Fluid Therapy

Question 1

Obj: Distribution of water in the body

Answer 1

Question 2

Obj: How to calculate bicarbonate and potassium deficits

Question 3

Obj: how to calculate the volume of fluid for a patient

Question 4

Obj: familiarity with fluid and electrolyte therapy options

Question 5

How can a patients level of dehydration be assessed?

Answer 5

• Clinical signs:
  
  • tachycardia
  • reduced jugular fill
  • cold extremities
  • tacky mucous membranes
  • sunken eyes
  • reduction in body weight
• Laboratory estimates:
  
  • PCV
  • Plasma protein - ⇡
  • Creatinine Concentration - ⇡
  • Urine Specific gravity - >1.030
  • Blood lactate concentrations

Question 6

What is the normal USG in foals?

Answer 6

1.001 - 1.005

Question 7

How are maintenance fluids calculated for adult horses?

Answer 7

• 60 ml/kg/day OR 30ml/lb/day
  
  • 500kg horse = 30L a day

Question 8

How are maintenance fluids calculated for foals?

Answer 8

• 80 - 120 ml/kg/day
• Can be concerned for overhydration in premature foals, or in foals with perinatal asphyxia:
  
  • 1st 10 kg = 100 ml/kg/day
  • 2nd 10kg = 50 ml/kg/day
  • further 10kg = 25 ml/kg/day

Question 9

What causes ongoing water losses in horses?

Answer 9

• colitis
• nasogastric reflux
• renal failure
• sweat loss
• third spacing of fluid (peritonitis, pleuritis)
• hemorrhage

Question 10

How can fluids be administered to horses? When would this route be indicated? Pros/Cons of each?

Answer 10

• Oral - mild dehydration, impactions
  
  • given as a bolus (4L q 30-60min) or as a CRI
  • Pro - easy, least expensive
  • Con - horse cannot be refluxing
• Intravenous - critically ill patients, when rate/volume of fluids are high
  
  • Jugular vein used most commonly
    
    • can use cephalic, lateral thoracic, saphenous
  • Cons - Expense, complications (thrombophlebitis)
• Subcutaneous - not commonly used
  
  • lack of subcutaneous space

Question 11

What is the fluid administration rate for horses in shock?

Answer 11

• 60 - 80 ml/kg/hr
  
  • usually only 1 hour at this rate, the rest over a 12-24 hr period (horse dependent)

Question 12

What are crystalloid fluids?

Answer 12

• contain electrolytes and non-electrolyte substances capable of entering all body fluid compartments
• distribute to the ECF w/in a few minutes of administration
• Most common: isotonic polyionic fluids

Question 13

What buffers are used in crystalloid fluids? where are they metabolized?

Answer 13

• Lactate - liver
• Acetate & Gluconate - plasma

Question 14

Why would lactic acid production be increased in horses?

Answer 14

• tissue hypoxia
  
  • poor tissue perfusion
• bacterial production of lactic acid absorption from the GIT
  
  • rumen acidosis
  • grain overload

Question 15

When would hypertonic saline (7% NaCl) be administered?

Answer 15

• to expand intravascular volume quickly
  
  • short lived, needs to be followed by large volume of isotonic fluids

Question 16

What is the ideal maintenance fluid for horses?

Answer 16

• Preferably less sodium and more Ca, Mg, K (15-30 mEq/L)
• No commercially available product
  
  • often add calcium gluconate (25-50 ml to 5L LRS) and Potassium Chloride (20 mEq/L to LRS)

Question 17

What fluids are used for hyponatremia?

Answer 17

• < 120 mEq/L
• concern for cerebral edema
  
  • Correct slowly
• Options:
  
  • LRS
  • 0.9% NaCl

Question 18

What fluids are used for hypernatremia?

Answer 18

• >160 mEq/L
• Concern for Cerebral dehydration, blindness, depression, seizures
  
  • Correct slowly
• Options:
  
  • 5% dextrose
  • 2.5% dextrose in 0.45% NaCl

Question 19

How do changes in acid-base balance affect intra/extracellular potassium?

Answer 19

• Acidosis promotes K leaving ICF
• Alkalosis promotes K entering ICF

Question 20

What fluids are used for hyperkalemia?

Answer 20

• > 5mEq/L
• Concern for cardiac arrhythmia (bradycardia, cardiac arrest)
• Choices:
  
  • Dextrose - promotes intracellular movement of K⁺
  • Insulin
  • Calcium gluconate - cardioprotective
  • NaHCO₃
  • Avoid Calcium containing fluids

Question 21

What is the concern for ongoing hypokalemia? What fluids are used for hypokalemia?

Answer 21

• < 3.0 mEq/L
• Could lead to neuromuscular, GI and cardiac conduction abnormalities
• Treat when low levels, anorexia for several days, or when low normal & ongoing acidosis
• Maximal rate to supplement is 0.5 mEq/kg/hr
• Options:
  
  • LRS
  • Plasmalyte A

Question 22

How is potassium deficit calculated?

Answer 22

• (4.0 - [K⁺]) x V_d(0.4) x BW

Question 23

When does hypochloremia occur? What fluids can be used for Hypochloremia?

Answer 23

• Occurs with: proximal enteritis, loss of saliva (long standing choke), colitis, renal failure
• Options:
  
  • 0.9% NaCl
  • LRS

Question 24

When does hyperchloremia occur? What fluids can be used for Hyperchloremia?

Answer 24

• Occurs with: renal tubular acidosis, severe colitis
• Options:
  
  • 5% dextrose (if accompanied with hypernatremia
  • Sodium bicarbonate

Question 25

How is calcium affected by albumin? by Acid-base balance?

Answer 25

* Total calcium = Protein bound Ca⁺ + **Ionized Ca⁺⁺** * tCa⁺ decreases with hypoalbuminemia * Acidosis increases Ca⁺⁺

Question 26

When does hypocalcemia occur? What fluids can be used to correct hypocalcemia?

Answer 26

* Occurs: canthardin toxicosis and GI disturbances * Clinical signs: muscle fasiculation, synchronis diaphragmatic flutter * Options: * 23% Cagluconate * \*do NOT use calcium fluids with bicarbonate

Question 27

When are dextrose fluids used?

Answer 27

* hypoglycemia * hyperkalemia * hyperosmolar states (loss of free water and hypernatremia)

Question 28

How is Acid-Base Status determined?

Answer 28

H⁺ + HCO₃^- ⇠⇢ H₂CO₃ ⇠⇢ H₂O + CO₂ * Normal: * pH 7.4 (Rang 7.35 - 7.45) * HCO₃ = 24 (range 22 - 26) * PaCO₂ = 40mmHg (Range 30-40) 1. Assess pH (acidosis \<7.4; alkalosis \> 7.4) 2. Assess HCO₃ (metabolic acidosis \< 24; metabolic alkalosis \> 24) 3. Assess PaCO₂ (respiratory alkalosis \<35 mmHg; Respiratory acidosis \>45-50

Question 29

What are the most common acid-base abnormalities with GI disease?

Answer 29

* Metabolic acidosis * lactic acidosis (due to tissue hypoxia/poor perfusion) * Loss of HCO₃ (feces/urine) * Metabolic alkalosis * Hypochloremic metabolic alkalosis due to proximal enteritis or esophageal obstruction

Question 30

How is metabolic acidosis treated in horses?

Answer 30

* **Correct Dehydration - Volume expansion\*\*\*\*** * LRS (w/ healthy liver), Plasmalyte, or 0.9% Saline (okay) * Reassess blood gas - determine further treatment * Use of sodium bicarbonate indicated when HCO₃ \< 10-15 mEq/L despite fluid therapy * HCO₃ deficit = (24 - HCO₃) x V_d x BW * V_d = 0.3 - 0.6 * 0.4 - 0.5 in most cases * Replace ½ of calculated deficit in first 1-2hrs, the rest over 12-24hrs * 5% NaHCO₃ = 595 mEq/L of HCO₃ but hypertonic (Osm = 1190) - Should Dilute * 1.3% NaHCO₃ = 156 mEq/L isotonic * Oral NaHCO₃ can be given 1gm NaHCO₃ = 12 mEq of HCO₃

Question 31

What is the Anion Gap?

Answer 31

* (Na⁺ + K⁺) - (Cl^- + HCO₃) = ~10-17 * Provides a measure of unmeasured anions: * lactate * ketones * sulfate * phosphate * albumin

Question 32

When do horses have an increased anion gap?

Answer 32

* metabolic acidosis due to lactate