44. Critical Care and Fluid Therapy Flashcards
ECFV in adult horses, newborn foals and foals 24 weeks old
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
Plasma volume in adult horses and foals
Adult Horses: 0.05 L/kg Foal (<2d): 0.09 L/kg
The Starling hypothesis
Net capillary filtration = Kf ( [Pcap - Pif] - σ[πp - πif] )
Kf is the capillary filtration coefficient
πp is the colloid osmotic pressure (COP) within the capillary
πif is the COP within the interstitium
Pcap is the hydrostatic pressure within the capillary
Pif is the hydrostatic pressure within the interstitium
σ is the capillary reflection coefficient for proteins
Normal Adult Equine Colloid Osmotic Pressure
20mmHg
The tonicity (or effective osmolality) of the ECFV calculation
Primary Determinants of ECFV tonicity
Sodium and Chloride
Primary determinants of ICFV tonicity
Potassium and related anions
Rate of fluid therapy for replacement.
‘Fluid Challenge Principle’
30 to 60-minute bolus of 10 to 20 mL/kg Isotonic Fluid
Rate of Hypertonic Saline administration
4 mL/kg IV once
Hetastarch administration rate and daily max
3 to 5 mL/kg
Up to 10 mL/kg may be administered per day
Adult Horse and Foal Maintenance Fluid Rate
2 to 3 mL/kg/h for adult horses
4 to 6 mL/kg/h for neonatal foals
How can CVP be used to monitor fluid administration?
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
Normal serum lactate levels in adult horses and foals
Adult horses: <2mmol/L
Neonatal Foals:
Decremental values after birth
around 5 mmol/L to less than 1 by 24 mmol/L hours
What is the rate of urine production in the horse?
0.4 to 2.0 mL/kg/h urine
What is the optimal urine output while on fluids?
1 to 2 mL/kg/h
What is the normal fractional excretion in adult horses and foals?
Adult horse: <1%
Neonatal Foal: 0.31%
What isotonic fluid is most appropriate for liver dysfunction and why?
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
How does hyperchloremic acidosis affect renal blood flow?
Produces a progressive renal vasoconstriction and fall in GFR
Equine dextrose supplementation rate?
Suggested starting rate?
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
At what level should you aim to keep blood glucose during dextrose supplementation (Equine)
<160 to 180 mg/dL
Dose of Vit C in fluids (Equine)
20 mg/kg/day
How can K+ supplementation minimize the risk of hyperammoniemia?
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
How can fluid choice be altered to reduce sodium load?
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)
What level of hypoalbuminemia is colloid administration warranted?
<1.5 g/dL
Why is hetastarch contraindicated in patients with bleeding tendencies?
Decreases Von Willebrand factor and Factor VIII and interfere with platelet function
Which fluids are preferential for colitis?
- Normosol-R
- Plasma-Lyte 148/A
- LRS
- Hartmann’s solution
- 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
How much does hypertonic saline increase plasma volume by per ml?
3-4ml
How much do crystalloids increase plasma volume per ml?
0.25 to 0.33 mL for each milliliter administered
Other than volume expansion, how is hypertonic saline beneficial in horses with endotoxemia (4)
- 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
How long can it take to see improvement in azotemia following the instigation of treatment?
Up to 72 hours after initiation of fluid therapy when acute renal failure is severe
What fluids are recommended form use in patients with severe hyperkalemia (>6mmol)
isotonic sodium bicarbonate
When should you suspect oliguric renal failure in horses?
Suspected in azotemic horses with urine production below 0.5 mL/kg/h despite the administration of intravenous fluids
Dobutamine ionotropic dose
5 to 10 µg/kg/min
When and how should Furosemide be used in treatment of anuria or oliguria
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
When and how should Mannitol be used in treatment of anuria or oliguria
- 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.
When and how should Dopamine be used in the treatment of anuria or oliguria
- 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
