Hyponatremia Flashcards
What is the main cause of feeling “sick” when there are acute changes in tonicity?
changes in cell shape and size
What are effective osmols?
solutes that are trapped on one side of the cell membrane, which cause movement in total H2O to compensate for changes in tonicity
Alcohol and urea are what kind of osmols?
ineffective - they cross the cell membrane
Is tonicity estimated or measured?
estimated
is osmolarity estimated or measured?
measured
How do you calculate estimated osmolarity?
(NaX2) + (glucose/18) + (urea/2.8)
What is a normal serum osmolarity?
285 mOsms/L
A decrease in total body water would cause hyper/hypotonicity and hyper/hyponatremia?
hypertonicity and hypernatremia
An increase in total body water would cause hyper/hypotonicity or hyper/hyponatremia?
hypotonicity and hyponatremia
Do osmoreceptors respond to plasma tonicity or osmolarity?
plasma tonicity = by degree of stretch of the cell membrane under changing tonicity
What signaling in the posterior pituitary causes ADH release?
osmoreceptors + tonicity, AngII, volume depletion, nausea, pain, sedation, and drugs
How is electrolyte free water clearance calculated?
solute excretion/urinemOsm * (1- UNA+ UK/SNA)
At low osmolalities, what is true of the relationship between solute excretion and the water excretion ceiling?
at low osmolalities, excretion is much lower compared to other osmolalities at the same water volume ??
With or without ADH, what is true of the relationship between urine concentration and solute excretion?
solute excretion increases as urine concentration drops, regardless
What are the 3 types of hyponatremia?
isotonic/artifactual hyponatremia
hypotonic hyponatremia
hypertonic hyponatremia
What type of hyponatremia would be caused by hypergammaglobulinemia, hypertriglyceridemia, or hyperchylomicronemia?
artifactual/isotonic hyponatremia
What causes hypertonic hyponatremia?
addition of new effective osmoles to the ECF, causing water to flow out into the ECF and dilute Na
When do symptoms of hypotonic hypernatremia begin?
when SNa drops below 125 mEq/L
What are the symptoms of hypotonic hyponatremia, in order of appearance?
nausea fatigue headache lethargy somnolence coma seizures
What determines the number and severity of classic hypotonic hyponatremia symptoms, prior to the start of seizures?
rate of change in hypotonicity - if very quickly, seizures will appear without the other symptoms
When is aggressive treatment for hypotonic hyponatremia started?
when SNa is below 118 mEq/L regardless of symptoms
What is the immediate/rapid adaptation of the brain to hypotonic hyponatremia?
loss of sodium, potassium and chloride
what is the slow adaptation of the brain to hypotonic hyponatremia?
loss of organic osmolytes
HOw quickly should SNa increase when treating hypotonic hyponatremia?
< 8 mEq/L/day
What happens if SNa increases too quickly when treating hypotonic hyponatremia?
osmotic demyelination
What type of hypotonic hyponatremia would be caused by addisons diseases, vomiting/diarrhea, diuretic agents, osmotic diuresis, sweating, or 3rd spacing?
volume depletion, (increased H2o and decreased TB sodium relative to each other)
What type of hypotonic hyponatremia would be caused by psychogenic polydipsia, potomania, thiazides, SIADH, or a reset osmostat?
euvolemic (increased water but normal TB Na)
What type of hypotonic hyponatremia would be caused by cirrhosis, nephrosis, and renal/heart failure?
edema (increased water and sodium)
What kind of euvolemic hyponatremia would be caused by low ACTH, T4, CNS issues, pulmonary issues, malignancy, ecstasy, drugs or post op complications?
SIADH
What is the main cause in volume depleted or volume overloaded hypotonic hyponatremia?
oliguria due to reduced EABV and persistent aldosterone/ADH/ATII followed by excessive TB intake relative to effective osmoles
What causes hyponatremia in psychogenic polydipsia?
water intake exceeds the mechanical limits of the kidney to excrete water, leading to dilution of Na
What effect does alcohol have on ADH release? what can this cause?
inhibits it, causes increased urine volume beyond what can be excreted , especially in the setting of low solute intake
When does thiazide induced hyponatremia occur?
usually 2 weeks after starting the drug
What is a normal SNa in an individual with hyponatremia who is taking thiazide diuretics?
127-130 mEq
If a patient has heart disease, liver disease, edema or orthostasis, can they be diagnosed with syndrome of inappropriate ADH secretion?
nope
Define SIADH
Uosm is inappopriate for Posm (ie. too high ) due to excessive ADH release
What is the urine Na in SIADH?
it can be any value - it will just reflect the dietary intake
what is the BUN and uric acid level in SIADH?
usually low
What is reset osmostat?
the set point for osmoreceptors is lower, looks like SIADH except that patients excrete water load
When is reset osmostat commonly seen?
during pregnancy
What is the safest approach for treating hypotonic hyponatremia?
water restriction
if the spot Una + Uk/SNa is over 1, should you give water to a hyponatremic patient?
nope
if the spot Una + Uk/SNa is 0.5 to 1, should you give water to a hyponatremic patient?
500 ml/day
if the spot Una + Uk/SNa is less than 0.5, should you give water to a hyponatremic patient?
restrict to 1000 ml/day
When can oral V2 receptor antagonists be used?
to raise tonicity in SIADH and CHF but NOT liver failure
When should limited administration of 3% saline be given?
during acute intoxication with symptoms of cerebral edema - goal is NOT to get SNa to normal
What should you avoid doing in treating SIADH?
giving normal saline UNLESS there are loop diuretics as well
