Clinical Pathology: Approach To Water and Electrolyte Imbalances Flashcards
How are the following electrolytes distributed (inside/outside cells) generally?
Inside
* K
* Mg
* S- sulfate
* P
Outside
* Na
* Cl
Why is sodium not found in cells?
Na/K pump- maintains the balance of Na outside
- What are sodiums balancing anions?
- What is the function of Na?
- How is is regulated?
- What can alter sodium levels?
- Chloride or bicarbonate
- Maintains water in the body
- RAAS (circulating volume), ADH (osmolarity)
- Loss of sodium/water (volume depletion), loss of water alone
- What activates the RAAS system?
- What produces renin?
- What converts angiotensin I to II
- What is the function of angiotensin II?
- What does aldosterone cause?
- Low blood pressure, low perfusion, renal ishaemia, low Na in DCT
- Kidneys
- ACE- angitensin converting enzymes
- Vasoconstriction and acts on adrenal gland to produce aldosterone
- Na retention, H20, K loss
Describe the activation, production and action of ADH
- Blood osmotic pressure increases
- Osmoreceptors in hypothalamus
- Increases thirst response
- Produces ADH
- H20 reabsorbed in collecting duct to prevent dehydration
What can be caused hyponatraemia?
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
What can cause hypernatraemia?
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
What controls the concentration of K in plasma?
Aldosterone
and insulin
Important for the cell membrane potential- cannot fire properly
What are the clinical signs of hypokalaemia?
Muscle weakness
PUPD
Anorexia
Ileus/constipation
< 3mmol/l
Mainly Intra cellular so extracellular changes (plasma) matter
What can cause hypokalaemia?
Decreased intake
* Anorexia
* Fluid therapy
Translocation- ECF to ICF
* Insulin
* Catecholamines
Potassium loss
* GI
* Renal
* Excess aldosterone
* Drugs- loop diurectics
What are the clinical signs of hyperkalaemia?
- Muscle weakness
- Cardiac abnormalities
- Bradycardia- atrial standstill, life threatening conduction abnormalities
How can hyperkalaemia be artefactual?
Common
* K+ EDTA contamination
Hyperkalaemia
Hypocalcaemia
ALP low
* Aged samples- leukocytosis, thrombosis
What can cause hyperkalaemia?
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
How is hyperkalaemia treated?
IVFT
* 0.9% NaCL or Hartmanns
* ± 5% glucose
Insulin
Calcium gluconate- cardiac effects, monitor on ECG
What hormone is most important for controlling plasma osmolarity?
ADH
Which organ failure is commonly associated with hyponatraemia?
Heart
What are the three fractions calcium is found in the body?
Protein bound- albumin mainly
Complexed- other anions- P, S, Bicarb
Ionised- biologically active- regulated by PTH and vit D
- What are the clinical signs of hypercalcaemia?
- What are the most common causes?
- What are less common causes?
- PUPD
- Malignancy- lymphoproliferative disease, anal sac adenocarcinoma
Renal Failure
Primary hyperparathyroidism - Addisons, vitamin D toxicity, bone lesions, artefact
What are the clinical signs of hypocalcaemia?
Muscle tremors, twitches, cramps
Seizures
Restlessness, behavioural changes
What diseases/causes need to be ruled out for hypocalcaemia?
What can cause hypocalcaemia?
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
What regulates phosphate?
Parathyroid hormone
Over all effect of PTH is to retain calcium and increase P excretion
What can cause hyperphosphataemia?
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
What can cause hypophosphataemia?
Rarely a concern
* Anorexia
* Insulin use in DKA
* Primary hyperparathyroidism
* Hepatic lipidosis
How does EDTA affect blood samples?
High K, low Ca
