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two compartments involved in fluid distribution..
- Intracellular compartment
- extracellular compartment
- -interstitial spaces
- -plasma (vascular) compartment
- -transcellular compartment
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what is osmosis
movement of water across a semipermeable membrane
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what is diffusion
movement of particles from and area of higher concentration to an area of lesser concentration
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osmolarity =
- osmolar concentration in 1 liter of solution
- (mOsm/L)
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osmolality =
a measure of the number of dissolved particles (solutes) in 1 kg (1liter) of water
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what are the three solutes that have the largest role in determining osmolality
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what is normal serum osmolality
275 - 295 mOsm/kg
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how does fluid shift in regards to the ECF and ICF
fluid shifts from the area of lesser concentration to the area of greater concentration
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tonicity =
ability of a solution to cause a change in water movement across a membrane due to osmotic forces
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hypotonic fluids make cells...
why?
- swell
- the fluid has lesser concentration of solutes than plasma
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hypertonic fluids make cells....
why?
- shrink
- the fluid has a greater concentration of solutes than plasma
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isotonic fluids cause ...
no change in the size of the cell
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capillary hydrostatic pressure does what to fluid
pushes water from intravascular to interstitia
out of the capillary into the interstitial space
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capillary oncotic pressure is caused by
plasma proteins
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capillary oncotic pressure does what to fluid
pulls fluid into to intravascula space
into the capillary from interstitial space
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lymphatics do what
return fluid from the interstitial space to the systemic circulation
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why does IV therapy work
because of osmosis
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fluids with the same osmolality as the plasma are termed
isotonic
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solutions in which the solutes are less concentrated than the plasma are termed
hypotonic
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solutions with solutes in greater concentration than the plasma are termed
hypertonic
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where do administered isotonic IV fluids remain primarily?
in the ECF
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when are isotonic fluids used
- to replace ECF loos (diarrhea, vomiting, surgical blood loss)
- when BP is low and to expand vascual volume quickly
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examples of isotonic fluids =
- normal saline = 0,9% NaCl
- Ringer's solution = contains sodium, potassium and calcium
- Lactated Ringer's solution = sodium, potassium, calcium, lactate
- D5 1/4 NS
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administration of hypotonic solutions results in what
- water being pulled out of vessels into the cells and interstitial spaces
- resulting in decreased vascular volume and increased cell water
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hypotonic fluids are used to prevent and treat what
- cellular dehydration
- hypernatremia = elevated sodium levels
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examples of hypotonic fluids =
- D5W
- 0.45% saline (1/2NS)
- 0.225% saline (1/4NS)
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if D5W is isotonic in IV bag why is it a hypotonic fluid
- the dextrose is rapidly metabolized once infused
- 2/3 of water enters cells and 1/3 remains in ECF
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1/2 NS means what
- 0.45% saline
- 1/2 of each liter infused mover into cells other half remains in ECF
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what is a plasma expander
fluid that moves water from cell into plasma
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examples of hypertonic solutions
- saline solutions > 0.9% ie 3% saline and 5% saline
- dextrose solutions > than 5% ie 10% and 50%
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what is a colloid
a large solute particel, such as protein or starch, that normally does not pass through cell and capillary membranes; they pull fluid from tissue into the vessels, increasing vascular volume
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what do colloid volume expanders do
mobilize edema from the interstitial space into the vascular space
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examples of colloid volume expanders =
- albumin
- plasma protein fraction (plasmanate)
- Dextran
- Hetastarch (Hespan)
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what is normal fluid intake a day
2500 ml
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what is the most objective measurement of fluid volume status
daily weight
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what is the most important mechanism regulating intake of fluids
thirst
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what happens to elderly thirst
decreases
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hypodipsia
decreased stimulus to drink
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polydipsia =
excessive thirst
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treatment of fluid volume deficit in non acute situation
- encourage fluid intake
- probably not just water
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what lab values do you look at to see if patient needs blood
- H & H
- hemoglobin and hematocrit
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if you over hydrate someone you increase which capillary pressure
hydrostatic pressure
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in isotonic contraction dehydration what fluid is lost
water and sodium lost in equal proportions
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what causes isotonic dehydration
vomiting, diarrhea, renal disease, diuretics
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hypotonic contraction dehydration - what fluid is lost
loss of sodium, without corresponding loss of water
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hypertonic contraction dehydration - what fluid is lost
loss of water without a corresponding loss of sodium
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what can cause hypotonic dehydration
- diuretics and renal disease
- because sodium is lost without correspondig loss of water
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what can cause hypertonic dehyration
excessive sweating without replenishment, osomotic diuresis, burns
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normal urine output is
- ml of fluid per kg per hour
- or
- 30 - 50 ml/hr
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what happens pathophysiolgically with hypotonic contraction
ECF becomes hypotonic fluid shifts from ECF to ICF lowering plasma fluid volume
why
becasue there is a loss of sodium without loss of water
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pathophysiology of hypertonic contraction
ECF becomes hypertonic fluid shifts from ICF to ECF, causing cellular dehydration
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when can you assess JVD
when head of bed is elevated at least 45 degrees JVD should be flat
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clinical manifestations of isotonic fluid volume excess
- weight gain
- edem
- JVD
- full bounding pulses
- decreased serum osmolality < 275
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isotonic fluid volume excess can be casued by
- decreased water and sodium elimination
- excessive admin of IV fluids
- excessive secretion of aldosterone
- shift of fluids into the plasma
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accumulation of fluid in the interstitial space is caused by
- increased hydrostatic pressure
- decreased capillary oncotic ressure
- increased capilary permeability - burns, allergies, inflammation, immune response
- decreased lymphatic flow
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aldosterone is secreted in response to
low sodium or high potassium levels
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ADH causes
the reabsorption of water from the renal tubules
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decreased ADH release =
water lost in urine
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water sodium and potassium balance is regulated by
aldosterone (from adrenal cortex)
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aldosterone causes the reabsorption of
Na and H2O and the elimination of K
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Aldosterone is secreted in response to
low sodium or high potassium levels
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dependent edema is where
- the location of the edema is dependent on the postion of the patient
- ie if upright edema in legs and feet, if lying flat edema in back and butt
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if you give albumin to a pt with edema what would it do
increase the oncotic pressure and pull fluid into the Intravascular space
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venous and lymph edema can be controlled by what
elevation and compression
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third spacing =
trapping of ECF in the transcellular space (peritoneal cavity -ascites, periorbital, pericardial)
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ADH is secreted in response to
high serum osmolality or when blood pressure decreases or blood volume
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ADH is secreted from the
posterior pituitary
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increased serum osmolality can be a
water deficit or sodium excess
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low osmolality and or increased intravascula voume causes
- lack of thirst --> decreased water intake
- decreased ADH release --> water lost in urine
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decreased renal perfusion (because of low blood volume or low blood pressure)leads to release of
renin and activation of the renin-angiotensin aldosterone system (RASS)
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electrolytes are
charged particles called ions
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what is the chief intracellular cation
potassium (the cell has 28X more potassium than the ECF)
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why does aldosterone hold onto Na and water and releases K
to maintain electrical nuetrality
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is the potassium in blood a good indicator of the amount of potassium in body, why
NO because most of potassium is inside the cell
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normal level of sodium is
135-145 mEq/L
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sodium regulates
extracellular fluid volume and osmolality
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sodium is important in
the generation and transmission of nerve impulses and regulation of acid-base balance
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what is most predominant cation in the ECF
sodium
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what is the primary regulator of sodium balance
kidneys
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avg adult daily requiremnt of sodium is
.5-2.7g
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sodium level <135 mEq/L =
hyponatremia
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hyponatremia is common in elderly why
decreased renal ability to conserve sodium
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hyponatremia can be caused by
excessive sweating with water replacement instead of replacement with electrolyte/fluid
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one case where sodium does not follow Na is in
the secretion of ADH
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why does excessive secretion of ADH cause hyponatremia
because the body holds onto water and dilutes Na levels in the body
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clinical manifestations of hyponatremia =
- N/V
- anorexia
- abdominal cramping
- altered neurolgical functioning
- coma
- muscle twitching, tremors
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why would hypoaldosteronism casue hyponatremia
because aldosterone makes you hold onto Na and water so if you do not have enough aldosterone you don't hold onto Na
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two big symptoms of hyponatremia =
fluid volume deficit and neurological symptoms
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if dilutional hyponatremia how do you treat
give loop diuretics
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most common cause of hypernatermia =
kidneys not secreting Na
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hypernatremia is
- too much Na
- can be water loos or sodium gain
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hypernatremia SALT =
- Seizures
- Altered mental status
- Lethargy; low grade fever
- Thirst
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hyperaldosteronism can cause
- hypernaremia
- because aldosterone keeps water and Na
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hypernatremia is treated with
- restricted sodium intake
- give sodium free IV fluids
- diuretics followed by water admin becasue diuretics get rid of sodium and water
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Diabetes insipidus =
- not enough ADH
- peeing out water not sodium
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is severe hypernatremia with hypovolemic you treat with
hypotonic fluids
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i sever hypernatremia and hypervolemic you treat with
diuretics
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