Sodium and H2O homeostasis Flashcards
Hypotonic hyponatremia
Requires ICU monitoring; hypertonic saline with fairly rapid correction to 120-125 (not to normal 135)
What is the most common electrolyte disturbance in hospitalized patients?
Hyponatremia
What level of Na do hyponatremia sxs start presenting?
<120 mmol, sxs result from cerebral edema
Early sxs of hyponatremia
HA, N/V
Late sxs of hyponatremia
lethargy, confusion, seizure, comas
Cause of hypotonic hyponatremia
ALWAYS from water gain, aka impaired free water excretion
Normal kidney capacity of water excretion per day
18-20L per day (hard to overwhelm from overintake, i.e. psychogenic polydipsia)
Initial work-up of hyponatremia
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
Causes of hypotonic hyponatremia
1) diuretic use
2) impaired hormonal response (e.g. adrenal insufficiency)
3) primary renal issue (e.g. ATN)
Treatment of hypovolemic hyponatremia
isotonic saline (NS 0.9%)
what is the significance of ordering a urine osm?
To see if the kidneys are capable of excreting free water normally
Urine osm <100mOsm signifies _____.
maximally dilute urine, kidneys excreting free water normally
Urine osm 150-200 mOsm signifies ______.
free water excretion is impaired, not maximally dilute at <100mOsm – rule out hypothyroidism and adrenal insufficiency
Why does hypothyroidism and adrenal insufficiency lead to hyponatremia
Thyroid hormone and cortisol are permissive to free water excretion, thus low levels leads to water retention
Causes of SIADH
Dx of EXCLUSION – due to pulmonary dz, CNS dz, pain, post-operatively, or paraneoplastic syndrome
Treatment of SIADH
1) if asymptomatic or minimal sxs, FREE WATER RESTRICT
2) severe neuro sxs – rapid partial correction with hypertonic saline (3%)
How do you treat euvolemic SIADH, but concern for volume overload
hypertonic saline w/IV furosemide
Consequences of rapid overcorrection
Central pontine myelinolysis resulting in quadriplegia, pseudobulbar palsies, “locked in” syndrome, coma, death
Sodium correction rate in CHRONIC hyponatremia
no faster than 0.5-1.0 mEq/hr
Treatment agents for hypervolemic hyponatremia
Vasopressin antagonists (tolvaptan and conivaptan)
Antidiuretic hormone (ADH) — what is it
1) primary hormone that regulates sodium concentration
ADH – stimuli for release
1) hyperosmolality
2) low effective arterial volume (hypoTN)
3) angiotensin II
ADH – action
inserts aquaporin channels in collecting ducts –> passive water reabsorption
Aldosterone – what is it
primary hormone that regulates TOTAL body sodium (vs ADH and sodium concentration)
Aldosterone – stimuli for release
1) hypovolemia
2) hyperkalemia
Aldosterone – action
iso-osmotic reabsorption of sodium in exchange for potassium of H+
Isotonic hyponatremia – etiologies
lab artifact of hyperproteinemia and HLD
Hypertonic hyponatremia – etiologies
excess of another osmotically active solute (e.g. mannitol, glucose) that draws water intravascularly
Urine Osm value helpful if ___ mmol/mL.
<100
T / F: Urine Osm >300 correlates with SIADH
FALSE, Urine Osm often >300 must determine if ADH release appropriate vs inappropriate
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%
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
Euvolemic hyponatremia – etiologies
1) SIADH
2) glucocorticoid def, severe hypothyroidism
3) psychogenic polydipsia
4) tea and toast / beer potomania diets
Hypervolemic hyponatremia – etiologies
CHF, cirrhosis, nephrotic syndrome, adv. renal failure
Hypovolemic hyponatremia – treatment
- NS 0.9% at slow rate
- if overcorrection: D5W +/- ddAVP
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)
Hypervolemia hyponatremia - treatment
- free water restrict +/- loop diuretic (NO thiazides)
- consider vasodilators to increase effective arterial volume
