Disorders of Na and K Regulation

Question 1

What is osmolarity?

Answer 1

the concentration of a solution expressed as the total number of solute particles per liter

Question 2

What is normal serum osmolarity?

Answer 2

280-290

Question 3

What is serum osmolarity regulated by?

Answer 3

ADH and thirst

Question 4

What are the osmotic stimuli that cause ADH release?

Answer 4

from increases in serum osmolarity detected by osmorecptors in the anterior hypothalamus

Question 5

What are non-osmotic stimuli that cause ADH release?

Answer 5

from decreases in BP or blood volume detected by arterial baroreceptors; other cases include nausea, hypoxia, pain, meds (opiates and antidepressants), pregnancy, multiple other stimuli

Question 6

What are some causes for someone with hypotonic hypovolemic hyponatremia with Uosm >300 and Urine Na >20?

Answer 6

Renal fluid losses such as diuretic excess, adrenal insufficiency, osmotic diuresis, post obstructive digress, RTA, cerebral salt wasting, salt losing nephropathy

Question 7

What are some causes for someone with hypotonic hypovolemic hyponatremia with Uosm >300 and Urine Na <20?

Answer 7

Extrarenal fluid losses such as vomiting, diarrhea, third spacing fluids (burns, pancreatitis), blood loss, excessive sweating, lung losses

Question 8

What are some causes for someone with hypotonic euvolemic hyponatremia with Uosm <100?

Answer 8

primary polydipsia

Question 9

What are some causes for someone with hypotonic euvolemic hyponatremia with Uosm >300 and urine Na >20?

Answer 9

SIADH (tumor, CNS or pulmonary disorder, drugs (SSRI), nausea, pain, hypoxia), hypothyroidism, adrenal insufficiency, thiazides

Question 10

What are some causes for someone with hypotonic hypervolemic hyponatremia with Uosm >300 and urine Na <20?

Answer 10

nephrotic syndrome, heart failure and cirrhosis

Question 11

What are some causes for someone with hypotonic hypervolemic hyponatremia with Uosm >300 and urine Na >20?

Answer 11

acute or chronic kidney failure

Question 12

What must be ruled out when determining if a pt has SIADH?

Answer 12

cortisol deficiency, hypothyroidism, and other causes

Question 13

What is the MC malignancy associated with ectopic ADH production?

Answer 13

Small cell lung cancer

Question 14

Which drugs are associated with SIADH?

Answer 14

Antidepressants, anticonvulsants, antipyschotics, anti-DM drugs, vasopressin analogs, misc

Question 15

What is the tx for hypovolemic hypotonic hyponatremia?

Answer 15

isotonic saline if no sx; hypertonic saline if symptomatic

Question 16

What is the treatment for primary polydipsia?

Answer 16

water restriction and hypertonic saline if symptomatic

Question 17

What is the treatment for hypotonic euvolemic hyponatremia with Uosm >300 and UrineNa >20?

Answer 17

Hypertonic saline if symptomatic; if SIADH then water restriction, furosemide, salt or urea tablets, vaptans, demeclocycline; thyroid replacement for hypothyroidism; prednisone for cortisol deficiency; discontinue thiazides if that’s the cause

Question 18

What is the treatment for hypervolemic hypotonic hyponatremia?

Answer 18

water restriction and furosemide

Question 19

Excess K is removed from the body primarily by what?

Answer 19

the kidneys with some loss in the feces

Question 20

The distribution of Na and K is maintained by what?

Answer 20

Na K ATPase pump

Question 21

What is the effect of K on RMP?

Answer 21

makes membrane potential less negative –> long term leads to a net decrease in membrane excitability leading to impaired cardiac conduction and neuromuscular weakness/paralysis

Question 22

Review EKG changes

Answer 22

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