Equine fluid therapy Flashcards
Routes of fluid administration in horses:
Intravenous fluids
Intragastric fluids
Rectal fluids
Can be divided into replacement fluids and maintenance fluids.
Replacement fluids are meant to
replace deficits, for example in case of hypovolemia and dehydration.
Have a similar composition to extracellular fluids (higher Na and Cl, lower K, Ca and Mg).
E.g. 0,9% NaCl (does not contain K)
Ringer’s lactate
Normosol-R
Plasma-lyte A
(Maintenance fluids have low Na and Cl; higher K, Mg, Ca.)
Maintenance fluids are meant to
maintain homeostasis by covering the body’s maintenance needs + expected losses.
Are more similar to the body’s general electrolyte composition taking into account both, extra- and intracellular spaces (low Na and Cl; higher K, Mg, Ca).
Hypotonic, unless dextrose is added.
Normosol-M
Plasma-lyte 56
Half strength basic fluids (e.g. 0,45% NaCl) with added K and Ca.
(Replacement fluids have higher Na and Cl, lower K, Ca and Mg.)
Replacement fluids vs Maintenance fluids
Replacement fluids have a similar composition to extracellular fluids, higher Na and Cl, lower K, Ca and Mg.
Maintenance fluids have a composition that takes both extra- and intracellular fluid spaces into account, low Na and Cl; higher K, Mg, Ca.
Hypertonic saline of what percentage is used at what dose?
What type of patient is this good for?
Hypertonic saline 7,2% at 2 – 4 ml/kg bolus.
Good for resuscitation of the hypovolemic patient.
Short effect (~60min) and always should be followed by at least 5 times the same volume of isotonic crystalloids.
Increases osmotic pressure in order to decrease the total volume of isotonic crystalloids needed.
How do you choose your crystalloid?
Choice depends on patient of course, but also check the blood electrolytes if possible (twice a day after beginning fluid therapy in horses).
Apart from few pathologies (e.g. foal with ruptured bladder), 0,9% saline should be a last choice. Use Ringer’s where possible.
Fluid therapy maintenance rate in horses.
Maintenance rate in adult horses 65 ml/kg/24h. (info in literature may vary from this)
For moderately dehydrated/hypovolemic patient - 20 to 40 mL/kg bolus over 1 to 2 hours.
Severe shock dose 80 ml/kg in the first hour.
Consider ongoing losses – reflux, diarrhea, third space losses.
For moderately dehydrated/hypovolemic patient - what bolus dosage do you give?
What about if its in shock?
For moderately dehydrated/hypovolemic patient give 20 to 40 mL/kg bolus over 1 to 2 hours.
Severe shock dose 80 ml/kg in the first hour.
Maintenance rate in adult horses 65 ml/kg/24h.
How is fluid requirement calculated in horses?
Fluid requirement = fluid deficit + estimated losses + maintenance needs
Fluid deficit = body weight + percent dehydrated
Parameters used for estimation of dehydration in horses. (5)
heart rate
CRT
PCV/TP (do twice a day)
creatinine (prerenal azotemia)
lactate (anaerobic celluar respiration marker for decreased perfusion)
NB in endotoxemia horses can have super fast CRT due to toxin induced vasodilation.
How do you know the IVFT fluids are helping the horse? (7)
Urination
Improved capillary refill time (may not become normal though)
Somewhat brighter demeanour
Decrease in heart rate (may not become normal)
Drop in PCV is normal with IVFT
Warmer extremities (really good indicator with foals)
Lab result changes: decreased plasma lactate and creatinine.
Colloid osmotic pressure = oncotic pressure = the amount of osmotic pressure created by colloids in a solution.
What determines the oncotic pressure?
What are colloids indictaed for?
The number of molecules determines the oncotic pressure.
(Natural colloids vs. synthetic)
Indicated for severe protein losses, severe hypovolemia etc.
Best Natural colloid?
Main side effect?
Dose?
Plasma is the best (whole blood and concentrated albumin are also natural colloids). Useful in case of protein losing enteropathies etc. Increase in blood pressure and in cardiac output in some studies.
Main drawback is the risk of anaphylactic reaction.
Give 5-10 ml/kg so e.g. 500 kg horse 2,5-5L.
Use blood giving set with a plasma filter.
Give 3 examples of synthetic colloids.
Problems with these?
hetastarch, pentastarch, oxyglobin
Hetastarch has been shown to worsen kidney injury and prolong coagulation times.
Changes in coagulation with syntetic colloids
Potential accumulation in tissues too.
These are no longer really recommended (already not recommended in case of sepsis, burns, or critical illness). Think twice before using.
Ongoing discussion and clinical studies if they should be banned completely from human medicine.
How colloids were thought to work:
improve osmotic pressure in the vascular space = movement of fluid from the interstitial space to the blood vessel.
BUT,
modification of the Starling equation hypothesis has come along.
Basically, colloids won’t work in a healthy patient, only in really sick ones.
Describe the modification of the Starling equation which disputes the action of colloids.
Blood vessel endothelial glycocalyx layer acts as a zone that modifies the interaction of the plasma volume and interstitial space. It is proposed that it limits the reuptake of fluid from the interstitium back into the capillaries when healthy.
So we can’t just pull back fluid from the tissues by increasing the osmotic pressure in the intravascular space.
NB Inflammation and other disease states can modify the interstitial space and create negative pressure that helps to pull fluid into the interstitial space and creates edemas.
Leaky vessels due to disease process also allow colloids to be accumulated into the tissues. Lower molecular weight synthetic colloids are likely to leak even through normal vessels.
Basically, colloids won’t work in a healthy patient, only in really sick ones.
Intragastric fluid therapy is administered via
nasogastric tube which can either be a very thin tube palced by endoscopy or blindly, and dripped in by reused IV bag (can use tapwater with added electrolytes since its going in the stomach), left image.
Or, use a bigger tube, same one used for reflux can be used to administer large volumes of water into the stomach.
Isotonic electrolyte solution is preferred (Pansalt mixed with water,add 45 cc of pansalt/6L H2O).
Intragastric fluid therapy is not sufficient for?
What is it good for?
severe hypovolemic shock etc. that type of thing.
But it is good for replacement of dehydration, general maintenance and treating specific GI diseases.
Isotonic electrolyte solution is preferred (Pansalt mixed with water).
add 45 cc of pansalt/6L H2O
Intragastric fluid therapy maintenance fluid rate?
65 ml/kg/day
As boluses every 2– 4h ( 4 – 6L at one time for a 500kg horse).
As CRI, 1– 2L per hour for 500kg horse.
add 45 cc of pansalt/6L H2O
Describe rectal fluid therapy.
Has gained more interest recently. Well tolerated and cheap.
Technique: Well lubricated esophageal tube, small (24Fr) soft enema tube, long foley catheter or red rubber catheter have been mentioned in the literature. Tube is passed 10- 15 cm into rectum.
Usual maintenance rate, 65ml/kg/day.
Tube tends to come out each time the horse passes feces but this is a cheaper fluid replacement option.
Body electrolyte concentrations in horses in mmol/L.
Magnesium, ionized 0,75 – 0,95 mmol/L (intracellular)
Calcium, ionized 1,4 – 1,6 mmol/L (intracellular)
Potassium 3,0 – 5,9 mmol/L (intracellular)
Chloride 92 – 115 mmol/L (intracellular)
Sodium 128 – 150 mmol/L (extracellular)
Why does hypokalemia occur in horses? (4)
Renal potassium loss due to fluid therapy or glucocorticoid release in the body.
Diarrhea
Sweat loss
Why do we care about hypokalemia in horses? (3)
Related to ileus (not proven yet but strong belief)
Muscle weakness
Lethargy
Tx of hypokalemia in horses.
Supplement KCl IV or PO.
- IV dose up to 0,5 mmol/kg/h IV
- PO 0,1 – 0,2 g/kg 2 – 4x/day
