Urea and Electrolytes Flashcards
Describe what is measured in U&Es
- Na, K and creatinine are fitted as standard,
- Urea for hospital patients on request by GP’s,
- Cl freely on request,
- Bicarbonate on request for hospital patients
What are the extracellular and intracellular concentrations of sodium and potassium
Sodium; ECF - 140. ICF - 10
Potassium; ECF - 5. ICF; 150
What are some physiological and theraputic compensatory mechanisms
Physiological - Thirst, ADH, renin.
Theraputic - IV therapy, diuretics and dialysis
What occurs when you replace fluid loss with isotonic or hypotonic fluid
Isotonic - Sodium remains slightly increased with no fluid redistribution.
Hypotonic - Na restored and fluid distribution.
How is ADH analysed?
- Measuring plasma and urine osmolality. If urine is greater than plasma then it suggests ADH is active
When is ADH released?
When there is a rise in concentration of osmotically active particles. It decreases renal water loss and increases thirst
How is the RAAS activated?
Reduced intra-vascular volume. This can be due to Na depletion or haemorrhage
How is RAAS status measured?
- Measure plasma and urine Na.
- If urine is <10mmol/L it suggests R/A/A active
What is the clinical significance of urine reference intervals
They are not as clinically important so blood results tend to be of more clinical importance. Gives a rough guide of kidney capacity
Describe features of urea
It is a normal breakdown product of protein and is a sensitive marker of dehydration. Often parallels sodium levels during fluid correction.
Describe what low and elevated urea levels are found in
Elevated - Gastric blead, CCF, shock, MI, severe burns.
Low - Low protein intake and increased IV fluids
Describe features of creatinine
Breakdown product of protein and muscle. Loss of renal function leads to a decrease in filtered volume and hence increase in plasma conc. Plasma and urine values typically reflect muscle mass
What is the GFR and what is influenced by?
It is the volume of fluid passing through the glomerulus in a given period of time. It is influenced by renal perfusion pressure, renal vascular resistance, glomerular damage and post-glomerular resistance. It is the best overall measure of kidney function
Describe features of eGFR and AKI flags
- Estimated GRF is used to aid staging CKD. Values based on creatinine.
- AKI flags used to flag up incipient acute kidney injury. Highlights subtle change in renal function. Values based on creatinine
What is pseudohyponatraemia?
Falsely low sodium levels when there is hyperlipidaemia or hyperproteinaemia
