Chempath 19: Assessment Of Renal Function 2

Question 1

Define acute kidney injury ?

Answer 1

Rapid abrupt reduction in kidney function leading to inability to maintain electrolytes, acid-base and fluid haemostasis

Question 2

A patient on the ward has an increase of creatinine clearance of 30 µmol/L. Is this patient having an AKI ?

Answer 2

Yes

AKI stage 1: increase of serum creatinine by >= 26µmol/L or >1.5 x reference serum creatinine

AKI stage 2: >2x reference serum creatinine

AKI stage 3: >3x reference serum creatinine or increase >= 354µmol/L

Question 3

Outline 2 physiological mechanisms that work to maintain GFR and renal blood flow at a constant rate ?

Answer 3

Myogenic stretch- If the afferent arteriole is stretched due to high pressure, it will constrict in order to keep blood pressure entering Glomerulus constant (and GFR)

Tubuloglomerular feedback- High chloride ions are detected in the afferent arteriole, this triggers it to constrict to reduce GFR and chloride ions in the distal tubule

Question 4

List 4 pre-renal causers of AKI (excluding drugs) ?

Answer 4

Haemorrhage
Hypotension (shock, sepsis, anaphylaxis)
Oedema (HF, Cirrhosis, nephrotic syndrome)
renal artery stenosis

Question 5

List 4 drugs that can cause pre-renal AKI ?

Answer 5

ACE inhibitors- reduce efferent arteriole vasoconstriction
NSAIDs - decreases afferent arteriole dilation
Calcineurin inhibitors- decrease afferent arteriole dilation
Diuretics- reduce preload, affect tubular function

Question 6

What is the difference between AKI and ATN (acute tubular necrosis) ?

Answer 6

AKI has no structural damage and responds immediately to restoration of the circulation volume.

ATN is caused by Ischaemic damage and will not respond to correction of the circulating volume.

Question 7

In ATN what feature may be seen in the urine on microscopy?

Answer 7

Epithelial cell casts

Question 8

List 4 post renal causes of AKI?

Answer 8

Renal calculi (stones)
BPH
Blocked urinary catheter 
Urethral strictures 
Cervical cancer

Anything that blocks the outflow of urine from the kidneys. This causes increased pressure in the tubules, which reduces the pressure gradient across the Bowman’s capsule and hence causes GFR to decline.

Question 9

List 4 renal causes AKI?

Answer 9

Glomerulonephritis
ATN
Small vessel vasculitis- (HSP, Churg-Strauss syndrome, microscopic polyangitis, granulomatosis with polyangitis)
Interstitial nephritis

Question 10

What measure is used to stage Chronic kidney disease (CKD)

Answer 10

GFR

Question 11

Which stage of CKD is considered end-stage kidney failure?

What GFR indicates this ?

Answer 11

Stage 5

GFR <15 or dialysis dependent

Question 12

Which one of these is not considered a common risk factor for CKD ?

A) Diabetes mellitus 
B) Obesity 
C) hypertension 
D) drinking 5 glasses of water per day 
E) Renal stones
F) Polycystic kidney disease

Answer 12

D) drinking 5 glasses of water per day

This is a healthy amount of water

All the others are risk factors for CKD

Question 13

Which 3 endocrine functions of the kidneys may be disturbed during CKD ?

Answer 13

EPO- required for haemopoiesis
RAS- renin release for ADH secretion
Vitamin D- The kidney activates vitamin D to calcitriol

Question 14

What kind of acid base dysfunction would you expect in CKD ?

Answer 14

Metabolic Acidosis

You can no longer make HCO3- ions to mop up excess H+

Question 15

List some signs/symptoms of Uraemia ?

Answer 15

Nausea and vomiting 
Progressive weakness
Shallow respiration 
coma 
Tremor

Question 16

Which electrolyte is most markedly abnormal in CKD ?

Answer 16

K+

There is a hyperkalaemia because the kidney exchanges the excess H+ ions in the blood with intracellular pottasium

Question 17

What treatments are there for hyperkalaemia ?

Answer 17

Calcium gluconate (cardioprotective) 
Insulin with glucose (Insulin causes uptake of K+ into cells)
Salbutamol (NA-K ATP pump on liver and muscles causes K+ uptake)
Sodium bicarbonate (corrects metabolic acidosis but slower)

Question 18

How does CKD cause Osteopenia ?

Answer 18

• Excess H+ ions are not mopped up by HCO3-

- H+ can be exchanged for calcium in the bone

Question 19

What type of anaemia is associated with CKD ?

Answer 19

Anaemia of chronic disease

Normocytic normochromic

Question 20

Are the levels low or high in CKD ?

Phosphate
Calcium
PTH
Calcitriol

Answer 20

Phosphate: High
Calcium: Low/ normal
PTH: high
Calcitriol: Low

Calcium is very confusing in CKD. It is low because of low activated vitamin D (calcitriol). But this causes high PTH which releases more calcium from the bone so can make the level normal. In long standing CKD there may be tertiary hyperparathyroidism which causes high calcium

Question 21

Give an example of a potassium sparing diuretic ?

Answer 21

Spironolactone

Question 22

What is renal osteodystrophy ?

What signs would you expect ?

Answer 22

A constellation of bone diseass associated with CKD in which phosphate is high and calcium is low causing increased PTH release. This causes bone resorption.

Signs: osteopenia, Osteomalacia, salt and pepper skull (osteoschlerosis), brown tumours, “rugger jersey spine”.