Chapter 8

Question 1

What breed is associated with spurious hyperkalaemia?

Answer 1

Akitas

Question 2

Ddx hyperkalaemia?

Answer 2

Spurious - Akitas, haemolysis, thrombocytopenia, massive leucocytosis
Increased intake
Reduced excretion - anuric renal failure, urinary obstruction, urinary tract rupture, hypoadrenocorticism, pleural effusion and repeated drainage, primary hypoaldosteronism, pseudohypoadrenocorticism, ACE-i
Redistribution - metabolic acidosis, insulin deficiency, massive tissue destruction - eg tumour lysis syndrome

Question 3

What is the mechanism of hyperkalaemia in urinary rupture?

Answer 3

Sodium diffused plasma => abdominal free fluid
Hyponatraemia => aldosterone release => hyperkalaemia

Question 4

What is the mechanism of hyperkalaemia in metabolic acidosis?

Answer 4

H+ diffuses into cells, Cl- unable to follow
H+ displaces K+ into ECF

Question 5

Ddx hypokalaemia

Answer 5

Decreased intake - anorexia, fluid therapy
Increased loss - GI, urinary (CKD, PU, RTA, hyperadrenocorticism, hyperaldosteronism, hypomanesaemia, metabolic acidosis, drugs)
Redistribution - metabolic alkalosis, insulin, beta adrenergic agonists, hypothermia, hypokalaemic myopathy (Burmese cats)

Question 6

How does vomiting/diarrhoea cause hypokalaemia?

Answer 6

Potassium loss
Volume contraction => aldosterone release => K loss
Metabolic alkalosis => K+ movement into cells

Question 7

Ddx hypernatraemia

Answer 7

Water loss - hypotonic fluid loss (GI disease, renal failure, DM, diuresis), pure water (CDI, nDI, adipsia, heatstroke, pyrexia, burns, water deprivation)
Sodium gain - salt, fluid therapy, IV HCO3, hyperaldosteronism, hyperadrenocorticism

Question 8

Ddx hyponatraemia

Answer 8

Sodium loss - GI, third spacing, hypoadrenocorticism, diuretics
Volume overload - CHF, nephrotic syndrome, liver disease, renal disease
Normovolaemia - hypotonic fluids, psychogenic polydipsia, inappropriate ADH, hypothyroid myxoedema coma, exercise-associated
Increased plasma osmolality - DM, mannitol
Pseudo-hyponatraemia - hyperlipidaemia, hyperproteinaemia

Question 9

What syndromes have been described in combination with inappropriate ADH secretion? How is it diagnosed?

Answer 9

GME, heart worm, hypothalamus tumour, hydrocephalus

Hyponatraemia
Natriuresis (^FE-Na)
Urine osmolality > plasma osmolality
Absence of oedema and volume depletion
Normal renal/adrenal function

Question 10

Ddx hyperchloraemia

Answer 10

Hyperchloraemia with hypernatraemia
Increased intake - iatrogenic or salt poisoning
Decreased excretion - renal failure

Hyperchloraemia without hypernatraemia
GI bicarbonate loss - non-anion gap metabolic acidosis
Chronic respiratory alkalosis
Chloride containing therapy
TPN
Pseudohyperchloraemia - KBr

Question 11

Ddx hypochloraemia (normal sodium)

Answer 11

Alkalosis - vomiting
(Diuretics)
(Hyperadrenocorticism)

Question 12

What is Mg++’s main role in the body?

Answer 12

Critical cofactor for Na/K ATPase

Question 13

Hypermagnesaemia ddx

Answer 13

Renal failure

Question 14

Hypomagnesaemia ddx

Answer 14

GI loss
Anorexia
Renal tubular disease
Hypercalacaemia
Glycosuria
Drugs (diuretics, digoxin, cisplatin, cyclosporine)
Endocrine - hyperthyroidism, hypoparathyroidism
Insulin/catecholamines

Question 15

Where is calcitonin produced? What is its role?

Answer 15

C-cells of thyroid gland
Prevents post prandial hypercalcaemia

Question 16

In what forms is calcium found in blood?

Answer 16

Ionised
Protein bound
Chelated to lactate, citrate, bicarbonate

Question 17

Why is anaerobic handling of samples for ionised calcium measurement important?

Answer 17

Exposure to air => CO2 loss => increased pH => decreased iCa++