Water-sodium balance tutorial Flashcards
What is osmolality?
The concentration of a solution expressed as the total number of solute particles per kilogram.
What is the formula for osmolality? what does it refer to?
Osmolality= 2(Na+) + Gluc/18 + BUN/2.8
Osmolality= Water in the blood ~ solute in the blood
What is Osmolality equal? what is hyper/hypo/iso osmotic?
285 = isoosmotic=isotonic
hyper> 285
hypo<285
What does Tonicity refer to?
Tonicity= Water in the cells ~ solute in the cell
What is the formula for tonicity?
Tonicity= 2(Na+) + Gluc/18
What is Hypovolemomic, hypervolemic and euvolemic?
Hypovolemic-low volume in ECM
euvolemic- normal ECF volume
Hypervolemic- high ECF volume
What is tonicity?
is the relative concentration of solutes dissolved in solution which determine the direction and extent of diffusion.
What is a hypertonic solution?
relative high solute concetration compare to a cell
water will diffuse out of cell and cell will shrink
What is a hypotonic soltion
relative low solute concetration compare to a cell
water will diffuse in of cell and cell will swell
What is hypotonic?
equal solute concentrations inside cell and in solution
What is hyponatremia?
Low concentration of sodium in ECF
What is the function of ADH?
ADH works at the collecting duct= reabsorbs free water back into blood decreases your sodium concentration
What is the function of aldosterone?
Aldosterone works at the collecting duct= reabsorbs free water and sodium back into blood
Why is there a big decrease in sodium concentration when just water is added?
Because water can freely diffuse across the membrane of cells into cells, salt does not stay in ECF. So volme is only a small increase in ECF. Salt is a large decrease
This is hyponatremia= decrease in sodium concentration
What is saline? What can happen when adding saline?
Salt and water
an isoosmotic substance that increases volume only because salt is added
ECF remains Isotonic
this will create edema
What happens in patients with only a ADH problem?
only adding water
no edema
Hyponatremia
In which situations will they have edema in a patient?
adding saline =
adding Aldosterone=
reabsorption of salt and water
both increases salt and water
How is Hyponatremia tested for?
test osmolalality
which test the overall sodium concentration in plasma
What is a hyponatrimia?
sodium concentration in plasma less than 135
What are the three states of hyponatremia?
remember osmolality=
2*(sodium concentration) +glucose/18+BUN/2.8
Isotonic(psuedohyponatremia)
Hypertonic
Hypotonic
How does a patient have isotonic-pseudo-hyponatremia? What must be done toget an accurate reading?
a patient has
hyperlipidemia and/or
Hyperproteinemia
and lab test is done that measures total blood volume. this will give a false positive.
Measure of sodium in the plasma portion will give a more accurate reading
How is Hypertonic Hyponatremia caused? What is BUN equal to?
remember osmolality=
2*(sodium concentration) +glucose/18+BUN/2.8
caused by increased solutes in the ECF (not sodium)
increased osmolality is caused by Hyperglycemia and/or
increased BUN
BUN= Mannitol, Ethylene glycol(antifreeze) and Toluene (paint thinner)
What are the three states of Hypotonic Hyponatremia?
Hypovolemic Hypotonic Hyponatremia
Hypervolemic Hypotonic Hyponatremia
Euvolemic Hypotonic Hyponatremia
What is Hypovolemic Hypotonic Hyponatremia?
decrease in sodium concentration caused by an decrease in water but a double decrease in salt
decreased concentration[Na+]= double decrease Na/decrease water
How is Hypovolemic Hypotonic Hyponatremia caused?
double lost of salt and lost of water
Renal= diuretic Non-renal = vomiting
What is Euvolemic Hypotonic Hyponatremia
No lost of salt and an increase in water
decreases salt concentration
What causes Euvolemic Hypotonic Hyponatremia?
Increase ADH=
Increases free
Water
What is Hypervolemic Hypotonic Hyponatremia?
an increase in salt
but a double increase
in water.
causes a decrease in sodium concentration
What causes Hypervolemic Hypotonic Hyponatremia?
An increase in ADH and aldosterone
CHF
Liver Disease
Nephrotic syndrome
All three increase
Adosterone because of poor flow
To kidneys
And ADH
What is hypernatremia?
increase in sodium concentration above 145
What causes hypernatremia?
ADH/vasopressin
What is Hypertonic Hypernatremia?
double decrease in water but no decrease in salt
causes an increase in sodium concentration
What is the MOA of water reabsorption in the principle cell of the CCD?
pituitary gland release AVP
AVP activates V2 on the principle cells on the basolateral membrane.
V2 activates AQP2 on the apical membrane
AQP2 allows diffusion of water across to apical membrane into the cytoplasm
Water in the cytoplasm diffuse through AQP3 across the basolateral membrane into blood
What is the MOA of Neruogenic DI?
decreases AVP release from pituratray.
V2 not activated
What is the MOA of Nephrogenic DI?
V2 lost sensitivity for AVP
How does the water deprivation test work?
Deprive water for a certain amount of time
you will see no increase in osmolality but increase in plasma osmolality
add AVP
if Nuerogenic DI-then there willbe an increase in Urine osmolality
if nephrogenic- no increase in plasma osmolality
What does SIADH cause?
what will it cause?
Syndrome of inappropriate ADH secretion.
Will cause hyponatremia because of high water retention
What is a defense against hyponatremia?
increased water intake -> decrease osmolality-> activates osmoreceptors cells-> causes decreased->AVP release-> excretetion of dilute urine
What is the algorythym for diagnosing hyponatremia?
check plasma osmolality
normal= hyperlipidemia and hyperproteinimia
High osmolality = mannitol(BUN) and/or Hyperglycemia
if osmolality is low check volume status
low volume =Volumeloss -GI tract -Skin -Renal(Diuretics)
High Volume= CHF Cirrhosis Nephrosis Hypoalbumin
Euuvolemic = hypothyroid or hypoadrenal= SIADH
Check urine osmolality
if urine osmolality is <100, then excess water ingestion
if > serum osmolality then SIADH
What are the majority cases of hyponatremia?
90% Hypotonic
What can cause excessive adh secretion by the hypothalnmus?
ECFV or effective circulating volume
pain
nasuea
drugs
CNS disruption
What are drugs associated with SIADH?
SSRI Carbamazepine Platinum compounds Proton Pump Inhibitors Alkylating agents
What are drugs that use for hyponatremia?
Vaptans - blocks V2
Lithium, Demeclocycline
Both block cAMP by V2
What can insufficient sodium damage cause?
Excessive sodium correction?
insufficient = osmotic demyelation syndrome (cells remain small)
excessive = cerebral edema ( cells are tool large)
What are barnes steps to Hyponatremia?
Identify there is a Low Serum Sodium level
Obtain Serum and Urine Osmolality
Identify the Serum Osmolality as low, as majority of the time it is low
Evaluate the patient’s volume status
Based on the patient’s volume status identify the source
Intervene on the source of the patient’s hyponatremia for correction or utilize fluid restriction, isotonic saline, or hypertonic saline as indicated.
If recurrent hyponatremia, consider the use of a “vaptan” or demeclocycline.
What is the bodies defense against hypernatremia?
Decrease in Free Water Intake
Increase Posm
Osmoreceptor Cells + Stimulation of Thirst
Increase Vasopressin Release (ADH)
Excretion of Concentrated Urine
What are causes of neurogenic DI?
Head Trauma
Hereditary
Pituitary Surgery
Aneurysm
CVA
Post-partum (Sheehan’s Syndrome)
What are causes of nephrogenic DI?
Lithium
Demeclocycline
“Vaptans
What are barnes steps to hypernatremia?
Identify there is an Elevated Serum Sodium level
Evaluate the patient’s volume status
Calculate a Free Water Deficit
Consider use of Free Water infusions or oral administration of free water
For Euvolemic (as most cases are) perform a water deprivation test to differentiate between Central DI or Nephrogenic DI
Attempt to identify the source of DI and correct
Consider DDAVP for Central DI vs. thiazides+ low Na diet or NSAIDs for Nephrogenic DI
