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Total Nody Water (TBW)=
- 60% OF BW
- 70% in LA <30 days old
- 60% of lean BW in obese animals (LBW= 0.7xBW)
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Why are cats more/less susceptible to volume overload than dogs?
MORE: cats normally have 4-6% of BW as intravasulcar water (dogs usually 8-9%)
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What is the barrier between the ICF and ECF, and what are its properties?
- cell membrane
- freely permeable to water (conc gradients)
- impermeable to electrolytes and proteins
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What is the barrier between the ISF and IVF, and what are its properties?
- endothelium
- freely permeable to water (conc gradients)
- freely permeable to electrolytes (conc gradients)
- relatively impermeable to proteins and large molecules
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What is the law of electroneutrality?
the number of positively and negatively charged ions must be equal
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Extracellular water is composed on __(2)__.
interstitial water + intravascular water
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In SA patients, TBW= _____ ICF + _____ ECF.
2/3; 1/3
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In LA patients, TBW= ______ ICF + _______ ECF.
1/2; 1/2
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In LA patients <30 days old, TBW= _____ICF + _____ECF.
1; 1
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How do you calculate intravascular water in a dog, cat, and horse?
- Dog: 8-9%*BW (5%*BW=plasma)
- Cat: 4-6%*BW (3%*BW=plasma)
- Horse: 8%*BW (5%*BW=plasma)
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__________ is the predominant extracellular ion; _________ is the predominant intracellular ion.
Sodium; potassium
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What is the clinical significance of K+ being an intracellular ion?
Blood levels of K+ may not be reflective of how much potassium is inside the cells (you can have ow potassium and maintain relatively normal blood K+ levels)
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Potassium is primarily responsible for ___________.
cell osmolality
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Sodium is predominantly responsible for __________.
blood osmolality
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When ions have a different conc on either side of a semi-permeable membrane, it creates ____________.
osmotic pressure
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Oncotic forces are generated by...
macromolecules that do not readily move across the endothelium.
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Generate osmotic pressure across a semi-permeable membrane that is not permeable to that particle, resulting in the movement of water.
effective osmoles
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What are the main effective osmoles? (2)
Na+, K+
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Effective osmoles determine _________.
tonicity
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Molecules that have osmotic potential but are able to diffuse across the barrier, resulting in no generation of osmotic pressure and no movement of water.
ineffective osmoles
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What are examples of ineffective osmoles? (2)
urea (diffusible), glucose (metabolized)
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Ineffective osmoles contribute to ___________ but not _________.
osmolality; tonicity
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What is the equation to calculate osmolality?
Osm= 2 (Na + K) + glucose/18 + BUN/2.8
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What are the consequences of hypotonic loss (loss of water in excess of electrolytes)? (4)
- water shifts from ICF to ECF
- ECF supported, ICF decreases, TBW decreased
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What are the consequences of hypertonic loss (loss of electrolytes in excess of water)? (4)
- water shifts from ECF to ICF
- ECF decreased, ICF increased, TBW stays the same
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What are the consequences of isotonic loss (loss of equal parts electrolytes and water)? (4)
- no shift in water from ECF to ICF
- ECF decreased, TBW decreased, no change in ICF
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What is capillary hydrostatic pressure, and what does it cause?
pressure of fluid within the capillary, causing net movement out of the vessel
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Capillary hydrostatic pressure is primarily dependent on __________ because...
venous pressure; arterial pressure is not transmitted across the pre-capillary sphincter (hypertension does not cause edema!)
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What are causes of increased capillary hydrostatic pressure? (4)
venous obstruction, congestion from CHF, thrombosis, volume overload
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What is the interstitial hydrostatic pressure and what does it cause?
- pressure of fluid within interstitium
- positive interstitial hydrostatic pressure causes net movement INTO vessels (negative causes fluid to move out of vessels)
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Interstitial hydrostatic pressure is primarily dependent on ____________; the clinical significance of this is...
- "looseness" of tissue (extracellular matrix arrangement)
- edema more common in looser tissues (skin)
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What is the capillary oncotic pressure and what does it cause?
- force exerted by proteins (primarily albumin) which do not readily move across the endothelium
- serves to keep fluid in the vessel; positive moves fluid into vessels
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What is the interstitial oncotic pressure and what does it cause?
- force of protein in tissue to draw out water
- net movement out of vessels
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With oncotic pressure, it's the _________, not the __________, that contributes to pressure.
quantitiy; size of the protein
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What is the safeguard system against edema?
lymphatic drainage (lymphatic obstruction can lead to edema); has a large capacity to drain fluid from interstitium
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What are crystalloids, and how are they categorized?
- varying electrolyte composition in water
- categories- tonicity [hypotonic, isotonic, hypertonic], electrolyte composition [saline, balanced electrolyte], effects of acid-base[ acidifying NaCl, alkalinizing LRS or plasmalyte]
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Describe hypotonic crystalloids.
osmolality less than that of blood--> net increase in free water
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Where is the volume of distribution of hypotonic crystalloids?
total body water (across all fluid compartments)
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What are examples of hypotonic crystalloids? (3)
- dextrose 5% in water (D5W- dextrose not effective osmole- metabolized leaving free water)
- 0.45% NaCl (half saline)
- Normosol M (maintenance fluid)
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What are the clinical indications for hypotonic crystalloids? (3)
- replace free water deficit (hypernatremia)
- heart and renal disease (can't handle sodium load)
- maintenance fluid
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When should you NEVER use hypotonic crystalloids and why?
- never use for resuscitation! never use as a bolus! (never administer rapidly)
- dramatic change in blood osmolarity causes RBC damage
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Describe isotonic crystalloids.
osmolality is approximately equal to blood--> replace electrolytes and water
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Where is the volume of distribution for isotonic crystalloids?
extracellular space (redistribution to interstitium within 20-30 min after being put in vasculature)
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What are examples of isotonic crystalloids? (4)
- Non-balanced acidifying electrolyte solution: Normal Saline (0.9% NaCl)
- Balanced alkalinizing electrolyte solutions: Plasmalyte, LRS, Norm-R
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Why is 0.9% NaCl acidifying?
it's equal parts sodium and chloride, but blood is more sodium that chloride--> relative increase in Cl- causes decrease in SID--> bicarb loss--> acidify
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Why are balanced electrolyte solutions alkalinizing?
they provide bicarbonate precursors, increasing the body's production of bicarb
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What are clinical indications for isotonic crystalloids? (4)
correct acid-base disorders, rehydrate, replace ongoing losses, resuscitation
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What are potential adverse effects of isotonic crystalloids? (3)
creation of acid-base disturbances, tissue edema (fluid goes to interstitium), pro-inflammatory effects
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Describe hypertonic crystalloids.
osmolality greater than that of blood--> shift fluid from interstitium into vascular space
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Where is the volume of distribution of hypertonic crystalloids?
- rapid volume expansion within the vascular space early on (transient)
- within 10-30min, redistributes across the extracellular fluid (interstitium)
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What are clinical indications for hypertonic crystalloids? (3)
resuscitation, head trauma/ cerebral edema, correction of acute hyponatremia
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What are potential adverse effects of hypertonic crystalloids? (4)
- short duration of volume expansion
- transient hypernatremia
- reflex bradycardia (with overly rapid administration)
- contraindicated in dehydration
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Describe colloids.
molecules that do not readily cross capillary membranes and stay in vascular space
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Where is the volume of distribution of colloids?
contribute to capillary oncotic pressure--> increase intravascular fluid (blood volume)
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__________ is the most important colloid in blood.
Albumin
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In states of increased vascular permeability, colloid administration can lead to...
colloid accumulation in the interstitium and edema.
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What is the synthetic colloid, and where is its volume of distribute?
- hydroxyethyl starch
- vascular space--> increases intravascular volume and prolonged vascular expansion
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What does it mean that synthetic colloids are polydispersed complex starches?
smaller molecules confer oncotic pressure and larger molecules confer duration of action
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What are the clinical indications for synthetic colloid use? (2)
- resuscitation and sustained vascular expansion
- oncotic support for hypoproteinemia
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What are the potential adverse effects of using synthetic colloids? (2)
- dose-dependent coagulopathy (dilution of clotting factors, impaired platelet aggregation, interference with clotting factors)
- renal injury (don't use in renal patients)
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What is the natural colloid and where is its volume of distribution?
- plasma
- vascular volume--> expands intravascular fluid equal to amount given
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What are clinical indications for use of natural colloids (plasma)? (1)
treat coagulopathy
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What is a potential adverse effect of administering natural colloids (plasma)? (1)
transfusion reaction
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What is the newer synthetic colloid formulation, and what is it's advantage?
VetStarch- decreased chance of coagulopathy
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What are advantages to using IV route of administration of fluids? (3)
- direct vascular access
- rapid administration possible
- almost all types of fluids can be given IV
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IV fluid administration is preferred for... (4)
resuscitation, anesthetic patient, significant dehydration and ongoing losses, critically ill patients
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What are the advantages of placing a peripheral IV catheter (as opposed to central)? (3)
- faster/ easier to place
- shore, large bore for faster administration
- less expensive
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What are disadvantages to placing a peripheral IV catheter (as opposed to central)? (3)
- position limb movement can cause occlusion
- relatively short term
- hypo-or hypertonic fluids and some drugs can be irritating
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What are advantages to placing a central catheter (as opposed to periph)? (4)
- safer administration of hypo- or hypertonic fluids
- large bore for rapid administration
- measurement of central venous pressure available
- serial blood sample possible
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What are disadvantages of placing a central IV catheter (as opposed to a periph)? (3)
- time/ cost/ expertise
- might require sedation
- caution with bleeding disorders
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What are potential complications with catheterization for fluid administration? (5)
- extravasation of catheter
- thrombosis/ thromboembolism
- thrombophlebitis
- infection (at catheter site or blood infection/ bacteremia)
- catheter fragment foreign body
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When is the intraosseous route of fluid administration used?
neonates and avian
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What are advantages to using the intraosseous route for fluids? (3)
- access to vascular space when IV not possible
- equivalent to IV
- relatively rapid placement
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What are disadvantages to using the intraosseous route for fluids? (3)
- osteomyelitis
- short-lived access
- technically challenging
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When is SQ route of fluid administration applicable?
for administration of fluid for gradual absorption and distribution across fluid compartments
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Uptake of SQ fluids is dictated by... (3)
- hydration status
- peripheral perfusion
- body temperature (worse absorption in cold patients)
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What types of fluids can be given SQ?
near-isotonic fluids (except: do not give dextrose SQ...it hurts!)
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Advantages of SQ fluids? (3)
practical, less expensive, out-patient basis
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SQ fluid administration is preferred for... (3)
- mild to moderate dehydration
- prevention of dehydration for anorexic/ NPO patients
- unable to hospitalize
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What are disadvantages of administering SQ fluids? (4)
- unreliable absorption
- cannot be used for resuscitation or replacement in shocky patients
- limited in options of types of fluid
- may cause pain/ irritation or pressure necrosis (uncommonly)
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What are advantages of enteral administration of fluids? (3)
- most natural way to provide fluids
- low cost
- can also provide nutritional support
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What are disadvantages of enteral administration of fluids? (4)
- need functional GI tract
- can't keep up with losses
- not effective for resuscitation
- potential risk for aspiration pneumonia
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