Disorders of Sodium Concentration

Question 1

What is the equation for plasma [Na+]?

Answer 1

Blood (plasma or serum) [Na+] = Total body sodium/Total body water

Question 2

What happens with water excess without a change in total body sodium content?

Answer 2

Hyponatremia

Question 3

What happens with water deficit without a change in total body sodium content?

Answer 3

Hypernatremia

Question 4

What happens to ADH levels with increased water intake?

Answer 4

ADH will decrease due to the decrease in [Na+]

Question 5

What is ADH a.k.a.?

Answer 5

AVP

Question 6

What are the actions of ADH?

Answer 6

ADH acts on the distal tubule collecting duct to increase water reabsorption and thus decrease renal water excretion. In the presence of substantial amounts of ADH the urine will be concentrated.

Question 7

What is the main mechanism controlling ADH release?

Answer 7

A small (1‐2%) increase in effective osmolality ([Na+] + [glucose]) will increase ADH release.

Question 8

What is a second mechanism controlling ADH release?

Answer 8

A large (10%) decrease in blood volume or blood pressure will also increase ADH release and can override the effect of osmolality.

Question 9

What would increased TBW with normal TBNa+ cause? What is an example of this?

Answer 9

Hyponatremia.

SIADH

Question 10

What would 􏰖 decreased TBW with greatly decreased TBNa+ cause? What is an example of this?

Answer 10

Hyponatremia

Diuretic drug with water intake

Question 11

What would 􏰖greatly increased TBW with increased TBNa+ cause? What is an example of this?

Answer 11

Hyponatremia

Congestive Heart Failure

Question 12

What is the pathogenesis of hyponatremia?

Answer 12

Hyponatremia almost always indicates impaired renal water excretion.

Question 13

Beer Drinker’s Potomania

Answer 13

Consumption of solely large amounts of beer which is poor in solutes, making the production of dilute urine difficult with low solutes leading to hyponatremia

Question 14

What 3 factors does the ability of the kidney to excrete water depend upon?

Answer 14

(1) Filtration of solute by the glomeruli
(2) Delivery of solute to distal (diluting) nephron sites
(3) Reabsorption of solute (but not water) at diluting nephron sites

Question 15

Hypovolemic Hyponatremia

Answer 15

• decrease in TBNa+

Question 16

What are some causes of hypovolemic hyponatremia?

Answer 16

– Renal Na+ losses – diuretics, primary adrenal insufficiency (Addison’s disease), salt‐wasting nephropathies
– Extrarenal Na+ losses – diarrhea, vomiting, excessive sweating

Question 17

What are clinical findings of Hypovolemic Hyponatremia?

Answer 17

(flat neck veins, decreased skin turgor, orthostatic hypotension)

Question 18

Euvolemic Hyponatremia

Answer 18

• normal TBNa+

Question 19

What are some causes of Euvolemic Hyponatremia?

Answer 19

– SIADH – most commonly due to (1) tumor (2) pulmonary disease (3) central nervous system disease
– “Beer drinker’s potomania”

Question 20

Hypervolemic Hyponatremia

Answer 20

• increased TBNa+

Question 21

What are some causes of Hypervolemic Hyponatremia?

Answer 21

– CHF
– Liver cirrhosis
– Renal failure

Question 22

What are some clinical findings of Hypervolemic Hyponatremia?

Answer 22

(edema)

Question 23

What does low UNa+ suggest?

Answer 23

It suggests extrarenal loss of Na+ or edematous disorder

Question 24

What does normal UNa+ suggest?

Answer 24

It suggests renal loss of Na+ or excess ADH in the absence of renal sodium avidity, as in SIADH.

Question 25

Hypovolemic hyponatremia Treatment

Answer 25

Physiologic Saline

Question 26

Hypervolemic hyponatremia Treatment

Answer 26

Fluid restriction and diuretics.

Question 27

Euvolemic hyponatremia Treatment (symptomatic)

Answer 27

Hypertonic saline with or without diuretics.

Question 28

What happens with decreased TBW with normal TBNa+? What are examples?

Answer 28

Hypernatremia.

1) patients with decreased thirst or inability to drink water; 2) diabetes insipidus (DI), in which ADH release is impaired or absent

Question 29

What happens with greatly decreased TBW with decreased TBNa+? What are examples?

Answer 29

Hypernatremia.

Diuretics without concomitant water ingestion.

Question 30

What happens with normal TBW with increased TBNa+? What are examples?

Answer 30

Hypernatremia.

Administration of hypertonic saline.

Question 31

Hypovolemic hypernatremia

Answer 31

• decrease in TBNa+

Question 32

Examples of hypovolemic hypernatremia

Answer 32

– Renal Na+ losses – diuretics (with inadequate water intake), osmotic or post‐obstructive diuresis, tubular injury
– Extrarenal Na+ losses – sweating, diarrhea, vomiting (with inadequate water intake).

Question 33

Euvolemic hypernatremia

Answer 33

• decrease in TBH2O

Question 34

Examples of euvolemic hypernatremia

Answer 34

– Central diabetes insipidus (trauma, idiopathic, tumor)
– Nephrogenic diabetes insipidus (congenital, drugs,
hypercalcemia, tubular disease)
– Decreased thirst, water intake (“nursing home syndrome”)

Question 35

Hypervolemic hypernatremia

Answer 35

• increase in TBNa+

Question 36

Examples of hypervolemic hypernatremia

Answer 36

– Hypertonic fluid administration
– Mineralocorticoid excess states
– Salt poisoning

Question 37

Hypovolemic hypernatremia Treatment

Answer 37

Hypotonic fluids

Question 38

Euvolemic hypernatremia Treatment

Answer 38

Water administration

Question 39

Hypervolemic hypernatremia Treatment

Answer 39

If severe, it may require both water administration plus either diuretics or dialysis to remove the excess sodium.

Question 40

A 60 year old man with known lung cancer presents with fatigue and cough. On exam his vital signs are normal. He is not orthostatic. His jugular veins are visible but not distended, skin turgor is normal, and he has no edema. He is alert and oriented and answers questions appropriately. Chest X‐ray shows a R lower lobe infiltrate. Serum electrolytes (in mmol/L) are: Na 114, K4, Cl 80 CO2 24. The BUN and Cr are 6 and 0.6 mg/dL, respectively. Urine chemistries (in mmol/L) are: Na 70 K 30 Cl 50 osm 500.

What is the most likely diagnosis?

A. Beer drinker’s syndrome
B. Psychogenic polydipsia
C. Addison’s disease
D. SIADH

Answer 40

D. SIADH

Euvolemic Hyponatremia

Question 41

A 60 year old man with known lung cancer presents with fatigue and cough. On exam his vital signs are normal. He is not orthostatic. His jugular veins are visible but not distended, skin turgor is normal, and he has no edema. He is alert and oriented and answers questions appropriately. Chest X‐ray shows a R lower lobe infiltrate. Serum electrolytes (in mmol/L) are: Na 114, K4, Cl 80 CO2 24. The BUN and Cr are 6 and 0.6 mg/dL, respectively. Urine chemistries (in mmol/L) are: Na 70 K 30 Cl 50 osm 500.

How do you treat the hyponatremia?

A. Isotonic saline
B. Hypertonic saline
C. Tolvaptan
D. Fluid restriction

Answer 41

D. Fluid restriction

Question 42

An 85‐year‐old woman with Alzheimer’s dementia is admitted from a nursing home for obtundation. On examination she has hypotension (BP 80/50 mmHg), flat neck veins, clear chest, and no edema. Chest X‐ray is clear. Serum electrolytes (in mmol/L) are: Na 164,K 4,Cl 130 CO2 24. The BUN and Cr are 16 and 1.2 mg/dL, respectively. Urine chemistries (in mmol/L) are: Na 20 K 30 Cl 15 osm 500.

What is your diagnosis?
A. Dehydration
B. Volume depletion 
C. Both
D. Neither

Answer 42

C. Both

Hypovolemic Hypernatremia

Question 43

An 85‐year‐old woman with Alzheimer’s dementia is admitted from a nursing home for obtundation. On examination she has hypotension (BP 80/50 mmHg), flat neck veins, clear chest, and no edema. Chest X‐ray is clear. Serum electrolytes (in mmol/L) are: Na 164,K 4,Cl 130 CO2 24. The BUN and Cr are 16 and 1.2 mg/dL, respectively. Urine chemistries (in mmol/L) are: Na 20 K 30 Cl 15 osm 500.

How do you initially treat this patient?

A. Isotonic saline
B. Hypotonic saline
C. Dextrose in water
D. Oral water replacement

Answer 43

A. Isotonic saline

Volume depletion more important then after the BP
is raised, it should be change to hypotonic saline