Ch5. Acid-Base, MDB and Electrolytes

Question 1

When should the anion gap be calculated, and what does it allow one to determine?

Answer 1

AG should be calculated if there is a metabolic acidosis. If

1. AG is increased then acid has been added to the system which = DUEL.
2. If AG is normal then likely to have a hyperchloraemic acidosis due to loss of HCO3. DDx:
   - Diarrhoea
   - Rental tubular acidosis
   - Hypoadrenocorticism
   - Compensation to respiratory alkalosis
   - NaCl administration

N.b. ANIon = a negative ion!

Question 2

What are the DDx for metabolic alkalosis and how can they be narrowed down?

Answer 2

Loss of acid = Hypochloraemic - often H+ and Cl- are lost together
 - Vomiting (e.g. upper GIT FB)
 - Loop diuretics
 - Response to respiratory acidosis
Gain of base
 - Hyperadrenocorticism (hypokalaemia causes H+ to be 
   drawn into the cells)
 - Hyperaldosteronism (hypokalaemia causes H+ to be 
   drawn into the cells)
 - Hypokalaemia
 - Sodium bicarbonate therapy
 - Alkalanising IVFT e.g. haartmans

Question 3

When would one expect a mixed acid-base disorder?

Answer 3

When both systems have moved in the same direction e.g. if both a respiratory acidosis and alkalosis. Or when the degree of compensation is unexpected.

Question 4

How to calculate the anion gap? Plus normal ranges

Answer 4

(Na+ + K+) - (HCO3- + Cl-)
Dog = 12 - 25
Cat = 17 - 31

Question 5

What are the differential diagnoses for respiratory acid-base abnormalities?

Answer 5

Acidosis:
- Increased tissue Co2 production (often the awake
animal will increase ventillation to compensate for this)
- Seizures
- Hyperthermia, fever, malignant hyperthermia
- Decreased ventilation
- Upper airway obstruction
- CNS disease/cervical spinal cord injury/peripheral
neuropathy
- Compensation for metabolic alkalosis
Alkalosis
- Hyperventillation/increased tidal volume
- In response to hypoxaemia
- Pulmonary parenchymal disease
- Pain or anxiety (physiologic)
- Decreased tissue production of CO2 - shock?
- Compensation for metabolic acidosis

Question 6

Normal PCV and TP for dogs and cats

Answer 6

DOG

• PCV: 35-55%
• TP: 55-75g/L

CAT

• PCV: 25-45%
• TP: 60 - 80g/L