Emergency medicine: Fluid therapy

Question 1

What are 5 examples of indications for fluid therapy?

Answer 1

(i) Resuscitation from shock
(ii) Correction of dehydration, hypokalaemia and metabolic acidosis
(iii) Correction of other electrolyte disturbances
(iv) Parenteral nutrition
(v) Treatment of anaemia and coagulopathies

Question 2

Describe the distribution of body water and electrolytes

Answer 2

A. Water

1. Total body water is about 50% to 70% of body weight in adults. Cats have slightly less body water; young animals and neonates have a higher percentage of body water.
2. Intracellular water is about 40% of body weight.
3. Extracellular water is about 20% of body weight.
4. Interstitial fluid is about 12% to 14% of body weight, and intravascular fluid is about 6 to 8% of body weight.

B. Electrolytes

1. Sodium and chloride are high in extracellular fluid and low in intracellular fluid.
2. Potassium, magnesium and phosphorus are low in extracellular fluid and high in intracellular fluid.

Question 3

Elaborate on 3 important aspects of maintenance requirements.

Answer 3

(i) Water intake should equal water loss in normal animals.
(ii) Insensible water loss is about 20 mL/kg/day.
(iii)Sensible losses are 20 to 40 mL/kg/day in normal animals consuming food.
(iv)

Question 4

Which of 0.45%, 0.9% NaCl solution and Lactated Ringer’s makes the best maintenance solution and explain why?

Answer 4

A 0.45% sodium chloride solution makes a good maintenance solution but does not contain adequate potassium. Lactated Ringer’s and 0.9% sodium chloride solution are not good maintenance solutions because they contain too much sodium and chloride.

Question 5

List the two main causes of dehydration.

Answer 5

1. Decreased water intake (decreased thirst and appetite centers in sick animals, decreased food intake)
2. Increased water loss (e.g polyuria, vomiting, diarrhea, salivation, burns)

Question 6

State and explain the three types of dehydration.

Answer 6

1. Isotonic dehydration
   - Normal serum sodium concentration in the presence of dehydration
   - Occurs when there is a loss of water and electrolytes in proportion to that in serum.
2. Hypertonic dehydration
   - Elevated serum sodium concentration in the presence of dehydration
   - Occurs when there is water loss in excess of electrolytes in serum
3. Hypotonic dehydration
   - Low serum sodium concentration in the presence of dehydration
   - Loss of isotonic fluid with intake and absorption of hypotonic fluids with a net dilutional effect

Question 7

At which body weight water % is dehydration detectable? When does it become life-threatening?

Answer 7

dehydration is detectable when approximately 5% of body weight in water has been lost, An acute loss of more than 12% body weight in water is life-threatening.

Question 8

What type of history would show that there is dehydration?

Answer 8

History of decreased water intake, vomiting, polyuria, diarrhea, excessive panting or salivation may suggest dehydration.

Question 9

During physical examination, list down some of the findings that are associated with dehydration. (8)

Answer 9

(i) Depression
(ii) Acute loss of body weight
(iii) Sunken eyes
(iv) Decreased skin turgor
(v) Dry mucous membranes
(vi) Tachycardia
(vii) Diminished capillary refill
(viii) Signs of shock

Question 10

(i) Describe the test performed with the skin in order to check for dehydration.
(ii) What happens in the case of dehydration?
(iii) At what % of dehydration is a skin turgor seen?

Answer 10

(i) Skin turgor is checked: when the skin is lifted a short distance, it should return quickly
(ii) As dehydration progresses, the time required for the skin to return to its normal position increases.
(iii) Dehydration is as much as 5% to 10% before a loss of skin turgor can be detected.

Question 11

What parameters related to blood count would indicate dehydration?

Answer 11

Packed cell volume(PCV) and total plasma protein both increase with dehydration.

Question 12

What happens to the urine specific gravity in a dehydrated animal?

Answer 12

The urine specific gravity should increase in a dehydrated animal if the kidneys are healthy.

Question 13

What pH disorder is usually present with dehydration?

Answer 13

Metabolic acidosis is common in dehydration.

Question 14

How is dehydration corrected(how much fluid should be given)?

Answer 14

Volume of fluid = % dehydration x weight(kg) = litres of fluid to be replaced

Question 15

How is the type of fluid chosen when correcting dehydration?

Answer 15

Type of fluid is chosen based in electrolyte status and acid-base status.

Question 16

What types of fluids are best for rehydration or replacement of fluid loss and why?

Answer 16

Crystalloid solutions are best for rehydration or replacement of fluid loss as they redistribute quickly.

Question 17

State the osmolality in mOsm/kg for the following replacement fluids:

(i) Hypotonic
(ii) Hypertonic
(iii) Isotonic

Answer 17

(i)Hypotonic: Osmolality less than 300 mOsm/kg (0.45% saline)
(ii)Hypertonic: Osmolality greater than 300 mOsm/kg (5% dextrose in 0.9% saline)
(iii) Isotonic: Osmolality near 300 mOsm/kg (lactated Ringer’s solution, Plasma-Lyte 148, Normosol-R, 0.9% saline)
NOTE: Replacement fluids are formulated for specific electrolyte deficits.

Question 18

What is the difference between maintenance fluids and serum?

Answer 18

Maintenance fluids may differ greatly from serum and because they usually contain glucose, their effect is hypotonic. The energy available from these fluids is insufficient to meet nutritional needs.

Question 19

Are colloid solutions ideally used to replace intravascular or extravascular volume? Explain why.

Answer 19

Colloid solutions contain large macromolecules and attract water out of interstitial spaces. They are ideal for replacing intravascular volume but are not good for replacing extravascular volume.

Question 20

What is the difference between natural and synthetic colloids?

Answer 20

Natural colloids are produced in the body and harvested for later use(blood transfusion components) whereas synthetic colloids(such as hetastarch) are complex polysaccharide molecules.

Question 21

What are colloid solutions used primarily for and which other fluids are they used together with?

Answer 21

Colloid solutions are used in conjunction with crystalloid fluid therapy. They are used primarily in patients with hypoproteinaemia and low oncotic pressure and in the treatment of shock.

Question 22

In which conditions should you use colloid solutions with caution?

Answer 22

Colloid solutions used with caution in those at risk for noncardiogenic pulmonary oedema, in patients with congestive heart failure, and in those with renal origin oliguria or anuria.

Question 23

What is the fluid of choice in the absence of laboratory data?

Answer 23

The fluid of choice in the absence of laboratory data is alkalinising basic electrolyte solution(lactated Ringer’s solution, Plasma-Lyte 148, Normosol-R).

Question 24

What is the fluid of choice when extra sodium or chloride is needed to maintain volume expansion or correct metabolic alkalosis?

Answer 24

If extra sodium or chloride is needed to maintain volume expansion or correct metabolic alkalosis, 0.9% saline is chosen.

Question 25

What is the fluid of choice when treating patients with hypernatraemia or a water deficit?

Answer 25

Choose a low sodium fluid (0.45% saline in 2.5% dextrose, Plasma-Lyte 56, Norsomol-M, or 5% dextrose in water)

Question 26

Which fluid(s) are used when rapid intravascular expansion is needed or if there is lowered oncotic pressure?

Answer 26

Keep a synthetic colloid on hand to administer in conjunctions with crystalloid fluids when rapid intravascular expansion is needed or if there is lowered oncotic pressure?

Question 27

When is potassium added to parenteral fluids as supplementation?

Answer 27

Potassium is added to fluids if serum potassium concentration is less than 3.5 mEq/L. May still be indicated if potassium is b/w 3.5 and 4.5 mEq/L if ventricular arrhythmias are present.

Question 28

How much potassium is to be added to maintenance fluids where it is indicated?

Answer 28

Add approximately 20 to 30 mEq/L of potassium to maintenance fluids if needed.

Question 29

What is the rate of infusion of potassium as supplementation to parenteral fluids? Why do you need to use potassium supplementation with caution?

Answer 29

The rate of infusion is most important. Do not exceed a rate a rate of 0.5 mEq/kg/hr. Use potassium supplementation with caution as death can result due to hyperkalaemia.