Sodium and H2O homeostasis

Question 1

Hypotonic hyponatremia

Answer 1

Requires ICU monitoring; hypertonic saline with fairly rapid correction to 120-125 (not to normal 135)

Question 2

What is the most common electrolyte disturbance in hospitalized patients?

Answer 2

Hyponatremia

Question 3

What level of Na do hyponatremia sxs start presenting?

Answer 3

<120 mmol, sxs result from cerebral edema

Question 4

Early sxs of hyponatremia

Answer 4

HA, N/V

Question 5

Late sxs of hyponatremia

Answer 5

lethargy, confusion, seizure, comas

Question 6

Cause of hypotonic hyponatremia

Answer 6

ALWAYS from water gain, aka impaired free water excretion

Question 7

Normal kidney capacity of water excretion per day

Answer 7

18-20L per day (hard to overwhelm from overintake, i.e. psychogenic polydipsia)

Question 8

Initial work-up of hyponatremia

Answer 8

1) history - N/V, dehydration, other losses, malignancy
2) Exam: mucous membranes, JVP, peripheral vasc, orthostatics, skin turgor
3) Urine Osm if euvolemic, SCr, BUN, uric acid

Question 9

Causes of hypotonic hyponatremia

Answer 9

1) diuretic use
2) impaired hormonal response (e.g. adrenal insufficiency)
3) primary renal issue (e.g. ATN)

Question 10

Treatment of hypovolemic hyponatremia

Answer 10

isotonic saline (NS 0.9%)

Question 11

what is the significance of ordering a urine osm?

Answer 11

To see if the kidneys are capable of excreting free water normally

Question 12

Urine osm <100mOsm signifies _____.

Answer 12

maximally dilute urine, kidneys excreting free water normally

Question 13

Urine osm 150-200 mOsm signifies ______.

Answer 13

free water excretion is impaired, not maximally dilute at <100mOsm – rule out hypothyroidism and adrenal insufficiency

Question 14

Why does hypothyroidism and adrenal insufficiency lead to hyponatremia

Answer 14

Thyroid hormone and cortisol are permissive to free water excretion, thus low levels leads to water retention

Question 15

Causes of SIADH

Answer 15

Dx of EXCLUSION – due to pulmonary dz, CNS dz, pain, post-operatively, or paraneoplastic syndrome

Question 16

Treatment of SIADH

Answer 16

1) if asymptomatic or minimal sxs, FREE WATER RESTRICT

2) severe neuro sxs – rapid partial correction with hypertonic saline (3%)

Question 17

How do you treat euvolemic SIADH, but concern for volume overload

Answer 17

hypertonic saline w/IV furosemide

Question 18

Consequences of rapid overcorrection

Answer 18

Central pontine myelinolysis resulting in quadriplegia, pseudobulbar palsies, “locked in” syndrome, coma, death

Question 19

Sodium correction rate in CHRONIC hyponatremia

Answer 19

no faster than 0.5-1.0 mEq/hr

Question 20

Treatment agents for hypervolemic hyponatremia

Answer 20

Vasopressin antagonists (tolvaptan and conivaptan)

Question 21

Antidiuretic hormone (ADH) — what is it

Answer 21

1) primary hormone that regulates sodium concentration

Question 22

ADH – stimuli for release

Answer 22

1) hyperosmolality
2) low effective arterial volume (hypoTN)
3) angiotensin II

Question 23

ADH – action

Answer 23

inserts aquaporin channels in collecting ducts –> passive water reabsorption

Question 24

Aldosterone – what is it

Answer 24

primary hormone that regulates TOTAL body sodium (vs ADH and sodium concentration)

Question 25

Aldosterone – stimuli for release

Answer 25

1) hypovolemia

2) hyperkalemia

Question 26

Aldosterone – action

Answer 26

iso-osmotic reabsorption of sodium in exchange for potassium of H+

Question 27

Isotonic hyponatremia – etiologies

Answer 27

lab artifact of hyperproteinemia and HLD

Question 28

Hypertonic hyponatremia – etiologies

Answer 28

excess of another osmotically active solute (e.g. mannitol, glucose) that draws water intravascularly

Question 29

Urine Osm value helpful if ___ mmol/mL.

Answer 29

<100

Question 30

T / F: Urine Osm >300 correlates with SIADH

Answer 30

FALSE, Urine Osm often >300 must determine if ADH release appropriate vs inappropriate

Question 31

Determining if ADH INappropriate

Answer 31

1) r/o hypothyroidism and adrenal insufficiency (TFTs and cosyntropin)
2) Plasma uric acid <4.0
3) BUN <10
4) FeNa > 1%
5) Fractional urea excretion >55%
6) does not correct with NS 0.9%

Question 32

Hypovolemic hyponatremia – etiologies

Answer 32

1) RENAL losses – diuretics (thiazides), salt wasting nephropathy, cerebral salt wasting, mineralcorticoid def.
2) EXTRARENAL losses – hemorrhage, GI losses, third-spacing, poor PO intake, insensible losses

Question 33

Euvolemic hyponatremia – etiologies

Answer 33

1) SIADH
2) glucocorticoid def, severe hypothyroidism
3) psychogenic polydipsia
4) tea and toast / beer potomania diets

Question 34

Hypervolemic hyponatremia – etiologies

Answer 34

CHF, cirrhosis, nephrotic syndrome, adv. renal failure

Question 35

Hypovolemic hyponatremia – treatment

Answer 35

• NS 0.9% at slow rate

- if overcorrection: D5W +/- ddAVP

Question 36

Euvolemic hyponatremia – treatment

Answer 36

• free water restrict + treat underlying

- if no correction, hypertonic saline +/- loop diuretic (1L NaCl 0.3% raises 10 mEq, adjust for 0.5-1.0 per hour)

Question 37

Hypervolemia hyponatremia - treatment

Answer 37

• free water restrict +/- loop diuretic (NO thiazides)

- consider vasodilators to increase effective arterial volume