#33 - disorders of sodium homeostasis

Question 1

What are the 3 main determinants of “Effective Arterial blood volume” (EABV)

Answer 1

• intravascular volume
• peripheral vascular resistance
• cardiac output

Question 2

EABV =

Answer 2

Effective Arterial blood volume

Question 3

how long does it take for the body to adjust to a diuretic and have equal inputs/outputs of Na??

Answer 3

about 3 days. on the 4th day, it is normal, Na intake = Na excretion.

The body increases other
mechanisms (angiotensin, aldosterone,
sympathetic drive) to compensate and
maintain balance

Question 4

Person is maintained on a constant sodium intake of 100 mmol / day. What is their urinary sodium excretion 7 days after starting a diuretic?

Answer 4

Equal to 100 mmol/day.

Question 5

a total body sodium deficit leads to what?

Answer 5

-depletion of extracellular volume (most sodium is outside cells)

this is associated with hypovolemia / low EABV

Question 6

hypovolemia ==

Answer 6

low plasma volume

Question 7

T/F - total body sodium excess can be associated with low or high EABV

Answer 7

true.
High EABV = primary hyperaldosteronism
low EABV = CHF/ cirrhosis.

Question 8

total body sodium excess leads to

Answer 8

expansion of the extracellular volume

Question 9

T/F CHF is the 2nd most common cause of hospital admissions

Answer 9

False. It is the 4th most common cause of hospital admissions

Question 10

T/F CHF is a disorder of sodium balance.

Answer 10

True. Baroreceptors detect low volume and order the kidney to pick up extra sodium through angiotensin/ aldosterone. This causes the symptoms of fluid overload.

Question 11

How does the bodies response to dehydration (ie constriction of the efferent arteriole) affect the post-glomerular capillary fluid?

Answer 11

• decreased pressure
• increased protein concentration.

This enhances salt and water reabsorption from the proximal tubule.

Question 12

3 most common etiologies for total body sodium deficit

Answer 12

• GI sodium losses (diarrhea, vomiting)
• Renal sodium losses (diuretics, osmotic diuresis)

Cutaneous sodium losses (sweating, burns)

Question 13

total body sodium deficit symptoms

Answer 13

fatigue
thirst
muscle cramps
dizziness 
syncope

Question 14

Most important diagnostic test for sodium deficit

Answer 14

Clinical exam!!

Question 15

clinical exam signs of sodium deficit/ low volume

Answer 15

• low BP
• tachycardia
• orthostatic tachycardia AND hypotension (MEASURE BOTH!!)
• decreased jugular venous pressure (can’t see neck veins when patient is lying flat)
• decreased skin turgor

Question 16

Define orthostatic tachycardia and hypotension. (These should both be present in volume depletion!!)

Answer 16

• pulse rises >20

- BP: systolic BP drops >20mmHg

Question 17

if orthostatic hypotension is observed, without rise in pulse, what is the differential?

Answer 17

• autonomic insufficiency

- drugs (eg beta blockers) that block sympathetic tone

Question 18

lab tests for total body sodium deficit

Answer 18

• serum BUN:Creatinine >20:1

- rise in hematocrit

Question 19

lab tests for total body sodium deficit due to renal sodium loss

Answer 19

urinary sodium >20
FEna>1%

(kidney not compensating with increased Na uptake appropriately)

Question 20

lab tests for total body sodium deficit due to extra-renal sodium losses

Answer 20

urinary sodium

Question 21

Treatment approach to total body sodium deficit (hypovolemia)

Answer 21

1-treat the underlying etology
2-give ISOTONIC saline to replace deficit
3-monitor symptoms/labas/physical exam to monitor response

Question 22

disorder of sodium excess - hypertension, no edema

Answer 22

primary hyperaldosteronism

Question 23

total body sodium excess - edema formation - what conditions cause it?

Answer 23

Secondary sodium retension - CHF, cirrhosis, nephrotic syndrome

Primary sodium retention-renal failure

Question 24

Case: man w/ CHF comes in w/ pulmonary and extremity edema. Why is his urinary sodium

Answer 24

it is due to activation of the sympathetic and renin - angiotensin-aldosterone systems, leading to avid renal sodium retention

Question 25

How does ANP affect sodium retention / edema?

Answer 25

ANP ((atrial natriuretic peptide) is released by the right atrium when stretched.
It makes the capillaries more leaky

Question 26

clinical picture of sodium excess due to cirrhosis.

Answer 26

• low BP
• high pulse
• low JVP
• extremity edema
• no pulmonary edema
• urinary sodium

Question 27

3 mechanisms that contribute to decrease in EABV during cirrhosis

Answer 27

1-splanchnic vasodilation w/ blood pooling

2-development of peripheral AV shunts that lower peripheral resistance and BP

3-hyperalbuminemia

Question 28

Case: man w/ progressive swelling of legs and decreased urine output

• lower extremity swelling into lower back.
• JVP 6cm
• urinary sodium - 20
• 24 hr protein = 8 grams

Answer 28

nephrotic syndrome. Biopsy will show scarred glomerulus

Question 29

How does nephrotic syndrome lead to sodium excess? (classical view)

Answer 29

glomerular damage leads to loss of albumin in urine. —> Loss of albumin exceeds increased production of albumin by the liver, leading to hypoalbuminemia. —-> Hypoalbuminemia leads to fluid flux out of the capillaries = edema formation. —> leak ofluid out of the vascular apace activates the renin/ang/aldosterone system and symathetic symptom.

Question 30

How does nephrotic syndrome lead to sodium excess? (new view)

Answer 30

leak of PLASMINOGEN protein in the urine cleaves PLASMIN, which cleaves and ACTIVATES ENac, leading to PRIMARY absorption of sodium

Question 31

T/F both primary and secondary sodium retention occur in nephrotic syndrome

Answer 31

true (activation of Renin/ang/aldosterone system + activation of ENac).

Question 32

Most discriminatory/useful test for sodium retention/ edematous disorders

Answer 32

jugular venous pressure

Question 33

in renal disease sodium excess, what happens to JVP?

Answer 33

goes up

Question 34

treatment for total body sodium excess

Answer 34

• treat underlyiing disorder
• restrict Na/H20
• compression stockings
• diuretics (inhibit Na retention)
• aldosterone antagonists

Question 35

2 most common causes of ECF volume depletion

Answer 35

GI losses

diuretics

Question 36

3 most common causes of ECF volume excess, w/ edema and secondary sodium retention

Answer 36

CHF
cirrhosis
nephrotic syndrome

Question 37

EABV is always low in ECF volume depletion and always high in ECF volume excess

Answer 37

False!! low EABV in many cases of volume excess - eg CHF, cirrhosis.