3. Electrolytes and the Kidney

Question 1

what is urea

Answer 1

produced in the liver
excretion of ammonia and breakdown products of amino acids
excreted in urine

Question 2

normal serum urea

Answer 2

1.7 - 8.3 mmol/l

Question 3

urea levels in disease

Answer 3

decreased in liver disease

increased in intravascular depletion, blood meal (GI haemorrhage) and renal failure

Question 4

symptoms when urea >20mmol/l

Answer 4

nausea
decreased appetite 
itchiness 
tiredness
smelly breath 
metallic taste in mouth

Question 5

symptoms when urea >60mmol/l

Answer 5

extreme uraemic frost
uraemic pericarditis
encephalopathy

Question 6

what is creatinine

Answer 6

breakdown of creatinine phosphate in muscle
usually produced at fairly constant rate by the body
not toxic itself
less affected by fluid shifts

Question 7

how is creatinine cleared

Answer 7

only cleared by the kidney

the less the number of nephrons, the more build up of creatinine

Question 8

normal creatinine level

Answer 8

62 - 106 umol/l - dependent on muscle mass
old lady - 63 umol/l
muscular male - 106 umol/l

Question 9

eGFR at CKD stages

Answer 9

CKD 1 - >90mls 
CKD 2 - >60mls 
CKD 3a - >45mls 
CKD3b - >30mls
CKD 4 - >15mls 
CKD 5 - <15mls

Question 10

calculations for eGFR

Answer 10

MDRD

Cockroft and Gault

Question 11

hyponatraemia and disorders of urine dilution

Answer 11

disorders of urine dilution underlie hyponatraemia
defect with Na/Cl transport out of thick ascending loop/distal convoluted tubule
continued secretion of ADH, stimulated by non-osmotic mechanism

Question 12

hyponatraemia diagnostic approach

Answer 12

assess volume status

• hypovolaemia: measure urinary Na+
• euvolaemia
• hypervolaemia: measure urinary Na+

Question 13

hyponatraemia and hypovolaemia with urinary Na+>20mmol/l

Answer 13

renal losses

• diuretic excess
• mineralocorticoid deficiency
• salt-losing neophripathy
• bicarbonaruria with renal tubular acidosis and metabolic alkalosis
• ketonuria
• osmotic diuresis
• cerebral salt wasting

Question 14

hyponatraemia and hypovolaemia with urinary Na+<20mmol/l

Answer 14

extrarenal losses

• vomiting
• diarrhoea
• third spacing of fluids in burns, pancreatitis, trauma

Question 15

hyponatraemia and euvolaemia

Answer 15

• glucocorticoid deficiency
• hypothyroidism
• stress
• drugs
• SIADH

Question 16

hyponatraemia and hypervolaemia with urinary Na+>20mmol/l

Answer 16

acute or chronic renal failure

Question 17

hyponatraemia and hypervolaemia with urinary Na+<20mmol/l

Answer 17

• nephrotic syndrome
• cirrhosis
• cardiac failure

Question 18

how is potassium abrosbed

Answer 18

efficiently absorbed from GI tract

present in most foods (bread, avocado, chocolate, leafy green veg)

Question 19

where is potassium distributed

Answer 19

major cellular cation

however, is distributed intracellularly and intracellularly

Question 20

normal serum K+

Answer 20

3.2 - 5.1 mmol/L

Question 21

causes of hypokalaemia

Answer 21

redistribution:
- insulin
- theophylline
- adrenergic use
non-renal loss:
- sweating
- vomiting
-diarrhoea
poor diet
renal loss

Question 22

hypokalaemia caused by renal loss

Answer 22

drugs - diuretics, aminoglycosides, amphotericin
RTA or metabolic acidosis
Low BP - Bartter’s or Gittleman’s
High BP
high aldosterone, normal cortisol - hyperaldosteronism
low aldoseterone, normal cortisol - Liddle’s
low aldosterone, high cortisol -Cushing’s

Question 23

cardiovascular complications in chronic hypokalaemia

Answer 23

hypertension

ventricular tachycardia

Question 24

endocrine complications in chronic hypokalaemia

Answer 24

impairs insulin and sensitivity

Question 25

muscular complications in chronic hypokalaemia

Answer 25

impairs muscle contraction

Question 26

renal complications in chronic hypokalaemia

Answer 26

mild tubulointerstitial fibrosis
renal cyst formation
metabolic alkalosis (increased net renal excretion)
polyuria

Question 27

liver complications in chronic hypokalaemia

Answer 27

increased renal ammonia production - may worse hepatic encephalopathy

Question 28

hyperkalaemia

Answer 28

present <1% healthy adults
kidneys have very large capacity to excrete K+
indicates impaired renal excretion

Question 29

causes of hyperkalaemia

Answer 29

impaired renal excretion - CKD 4/5
drugs imparing secretion - spironolactone, amiloride, ACE inhibitors, ARBs
increased K+ load - rhabdomyolysis, haemolysis, GI bleed
increased intake
peusdohyperkalaemia - haemolysis (during blood collection/storage, rheumatoid/infectious mononucleosis)

Question 30

drugs that impair K+ secretion

Answer 30

spironolactone
amiloride
ACE inhibitors
ARBs

Question 31

hyperkalaemia treatment

Answer 31

back into cells:
- salbutamol 
- insulin and dextrose 
- sodium bicarbonate (if acidotic) 
stablisation: calcium gluconate
removal: 
- pee it out, iv fluids and diuretics 
dialysis

Question 32

body pH

Answer 32

7.35 - 7.45

essential for functioning of proteins, enzymes etc

Question 33

how is body pH maintained

Answer 33

large net acid production: 1mmol H+/kg
buffers provide immediate defence against acid/alkali
resp system regulates CO2 tension
kidneys regulate HCO3 tension

Question 34

how is HCO3 recovered in kidneys?

Answer 34

in proximal tubule:
- broken down into water and CO2 in lumen
- combines with OH- in cell to reform HCO3
- transported out to interstitium
in cortical collecting duct:
- water and CO2 in cell broken to make HCO3-
- transported out of cell - exchanged with Cl-

Question 35

managing acid-base disturbance

Answer 35

determine underlying cause (drugs, AKI, CKD, dehydration)
reverse underlying cause
replace/remove
renal interventions

Question 36

sodium bicarbonate in severe metabolic acidaemia

Answer 36

generally safe to give isotonic NaHCO3 1.26%

removing stimulus to production of lactate/ketones will allow oxidative mechanisms