Fluid Therapy and Nutrition in Critical Care Flashcards
What percentage weight of the body is water in adults, neonates and paediatric patients?
Adult - 60%
Neonate - 80%
Paediatric - 75%
What is the 60% water in adults made up of?
40% weight is intracellular fluid , and 20% is extracellular fluid
What is extracellular fluid
Plasma in the blood (intravascular volume)
and fluid that bathes the cells in the rest of the body (interstitial fluid)
What is transcellular fluid?
CSF and synovial fluid
What kind of fluid loss does diarrhoea tend to cause?
Extracellular fluid loss
What is meant by the tonicity of a solution?
The concentration of solutes in it e.g. sodium, electrolytes
What is a hypotonic solution?
A solution which has a lower concentration of sodium than the plasma
What is a hypertonic solution?
A solution which has a higher sodium concentration that the plasma
What is an isotonic solution?
Sodium concentrtion similar to the plasma e.g. Hartmanns
What effect does sodium concentrations of solutions have on water?
The water will cross the semi-permeable membrane to try and even out the concentrations. The electrolytes/solutes cannot pass this membrane.
What is hypotonic dehydration?
When too little solute in the body.
What is hypertonic dehydration?
Losing too much water whilst keeping too much sodium in the fluid outside your cells.
What is isotonic dehydration?
When you lose equal amounts of solutes and water
How can fluids be administered intra-osseously?
Via a cannula into the medullary cavity of a long lone e.g. femur.
How long does SC fluid take to fully absorb?
6-8 hours
What type of fluids cannot be administered sc?
Those containing glucose
What are crystalloids?
Solution of cystalline solids that are dissolved in water e.g. sodium or dextrose based.
What fluids are good for correcting extracellular fluid losses?
Fluids with concentrations of sodium similar to the ECF sodium concentration stay in the ECF compartment
How much fluid is required to replace blood loss? Why?
Approx 3 times the amount lost. Because only 1/4-1/3rd of the replaced volume remains in the intravascular space after 1-2 hours - the rest is redistributed to the interstitial spaces.
Define maintenance requirement of fluids
The amount of water and electrolytes required to replace those lost through normal physiological processes i.e. respiration, perspiration, excretion.
What is the maintenance fluid calculation for cats and also dogs?
Cats:
80 x BW^0.75 over 24 hrs
(2-3mls/kg/hr)
Dogs:
132 x BW^0.75 over 24hrs
(2-6mls/kg/hr)
What is the make up of maintenance fluid solutions compared to ECF?
Lower sodium and chloride concentrations and higher potassium
Why cant hypotonic solutions be used for maintenance?
They can cause red blood cells to lyse if given too fast.
What is the level of potassium in supplemented fluid that is a minimum and then needs supplemented?
20mmol/L
What is the maximum rate for potassium infusion?
0.5mEq/kg/hr
How does hypertonic saline work? What must be done after?
Given during shock as increases the BP by:
- drawing water from the interstitial space.
Effects of this are transient (last 30-120min). The use of hypertonic saline must be followed by administration of isotonic crystalloids to replace borrowed water and provide a long term increase in circulating volume.
What is the suggested dose of hypertonic saline?
4mls/kg over 10 minutes
How do colloids work?
They are fluids which contain large molecules that cannot pass out of the vasculature, they increase the colloid osmotic pressure of the plasma. In addition to the fluid they add, they also ‘pull’ water from the interstitial space into the intravascular space.
What must be done after colloid administration and why?
Administer crystalloids concurrently or just after to pay back the fluid drawn from the interstitial spaceto avoid dehydrating the interstitium.
What is the general rule for the dose of colloids that can be given?
Why?
No more than 25% (usually 20mls/kg) of the circulating volume of an animal should be administered as a colloid at any one time.
Otherwise the haemodilution will dilute out clotting factors.
Name some artificial and natural colloids?
Artificial - starches, gelofusin, dextrans
Natural - plasma, albumin preparations, whole blood
What are the disadvantages of colloids?
- volume overload
- anaphylactic reactions
- clotting problems
How long do the various plasma volume expanders work?
Gelatin based (gelofusin) lasts for max 6-8hrs
Dextran based lasts approx 12 hrs
Starch based 24-36hrs
How can we visually assess dehydration?
- moistness of mm
- skin turgor (tent)
- sunkness of eyes
How can we diagnostically assess dehydration?
- PCV
- TP
-UREA
-USG
NA+
What are the clinical signs of less than 5% dehydration?
NOne
What are the clinical signs of 5% dehydration?
- semi-dry mm
- skin turgor normal
- eyes moist
What are the clinical signs of 6-7% dehydration?
- dry mm
- eyes moist
- mild loss of skin turgor
What are the clinical signs of 8-10% dehydration?
Dry mm
Eyes retracted
Considerable loss of skin turgor
signs of hypoperfusion
What are the clinical signs of 10% dehydration?
Very dry mm
Severe eyeball retraction
Eyes dull
Complete loss of skin turgor
Altered consciousness
Greater signs of hypoperfusion
What are the clinical signs of 12% and 12-15% dehydration?
Same as 10%, but 12 moribund and 15 dying
What is the difference between dehydration and hypoperfusion?
Dehydration is when water is lost from all fluid compartments and hypoperfusion is due to inadequate circulating volume. Often seen alongside each other but not the same thing.
How do we calculate the fluid deficit in an animal?
Pecentage dehydration (as clinically observed) x BW
What is the density of water?
1g/ml
If you dont want to weight vomit or diarrhoea, what value can we assume needs to be replaced after each episode in a dog?
50ml per vomit and 100ml per diarrhoea
What fluids would you select for a dehydrated patient and why?
Crystalloids as they will cause water to distribute freelly across all compartments to restore fluid deficits
If you wanted to replace a fluid deficit in a dehydrated patient quickly , what fluid woudl you choose and why?
An extracellular volume replacer such as Hartmanns. Because it has a similar sodium concentration to plasma than a maintenance crystalloid and is therefore safer to infuse at a faster rate
How do we calculate the number of drops per minute if we know the fluid therapy rate (FTR) and the drops per ml (DPMl) of the giving set ?
First calculate the drops per hour so FTR X DPMl = drops per hour.
Divide drops per hour by 60 to get drops per minute.
What is the AAHA recommendations for fluid therapy under GA?
Dogs 5mls/kg/hr
Cats 3mls/kg/hr
every hour reduce by 25% until maintenance reached
What are the values of systolic, mean and diastolic BP if hypotension present?
Systolic <80-90mmHg
Mean <60-70mmHg
Diastolic <40mmHg