Biol 131 L8.pdf

Urea and electrolytes (‘U and Es’) • Sodium, potassium, urea, creatinine, chloride, bicarbonate • Testing patient’s fluid and electrolyte balance and renal function The kidney • Regulates extracellular fluid volume and electrolyte balance • Excretion of waste products • Selective reabsorption • Sec...

Urea and electrolytes (‘U and Es’) • Sodium, potassium, urea, creatinine, chloride, bicarbonate • Testing patient’s fluid and electrolyte balance and renal function The kidney • Regulates extracellular fluid volume and electrolyte balance • Excretion of waste products • Selective reabsorption • Secondary endocrine function 20 Urea and creatinine • Urea – breakdown product of protein (occurs in the liver) • Creatinine produced in muscles Serum urea and creatinine increase if the Glomerular Filtration Rate (GFR) in kidney is reduced (so less excreted). P36-37 Gaw 21 Electrolyte abnormalities - Intake, uptake and loss of sodium and potassium - Intricately linked to water balance Where sodium goes, water follows! 22 Reabsorption of sodium and water ADH (vasopressin) from pituitary gland causes reabsorption of water in collecting ducts Aldosterone from adrenal gland causes reabsorption of sodium in nephron and hence water. 23 Sodium (135-145 mmol/l) • Intake balances loss normally • Gastrointestinal tract (GI tract) major site of sodium loss in non-renal associated disease 24 HYPERNATRAEMIA (Na > 145mmol/l) • Examples of causes P20-21 Gaw • Water depletion • Excessive sodium intake • Renal failure • Clinical signs: blood pressure decreased (or increased if salt gain); urine output down; dry mucous membranes… • Treat: • Oral water • IV 5% dextrose Decreased skin turgor in severe dehydration 25 HYPONATRAEMIA via water retention (Na < 135 mmol/l) Oedematous • Heart failure? • Decrease in effective blood volume • Aldosterone and ADH secreted • SALT and water retained P16-19 Gaw Treatment: diuretic and restrict fluid + treat condition. Non-oedematous • ADH released all the time (infection,malignancy,…), Syndrome of inappropriate antidiuresis (SIAD). • Too much water reabsorbed by kidney • If occurs over long period of time – body adapts so non-oedematous. Treatment: restrict fluid 26 HYPONATRAEMIA via sodium loss Na < 135 mmol/l Examples of causes: • Vomiting, diarrhoea • Lack of Na intake • Lack of aldosterone (Na lost in urine) Clinical signs e.g.: • Tachycardia • Hypotension Treatment: oral correction of sodium loss 27 P16-19 Gaw POTASSIUM (3.4-4.9 mmol/l) • K+ determines resting potential of cells. • Excitable cells (nerves and muscles) behave differently if K concentration alters • Rapid changes (acute) cause dangerous cardiac arrhythmias that can result in death! 28 Potassium HYPERKALAEMIA HYPOKALAEMIA K + > 4.9 mmol/l Can lead to cardiac arrest. K + < 3.4 mmol/l Weak, cardiac arrhythmias. • Examples of causes: renal failure, adrenal failure, K+ release from damaged cells. • Examples of causes: Vomiting, diarrhoea, diuretics Treatment examples: Calcium gluconate, Insulin + glucose, Dialysis P22-25 Gaw Treatment: Oral or IV potassium (slowly with ECG monitoring). 29 Acute Renal Failure (ARF) • Anuric (no urine) or oliguric (<400ml/day) • Fast onset (hours, days) - Reversible • Biochemical findings: • Concentrated urine • Serum urea and creatinine increase • Hyperkalaemia -nephron can’t excrete K when GFR decreases. • Treatment – treat underlying disease; dialysis if severe P37 Gaw • Causes: • Pre-renal – blood supply to kidney failure • Renal – damage to kidney tissue • Post-renal –Obstruction blocks urinary drainage 30 Chronic renal failure • Slow onset (months, years) - IRREVERSIBLE • Biochemical findings: • Hyperkalaemia -nephron can’t excrete K when GFR decreases. Danger • Serum urea and creatinine high P38-39 Gaw • Management: • sodium restriction • diuretics • dietary restriction of protein • oral ion exchange resin (K removal) • Longer term: dialysis or transplant 31 Some example reference ranges *NOTE – always use the reference ranges provided by the lab performing the test – these are just examples. You are not expected to learn these values. In a test or exam, you would be provided with these, if necessary. Analyte Plasma Reference Range/Interval Na+ 135-145 mmol/l K+ 3.4-4.9 mmol/l Cl- 95-105 mmol/l Urea 2.5-8.0 mmol/l HCO3Creatinine 21-28 mmol/l 40-130 µmol/l 32 Mnemonics that may help you remember symptoms/causes of electrolyte imbalances 33