This document discusses fluid and electrolyte therapy in veterinary medicine. It describes the normal distribution of body water and outlines causes of abnormal fluid balance like decreased intake, increased output, and third spacing of fluids. The key aspects of fluid therapy are estimating fluid deficits, calculating fluid requirements, selecting appropriate replacement or maintenance fluids, and administering fluids via various routes. Common intravenous fluids used include lactated Ringer's, normal saline, plasmalyte, and colloids like hetastarch. Guidelines are provided for administering fluids and supplementing electrolytes like potassium and bicarbonate as needed. Signs of overhydration are also reviewed.

1. Fluid and Electrolyte Therapy
Dr. VIVEK JOSHI
Division of Medicine
ICAR-IVRI

2. Intracellular fluid
2/3rd
of total body water
(40 % of body weight)
Total body water
(60 % of BW)
Extracellular fluid
1/3rd
of total body water
(20 % of body weight)
Interstitial fluid. 3/12 of total body
water (15 % of body weight)
Intravascular fluid. 1/12 of total body
water
(5 % of body weight)
Distribution

3. Normal fluid turnover
Intake
FOOD + FREE WATER
• (45-60 ml/kg/day)
METABOLISM
•CHO + O₂ → CO + H O₂ ₂
( 4-6 ml/kg/day )
Output
URINE
(24-48 ml/kg/day)
INSENSIBLE
(25 ml/kg/day)
DIGESTIVE
SA - (small)
LA – (Significant)

4. ABNORMAL FLUID BALANCE
(FLUID LOSS)
• Decreased intake.
– Fasting & thirsting
– No abnormality in the concentration of serum
electrolytes or acid base‑
• Increased output
– Urine
– Insensible
– Digestive
– Third space

5. Urinary loss
Various diseases :
1.Renal failure
– An increased obligatory loss of urine in chronic
renal failure
1.Diabetes
– Polyuria
1.Cushing’s

6. Insensible fluid losses
• Water vapour lost with respiration is an insensible
loss
• Sweating
• Excessive losses may occur with pyrexia &
anesthesia
• The loss is primarily electrolyte free water

7. Digestive system losses
Vomiting
•Results in loss of H O, H+, Cl-, Na+, K+, HCO3₂ -
•If vomit is primarily stomach contents, 10
loss is HCl,
H₂O
•Gastric outflow obstruction is classically associated
with a hypochloremic metabolic alkalosis
•Most vomit includes proximal duodenal contents,
therefore HCO3-
is also lost

8. Diarrhoea
• Results in loss of H₂O & electrolytes
• Resulting in dehydration, electrolyte depletion/imbalance,
acid base imbalance, shock‑
• Intestinal contents are basically ECF; also can lose large
amounts of K+
• Fluid losses from diarrhea can be particularly severe in the
cow and horse (salmonellosis, neonatal calf diarrhea)
• The primary acid base disturbance is‑ metabolic acidosis

9. Third Space Fluid Loss
• Functionally lost from the animal, but still within the body
• It can be considered a pathologic expansion of the
transcellular space; eg.
1. Ascites
2. Peritonitis
3. Fluid filled obstructed bowel‑
4. Pleuritis in horses
5. Fracture hematoma

10. FLUID THERAPY
1. How much fluid does the animal require ?
2. What route should the fluid be given ?
3. What kind of fluid should be given ?
4. What is the frequency/rate of administration ?

11. Fluid Therapy : 3 Phases
1. Emergency phase
2. Replacement phase
3. Maintenance phase

12. Fluid deficits
• Acute loss – Circulatory shock
• Chronic loss – Dehydration
• First goal of fluid therapy → to assess how dehydrated the
patient is ?
1. Physical exam.
2. Skin turgor
3. Body weight
4. PCV & Total Solid (TS) measurement
5. Urine output & urine specific gravity

13. Estimating % dehydration based on P/E
%
Dehydration
Physical Examination Findings
< 5 History of fluid loss but no findings on physical examination
5
Dry oral mucous membranes but no panting or pathological
tachycardia
7
Mild to moderate decreased skin turgor, dry oral mucous
membranes, slight tachycardia, and normal pulse pressure
10
Moderate to marked degree of decreased skin turgor, dry
oral mucous membranes, tachycardia, and decreased
pulse pressure
12
Marked loss of skin turgor, dry oral mucous membranes, and
significant signs of shock

14. How much fluid should be given ?
Based on an assessment of fluid needs for the following :
1. Returning the patient's status to normal
(Deficit volume)
2. Replacing normal ongoing losses
(Maintenance volume)
3. Replacing continuing abnormal losses
(Continuing losses volume)

15. Calculations
Deficit replacement volume (ml)
= % dehydration x BW (kg) x 1000 x 0.80
• Inevitable water losses @ 20 ml/kgBW/day
• Urinary losses @ 20 ml/kg BW/day
• Losses from vomiting @ 4 ml/kg BW/vomit
• PCV deficit x 10 x 30 (ml)
• Plasma deficit (1/4 of extracellular fluid loss or 1/12 of total)

16. Practically speaking
Total amount of fluid to give is equal to
1. Deficit
% dehydration x BW (kg) x1000 x 0.80
1. Maintenance
60 ml/kg/day [dog]
48 ml/kg/day [cat]
1. Any ongoing losses (estimate)

17. Which route ?

18. What kind ?
The choice of fluid is based on 3 factors :
1. Knowledge of disease process (e.g., blood loss,
Addison's)
2. Laboratory data (e.g., hypokalemia, metabolic
alkalosis, hypoproteinemia)
3. Purpose of fluids (i.e., replacement or maintenance)

19. Replacement vs Maintenance
• Replace existing fluid
deficits
• Replacement of both water
and electrolytes
• Sodium concentrations
similar to plasma
• Meet sensible & insensible
fluid & electrolyte losses,
assuming a normal ECF
volume
• Hypotonic , lower in sodium
& chloride, & higher in
potassium than plasma
• Not used when high fluid
rates or rapid infusion (i.e
bolusing) are needed
Crystalloids

20. Replacement fluid
1. Lactated Ringer's Solution (LRS)
2. Normosol R
3. Plasmalyte A
4. Normal Saline (0.9% NaCl)
5. Hypertonic saline (7.2% NaCl)

21. Lactated Ringer's Solution (LRS)
• Balanced (electrolyte conc. similar to serum)
• Isotonic (osmolality similar to serum) solution
– Na+ = 131
– K+ = 4
– Ca++ = 3, Cl- = 110
– Lactate = 28 mEq/L‑
• Lactate is metabolized by liver
– (Na+ C3H5O3- + 3 O2 → 2CO2 + 2H2O + Na+ HCO3-).
• Excellent ECF replacement fluid
• It is the most commonly used fluid for a multitude of disease
processes in all species
• Also of use in metabolic acidosis

22. Normosol R & Plasmalyte A
• Balanced/ Isotonic
• HCO3- precursor may be Acetate or Gluconate
• Normosol R has 27 mEq/L of acetate & 23 mEq/L of
gluconate
• Since acetate is metabolized by more tissues than
liver, it is a better bicarbonate precursor

23. Normal Saline (0.9% NaCl)
• Unbalanced/ Isotonic
• Na+ = 154, Cl- = 154
• There is an excess of Cl- so HCO3- tends to be low
– anion gap equation AG = (Na + K) – (Cl + HCO3- )
• Tends to produce an acidosis
• It is used for metabolic alkalosis
• As a replacement fluid in
 Hyperkalemia
 Hypercalcemia
 Patients with a deficit in total body sodium (eg. DKA)

24. Hypertonic saline (7.2% NaCl)
• Unbalanced/ Hypertonic (8x normal saline)
• MOA : elevating the [Na+
]; elevated [Na+
] draws water out of
the cell to rapidly expand the ECF
• Expanding ECF at the expense of ICF
• Less volume & quicker
• Indications :
– Shock states where vascular access is limited
– Where excessive shifting of fluids into the interstitial and
intracellular spaces could be deleterious (eg. head trauma)
– Field use (don’t have to carry as much volume) & in large
animals (e.g. cow with toxic mastitis)

25. Maintenance fluid
• Water requirement = 45-60 ml/kg/day
• Na+ ; K+ requirement = 1 2 mEq/kg/day‑
1. Dextrose 5% (D5W)
2. D2.5 in 0.45% NaCl
3. Plasmalyte-56 & 5% Dextrose
4. Normosol M

26. Dextrose 5% (D5W)
• 50 gm of dextrose in 1L of distilled water
• Unbalanced/ Isotonic
• No electrolytes & 225 cal/liter
• Diluent for certain medications, or as a supplement
in maintenance fluid

27. D2.5 in 0.45% NaCl
• Half -strength dextrose in half-strength saline
• Unbalanced/ Isotonic
• Na+ = 77, Cl- = 77 mEq/L, Dextrose = 25 gm/L
• Good maintenance solution, after the addition of
K+

28. Plasmalyte-56 & 5% Dextrose
• Commercial maintenance fluid
• It contains, in mEq per liter,
 Na = 40, K = 16
 Ca = 5, Mg = 3, Cl = 40
 Acetate =16 gm, Glucose = 50 gm
 Osmolality of 362

29. Frequency/Rate of Administration
• Maintenance fluid rate is 40-60 ml/kg/day (higher end
in the dog, lower end in the cat)
• In Shock, rate is:
 90 ml/kg (dog)
 66 ml/kg (cat)
 Give in less than one hour
• Fluid rate for anesthesia/surgery is 10-20 ml/kg/hour

30. Administration guidelines
• First goal is to replace the ECF & stabilize the
patient (1/3 of total as fast as possible)
• Once its done
1. Remainder of fluid deficit may be given over 24
hours,
2. Fluids given as appropriate for surgery/ anesthesia
3. Fluid status/need is reassessed & recalculated

31. Colloids
• Add oncotic pressure to plasma
• Decrease blood viscosity
• May alter hemostasis
• Used in hypoalbuminemic/ hypooncotic states
• High molecular wt. compounds

32. Dextrans
•Low (Dextran 40, MW = 40,000)‑
•High (Dextran 70, MW = 70,000)‑
•Half lives‑ are short (3hrs Dextran 40,‑
6 hrs Dextran 70)‑
•They are less expensive than hetastarch
but more likely than hetastarch to result
in inhibition of platelet function
•Therefore less frequently used
Hetastarch
•Branched polymer of glucose that
is soluble in plasma
•MW of 450,000 (compared to
69,000 daltons for albumin)
•Colloid oncotic pressure of 30
mmHg
•Available as a 6% solution in 0.9%
saline
•40 % increase in vascular volume
persists for 24-36 hrs
•Decreased PLT aggregation has
been reported at high doses

33. Hetastarch (HES) adminstration
• Dose :
Dog = 20 ml/kg/day (up to 40)
Cat = 5-10 ml/kg/day
• After initial volume administration, can be mixed with
crystalloids in a ratio of 30% HES : 70% crystalloid
• Monitor for overhydration with all synthetic colloids

34. Each 100 ml contains :
Polygeline polypeptides of
degraded gelatin, cross-linked
via urea bridges 3.5g (equivalent
to 0.63g of nitrogen)
Sodium Chloride 0.85g
Potassium Chloride 0.038g
Calcium Chloride 0.070g
Water
Electrolytes in m mol / litre :
Na+ 145, K+ 5.1, Ca++ 6.25, Cl-
145
Mean molecular weight 30,000
Infusion bottles of 500ml

35. Potassium supplementation
• Requirement = 1mEq/kg/day
• Potassium depletion (Hypokalemia) occurs with
o Anorexia
o Prolonged fluid therapy with potassium-free solutions
o Vomiting/ diarrhea
o Alkalosis
o Diuresis
o Post-operative complication of thyroidectomy in cat
• Assessment of K+ debt is difficult since ion is primarily
intracellular

36. Sliding Scale Of Scott
Max. rate of potassium infusion should not exceed 0.5 mEq/kg/hr.

37. Bicarbonate Therapy
• To correct acidosis
• mmol bicarbonate required
= Body weight (kg) x base deficit x 0.33
• Base deficit is the 'normal' minus actual plasma bicarbonate
concentration ('normal' taken to be 25 mmol/litre)
• Availability
o 7.5 % ,10 & 25 ml ampoule
o Isotonic 1.3 %
o 5 & 8 % also available

38. Normal Serum Concentrations

40. Solutions’ composition

42. Recommended fluids

44. Signs of Overhydration
• Pulmonary edema → terminal event of overhydration
• Before pulmonary edema results, signs include :
a) increased serous nasal discharge
b) followed by chemosis
c) finally pulmonary congestion before edema