Nephrology: Fluid and Electrolyte Disturbances

Question 1

Hyponatremia

Answer 1

osmolality is low (2*Na + 10) if glucose and BUN are normal

serum sodium IS osmolality (for the most part)

all symptoms are neurologic, CNS not peripheral - low AND high sodium

worst CNS symptom is seizures

if you correct too quickly either way, more CNS problems

• can’t get CNS problems from potassium because you die of arrhythmia first

mild, moderate, and severe is defined by the symptoms, not the actual values

mild is no symptoms, no matter the value

sever is seizures, no matter the value

Question 2

Hyponatremia - hypervolumic

Answer 2

congestive failure, cirrhosis, nephrotic

all cause intravascular volume depletion

pressure sensors in carotid body perceive low intravascular volume, hypothalamus makes more ADH, released from posterior pituitary to retain water.

• this is appropriate because volume status is more important than Na level

Question 3

Hyponatremia: hypovolumic

Answer 3

hypovolemic - low volume - dehydration from vomitting, diarrhea, sweating (addisons dz)

*aldosterone from the kidneys makes you retain Na, and lose K+ and H+ ions

diuretics work by inhibiting Na and Cl reabsorption

salt wasting, losing salt in kidneys

Question 4

Hyponatremia: Euvolumic

Answer 4

psychogentic polydipsia - may have low sodium

lithium - nephrogenic diabetes insipidus - may have high sodium

but both could have normal sodium, and therefore cannot differentiate

both will have high urine volume, and low urine osmolality, and low urine sodium

• -psychogenic polydipsia is the only one that does not have nocturia - can do water deprivation to see which it is, or just ask if they pee at night. If they pee at night, then it is nephrogenic diabetes insipidus

SIADH

• anything in the brain can cause this - tumor, stroke, trauma, infection, etc.
• anything in the lung can cause this
• drugs (SSRIs)
• cancer
• normal person with low Na will have low urine osmolality (low urine Na)
• person with SIADH will have high urine osmolality even though they have low serum Na (inappropriately pissing off Na even though they have low serum Na) - most accurate test is the ADH level.

hypothryroidism - no idea why

diuretics

ACE inhibitors

Question 5

Hyponatremia - treatment

Answer 5

mild: fluid restrictions

if you bring up the na too quickly, pons will melt

12 points a day if no symptoms (.5 points/hr)

24-48 points per hour if severe symptoms (1-2 points/hr)

tx: NaCl, plus loop diuretic to lose the water

Question 6

Pseudohyponatremia

Answer 6

Total body Na is actually normal

serum Na is artificially low

main reason: for every 100 points above normal of glucose, there is 1.6 point drop in Na

with very high glucose, osmolality is high and causes water to be drawn into vasculature. Na is fixed, but increased water makes the Na look low.

fix the glucose, water will go out

hyperlipidemia is old reason for pseudo, related to old testing method

Question 7

Hypernatremia

Answer 7

anything that causes skin, urine, or GI loss of fluid, and without water replacement

diabetes insipidus - opposite of SIADH , not making enough ADH - pees even though they are getting dehydrating

CNS problems

if correct too quickly, more CNS problems

dehydration - serum osmolality is increasing, volume of urine should be lower

give ADH - if volume drops then it is central diabetes insipidus, if volume does not drop, then it is nephrogenic diabetes insipidus

central - stroke, tumors, anything that effects hypothalamus

nephrogenic - can be caused by hypercalcemia and hypokalemia (hypercalcemia inhibits ADH activity in kidney)

• may have to give diuretic to someone urinating lots of urine (residual concentrating ability)
• NSAIDS may work

Question 8

Hypokalemia

Answer 8

insulin drives potassium into cells with glucose

*decreased insulin (diabetes) can cause hyperkalemia

Na/K ATPase , drives K into cells - beta agonist

digoxin inhibits the Na/K ATPase, causes hyperkalemia

acid/base also effects this

alkalosis causes H+ to come out of cell, potassium goes in

b12 and folate can cause such rapid cell production that it gives you hypokalemia (rare)

increased aldosterone causes hypokalemia - cohn’s syndrome, cushings, licorice

Barter’s syndrome - like being on lasix all the time,

• magnesium dependent potassium channels in the kidney, low magnesium leads to urinary loss of potassium

GI loss (colon)

die of cardiac problems - U wave is extra wave after T wave

GI tract cannot absorb faster than kidney can excrete it, so therefore no maximum dose of ORAL potassium

max IV rate is 10-20 meq per hour

do not use dextrose containing IV solutions, this will drive potassium into cells (because of insulin)

periodic paralysis

Question 9

Hyperkalemia

Answer 9

acidosis causes H+ to go in cell, and potassium comes out

most potassium is in cells, so anything that causes damage to cell can cause hyperkalemia

• rhabdomyolysis, tumor lysis, hemolysis
• decreased aldosterone causes hyperkalemia -addison’s dz

die of cardiac - T wave is peaked - tx: calcium chloride and calcium gloconate protect the heart

bicarbonate drives potassium inside cell

kayexelate removes potassium from the body

insulin deficiency can cause this (diabetes)

periodic paralysis

Question 10

pseudohyperkalemia

Answer 10

tourniquet on too long, or cell lysis because in tube too long