Fluid therapy Flashcards
Describe the distribution of fluids in the body
60% body weight is water
5% intravascular
55% extravascular- 40% intracellular, 15% extracellular
What is meant by starlings forces?
Passive exchange of water between capillaries and interstitial fluid, determined by hydrostatic and oncotic pressure
What are the mechanisms of fluid movement between body compartments?
Osmosis
Starlings forces
What are causes of fluid in balance, and examples of each?
Change in volume- dehydration, hypovolaemia
Changes in content- electrolyte imbalance, changed blood glucose, changed blood protein
Changes in distribution- third spacing (too much fluid moves from intravascular to interstitial space)
Define hypovolaemia
State of decreased intravascular volume
Define hypervolemia
Fluid overload, too much fluid in the blood
Define normovolaemia
Normal blood volume
Define hypoperfusion
Condition brought on by sudden and global deficit in tissue perfusion causing inadequate oxygen and nutrient delivery to tissues
Define shock
Cellular or tissue hypoxia, commonly due to hypoperfusion
Define dehydration
Excessive loss of water from extravascular compartment (slowly so has time to redistribute meaning equal loss across all body compartments)
Define intravenous
Within veins
Define colloid osmotic pressure
Pressure exerted by large molecules to hold water in vascular space
Define oncotic pressure
Pressure exerted by proteins in capillaries causing fluid to be pulled back into them
Define oncotic pressure
Pressure exerted by proteins in capillaries causing fluid to be pulled back into them
Describe the physiological consequences of hypovolaemia
Blood loss Reduced pre-load Reduced stroke volume Reduced CO Decreased BP Vasoconstriction and tachycardia to increase peripheral resistance and perfusion to vital organs Blood pressure to vital organs maintained Changes to MM and CRT
What are normal values expected to be seen in normovolaemia in dogs? (HR, MM, CRT, pulse quality, systolic BP, mentation)
HR- 60-120 MM- pink CRT- less than 2 Pulse quality- normal Systolic BP- over 90 Mentation- normal
What are normal values expected to be seen in mild/compensatory shock in dogs? (HR, MM, CRT, pulse quality, systolic BP, mentation)
HR- 130-150 MM- normal to pinker CRT- less than 1 Pulse quality- bounding Systolic BP- over 90 Mentation- normal
What are normal values expected to be seen in moderate shock in dogs? (HR, MM, CRT, pulse quality, systolic BP, mentation)
HR- 150-170 MM- pale pink CRT- 2 Pulse quality- weak Systolic BP- over 90 Mentation- normal to obtunded
What are normal values expected to be seen in severe/decompensatory shock in dogs? (HR, MM, CRT, pulse quality, systolic BP, mentation)
HR- 170-220 MM- pale pink to white CRT- more than 2 Pulse quality- very weak Systolic BP- less than 90 Mentation- obtunded
What is meant by compensatory and decompensatory shock
Compensatory- perfusion maintained as CO and BP maintained
Decompensatory- unable to maintain perfusion to vital tissues
Define obtunded
Slowed responses and lack of interest in environment
Why in decompensatory shock does the heart rate not exceed 220?
Diastole would be too short to properly fill with blood which would further decrease CO
What are the aims of fluid therapy for treating hypovolaemia?
Need to stabilise as life threatening
Rapid fluid resuscitation using large fluid boluses
What are the 3 body compartments?
Intravascular
Intercellular
Interstitial
What clinicopathological parameters indicate dehydration?
Increased PCV- haemoconcentration
Increased urea, creatinine- pre-renal azotaemia (build up of nitrogenous products)
Increased SG of urine- concentrated urine
What physical parameters indicate less than 5% dehydration?
Not clinically detectable but suspected from clinical history
What physical parameters indicate 5-6% dehydration?
Tacky MM
Mild skin tent
What physical parameters indicate 6-8% dehydration?
Dry MM
Mild increase in CRT
Mild to moderate skin tent
Some signs of sunken eyes
What physical parameters indicate 10-12% dehydration?
Dry MM CRT 2-3 seconds Signs of shock Prolonged skin tent Sunken eyes
What physical parameters indicate more than 15% dehydration?
Incompatible with life
What are the aims of fluid therapy for treating dehydration?
Patient is stable so slowly correct extravascular fluid losses, if done to fast increases arterial pressure, triggering baroreceptors and increased diuretic hormone production and urine output which wont help correct dehydration. If patient is renally compromised may become hypervolaemic
Define crystalloid fluids
Solutions containing solutes dissolved in water
Define colloid fluids
Solutions containing large molecules
What are some complications associated with using fluid therapy?
Are drugs
Consider use when patient has cardiac disease, heart failure, renal disease, respiratory disease etc. as more likely to become hypervolaemic
Volume overload causing pulmonary oedema, cavity effusions, chemosis (eye irritation, outer surface of eye swollen) etc.
What are maintainance fluid requirements?
2ml/kg/hour or 50ml/kg/day
What is the calculation for dehydration deficit?
body weight(kg) x % dehydrated(decimal) then convert from kg to ml (1kg=1000ml)
or
(actual PCV-normal PCV) x bodyweight(kg) x 10
What is the calculation for ongoing losses?
number of times vomited/diarrhoea x 4ml x bodyweight(kg)
How do you calculate total fluid requirement over 24 hours?
Total fluid requirement in 24 hours(ml) = dehydration deficit + maintenance volume + ongoing losses
Total fluid requirement / 24 = ml/hour
ml/hour / 60 = ml/minute
ml/minute x giving set factor = drops/minute
60 / drops/minute = seconds between each drop
List routes of administration of fluid therapy and explain how they work
Per-os- through the mouth by drinking or feeding tube, water absorbed by intestinal tract
Subcutaneous- injected under skin, absorbed into capillaries
Intravenous- IV catheter delivers fluid to veins
Intraosseous- injected into bones medullary cavity, absorbed into vessels
Central venous access- intravenous catheter delivers to non-peripheral vein
What are advantages and disadvantages on per-os fluid administration?
Advantages- non-invasive, least stressful, natural so body controls uptake and electrolytes
Disadvantages- slow uptake, cant if vomiting, body needs to be able to balance fluids, must be willing to drink, harder to monitor
What are advantages and disadvantages on subcutaneous fluid administration?
Advantages- body distributes as needed, good when IV access hard
Disadvantages- more invasive, cant give large boluses, slow absorption
What are advantages and disadvantages on intravenous fluid administration?
Advantages- can give large boluses, can give drugs or electrolytes alongside
Disadvantages- need IV access, more invasive, infection risk, body needs ability to redistribute
What are advantages and disadvantages on intraosseous fluid administration?
Advantages- quickly absorbed, good when cant gain IV access
Disadvantages- painful, invasive, body needs to redistribute, risk of infection
What are advantages and disadvantages on central venous fluid administration?
Advantages- rapid absorption, can give large boluses, easier location to place IV when critical
Disadvantages- invasive, haemorrhage, body needs ability to redistribute
How do crystalloid fluids work?
Water and solutes move freely across membranes allowing distribution within hour of admin
Define isotonic crystalloids, hypotonic crystalloids and hypertonic crystalloids
Isotonic- same tonicity as plasma
Hypotonic- lower tonicity than plasma
Hypertonic- higher tonicity than plasma
What are examples of isotonic crystalloids?
0.9% NaCl
Hartman’s
What is the general electrolyte concentration of isotonic crystalloids?
Mimic intravascular electrolytes, high sodium and low potassium
