Sodium and H2O homeostasis Flashcards

1
Q

Hypotonic hyponatremia

A

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

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2
Q

What is the most common electrolyte disturbance in hospitalized patients?

A

Hyponatremia

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3
Q

What level of Na do hyponatremia sxs start presenting?

A

<120 mmol, sxs result from cerebral edema

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4
Q

Early sxs of hyponatremia

A

HA, N/V

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5
Q

Late sxs of hyponatremia

A

lethargy, confusion, seizure, comas

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6
Q

Cause of hypotonic hyponatremia

A

ALWAYS from water gain, aka impaired free water excretion

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7
Q

Normal kidney capacity of water excretion per day

A

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

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8
Q

Initial work-up of hyponatremia

A

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

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9
Q

Causes of hypotonic hyponatremia

A

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

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10
Q

Treatment of hypovolemic hyponatremia

A

isotonic saline (NS 0.9%)

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11
Q

what is the significance of ordering a urine osm?

A

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

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12
Q

Urine osm <100mOsm signifies _____.

A

maximally dilute urine, kidneys excreting free water normally

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13
Q

Urine osm 150-200 mOsm signifies ______.

A

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

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14
Q

Why does hypothyroidism and adrenal insufficiency lead to hyponatremia

A

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

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15
Q

Causes of SIADH

A

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

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16
Q

Treatment of SIADH

A

1) if asymptomatic or minimal sxs, FREE WATER RESTRICT

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

17
Q

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

A

hypertonic saline w/IV furosemide

18
Q

Consequences of rapid overcorrection

A

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

19
Q

Sodium correction rate in CHRONIC hyponatremia

A

no faster than 0.5-1.0 mEq/hr

20
Q

Treatment agents for hypervolemic hyponatremia

A

Vasopressin antagonists (tolvaptan and conivaptan)

21
Q

Antidiuretic hormone (ADH) — what is it

A

1) primary hormone that regulates sodium concentration

22
Q

ADH – stimuli for release

A

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

23
Q

ADH – action

A

inserts aquaporin channels in collecting ducts –> passive water reabsorption

24
Q

Aldosterone – what is it

A

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

25
Aldosterone -- stimuli for release
1) hypovolemia | 2) hyperkalemia
26
Aldosterone -- action
iso-osmotic reabsorption of sodium in exchange for potassium of H+
27
Isotonic hyponatremia -- etiologies
lab artifact of hyperproteinemia and HLD
28
Hypertonic hyponatremia -- etiologies
excess of another osmotically active solute (e.g. mannitol, glucose) that draws water intravascularly
29
Urine Osm value helpful if ___ mmol/mL.
<100
30
T / F: Urine Osm >300 correlates with SIADH
FALSE, Urine Osm often >300 must determine if ADH release appropriate vs inappropriate
31
Determining if ADH INappropriate
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%
32
Hypovolemic hyponatremia -- etiologies
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
33
Euvolemic hyponatremia -- etiologies
1) SIADH 2) glucocorticoid def, severe hypothyroidism 3) psychogenic polydipsia 4) tea and toast / beer potomania diets
34
Hypervolemic hyponatremia -- etiologies
CHF, cirrhosis, nephrotic syndrome, adv. renal failure
35
Hypovolemic hyponatremia -- treatment
- NS 0.9% at slow rate | - if overcorrection: D5W +/- ddAVP
36
Euvolemic hyponatremia -- treatment
- 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)
37
Hypervolemia hyponatremia - treatment
- free water restrict +/- loop diuretic (NO thiazides) | - consider vasodilators to increase effective arterial volume