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
Types of colloids
Hydroxy-ethyl starch (HES)
Most common: Hetastarch, Vestarch
May alter hemostasis @ high doses in already sick animals (vWD)
Concerns with HES
? renal failur in septic pts (human)
Use crystalloids as first line tx of shock
Routes of administration ofr crystalloid solutions
IV
For ansthetized pt it happens almost invariably IV
IO
SC
IP
Forms of water loss
physiological
pathological
anesthesia
Fluid therapy plan during anesthesia
10 mL/kg/h of crystalloid for maintenance
Give 10mL/kg fluid boluses (within 15 min) in case of hypotension
Replace blood loss immediately with:
Crystalloids (3 x volume of blood lost) or Colloids (exact volume)
If >20% of total blood volume is lost, consider whole blood transfusion
FFP for tx of coagulopathy
