Plasma electrolytes Flashcards
Sodium
Major extracellular cation, major effect on osmotic pressure
Hyponatremia: usually due to excess water in thebody >> dilutes the sodium
Hypernatremia: excessive sweating, vomiting, diarrhoea, use of diuretics, diabetic ketoacidosis
Kidney failure = hyponatremia because excess fluid is not removed from the body
Potassium
Major intracellular cation
Very little effect on osmotic pressure
Hypokalameia: due to poor uptake, vomiting, diarrhoea, alkalosis, when insulin is given (K+ follows glucose into cells)
Hyperkalaemia: results in depolarisation of skeletal muscle fibres, neruons and cardiac cells and does not allow for repolarisation - causes heart to seize. Causes mental confusion, numbness and weak resp. muscles
Chloride
Main extracellular anion
Hypochloraemia: due to defective renal tubular absorption, vomiting, diarrhoea and metabolic acidosis
Hyperchloraemia: dehydration, excessive dietary salt, aspirin toxicity, CHF, cystic fibrosis
*In CF sweat Cl levels are 2-5x higher than normal
Bicarbonate
Principal function is to maintain acid-base balance as part of the buffer system
Calcium
Needed for muscle contraction, anzyme activity and coagulation
Absorbed in the intestine through the action of vitamin D >> low vitamin D >> poor absorption
Hypocalcaemia: hypoparathyroidism
Hypercalcaemia: primary hyperparathyroidism, malignancies (breast, lung and multiple myeloma)
Phosphate
Hypophosphatemia: use of antacids, during alcohol withdrawal and malnutrition
Hyperphosphatemia: impaired renal function and acute lymphocytic leukaemia
Creatinine
Indicator of renal health
Breakdown product of creatine phosphate
Removed purely by the kidneys therefore a good measure of GFR ‘rough and dirty GFR measurement’
High creatinine = low GFR
60-110micromol/ L for men
45-90micromol/L for women
Urea
Small nitrogenous compound, main end-product of protein catabolism
Made in the liver from ammonia and bicarbonate
Main component of urine
Blood urea nitrogen (BUN) rises in AKI 🧁
Decreased GFR = less urea and creatinine filtered out, levels in the blood rise
Urine osmolality
Determined by the concentration of solutes
High osmolality = high solute concentration
Patient is hyponatremia, this will be corrected with fluids but what are the risks?
Too fast: osmotic demyelination
Improvement of electrolyte distrubance followed by pseudobulbar palsy, LOC level, coma, death
* To avoid this, Na+ levels are only raised by 4 to 6 mmol/l in a 24-hour period
Too slow: cerebral oedema
