Fluids and Fluid Therapy
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total body water (TBW) in adults and neonates
- Adults 50-70%
- neonatals 80%. Easy to over-hydrate
factors affecting TBW
age, body fat
Distribution of TBW
- 40% in intracellular space
- 20% in extracellular space (15% interstitial, 5% intravascular)
Body water solutes, particularly in ECF vs. ICF
- Electrolytes become ions
- cations = anions. Balanced
- cations in ECF are Na
- cations in ICF are K and Mg
- anions in ECF are Cl and HCO3 (bicarb)
- anions in ICF are phosphates and proteins
- ECF - Na, Cl, HCO3
- ICF - K, Mg, phosphate, protein
What is balanced therapeutic fluid?
resembles ECF (Na, Cl, HCO3)
- unit of measure expressing electrolyte concentration.
- 1:1000 of an equivalent weight (weight of element that will combine with 1 g of H+, gram molecular weight/positive valance)
Osmolarity of dog/cat plasma or serum
What shouldn't you do while administering calcium
blood transfusion, calcium precipitates out red blood cells.
relative number of solute particles in 1 kg of solution. More particles = more pressure
number of solute particles per liter of solution
When effective solute particles attract water to cross a semipermeable membrane, the pressure required to stop them or the pressure until equilibrium is reached.
effective vs. ineffective osmoles
not all particles contribute to osmotic pressure. Effective are Na and glucose, for example. Albumin pulls water very well. Ineffective are not clinically useful.
total osmolarity or osmolality of a solution
tonicity (effective osmolarity) approximately equal to tonicity of blood plasma
- tonicity less than that of blood plasma.
- Fluid is pulled into ECF
- tonicity greater than that of blood plasma.
- Fluid is pulled into IVF (critical care patients, faster hydration from inside)
Fluid disturbances in patients (3)
- changes in volume (dehydration or blood loss)
- changes in content (hyperkalemia in a blocked cat, etc)
- changes in distribution (pleural effusion)
dehydration and how you recognize it
- hydration status, water loss>water intake.
- Check history (V? D? Bleeding?), physical exam (skin turgor, mucus membranes, heartbeat, pulses, breathing), MDB (basic tests)
- Also check for ongoing fluid loss, and think of replacing electrolytes etc.
Ways of taking food in
- drinking water
- water from ingested food (especially cats)
- metabolic water
ways of losing water
- urine, feces, sweat (horses), respiration (dogs)
- anorexia, PU, V, D, third spacing, extensive burns
- includes sensible and insensible losses
- early dehydration. drop in skin turgor and dry mucous membranes.
- Weight or age of animals can affect skin turgor
- more serious dehydration.
- hypotension (low BP), tachycardia, pale mucous membranes, increased CRT, weak pulse. Increased skin turgor and dry membranes.
- Massive dehydration leading to cerebral obtundation.
- Shock, nonresponsive, can't stand up or move.
< 5% dehydration
history of fluid loss but no findings in physical examination
dry oral mucous membranes but no panting or pathological tachycardia
mild to moderate decreased skin turgor, dry oral mucous membranes, slight tachycardia, and normal pulse pressure
moderate to marked degree of decreased skin turgor, dry oral mucous membranes, tachycardia, and decreased pulse pressure
marked loss of skin turgor, dry oral mucous membranes and significant signs of shock.
Three things you need to calculate amount if IV fluid to administer
- Hydration deficit
- maintenance requirements
- ongoing losses
- amount of fluid that must be replaced to bring animal back to normal hydration status.
- %dehydration x body weight = lbs of fluid lost.
- 500mL = 1 lb
- Use 75% over 24 hours because this is an ESTIMATE
- (add to maintenance requirement and ongoing loss to replace)
mL to lb conversion
500mL to 1 lb
Maintenance requirements, traditional method
- Volume of fluid needed to replace normal sensible and insensible losses.
- (add to hydration deficit and ongoing losses to replace)
alternate calculation of maintenance requirements, or wheel maintenance
30 x kg +70 = mL
new AAHA maintenance
- cat = 80 x kg0.75 = 2-3 ml/kg/hr
- dog = 132 x kg0.75 = 2-6 ml/kg/hr
Blood volume in cats and dogs and why it's important
- don't bolus more than the blood volume per hour.
- cat = 40-60 ml/kg
- dog = 90 ml/kg
- Bolus in 25% increments, 15 minutes at a time.
Ongoing or continuing abnormal losses
- Estimated fluid losses from vomiting, diarrhea and/or excessive urination.
- Add to hydration deficit and maintenance requirement.
- Administer CRI over 24 hours.
drip rate equation
gtt/min = (volume of infusion)/(time of infusion) x drip factor
fluid therapy routes of administration, and how you choose
- condition being treated, duration of condition and severity of condition
- IV, SQ, PO, IP, IO
IV fluid administration
- quickest and most precise
- requires IV catheter
- Preferred with significant fluid loss or severe condition
- For less severe needs
- Amount depends on animal size, usu 5-10mL/lb per injection site
- Use Isotonic fluids
- can't use in severe GI disorders
- Allows normal physiological processes to control amount
- not good for large volumes
- can administer a large volume but absorption is slow
- Rarely used
- very small animals or poor venous access
- rapid delivery of fluids
- requires expertise in placing IO needle.
Ways to monitor fluid administration
- physical status: weight, skin turgor, mm/crt, lung sounds, oculonasal discharge, urine output
- laboratory: PCV/TP, CVP
central venous pressure.
To judge central venous pressure
- requires placement of jugular catheter.
- Extension set, stopcock, manometer, saline.
- Hold "O" of manometer at level of heart. Optimal is 5-8 cm H2O. <5 insufficient. > 14 overload.
- Fluctuates with respiration.
clinical signs of overhydration
- serous oculonasal dishcharge
- pitting edema
- inappropriate weight gain
Selection of fluids
- give fluids that most closely resemble what has been lost
- Give in body compartment where fluid deficit lies
- true solutions containing small molecular weight particles that can move through pores in capillary walls.
- Particles can also move slowly through cell membranes
- Includes electrolytes, buffers and/or dextrose
Balanced crystalloids vs non-balanced crystalloids
- balanced contain electrolytes in approx same concentrations as blood plasma
- balanced also are fluids containing buffers (lactate, acetate or gluconate)
- non-balanced do not resemble composition of blood plasma or ICF
balanced crystalloids examples
- balanced crystalloid
- replacement solution
- buffer is lactate (converted by liver to bicarb, buffers against acidosis)
- do not administer with blood
- balanced crystalloid replacement solution
- dual buffer of acetate and gluconate (metabolized outside liver, precursers to bicarb)
- Can be administered with blood.
balanced crystalloid replacement solutiondual buffer of acetate and gluconate (metabolized outside liver, precursers to bicarb)Can be administered with blood.
unbalanced crystalloid examples
- 0.9% NaCl
- 2.5% dextrose + 0.45% NaCl
- Unbalanced crystalloid
- contains dextrose at 5g/L and water
- dextrose metabolized to H2O and CO2
- Not given SQ
- not used for maintinence
- Isotonic saline, unbalanced crystalloid
- Indications: hyperkalemia, increases plasma volume, Na deficiency, bathe tissues intraop
- Contraindicated in heart disease
- Not used for maintinence
2.5% dextrose and 0.45% NaCl
- "half-strength" saline, unbalanced crystalloid
- Indicated for patients with Na restrictions (Heart disease, renal disease, hypertension)
- maintinence okay with KCl added
- contain large molecular weight molecules unable to cross cell membranes
- used to increase oncotic pressure (osmotic pressure exerted by colloids in blood plasma)
- AKA plasma volume expanders
plasma volume expanders
when to administer colloids
- patients with large volume losses where crystalloids are not improving/maintaining blood volume
- When increased O2 or tissue perfusion needed
- If edema develops before blood volume restoration
- decreased oncotic pressure (TP<3.5 or alb<1.5g/dL)
- for longer duration of effect
- difficult to administer in sufficient amount for resuscitation
- goal is least volume with highest CV benefit
- whole blood, plasma, albumin
- Choose depending on animal problem--whole blood or fresh frozen plasma for coagulation factors, whole blood or packed RBCs for blood cells.
- Adverse reactions include bleeding, vomiting, fever, urticaria (rash, hives), facial edema and others
- Plasma volume expanders (administer slowly)
- Dextran 70 (polysaccharide, can cause allergic reaction or clotting deficits)
- Hetastarch (Hespan) (from maize, hydroxyethyl starch, less antigenic than dextran, expensive)
- synthetic colloid, plasma volume expander. Administer slowly.
- Polysaccharide solution
- can cause allergic reactions or clotting deficits
- derived from maize (hydroxyethyl starch)
- less antigenic than dextran
- modified biological colloid
- ultrapure, bovine-origin polymerized hemoglobin solution (for dogs with anemia)
- O2 carrying substitute for RBCs, temporary, universal compatability
- stored at room temp (2 yr shelf life, opened 24hr expiration)
- adverse reactions include pulmonary edema, V/D, yellow-orange skin discoloration of skin, urine serum, sclera etc.
Common additives to fluids
- potassium chloride
- 50% dextrose
- Vitamin B complex
- common additive, prevents k deficits
- Usu 2 mEq/ml
- amount added depends on serum k level
- adverse effects include muscle weakness and cardiac conduction (hyperkalemia)
common additive for hypoglycemic patients or ketosis in ruminants
Vitamin B complex
- common additive, water soluble vitamins which are lost in animals with diuresis
- Generally add 2mL/L
- adverse include hypersensitivity (thiamine)
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