favors water influx into neurons, causing the brain to swell until it can compensate

38
Q

What blood volumes does hypotonicity occur at?

A

Hypotonicity can occur at any blood volume

39
Q

Can hyponatremia arise from the kidney excreting more sodium than water?

A

Never

40
Q

Can hyponatremia arise from the kidney failing to excrete the water it takes in?

A

Yes, hyponatremia results if water intake exceeds the free water clearance

41
Q

What are the 3 types of hypotonic hyponatremia?

A

Volume depletion, euvolemic, and edema

Low, normal, and high volume states

42
Q

How do diuretics and vomiting/diarrhea cause hyponatremia?

A

Diuretics and vomiting/diarrhea cause hypotonic hyponatremia through volume depletion

43
Q

How do psychogenic polydipsia and thiazide-induced SIADH induce hyponatremia?

A

Psychogenic polydipsia and thiazide-induced SIADH cause euvolemic hypotonic hyponatremia

Thiazides cause water retention for unknown reasons
Patient drinks too much water

Both involve elevated water and normal total body sodium

44
Q

How do cirrhosis, nephrosis, and heart failure induce hyponatremia?

A

Cirrhosis, nephrosis, and heart failure cause excessive water retention leading to hypotonic hyponatremia

45
Q

How does volume depletion lead to hypotonic hyponatremia?

A

Reduced EABV activates the RAAS system and constricts renal arteries via Angiotensin II
Angiotensin II promotes the activity of the Na/H and Na/Cl transporters leading to more Na reabsorption
AngII promotes Ald which leads to more Na reabsorption

Person then drinks water to lower the Na concentration further

46
Q

How does edema lead to hypotonic hyponatremia?

A

Edema involves blood pooling in the veins and lowers the perceived EABV
Low EABV leads to activation of the RAAS system and further promotes water reabsorption

47
Q

What causes psychogenic polydipsia leading to hyponatremia?

A

Patient consumes large amounts of water in excess of the kidney’s ability to release water, leading to water retention and hyponatremia

48
Q

What is a normal urine volume?

A

There isn’t one - it’s set by the amount needed to excrete solutes from diet and metabolism

49
Q

What is SIADH?

A

Syndrome of Inappropriate ADH secretion

Patients with SIADH cannot excrete a water load due to overproduction of ADH leading to high urine sodium concentration and low plasma osmolarity

50
Q

How should you treat hypotoninc hyponatremia?

A

Water restriction
Administer normal saline if the patient is volume depleted
Treat a primary cause if possible

51
Q

How should SIADH be treated?

A

ADH V2 Receptor anagonists

52
Q

When should 3% Saline be administered?

A

Use 3% saline (higher than the normal 0.9%) to treat cerebral edema from water overload, such as during SIADH

Renal (19 decks)

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