Fluid Therapy Dr. Ambrisko

Question 1

What is total body water

Answer 1

≈ 60% of BW in average adult

≈ 80% in newborn

Less in obese animals

Question 2

What is the distribution of fluids?

Answer 2

Of the 60% TBW:

40% ICF (intracellular)

15% Interstitial (ISF)

5% Intravascular (IVF) (plasma)

Question 3

Fluid rule of thumb

Answer 3

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)

Question 4

Blood volume (mL/kg) of dogs

Answer 4

90 mL/kg

Question 5

Blood volume (mL/kg) of cats

Answer 5

65 mL/kg

Question 6

Blood volume (mL/kg) of equines

Answer 6

70 mL/kg (TBs 100 mL/kg)

Question 7

Blood volume (mL/kg) of Bovine/Ovine

Answer 7

60 mL/kg

Question 8

Blood volume (mL/kg) of porcine

Answer 8

50 mL/kg

Question 9

What are the “skeletons” of fluid compartments

Answer 9

K⁺ = ICF skeleton

Na⁺ = ECF skeleton

Protein (Albumin) = IVF skeleton

Question 10

What helps the cell mebrane as ion barrier

Answer 10

Na⁺/K⁺ ATP-ase pump

Question 11

Osmosis

Answer 11

Osmotic pressure = pressure req to prevent water movement

Osmolality = # of particles (osmoles) per kg of H₂O

Question 12

What are the effects of osmolality of solutions on RBCs

Answer 12

Isotonic ⇒ no change in RBC volume

Hypotonic ⇒ increase in RBC volume (hemolysis)

Hypertonic ⇒ decrease in RBC volume

Question 14

What is oncotic pressure

Answer 14

Osmotic pressure exerted by proteins

aka colloid osmotic pressure

Albumin is most important/abundant protein

physiological plasma oncotic pressure is 23 mmHg

Question 15

Albumin

Answer 15

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

Question 16

Starling equation

Answer 16

Hydrostatic pressure drives fluids out of vascular compartment

Oncotic pressure drives fluids into vascular compartment

Fluid shift outward = k (P_c-P_i) - σ (π_c-π_i)
P_c, P_i: hydrostatic pressures
π_c, π_i: oncotic pressures
k, σ: constants
c: capillary, i: interstitial

Question 17

Balanced electrolyte solutions

Answer 17

Only 1/3 stays intravascular (30 min later)

Replacement of blood loss (3 x volume lost)

Initial phase of shock tx

Question 18

Maintenance solutions

Answer 18

Not generally appropriate for peri-operative use!

Less Na⁺

More K⁺

Daily volume demand: 40-60 mL/kg

Should be administered over 24 hours

Question 19

Physiological saline

Answer 19

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

Question 20

Hypertonic saline

Answer 20

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*

Question 21

Indications for use of hypertonic saline

Contraindications

Answer 21

Need for quick IV vilume expansion, severe shock (initial phase), head injury w/ elevated ICP

Uncontrolled hemorrhage, dehydration, cardiac dysrhythmias

Question 22

Dextrose solutions

Answer 22

5% is isotonic ⇒ hypotonic after metabolism

Not generally appropriate for peri-operative use!

Question 23

Colloids

Answer 23

Increase plasma oncotic pressure & vascular volume

Consider when:

Albumin is low (<1.5 or TP < 3.5)

or

expected to become low

Question 24

What are some issues with colloids to watch for

Answer 24

Volume overloading

Allergic reaction (less likely w HES)

possible tendency to bleed

Question 25

Types of colloids

Answer 25

Hydroxy-ethyl starch (HES)

Most common: Hetastarch, Vestarch

May alter hemostasis @ high doses in already sick animals (vWD)

Question 26

Concerns with HES

Answer 26

? renal failur in septic pts (human)

Use crystalloids as first line tx of shock

Question 27

Routes of administration ofr crystalloid solutions

Answer 27

IV

For ansthetized pt it happens almost invariably IV

IO

SC

IP

Question 28

Forms of water loss

Answer 28

physiological

pathological

anesthesia

Question 29

Fluid therapy plan during anesthesia

Answer 29

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