Session 9 - Acute Kidney Injury

Question 1

Give 2 clinical methods for defining AKI

Answer 1

• Increase in serum creatinine by >26.5 umol/L within 48 hours OR
• Increase in serum creatinine by >1.5 times baseline within 7 days OR
• Urine volume <0.5 ml/kg/h for 6 hrs - oligouria

Question 2

What are the 3 main types of AKI?

Answer 2

1) Pre-renal 2) Renal 3) Post-renal

Question 3

What is pre renal AKI? What causes pre renal AKI?

Answer 3

• Reduction in renal perfusion
• Is a physiological response to renal hypoperfusion

Pre-renal failure can also be caused by a reduction in the effective ECF volume such as in hypovolemia due to blood loss, systemic vasodilation as in anaphylaxis and sepsis, or in cardiac failure.

Question 4

How can the autoregulatory mechanisms of the renal system be overcome to cause pre renal AKI?

Answer 4

o NSAIDS – prevent vasodilation of afferent arteriole

o ACE inhibitors – prevents vasoconstriction of efferent arteriole

o Disease of afferent arteriole – diabetes mellitus, hypertension etc.

Question 5

What happens in acute tubular necrosis? What is it caused by?

Answer 5

• Ischemia
• Nephrotoxin
• Sepsis

ATN – Renal cells damaged, cannot be immediately reversed. Damaged cells cannot reabsorb salt and water efficiently or expel excess water

Question 6

How would you differentiate between pre renal and ATN? Why does this method work?

Answer 6

• Na+ reabsorbed in pre-renal AKI to restore volume but reduced in renal AKI due to tubular cell damage
• Can therefore use sodium reabsorption to tell what stage the AKI is in.
• Fractional Sodium Excretion = (urine Na+/Plasma Na+) / (urine Creatinine / plasma creatinine) x 100
• In pre-renal the FENa is <1%. In ATN the FENa is >1%.

Question 7

What is a nephrotoxin?

Answer 7

Damage the epithelial cells lining the tubules and cause cell death and shedding into the lumen. Can be endogenous or exogenous e.g. drugs

Question 8

Give 2 examples of an endogenous nephrotoxin

Answer 8

myoglobin, urate, bilirubin

Question 9

Give 2 examples of an exogenous nephrotoxin

Answer 9

drugs (e.g. ace inhibitors, NSAIDs, gentamicin), x-ray contrast, other poisons.

Question 10

What is rhabdomyolysis and how does it cause AKI? In whom does it occur?

Answer 10

• Muscle necrosis results in large release of myoglobin.
• Can occur from drug users, elderly, wars, natural disasters
• Results in AKI

Question 11

What is acute glomerulonephritis? What forms can it take?

Answer 11

o Immune disease affecting the glomeruli

o Can be primary (only affecting kidneys) or secondary (systemic)

o Secondary e.g. systemic lupus erythematosis

Question 12

How does endothelium damage lead to RBC destruction?

Answer 12

o Endothelium damage results in platelet thrombus, which results in partial obstruction of small arteries and the destruction of RBCs

Question 13

Give the pathology of a post-renal AKI

Answer 13

1) Obstruction with continuous urine production results in rise in intraluminal pressure
2) Results in dilatation of renal pelvis
3) Which produces a decrease in renal function

Question 14

Give the 3 types of post renal AKI

Answer 14

1) Obstruction within the lumen
2) Obstruction within the wall
3) Obstruction by pressure from the outside

Question 15

Give 2 things that can cause an obstruction in the lumen of the ureters

Answer 15

• Stones
• Blood clots
• Papillary necrosis – sloughed papillae following infection and ischaemia
• Tumour of renal pelvis, ureter, bladder

Question 16

Give 2 causes of post renal AKI within the wall of the ureters

Answer 16

Congenital causes:

• Pelviureteric neuromuscular dysfunction
• Megaureter – Dilated ureter
• Neurogenic bladder – lack of bladder control

Non congenital:

• Ureteric stricture e.g. post-TB

Question 17

Give 3 causes of post renal AKI due to pressure from the outside

Answer 17

• Prostatic hypertrophy
• Tumours
• Aortic aneurysm
• Diverticulitis
• Accidental ligation of ureter

Question 18

What indications in serum biochemistry would occur in AKI?

Answer 18

Increased urea and creatinine in all causes of AKI

Question 19

Fill in

Answer 19

Question 20

What is a RBC cast?

Answer 20

Cylindrical structure in urine made up of RBC

Question 21

How would you treat pre renal AKI?

Answer 21

• Immediate infusion of IV fluids to increase renal perfusion
• Avoid nephrotoxins
• Can force alkaline diuresis to remove myoglobin – use a drug to make the urine alkaline to draw out myoglobin

Question 22

How would you treat ATN?

Answer 22

• Prevent volume overload by restricting dietary NA and water intake (<1L per day)
• Prevent hyperkalaemia – restrict dietary K, Ca gluconate, dextrose and insulin (uptake of K into cells),
• Prevent acidosis – Protein restriction, sodium bicarbonate infusion

Question 23

When would you use dialysis for ATN?

Answer 23

• Metabolic acidosis where sodium bicarbonate infusion is not appropriate
• Fluid overload refractory to diuretics
• Presence of dialyzable nephrotoxin
• High K+ refractory to treatment (not treatable with treatment due to refractory period)

Question 24

What are the 3 main types of proteinuria? Define them

Answer 24

1) Glomerular proteinuria – An increase in the permeability of the glomerulus to protein due to damage of the bowman’s capsule
2) Tubular proteinuria – Tubulointersitial disease impairs reabsorption of low molecular weight proteins at the PCT
3) Overflow proteinuria – Overproduction of smaller proteins leads to a rate of filtration that exceeds the transport maximum for reabsorption at the PCT.

Question 25

Define nephrotic syndrome

Answer 25

Defined as proteinuria sufficient to cause hypoalbuminaemia and hence peripheral oedema. Proteinuria needs to exceed 5g/24hr.

Question 26

Describe how lowered oncotic pressure can lead to oedema in 2 ways

Answer 26

1) Lowered oncotic pressure –> oedema
2) Hypovolemia results which stimulates RAS –> increase in aldosterone production
3) Aldosterone stimulates salt and water retention –> increased oedema.

Question 27

What is nephrological and urological haematuria?

Answer 27

Nephrological haematuria – results from glomerular inflammation and bleeding

Urological haematuria – Due to renal stones, renal cell carcinoma, tubular cell carcinoma

Question 28

What features would suggest nephrological as opposed to urological haematuria? Give 3 things

Answer 28

o Abnormal renal function

o Proteinuria

o Salt and water retention

o Hypertension

o Young age (uroepithelial malignancy unlikely)

Question 29

What 2 urinary features would you find in glomerulonephritis?

Answer 29

• Dysmorphic red cells
• Red cell cast