Electrolytes & minerals Flashcards
Which electrolytes/minerals are extracellular?
Sodium
Chloride
Bicarbonate
Which electrolytes/minerals are intracellular?
Potassium
Phosphate
Proteins
Magnesium
Sulphate
Name the major cation in the ECF
Sodium
What is the function of sodium?
Maintains water in the body
How are sodium and water regulated in the body?
RAAS - controls circulating volume
ADH - controls osmolarity
Describe the RAAS
- Renin converts angiotensinogen into angiotensin I
- Conversion of angiotensin 1 to angiotensin 2 is done by angiotensin converting enzyme (ACE)
- Angiotensin 2 acts on the adrenal gland to release aldosterone
- Angiotensin 2 also causes vasoconstriction -> increased BP
- Increased BP + aldosterone -> Na retention and water retention with K loss
Describe the function of ADH
- ADH is released from the pituitary gland in response to an increase in blood osmotic pressure
- ADH causes increased permeability of the collecting duct
- Water is reabsorbed to prevent further dehydration
Loss of sodium and water is due to?
Volume depletion
What are the causes of hyponatraemia?
- Losing sodium: GI loss, kidney loss, Addisons, Drugs (Furosemide)
- Gaining water: CHF, iatrogenic
- Other: Increased plasma osmolarity e.g. severe hyperglycaemia
What are the causes of hypernatremia?
- Hypotonic fluid loss - lose water and abit of sodium: GI loss, kidney loss
- Free water loss - losing water: heat stroke, pyrexia, diabetes insipidus, no access to water, adipsia
- Gain salt - excessive intake
Potassium concentration in plasma is controlled by?
Aldosterone
Describe filtration of potassium
Freely filtered at the renal glomerulus then resorbed
How are hypo and hyperkalaemia defined by plasma K concentrations?
Hypo = K < 3mmol/l
Hyper = K > 7.5mmol/l
List the clinical signs of hypokalaemia
Muscle weakness
PU/PD
Anorexia
Ileus / constipation
What are the causes of hypokalaemia
- Decreased intake: anorexia, fluid therapy with a low K fluid
- Translocation from ECF to ICF: insulin, catecholamines
- Loss: GI, renal, drugs
What are the clinical signs of hyperkalaemia?
Muscle weakness
Cardiac abnormalities
- Bradycardia
Describe the ECG of a pateint with hyperkalaemia
Lost P wave as the AV node cant work, spikey tall T waves
Atrial standstill
Life threatening conduction abnormalities
Fast rhythms are also possible
What are the causes of hyperkalaemia?
- Artefactual
- Decreased urinary excretion: urethral obstruction, bladder rupture, addisons, drugs
- Translocation from ICF to ECF: insulin deficiency, tumour lysis syndrome
- Increased intake: iatrogenic, excess supplementation
Name 2 drugs that could cause hyperkalaemia
ACE inhibitors
K sparing diuretics
How is hyperkalaemia treated?
- IVFT: 0.9% NaCl, or Hartmann’s
- Insulin: can help drive potassium into cells
- Calcium gluconate
- Treat primary cause e.g. Addison’s, DKA, AKI, FLUTD, etc
Name a hormone that affects potassium levels
Insulin
Name a hormone that affects sodium levels
ADH
What is the most important hormone for controlling plasma osmolarity?
ADH
Failure of which organ is commonly associated with hyponatraemia?
Heart
What % of calcium is ioinised?
50%
What % of calcium is protein bound?
40%
What is the main clinical sign of hypercalcaemia?
PUPD
What are the most common causes of hypercalcaemia?
- Malignancy
- LYMPHOPROLIFERATIVE DISEASES = By far the most common cause
- Anal sac adenocarcinoma
- Many others - Renal failure
- Primary hyperparathyroidism
List some less common causes of hypocalcaemia
Addison’s disease
Vitamin D toxicity E.g. Cholecalciferol rodenticide toxicity
Bone lesions e.g. OSA
Artefact: Lipaemia, haemolysis
List the clinical signs of hypocalcaemia
Muscle tremors, twitches, cramps
Seizures
Restlessness, behavioural changes
What needs to be ruled out as the cause of hypocalcaemia?
Hypoalbuminaemia
Error: EDTA or citrate tube
List the causes of hypocalcaemia
- Eclampsia
- From the day before whelping to about 2 days after
- Emergence - Renal disease
- Hypoparathyroidism
- Post thyroidectomy in cats
- Nutritional - all meat diet
- Ethylene glycol toxicity
- Acute pancreatitis
Phosphate homeostasis is regulated by …?
Parathyroid hormone (PTH)
What is the overall effect of PTH?
Retain calcium and increase phosphorus excretion…i.e. to reduce plasma [PO4]
List the causes of hyperphosphataemia
- Failure to excrete
- Decreased GFR e.g kidney disease
- UT obstruction/rupture - Increased release from bone - Young animals
- Increased intake
- Hypervitaminosis D
- High phosphate diet - Hypoparathyroidism
- Tumour lysis syndrome
- Spurious: Haemolysis: tends to be mild
List the causes of hypophosphataemia
Rarely a clinical concern but can be sometimes:
- Anorexia (cat)
- Insulin use in DKA
- Primary hyperparathyroidism
- Hepatic lipidosis in cats
In hypoparathyroidism, what happens to serum phosphate?
Increases
You get some EDTA in your serum sample by mistake. What is the effect?
High K, low Ca
A dog is overdosed on benazepril. What is the effect on serum electrolytes?
High potassium as RAAS is inhibited
A dog presents with tremors, focal seizures, and pawing at the face. What electrolyte change is present?
Hypocalacemia
