Fluid and Electrolytes Balance Flashcards
How is sodium excreted? What hormones regulate sodium output?
excreted via
- kidneys (urine), sweat and gut (faeces/diarrhoea/prolonged vomiting)
aldosterone
- secreted by the adrenal gland
- increases expression of Na channels and Na/ATPase pump in the cell membrane of the distal tubule and collecting duct
= sodium and water reabsorption, potassium excretion
atrial natriuretic peptide
= increases renal excretion of sodium and water
What causes hyponatraemia?
loss of sodium
- vomiting, fistulae, Addison’s disease (low cortisol, aldosterone and adrenaline)
water retention
- inappropriate secretion of anti-diuretic hormone/vasopressin
diuretics
selective serotonin reuptake inhibitors (SSRI’s)
What are the signs and symptoms of hyponatraemia?
signs = volume depletion due to reduced osmotic pressure
- hypotension, decreased urine output, decreased skin turgor, soft/sunken eyeballs, dry mucous membrane
symptoms
- nausea, malaise, headache, lethargy, reduced level of consciousness
seizure and coma are not normally seen until sodium levels are < 100-115mmol/L
What is the effect of hyponatraemia on lithium?
toxicity of lithium is made worse by sodium depletion
- tremor, nausea, diarrhoea, headache, dry mouth, poor concentration
What causes hypernatraemia?
water depletion
- reduced water intake
= dysphagia, post operative
- excessive water loss
- diabetes insipidus
- sweating
- hyperventilation
sodium retention
- excessive intake
= over infusion of saline
- excessive adrenocorticol hormones
= conn’s syndrome (excessive aldosterone), Cushing’s syndrome (purple stretch marks, weight gain)
What are the symptoms of hypernatraemia?
manifest when 2L of water has been lost
thirst, dry mouth, apathy, oliguria (reduced urine output), skin turgor, general weakness
What is the main function of potassium? How is potassium excreted? What hormones regulates potassium? What is the relationship between potassium and hydrogen?
function
- maintenance of neuromuscular excitability
excretion
- kidneys (urine), gut (faeces)
insulin
- stimulates cellular uptake of potassium
reciprocal relationship between potassium and hydrogen
high H+ = low K+
low H+ = high K+
What is hyperkalaemia caused by?
renal failure
mineralocorticoid deficiency
- hypoaldosteronism/Addison’s disease
acidosis
hormonal effects
drugs
- ACE inhibitors, spironolactone (K sparing diuretic)
excessive doses of potassium supplements
How can hyperkalaemia be managed?
insulin - moves potassium into cells
salbutamol - lowers potassium levels
theophylline - lowers potassium levels
bicarbonate - goes from acidosis to alkalosis
calcium gluconate (cannot be given with bicarbonate or will form sodium gluconate salt)
What are the symptoms of hyperkalemia?
cardiac toxicity
- tachycardia
- ventricular fibrillation
- asystole
What causes hypokalaemia?
GI losses - vomiting, diarrhoea
renal losses in renal tubular failure
alkalosis
drug induced - diuretics, corticosteroids, beta agonists, theophylline
hyperaldosteronism - conn’s syndrome
What drug can worsen hypokalaemia?
digoxin
- can cause digoxin toxicity
= acts on the Na/K ATPase pump and in the absence of K, it has increased effects
What is hypocalcaemia caused by?
What are the symptoms of hypocalcaemia?
hypoparathyroidism
- typically causes Ca release from bones
vitamin D deficiency
renal disease
numbness of fingers
tingling
burning of extremities
tetany when levels fall to 1.5-1.6mmol/L
What is hypercalcaemia caused by?
What are the symptoms of hypercalcaemia?
hyperparathyroidism
vitamin D overdose
neoplasms
bone diseases - Paget’s disease
lethargy
confusion
depression
dementia
irritability
headache
generalised muscle weakness
GI problems - anorexia, constipation
cardiac arrhythmia
