Page 78 - WSAVA2017
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An Urban Experience
D. McBride1
1Royal Veterinary College, Queen Mother Hospital for Animals, London, United Kingdom
Royal Veterinary College, Hawkshead Lane, North Mymms, United Kingdom
Intravenous fluid therapy can be used for a variety of reasons, including, treatment of shock, maintaining fluid balance in anorectic patients, rehydration, providing electrolytes and glucose, treating intoxications, and for renal support.
Approximately 60% of an adult animal’s body weight
is water. Of this 60% of water, two thirds of this fluid
is in the intracellular space and one third is in the extracellular space. Of this extracellular fluid, 3⁄4 of this
is in the interstitial space and 1⁄4 is in the intravascular space. Therefore, the approximate blood volume is
77 – 78 mL/kg in a dog and 62 – 66 mL/kg in cats. It
is interesting that cats have a lower total blood volume compared to dogs, which is one of the few reasons they are predisposed to fluid overload. Overall, there is net filtration of fluid from the intravascular to the interstitial space which is determined by Starling’s principle. Starling’s principle is based on the understanding
that transvascular fluid dynamics is dependent on the hydrostatic and oncotic pressures (determined by plasma protein concentration) of the intravascular and interstitial space, as well as capillary permeability, and is described by the equation:
Jv = Kfc[(Pc – Pi) – σ(πc – πi)]
Jv = transvascular fluid flux
Kfc = filtration coefficient (which is dependent on hydraulic conductance and surface area)
Pc = intravascular hydrostatic pressure Pi = interstitial hydrostatic pressure
σ = reflection coefficient (which is the fraction of total osmotic pressure exerted by a solute)
πc = plasma oncotic pressure πi = interstitial oncotic pressure Fluid Types
Hartmann’s, compound sodium lactate (CSL)
· Isotonic crystalloids (same tonicity as blood).
· Na 130 mmol/L, K 4 mmol/L, Cl 109 mmol/L, Ca 4 mmol/L, lactate 26 mmol/L
· Indications: most common type of fluid which can be used in most situations (shock and maintenance therapy). Because it includes lactate which is metabolised into bicarbonate, it is useful in treating metabolic acidosis.
· Contraindications: Do not give through the same IV line as blood products, as the calcium chelates with the sodium citrate in blood products.
· Although it contains potassium, it can still be used in patients with hyperkalaemia, as the concentration is minimal.
· Shock dose: Dogs 10 – 20 mL/kg IV; Cats 5 – 10 mL/kg delivered over 15 minutes IV. Can be repeated up to a total of 4 times.
0.9% NaCl
· Isotonic crystalloid (same tonicity as blood).
· Na 154 mmol/L, Cl 154 mmol/L
· Indications: Ideal in metabolic alkalosis (although this situation is rare)
· Shock dose: Dogs 10 – 20 mL/kg IV; Cats 5 – 10 mL/kg IV deliver over 15 minutes IV. Can be repeated up to a total of 4 times.
0.45% NaCl
· Hypotonic crystalloids (lower tonicity than blood). · Na 77 mmol/L, Cl 77 mmol/L
· Indications: Treatment of hypernatraemia
· Contraindications: Treatment of shock Hypertonic saline (7.5% NaCl)
· Higher tonicity than blood
· Na 1283 mmol/L, Cl 1283 mmol/L
· Due to the higher tonicity, free water will be absorbed from the interstitial and intracellular compartments, increasing the intravascular volume.
· Indications: Traumatic brain injury, cerebral oedema, large breed dogs, during cardiopulmonary resuscitation
· Contraindications: Hypernatraemia; hyponatraemia; dehydration
· Shock dose: 2 – 4 mL/kg over 10 - 15 minutes IV (Do not bolus rapidly)
· Always administer isotonic crystalloids during or after as a bolus or continuous rate infusion.

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