Clinical Pathology: Approach To Water and Electrolyte Imbalances

Question 1

How are the following electrolytes distributed (inside/outside cells) generally?

Answer 1

Inside
* K
* Mg
* S- sulfate
* P

Outside
* Na
* Cl

Question 2

Why is sodium not found in cells?

Answer 2

Na/K pump- maintains the balance of Na outside

Question 3

1. What are sodiums balancing anions?
2. What is the function of Na?
3. How is is regulated?
4. What can alter sodium levels?

Answer 3

1. Chloride or bicarbonate
2. Maintains water in the body
3. RAAS (circulating volume), ADH (osmolarity)
4. Loss of sodium/water (volume depletion), loss of water alone

Question 4

1. What activates the RAAS system?
2. What produces renin?
3. What converts angiotensin I to II
4. What is the function of angiotensin II?
5. What does aldosterone cause?

Answer 4

1. Low blood pressure, low perfusion, renal ishaemia, low Na in DCT
2. Kidneys
3. ACE- angitensin converting enzymes
4. Vasoconstriction and acts on adrenal gland to produce aldosterone
5. Na retention, H20, K loss

Question 5

Describe the activation, production and action of ADH

Answer 5

• Blood osmotic pressure increases
• Osmoreceptors in hypothalamus
• Increases thirst response
• Produces ADH
• H20 reabsorbed in collecting duct to prevent dehydration

Question 6

What can be caused hyponatraemia?

Answer 6

Lose
* GI losses
* Kidney losses
* ‘third space loss’
* Addisons- no aldesterone
* Drugs- furosemide

Gain water- CHF, iatrogenic

Random
* Increased plasma osmolarity- severe hyperglycemia, mannitol therapy

Question 7

What can cause hypernatraemia?

Answer 7

Lose water and a bit of sodium- hypotonic fluid loss
* GI losses
* Kidney losses
* Post-obstructive diuresis

Lose water
* Heat stroke
* Pyrexia
* Diabetes insipidus- when deprived of water
* No access to water
* Adipsia

Gain salt
* Excessive intake
* Iatrogenic

Question 8

What controls the concentration of K in plasma?

Answer 8

Aldosterone
and insulin

Important for the cell membrane potential- cannot fire properly

Question 9

What are the clinical signs of hypokalaemia?

Answer 9

Muscle weakness
PUPD
Anorexia
Ileus/constipation

< 3mmol/l
Mainly Intra cellular so extracellular changes (plasma) matter

Question 10

What can cause hypokalaemia?

Answer 10

Decreased intake
* Anorexia
* Fluid therapy

Translocation- ECF to ICF
* Insulin
* Catecholamines

Potassium loss
* GI
* Renal
* Excess aldosterone
* Drugs- loop diurectics

Question 11

What are the clinical signs of hyperkalaemia?

Answer 11

• Muscle weakness
• Cardiac abnormalities
• Bradycardia- atrial standstill, life threatening conduction abnormalities

Question 12

How can hyperkalaemia be artefactual?

Answer 12

Common
* K+ EDTA contamination
Hyperkalaemia
Hypocalcaemia
ALP low
* Aged samples- leukocytosis, thrombosis

Question 13

What can cause hyperkalaemia?

Answer 13

Decreased urinary excretion
* Urethral obstruction
* Bladder rupture
* Anuric
* Addisons
* Drugs- ACE inhibitors, K sparing diurectics

Translocation
* Insulin defiency
* Tumour lysis syndrome
* Extensive reperfusion injuries

Increased intake
* iatrogenic
* exccessive K supplementation

Question 14

How is hyperkalaemia treated?

Answer 14

IVFT
* 0.9% NaCL or Hartmanns
* ± 5% glucose

Insulin
Calcium gluconate- cardiac effects, monitor on ECG

Question 15

What hormone is most important for controlling plasma osmolarity?

Answer 15

ADH

Question 16

Which organ failure is commonly associated with hyponatraemia?

Answer 16

Heart

Question 17

What are the three fractions calcium is found in the body?

Answer 17

Protein bound- albumin mainly
Complexed- other anions- P, S, Bicarb
Ionised- biologically active- regulated by PTH and vit D

Question 18

1. What are the clinical signs of hypercalcaemia?
2. What are the most common causes?
3. What are less common causes?

Answer 18

1. PUPD
2. Malignancy- lymphoproliferative disease, anal sac adenocarcinoma
   Renal Failure
   Primary hyperparathyroidism
3. Addisons, vitamin D toxicity, bone lesions, artefact

Question 19

What are the clinical signs of hypocalcaemia?

Answer 19

Muscle tremors, twitches, cramps
Seizures
Restlessness, behavioural changes

Question 20

What diseases/causes need to be ruled out for hypocalcaemia?

What can cause hypocalcaemia?

Answer 20

Rule out- hypoalbuminaemia
Error- EDTA or citrate tube

Real
* Eclampsia- pregnancy
* Renal disease
* Hypoparathyroidism
* Post thyroidectomy in cats
* Nutritional- all meat diet
* Ethylene glycol toxicity
* Acute pancreatitis

Question 21

What regulates phosphate?

Answer 21

Parathyroid hormone

Over all effect of PTH is to retain calcium and increase P excretion

Question 22

What can cause hyperphosphataemia?

Answer 22

Failure to excrete
* Decreased GFR
* UT obstruction/rupture

Increased release from bone
* Young animals

Increased intake
* Hypervitaminosis D
* High phosphate diet

Hypoparathyroidism
Tumour lysis syndrome

Question 23

What can cause hypophosphataemia?

Answer 23

Rarely a concern
* Anorexia
* Insulin use in DKA
* Primary hyperparathyroidism
* Hepatic lipidosis

Question 24

How does EDTA affect blood samples?

Answer 24

High K, low Ca