Fluid Therapy Dr. Ambrisko Flashcards
What is total body water
≈ 60% of BW in average adult
≈ 80% in newborn
Less in obese animals
What is the distribution of fluids?
Of the 60% TBW:
40% ICF (intracellular)
15% Interstitial (ISF)
5% Intravascular (IVF) (plasma)
Fluid rule of thumb
2/3 of BW = water
2/3 of TBW = ICF
2/3 of ECF = ISF
* the intravascular portion of ECF is plasma not whole blood)
Blood volume (mL/kg) of dogs
90 mL/kg
Blood volume (mL/kg) of cats
65 mL/kg
Blood volume (mL/kg) of equines
70 mL/kg (TBs 100 mL/kg)
Blood volume (mL/kg) of Bovine/Ovine
60 mL/kg
Blood volume (mL/kg) of porcine
50 mL/kg
What are the “skeletons” of fluid compartments
K+ = ICF skeleton
Na+ = ECF skeleton
Protein (Albumin) = IVF skeleton
What helps the cell mebrane as ion barrier
Na+/K+ ATP-ase pump
Osmosis
Osmotic pressure = pressure req to prevent water movement
Osmolality = # of particles (osmoles) per kg of H2O
What are the effects of osmolality of solutions on RBCs
Isotonic ⇒ no change in RBC volume
Hypotonic ⇒ increase in RBC volume (hemolysis)
Hypertonic ⇒ decrease in RBC volume
What is oncotic pressure
Osmotic pressure exerted by proteins
aka colloid osmotic pressure
Albumin is most important/abundant protein
physiological plasma oncotic pressure is 23 mmHg
Albumin
Normal plasma values: 2.5-4 g/dL
Edema formation is likely < 1.5 g/dL
Hypoalbuminemia is common in severely ill pts (e.g. sepsis) & is a prognostic factor
Starling equation
Hydrostatic pressure drives fluids out of vascular compartment
Oncotic pressure drives fluids into vascular compartment
Fluid shift outward = k (Pc-Pi) - σ (πc-πi)
Pc, Pi: hydrostatic pressures
πc, πi: oncotic pressures
k, σ: constants
c: capillary, i: interstitial
Balanced electrolyte solutions
Only 1/3 stays intravascular (30 min later)
Replacement of blood loss (3 x volume lost)
Initial phase of shock tx
Maintenance solutions
Not generally appropriate for peri-operative use!
Less Na+
More K+
Daily volume demand: 40-60 mL/kg
Should be administered over 24 hours
Physiological saline
0.9% NaCl (308 mOsm/L)
Used for rapid ECF volume expansion if balance sloutionns are not available
Excessive use may dilute other EC electrolytes & cause hyperchloremic metabolic acidosis
Hypertonic saline
7.5% NaCl
Rapidly draw water from ICF to ECF
Enhance cardiac function
Fast onset/short duration
- 4/6 mL/kg over 3-5 min*
- 1-4 mL/kg only for cats*
Indications for use of hypertonic saline
Contraindications
Need for quick IV vilume expansion, severe shock (initial phase), head injury w/ elevated ICP
Uncontrolled hemorrhage, dehydration, cardiac dysrhythmias
Dextrose solutions
5% is isotonic ⇒ hypotonic after metabolism
Not generally appropriate for peri-operative use!
Colloids
Increase plasma oncotic pressure & vascular volume
Consider when:
Albumin is low (<1.5 or TP < 3.5)
or
expected to become low
What are some issues with colloids to watch for
Volume overloading
Allergic reaction (less likely w HES)
possible tendency to bleed