44. Critical Care and Fluid Therapy

Question 1

ECFV in adult horses, newborn foals and foals 24 weeks old

Answer 1

Adult horse: 0.214 to 0.253 L/kg Newborn foal: 0.38 to 0.40 L/kg 24 week old: 0.29 L/kg

Question 2

Plasma volume in adult horses and foals

Answer 2

Adult Horses: 0.05 L/kg Foal (<2d): 0.09 L/kg

Question 3

The Starling hypothesis

Answer 3

Net capillary filtration = K_f ( [P_cap - P_if] - σ[π_p - π_if] )

K_f is the capillary filtration coefficient

π_p is the colloid osmotic pressure (COP) within the capillary

π_if is the COP within the interstitium

P_cap is the hydrostatic pressure within the capillary

P_if is the hydrostatic pressure within the interstitium

σ is the capillary reflection coefficient for proteins

Question 4

Normal Adult Equine Colloid Osmotic Pressure

Answer 4

20mmHg

Question 5

The tonicity (or effective osmolality) of the ECFV calculation

Answer 5

Question 6

Primary Determinants of ECFV tonicity

Answer 6

Sodium and Chloride

Question 7

Primary determinants of ICFV tonicity

Answer 7

Potassium and related anions

Question 8

Rate of fluid therapy for replacement.

‘Fluid Challenge Principle’

Answer 8

30 to 60-minute bolus of 10 to 20 mL/kg Isotonic Fluid

Question 9

Rate of Hypertonic Saline administration

Answer 9

4 mL/kg IV once

Question 10

Hetastarch administration rate and daily max

Answer 10

3 to 5 mL/kg

Up to 10 mL/kg may be administered per day

Question 11

Adult Horse and Foal Maintenance Fluid Rate

Answer 11

2 to 3 mL/kg/h for adult horses

4 to 6 mL/kg/h for neonatal foals

Question 12

How can CVP be used to monitor fluid administration?

Answer 12

Normal CVP is approximately 2 to 12 cm H₂O in foals and 5 to 15 cm H₂O in adults

If it increases by 2-3 cm H20 then continue

Increases 3-7 cm H₂0 then pause and dresses after 10 minutes

If increases by over 7 cm H₂0 then stop

Question 13

Normal serum lactate levels in adult horses and foals

Answer 13

Adult horses: <2mmol/L

Neonatal Foals:

Decremental values after birth

around 5 mmol/L to less than 1 by 24 mmol/L hours

Question 14

What is the rate of urine production in the horse?

Answer 14

0.4 to 2.0 mL/kg/h urine

Question 15

What is the optimal urine output while on fluids?

Answer 15

1 to 2 mL/kg/h

Question 16

What is the normal fractional excretion in adult horses and foals?

Answer 16

Adult horse: <1%

Neonatal Foal: 0.31%

Question 17

What isotonic fluid is most appropriate for liver dysfunction and why?

Answer 17

Normosol-R or Plasma-Lyte.

Lactate clearance primarily occurs in the liver, fluids containing lactate optimally should be avoided

Isotonic replacement fluids containing acetate rather than lactate as the alkalinizing anion

Question 18

How does hyperchloremic acidosis affect renal blood flow?

Answer 18

Produces a progressive renal vasoconstriction and fall in GFR

Question 19

Equine dextrose supplementation rate?

Suggested starting rate?

Answer 19

1 mg/kg/min

(Equates to 3% dextrose in fluids if 1 L/h of crystalloid is administered to a 500-kg horse)

Begin with 0.3 to 0.5 mg/kg/min of dextrose and gradually advance the rate of administration

Question 20

At what level should you aim to keep blood glucose during dextrose supplementation (Equine)

Answer 20

<160 to 180 mg/dL

Question 21

Dose of Vit C in fluids (Equine)

Answer 21

20 mg/kg/day

Question 22

How can K+ supplementation minimize the risk of hyperammoniemia?

Answer 22

Provision of potassium, even in the presence of normokalemia, enables an electrolyte draw of hydrogen atoms from intracellular stores, thereby lowering pH and promoting ionization of ammonia to its less diffusible form, ammonium ion, which is not able to cross the blood-brain barrier

Hypokalemia also promotes metabolic alkalosis and may compound hepatoencephalopathy due to increased urinary losses of hydrogen ion (H+) and increased tubular absorption of ammonia

Question 23

How can fluid choice be altered to reduce sodium load?

Answer 23

Foals:

Commercially available solutions with restricted sodium concentrations (maintenance crystalloids), such as Plasma-Lyte 56 or Normosol-M (Only 1L Bags)

Adults:

Combinations of isotonic crystalloids and sterile water or 5% dextrose in water (D₅W) can be used as maintenance fluids in larger patients (half isotonic fluid and half water or D₅W)

Question 24

What level of hypoalbuminemia is colloid administration warranted?

Answer 24

<1.5 g/dL

Question 25

Why is hetastarch contraindicated in patients with bleeding tendencies?

Answer 25

Decreases Von Willebrand factor and Factor VIII and interfere with platelet function

Question 26

Which fluids are preferential for colitis?

1. Normosol-R
2. Plasma-Lyte 148/A
3. LRS
4. Hartmann’s solution

Answer 26

• Normosol-R and Plasma-Lyte 148/A are slightly advantageous over LRS or Hartmann’s solution.
• Providing a wider strong ion difference (sodium-chloride difference)
• The lactated fluids have a chloride concentration greater than that of equine plasma
• This chloride excess can potentially compound an inorganic acidosis with large volume or duration of administration

Question 28

How much does hypertonic saline increase plasma volume by per ml?

Answer 28

3-4ml

Question 29

How much do crystalloids increase plasma volume per ml?

Answer 29

0.25 to 0.33 mL for each milliliter administered

Question 30

Other than volume expansion, how is hypertonic saline beneficial in horses with endotoxemia (4)

Answer 30

• Immunomodulatory, anti-inflammatory, anti-edema (particularly of the endothelium and erythrocytes), and inotropic effects.
• Microvasculature effects enhance microcirculatory perfusion. Reduction of endothelial and erythrocyte edema, two processes that contribute to multiple organ dysfunction during sepsis, results in reduced vascular resistance and blood viscosity.
• The hypertonicity created evokes vasodilation, which also contributes to microperfusion when coupled with an increase in cardiac output caused by contractility-enhancing effects of hypertonic saline.
• The anti-inflammatory and immunomodulatory effects include anti-apoptosis, free-radical scavenging properties, inhibition of leukoactivation, and prevention of immunosuppression after sepsis

Question 31

How long can it take to see improvement in azotemia following the instigation of treatment?

Answer 31

Up to 72 hours after initiation of fluid therapy when acute renal failure is severe

Question 32

What fluids are recommended form use in patients with severe hyperkalemia (>6mmol)

Answer 32

isotonic sodium bicarbonate

Question 33

When should you suspect oliguric renal failure in horses?

Answer 33

Suspected in azotemic horses with urine production below 0.5 mL/kg/h despite the administration of intravenous fluids

Question 34

Dobutamine ionotropic dose

Answer 34

5 to 10 µg/kg/min

Question 35

When and how should Furosemide be used in treatment of anuria or oliguria

Answer 35

If urine flow does not begin over the next 30 to 60 minutes with fluid challenge, furosemide should be started with an initial bolus of 0.12 mg/kg IV followed by a CRI of 0.12 mg/kg/h

Question 36

When and how should Mannitol be used in treatment of anuria or oliguria

Answer 36

• If urine production does not begin within 30 to 60 minutes of instituting furosemide therapy, a dose of mannitol should be administered (0.25 to 0.5 g/kg bolus as a 20% solution).
• If still no urine is produced after an additional 30 minutes, another dose of mannitol can be administered; a total dose of 1 g/kg should not be exceeded in the anuric patient to prevent hypervolemia and edema formation.
• Alternatively, a CRI of mannitol (1 to 2 mg/kg/min) can be used, with a maximum cumulative dose of 1 g/kg.
• Plasma osmolarity should be monitored.

Question 37

When and how should Dopamine be used in the treatment of anuria or oliguria

Answer 37

• Following furosemide and mannitol
• When dialysis is not an option
• Dopamine can be tried (2 to 3 µg/kg/min)
• Proposed action is increasing renal perfusion with renal afferent arteriolar vasodilation