Urea and Electrolytes Flashcards
1
Q
What is measured in Us and Es?
A
- standard: Na, K and creatinine
- on request: urea, Cl, bicarbonate
- calculated additions: eGFR, AKI flags
2
Q
How would you assess ADH function?
A
- measure plasma and urine osmolality
- urine > plasma suggests ADH is active
3
Q
How would you assess renin/angiotensin/aldosterone status?
A
- measure plasma and urine Na+
- if urine <10 mmol/L then renin/angiotensin/aldosterone is active
4
Q
Describe the importance of urea
A
- sensitive marker of dehydration
- sodium and urea concentrations often parallel each other during fluid correction
- elevated: gastric bleed, congestive heart failure, shock, MI, severe burns
- low: low protein intake, increased IV fluids
5
Q
Describe features of creatinine
A
- breakdown product of protein and muscle
- filtered freely at glomerulus
- plasma and urine values reflect muscle mass
6
Q
How is urea and creatinine used together?
A
- markers of renal dysfunction
- loss of renal function leads to decrease in filtered volume and increased plasma concentrations of urea and creatinine (waste products not being excreted)
- why it is important to get baseline measurements so you can keep an eye on pattern
7
Q
What is eGFR and AKI flags used for?
A
- eGFR (estikmated glomerular filtration rate): aids staging of chronic kidney disease
- AKI flag: used to flag developing acute kidney injury by highlighting subtle changes in renal function
- both calculated based on creatinine
8
Q
What are the dangerous values for potassium and reasons for it?
A
- <3 or >6 mmol/L
- cardiac conduction defects
- abnormal neuromuscular excitability
9
Q
How does potassium affect acid base balance?
A
- K+ and H+ are exchanged across the cell membrane so changes in pH can causes changes in K+
- acidosis: potassium moves out of cells => high potassium
- alkalosis: potassium moves into cells => low potassium
- K+ excess/depletion can also have an effect
10
Q
What are some causes of high potassium?
A
- delay in sample analysis/haemolysis/drug therapy
- renal: acute/chronic renal failure
- acidosis
- mineralcorticoid dysfunction: adrenocortical failure/mineralcorticoid resistance
- cell death: cytotoxic therapy
11
Q
What are some causes of low potassium?
A
- low intake
- increased fluid loss (diuretics/osmotic diuresis/tubular dysfunction/mineralcorticoid excess)
- GI (vomiting/diarrhoea/fistulae)
- low serum K+ without depletion (alkalosis/insulin/glucose therapy)
12
Q
Describe the effects of potassium depletion
A
- acute changes in ICF and ECF ratios which have a neuromuscular effect:
- lethargy, muscule weakness, heart arrhythmias
- chronic loss from ICF (same effect as ^)
- affects kidneys: polyuria and alkalosis (increased renal HCO3 production)
- affects vascular system and gut
13
Q
What are the considerations when looking at Us and Es?
A
- steady state
- patient’s clinical state
- effects of compensatory mechanism
- effect of drugs and infusions
