Fluid Therapy Flashcards
What is the 60-40-20 rule?
body fluid composition
60 % of body weight is water:
40% bw is intracellular fluid
20% of bw is extracellular fluid
ICF is a solution containing what? homogeneity? pH?
– Primarily a solution of potassium, organic anions (phosphate, sulfate), proteins
– ICF is not homogeneous in the body
– pH is close to 7.0
ECF contains what molecules in solution primarily
NaCl and NaHCO3
– ECF is subdivided into three subcompartments:
- Interstitial Fluid (ISF) surrounds the cells, but does not
circulate. It comprises about 3/4 of the ECF. - Plasma circulates as the extracellular component of blood. It makes up about 1/4 of the ECF.
- Transcellular fluid is a set of fluids that are outside of the normal compartments (CSF, Digestive Juices, Mucus, etc.)
pH of extracellular fluid
– pH is 7.40-7.45
Dog plasma and blood volume based on BW
– Plasma volume- 49 mL/kg
– Blood volume- 80 mL/kg (8% bw)
Cat blood volume based on BW
– Blood volume- 50-70 mL/kg (5-7%)
Horse blood volume based on BW
– Blood volume- 100 mL/kg (10%)
Ruminant blood volume based on BW
– Blood volume- 60 mL/kg (6%)
Pigs blood volume based on BW
– Blood volume- 65-75 mL/kg (6.5-7.5%)
what fraction of blood volume is plasma vs PCV?
Plasma: 55-65%
PCV: 35-45%
blood volume for 20Kg dog:
– 20 kg x 80 mL/kg = 1600 mL
blood volume for 4 Kg cat
– 4 kg x 65 mL/kg = 260 mL
blood volume for 500 kg horse
– 500 kg x 100 mL/kg = 50 L
blood volume for 600 kg cow
– 600 kg x 60 mL/kg = 36 L
Osmolality mathematical definition, and how calculate it
Ratio of Solute/Volume
Osmolality = 2*Na+ + Glu/18 + BUN/2.8 (mg/dL)
Osmolality= 2 x Na+ + Glu + BUN (mOsm/L)
normal osmolality value in the body
- Normal value = 290 +/- 10 mOsm/liter
how do the osmolalities of ICF, ECF, and Plasma compare?
- Osm of ICF=ECF=Plasma
- Fluid compartments are in osmotic equilibrium
- Water moves freely
what is starling’s equation and what does it tell us?
J = k (Pc - Pi) – σ (Πc – Πi) – Qlymph
=> flow rate is a balance between hydrostatic pressures (P) and oncotic pressures (pi)
Pc is higher for arteries than veins, so generally we see more filtration on the arterial end, and reabsorption on the venule end
>lymph term is required because on balance fluid is being pushed out of circulation and the body must handle that
broad categories of crystalloids
maintenance and replacement solutions
what are maintenance solutions? what are some examples and their purpose?
– Plasmalyte-56, Normosol-M
– NaCl 0.45% (+ KCl)
– Replacement + KCl
– To maintain volume and electrolyte composition
– A.) Sensible losses
* urine production (1-2 mL/kg/h)
– B.) Insensible losses
* Breathing, faeces, sweating (1 mL/kg/h)
– A + B = 2-4 mL/kg/h
what are sensible and insensible losses? how are these relevant for calculating a maintenance rate?
– To maintain volume and electrolyte composition
– A.) Sensible losses
* urine production (1-2 mL/kg/h)
– B.) Insensible losses
* Breathing, faeces, sweating (1 mL/kg/h)
– A + B = 2-4 mL/kg/h
what are replacement solutions? what are examples and what is their purpose? what is a normal replacement rate?
– Lactated Ringer Solution, Plasmalyte-A, Plasmalyte 148, Normosol-R
– NaCl 0.9% (± KCl)
– To replace volume without altering the electrolyte
composition of plasma
– Maintenance requirements + Blood/Fluid loss
– 5-10 mL/kg/h
properties of replacement solutions: what types do we have generally?
- Isotonic, polyionic (LRS, N-R, PLA, NaCl 0.9%)
do replacement solutions result in oncotic pressure? how much remains in the vascular space after 1-2h and what does this mean practically?
- No oncotic pressure
- 20-30% remain in vascular space after 1-2 h
– Rule: To replace the amount of blood loss with 3 times the amount of crystalloids
large volumes of replacement solutions given at once can cause what?
- Large volumes can cause excessive extravasation
Blood loss of less than ____% blood volume can be effectively treated with crystalloids
Why can’t we treat greater losses with crystalloids?
10%
* Higher losses would require too much time and fluid
If a 20kg dog has 10% blood loss, what volume of crystalloids should we give? how long will this take at the normal replacement rate
20 kg dog
– 10% blood loss
* 8% blood volume: 1.6 L
* 10% blood loss: 160 mL
- Effective replacement:
– 3 x blood loss with crystalloids
– 480 mL of crystalloids
Replacement rate
– 5-10 mL/kg/h
– 10 mL/kg/h- will require 2 1⁄2 hours
– 60 mL/kg/h (shock rate)- will require 25 min
* Safety
* Effect on PCV, TP
what is hypertonic saline? what are its properties? what does it do and how should we administer it?
– 5 – 7.5% solutions
– Volume expansion lasts less than 60 min
– Small volume- 2-6 mL/kg
* 20 kg: 40-120 mL
* 1-2 mL/kg/min- Volume can be injected in 1-6 min
– Monitor electrolytes
what is the purpose of lactate 28 in ringer’s lactate solution? what substances filfil this role in other replacement solutions?
body uses it as a substrate to create bicarbonate
>lactate is a bicarbonate precursor (as are acetate and gluconate that are used in plasmalte-A and normosol-R)
what is an isotonic solution?
resembles plasma - has a similar concentration of electrolytes
plasma osmolality = 290, isotonic ~275-310
if a negative ion is increased in the blood, how do we deal with this?
decrease concentration of one of the other negatives
we can equate high chloride with what state
acidosis
low chloride = alkaline
if we give a maintenance solution in excess, what effect will this have on ion concentrations in the body?
hypo Na+
hyper K+
hypo Cl-
=>only if given in rates that are significant
can a maintenance solution be used as a replacement solution or vice versa?
a maintenance solution CANNOT be used as a replacement solution
BUT
a replacement solution CAN be used as a maintenance solution
our normal losses of electrolytes throughout the day resemble what?
concentration of ions in a maintenance solution
ie
40 Na+
13 K+
40 Cl-
