Fluid therapy Flashcards
What is the normal fluid intake for an animal?
2ml/kg/hr
What is sensible loss? How much is lost?
Water lost via the kidneys
1ml/kg/hr
What is insensible loss?
Water lost via evaporation of skin, exhalation from lungs and faeces
Do receptors respond directly to electrolyte balance?
No
Respond to changes in osmolarity, plasma volume and blood pressure
What homeostatic mechanisms does dehydration cause that lead to increased fluid intake?
Decreased saliva –> dry mouth and pharynx
Increased blood osmolarity stimulates osmoreceptors in hypothalamus
Decreased blood volume an and pressure causes increased renin production from juxtaglomerular cells and increased ANG II
All leads to stimulating thirst centre in hypothalamus
Dehydration leads to a drop in blood volume and pressure. What does this stimulate?
Baroreceptor reflex and RAAS
Baroreceptors cause increased sympathetic activity via medulla oblongata
Increased renin released from JG cells
What does Ang II act on? What does it cause?
Arterioles - vasoconstriction
CV control centre in medulla - increased CV response
Hypothalamus -increased thirst and ADH
Adrenal cortex and proximal tubule - aldosterone and sodium reabsorption
How are fluids given?
Enteral route Parenteral route (IV, IO, IP, SC)
When are fluids given orally?
If GI tract is functional
For mild moderate disturbances
Why are fluids not given orally for severe dehydration?
Severe drop in blood pressure causes vasoconstriction of the GI tract
What type of Na/Glucose transport is used for oral fluid therapy? What ratio should they be in?
Active sodium glucose co transport
Give equimolar sodium and glucose
What are the 4 generations of oral fluids?
1st - sodium and equimolar glucose
2nd - adds alkalising agent to prevent metabolic acidosis
3rd - high glucose for additional nutrition
4th generation - contains glutamine - promotes villi repair and regeneration
What are the 2 types of parenteral fluids?
Crystalloids
Colloids
What are crystalloid solutions?
Salt solutions that move freely across capillary walls
What are colloid solutions?
Non-crstalline solutions
Large molecules diluted in crystalloids
Are capillary endothelium permeable to crystalloids and colloids?
Crystalloids yes
Colloids -no as molecules too large
What percent sodium chloride can crystalloids be?
Hypotonic 0.9% - similar to plasma but chloride rich and unbalanced
Isotonic - mimic plasma
Hypertonic - 7.2% NaCl
Crystalloids can be buffered or balanced. What do these mean?
Buffered - contain HCO3- or molecules that are metabolised in liver to produce HCO3-
Balanced - contain electrolytes in addition to Na/Cl (K, Ca, Mg) to make similar to plasma
Crystalloids can also be isotonic, hypotonic and hypertonic. Describe hypotonic crystalloids
Lower concentration of electrolytes than plasma
High water conc
Describe hypertonic crystalloids
Plasma expanders
Cause water to move from interstitial and intracellular sites into blood vessels
Why may it not be appropriate to give high Na concentrated solutions over a long period of time?
Sodium accumulation
Must balance - cannot be solution too hypotonic (water into vessels)
Describe how tonicity of fluids affect fluid movement in and out of vessels
Isotonic - fluid distributed into ECF
Hypotonic - fluid moves out of vessel into cells
Hypertonic - fluid drawn into vessels
What are colloids
Water based replacement solutions
Molecules too large to pass across a capillary membrane
What are the types of colloids?
Natural = blood, plasma, albumin Synthetic = starches, gelatins, dextrans
When might natural colloids be given?
If animal needs RBCs, clotting factors or albumin
How do colloids cause plasma expansion?
Large molecules can’t pass out of blood endothelium
Increase colloidal osmotic pressure and pull water in from interstitial space
What are the adverse effects of colloids?
Anaphylactic reactions
Coagulopathies
Oedema (also risk with crystalloids)
