Regulation and Disorders of Salt and Water - Gyamlani Flashcards
What percent of weight is TBW?
60% males
50% females
As a core principle, what is water balance regulated by?
Plasma osmolality
As a core principle, what is Na balance regulated by?
Plasma volume
What is total body sodium proportional to?
TBW
What is an equation for plasma osmolarity?
2*Na + glucose / 18 + urea / 2.8
What is a normal plasma Na?
140 mEq / L
What is the effect of hypovolemia on EABV, ECFV, plasma volume, and CO?
EABV - decreased
ECFV - decreased
Plasma volume - decreased
CO - decreased
What is the effect of CHF on EABV, ECFV, plasma volume, and CO?
EABV - decreased
ECFV - increased
Plasma volume - increased
CO - decreased
What is the effect of cirrhosis on EABV, ECFV, plasma volume, and CO?
EABV - decreased
ECFV - increased
Plasma volume - increased
CO - increased
What are sensors of plasma osmolality?
Hypothalamic osmoreceptors?
What are effectors of plasma osmolality regulation?
ADH
Thirst
What is manipulated through osmoregulation?
Urine osmolality
Water intake
What are sensors of EABV?
Macula densa
Afferent arteriole
Atria
Carotid sinus
What are effectors of EABV regulation?
RAS Aldosterone ANP Norepinephrine ADH
What is manipulated through volume regulation
Urine Na
Thirst
What stimulates RAS?
Decreased sodium
Decreased ECFV
Decreased arterial pressure
What stimulates aldosterone?
Increased AT II
Increased plasma potassium
What are the actions of AT II?
Vasoconstriction
Increased Na absorption in PT
What are the actions of aldosterone?
Increased Na reabsorption in DT
Increased K secretion
What are the actions of atrial natriuretic peptide (ANP)?
Increased Na excretion
Afferent arteriolar vasodilation
What is the result of hypertonic stimulation of hypothalamic receptors?
Increased thirst
Increased AVP
Where is the thirst center located?
Third ventricle
What stimulates the thirst center?
Increased ECF osmolality
Volume depletion / Decreased EABV
Angiotensin II
What stimulates vasopressin / AVP / ADH?
Increased ECF osmolality Volume depletion / Decreased EABV Angiotensin II Pain Nausea / Vomiting Medications
Where is AVP formed and released?
Formed - Hypothalamus
Released - Posterior pituitary
Is sodium or water typically pathologic in hyponatremia?
Mostly water imbalance
What is the first thing you should do when working up a hyponatremic patient?
Assess volume status
Describe the underlying mechanism of hypovolemic hyponatremia.
Sodium depletion with reduction in ECFV and secondary water retention due to non-osmotic stimulation of vasopressin.
What are common mechanisms of sodium loss in hypovolemic hyponatremia?
Renal (U Na > 20 mEq / L) Parenchymal disease affecting tubular handling of sodium Mineralocorticoid deficiency Persistent solute diuresis (glucosuria) Diuretic therapy
Extrarenal
Vomiting / Diarrhea
Burns
Hemorrhage
What are signs of sodium depletion?
Orthostatic BP
Poor skin turgor
Disproportionate increase in BUN:creatinine (prerenal azotemia)
Reduced urine sodium excretion
Describe the underlying mechanism of euvolemic hyponatremia.
Water retention due to altered regulation of vasopressin (SIADH)
What causes SIADH?
Pulmonary / CNS disorders
Malignancy
Pain / nausea
Drug-induced water retention (anti-psychotics)
What are the diagnostic criteria for SIADH?
Decreased serum osmolarity (100 mosm/kg)
Euvolemia
Elevated U Na
Describe the underlying mechanism of hypervolemic hyponatremia.
Retention of both sodium and water (greater water)
What are common causes of hypervolemic hyponatremia?
CHF
Hepatic cirrhosis
Nephrotic syndrome
Renal disease
What are symptoms of hyponatremia?
Nausea / malaise
Headache, lethargy, obtundation
Seizures, coma
*Chronic - few symptoms
What can be caused by correcting hyponatremia too quickly?
Cerebral Demyelination Syndrome
How do you treat hypo-, eu-, and hyper- volemic hyponatremia?
Hypo - Isotonic saline
Eu - water restrict / 3% NS / Diuretic
Hyper - Na restrict / Diuretic
What is the equation for water excess?
.6 ( Wt ) * ( 1 - SNa / 140 )
What does U osm < 300 mOsm/kg signify in hypernatremia?
Dysfunction ADH
Diabetes insipidous
What does U osm > 500 mOsm/kg signify in hypernatremia?
Extra-renal water loss
Sodium ingestion/infusion
Decreased osmotic diuresis
What are the symptoms of hypernatremia?
Lethargy Weakness Irritability Seizure Coma Death
How do you treat hypo-, eu-, and hyper- volemic hypernatremia?
Hypo - Isotonic saline until hypovolemia resolved
Eu - Replace water (and ADH if dysfunctional)
Hyper - Remove Na
