Hyponatremia Flashcards by Alba Mariner Gonzalez

What is the main cause of feeling “sick” when there are acute changes in tonicity?

changes in cell shape and size

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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

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Alcohol and urea are what kind of osmols?

ineffective - they cross the cell membrane

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Is tonicity estimated or measured?

estimated

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is osmolarity estimated or measured?

measured

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How do you calculate estimated osmolarity?

(NaX2) + (glucose/18) + (urea/2.8)

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What is a normal serum osmolarity?

285 mOsms/L

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A decrease in total body water would cause hyper/hypotonicity and hyper/hyponatremia?

hypertonicity and hypernatremia

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An increase in total body water would cause hyper/hypotonicity or hyper/hyponatremia?

hypotonicity and hyponatremia

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Do osmoreceptors respond to plasma tonicity or osmolarity?

plasma tonicity = by degree of stretch of the cell membrane under changing tonicity

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What signaling in the posterior pituitary causes ADH release?

osmoreceptors + tonicity, AngII, volume depletion, nausea, pain, sedation, and drugs

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How is electrolyte free water clearance calculated?

solute excretion/urinemOsm * (1- UNA+ UK/SNA)

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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 ??

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With or without ADH, what is true of the relationship between urine concentration and solute excretion?

solute excretion increases as urine concentration drops, regardless

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What are the 3 types of hyponatremia?

isotonic/artifactual hyponatremia
hypotonic hyponatremia
hypertonic hyponatremia

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What type of hyponatremia would be caused by hypergammaglobulinemia, hypertriglyceridemia, or hyperchylomicronemia?

artifactual/isotonic hyponatremia

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What causes hypertonic hyponatremia?

addition of new effective osmoles to the ECF, causing water to flow out into the ECF and dilute Na

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When do symptoms of hypotonic hypernatremia begin?

when SNa drops below 125 mEq/L

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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