Principles of fluid therapy

1. Dr. Urfeya Mirza
Division of Veterinary Surgery and
Radiology

2. Why Give Fluids During Surgery?
Prevent hypotension:
 Vasodilation
 Decreased cardiovascular function
 Blood loss
 Evaporative fluid losses
(Maintenance during surgery 10 ml/kg/hr)
 Prevent/correct acid-base abnormalities (acidosis) due to:
 Respiratory depression: respiratory acidosis
 Decreased cardiac function: metabolic acidosis

3. Why Give Fluids At Other Times?
 Correct dehydration
 Correct acid-base abnormalities d/t disease
 Correct electrolyte abnormalities
 Deliver drugs in a constant-rate infusion
 Prevent dehydration (GI disease)
 Diuresis (renal disease, toxicities)

4. Signs of Dehydration
<5%
 No clinical signs
5-6% = “mild dehydration”:
 Tacky mucous membranes
 Slight skin tent
7-8% = “moderate dehydration”
 Dry mucous membranes
 Skin tent
 CRT 2-3 sec
 Slight depression of eyes into sockets

5. 10-12% = “severe dehydration”
Severe skin tent
CRT >3 sec
Markedly sunken eyeballs
Cold extremities
+/- shock
12-15%
Obvious shock, imminent death

6. Diagnosis Of Dehydration
 Physical exam
 Weight loss
 Skin Tent
 PCV (HCT)
 INCREASED
 Albumin or total protein
 INCREASED
 BUN, creatinine
 INCREASED =“Prerenal azotemia”

7. Fluid Needs
 Correct dehydration
 Maintenance needs
 On-going losses

8. Fluids: How Much to Give?
Correct dehydration
 Weight in kg times percent
dehydration equals the amount in
liters that the animal is dehydrated
 Example: 10 kg animal who is 8%
dehydrated
 10kg X 0.08 = 0.8 liters
 Patient is lacking 0.8 liters, or 800 ml
fluids
Maintenance Fluids
 30 ml/pound/day
 10 pound animal needs:
 10 X 30ml/lb =300 ml/day

9. On-going Losses
 Sensible losses
 GI disease
Vomiting/diarrhea
 Renal disease
Low specific gravity
 Diabetes mellitus
 Insensible losses
(evaporation/diffusion)
 Weigh to determine

10. Principles of Rehydration
 Correct dehydration,
electrolyte, and acid-base
abnormalities prior to surgery
 Do not attempt to replace
chronic fluid losses all at once
 Severe dilution of plasma proteins,
blood cells and electrolytes may
result
 Aim for 80% rehydration within
24 hours
 Monitor pulmonary, renal and
cardiac function closely

11. Types of Fluids
 Colloids (Natural and Synthetic)
 Crystalloids

12. Natural Colloids
 Blood products:
 Whole blood
 Plasma
 Platelet-rich plasma
 Packed RBC’s
Synthetic Colloids
 Dextrans, Hetastarch
 Used when quantity of a crystalloid is too great to be able
to infuse quickly
 Stays within the vasculature maintain blood pressure
 Duration of effect is determined by molecular size:
bigger = longer

13. Crystalloids
 Isotonic
Mimic plasma electrolyte concentrations
 Hypertonic
Follow with isotonic
 0.9% NaCl
 Lactated Ringers Solution
 Ringers Solution
 5% Dextrose in water
 Plasmalyte, Normosol, etc

14. Lactated Ringer’s Solution
 Composition closely resembles ECF
Contains physiological concentrations of: sodium,
chloride, potassium, and calcium
 Also contains lactate, which is metabolized by the liver
alkaline-forming
Because small animals that are sick or under anesthesia
tend towards acidosis

15. Ringer’s Solution
 Same as LRS except no lactate added
 Commonly used in Large animals
 Large animals who are sick tend towards alkalosis instead
of acidosis

16. Saline
 0.9% Sodium chloride = ISOTONIC
 Lacking in K+, Ca2+
 Used for hyperkalemia, hypercalcemia
 Used as a carrier for some drugs
 Used if don’t want lactate

17. Dextrose Solutions
 5% dextrose is isotonic
 50% dextrose commonly found
 C1V1= C2V2
 Used for hypoglycemia, neonates, hyperkalemia, as part of
Total Parenteral Nutrition

18. Additives for Crystalloid Solutions
 Potassium
 available as potassium chloride (KCl)
 available as potassium phosphate (K3PO4)
 Very common additive
 20 meq in 10 ml bottle
 DANGER: Rates higher than 0.5 meq/kg/hr will stop the heart
 Sodium Bicarbonate
 Alkalinizing
 Used for severe acidosis
 Antifreeze toxicity
 Ketoacidosis associated with diabetes mellitus
 Do not add to calcium-containing fluids or calcium precipitates
will occur

19.  B Vitamins
 B Complex
 Frequent additive; water-soluble effects
 Turns bag yellow
 Protect from light
 1-2 ml/liter
 Appetite Stimulant
 Replaces lost B vitamin
Always label the fluid bag with the amount and concentration of all
additives immediately!

20. Administration Routes
Oral
 If the stomach works, use it!
 Safest route if tolerated
Subcutaneous
 Works well in most animal
 Sometimes need to use multiple sites
 Can’t add glucose, large quantity KCl, or
some drugs

21.  Intravenous
 Best route in dehydrated animals
 Possible problems:
 Volume overload
 Catheter reactions (swelling, fever)
 24-hour maintenance
 INTRAOSSEOUS
 If situation is dire and no vein accessible
 Into the medullary (bone marrow) cavity of long bones
 Femur or Humerus are commonly used
 Used frequently in birds

22. Calculate Drops Per Hour
 Calculate ml/hr
 Calculate drops/hr by:
 ml/hr X drops/ml (from the package)
 Gives you drops needed in an hour
 Example: 100 ml X 10 drops per ml = 1000 drops in the first
hour
 Divide drops per hour by 60 min/hr to get drops per
minute
 Divide again by 60 to get drops per second

23. Daily Monitoring While on Fluids:
 Weigh patient daily
 Urine production
 Central venous pressure
 Auscult the lungs
 Crackles
 Wheezes
 Nasal discharge
 Overdose:
 Serous nasal discharge
 Dyspnea, crackles
 Restlessness
 Decreased PCV, TP
 Increased BP

24. References
 Crystalloid and Colloid Fluid Therapy. In Ettinger
SJ, Feldman EC, Textbook of Veterinary Internal
Medicine, 7th edn.
 Introduction to Fluid Therapy. In Di Bartola SP -
Fluid, Electrolyte and Acid Base Disorders, 4th
edn.