Sodium Disorders

Question 0

What equation can be used to estimate serum osmolality?

Answer 0

[Na]x2 + [Glucose]/18 + [BUN]/2.8

Question 1

What is normal sodium serum concentration?

Answer 1

135-145 mEq/L

Question 2

What are the symptoms of sodium concentration below 125 mEq? 120-115? <115?

Answer 2

120-125: Nausea/malaise
115-120: Headache/lethargy
<115: Seizures, obtundation, coma

Question 3

What is the main pathophysiological effect of hyponatremia?

Answer 3

Decreased extracellular osmolality results in brain cell swelling

Question 4

What are the symptoms of hypernatremia?

Answer 4

Lethargy, weakness, irritability, twitching, seizures, coma, death

Question 5

What is the key pathophysiological finding to hypernatremia?

Answer 5

Shrinkage of brain cells, leading to rupture of cerebral vasculature due to decreased volume

Question 6

What are the nonosmotic stimuli to increasing levels of ADH?

Answer 6

Baroreceptors (hypovolemia)
Pain (post-operative for instance)
Esophageal stimuli
Various medications

Question 7

If ADH is present, is serum osmolality increased or decreased?

Answer 7

decreased

Question 8

If plasma osmolality is high, is urine osmolality supposed to be high or low?

Answer 8

high

Question 9

If urine sodium is high, what does the body think about the body’s volume status?

Answer 9

Body thinks serum volume is expanded, wants to get rid of excess sodium

Question 10

What level of urine osmolality usually means ADH is involved in the system?

Answer 10

> 100 mOsm/L

Question 11

Given osmoles taken in per day and amount of urine osmolality, how can you calculate amount liquid excreted per day?

Answer 11

(Osm/day)/(urine osmolarity in Osm/day)

Question 12

In the nephron, what percentage of sodium is reabsorbed by each of the tubules?

Answer 12

Proximal tubule: 65%
LOH: 25-35%
Distal tubule: 5%
Collecting duct: 4% (dependent upon aldosterone, ANP)

Question 13

If the urine sodium concentration is <10 meq/L, then what is the body sensing the circulating volume to be?

Answer 13

low circulating volume

leads to increased water and sodium resorption

Question 14

If the urine sodium concentration is >10 mEq/L, then what does the body think is going on?

Answer 14

Increased volume of ECV
Kidney unable to retain Na
Na is leaving with something else (as an obligate cation)

Question 15

What is pseudohyponatremia with regular osmolality usually due to?

Answer 15

Hyperlipidemia, hyperproteinemia

Question 16

What is pseudohyponatremia with elevated osmolality due to?

Answer 16

Increased Glucose levels

Increased mannitol levels

Question 17

When evaluating Hyponatremia in the clinic, what steps should you follow?

Answer 17

Check serum osmolality (True or pseudo hyponatremia?)
Check urine osmolality (Is ADH acting?)
Check urine Na osmolality (What do kidneys think of ECV?)
Check H&P

Question 18

What are primary and secondary causes of hyponatremia with Uosm <100?

Answer 18

1. Increased water consumption
2. Alcohol
3. Tea and toast syndrome

Question 19

How do you treat primary polydipsia?

Answer 19

Let the kidneys do their thang

Question 20

If you have hyponatremia with Uosm >100, and UNa is <10 with volume depletion, what is the cause?

Answer 20

Normal kidney response to add fluid back into the depleted ECV.

From: Burns, diuretics, GI losses (vomiting, diarrhea), cortisol deficiency

Question 21

If you have hyponatremia with Uosm >100, and UNa <10 with expanded volume but ECV depletion, what is likely the cause?

Answer 21

Kidney is confused because of edema (CHF, cirrhosis, nephrosis)

Question 22

If you have hyponatremia with Uosm >100, and UNa >10 with depleted volume, what is likely the cause?

Answer 22

Salt-wasting (kidney is failing)

Causes:
Diuretics (early), renal diseases, adrenal insufficiency, hypokalemia/metabolic alkylosis after vomiting, hypothyroidism

Question 23

If you have hyponatremia with Uosm >100, and UNa >10 with expanded volume, what is likely the cause?

Answer 23

Brain or kidney confused (inappropriate ADH secretion)

Question 24

What are some causes of inappropriate ADH secretion?

Answer 24

Tumor
Pulmonary process
Drugs (oxytocin, cytoxan, tegretol, chlorpropramide)
Esophageal process
Pain
Neuropsychiatric disorders

Question 25

What should you give patients with volume depleted hyponatremia?

Answer 25

Normal saline

Question 26

What should you give patients with volume expanded hyponatremia?

Answer 26

Nothing. Restrict free water intake.

Question 27

What should you give patients with hyponatremia causing neurologic symptoms?

Answer 27

Hypertonic saline

Question 28

What is the oral ADH antagonist?

Answer 28

Tolvaptan

Question 29

What is the IV ADH antagonist?

Answer 29

Conivaptan

Question 30

What drug can cause Nephrogenic diabetes insipidus after long term use?

Answer 30

Lithium