Acute Kidney Injury

Question 1

How much of the the CO does the kidney receive?

Answer 1

25%

Question 2

How can you define AKI?

Answer 2

a decline in the GFR that occurs during a short period of time (2-7 days)

Question 3

How is GFR measured?

Answer 3

Creatinine - endogenous product in muscle cells at a constant rate e.g if excretion rate drops your kidney function has dropped (whole lecture on this)

Question 4

Whats the difference between AKI stage 1, 2 and 3 on blood tests?

Answer 4

Stage 1 - serum creatine increased by 50%
Stage 2 - serum creatine increased 2 fold
Stage 3 - serum creatinine increased 3 fold

Question 5

What are some issues with serum creatinine testing?

Answer 5

As creatinine is a marker of muscle breakdown, if you don’t eat enough, your serum creatinine will be low - same as if low muscle mass

Question 6

What are the 3 causes of AKI?

Answer 6

Pre-renal, renal and post-renal

Question 7

What does pre-renal causes include?

Answer 7

Perfusion problems - the kidneys not receiving a lot of blood;

• hypovolaemia due to shock, burns, dehydration, sepsis, haemorrhage
• reduced effective circulating volume e.g. congestive cardiac failure and liver disease
• Drugs
• Renal artery stenosis

Question 8

How does hypovolaemia cause AKI?

Answer 8

there is decreased effective circulating volume so less blood reaches the kidney so less blood is filtered so GFR decreases

Question 9

What kind of drugs cause AKI and how do they do this?

Answer 9

NSAIDS, ACE inhibitors and antihypertensives

-they alter the renal haemodynamics - imparted renal auto regulation

Question 10

Is pre-renal disease reversible?

Answer 10

Yes because kidney injury has not occurred yet, they are just unable to maintain the blood flow and hence GFR but it has to be recognised quickly

Question 11

What is ATI?

Answer 11

Acute tubular injury - this is when the kidney cells get damaged and stop working - ischaemia or toxin damage

Question 12

In what case does ATI develop from pre-renal AKI?

Answer 12

if pre-renal AKI is sustained for long enough, ATI can occur. The kidney cells can become starved of oxygen and the cells with the highest metabolic requirements and those in the areas that are less well perfused are at risk i.e. PCT

Question 13

What other renal causes are there of AKI?,

Answer 13

• drug toxicity - NSAIDS, antibiotics, ACE inhibitors (cause low blood pressure as hypotension leads to hypo perfusion of kidneys)
• Sepsis
• Hypertension
• vasculitis
• emboli
• kidney stones?

Question 14

What is vasculitis?

Answer 14

inflammation of the blood vessels - can cause AKI as protein and blood can leak into the urine caused by decreased kidney function

Question 15

What are the post-renal causes or AKI?

Answer 15

post-renal indicates an obstruction of urine flow after urine has left the tubules

• bladder outflow obstruction (BPH, urethral strictures)
• retroperitoneal fibrosis
• tumours
• stones

Question 16

What is significant about renal stones in renal failure and AKI?

Answer 16

For renal stones to cause AKI/renal failure, they must occur in both kidneys or in a single functioning kidney

Question 17

What is the difference between AKI and CKD?

Answer 17

AKI is an acute change in renal function whereas CKD is a decline in GFR that occurs over months to years

Question 18

What is the treatment for AKI?

Answer 18

Depends on the cause;

• with pre-renal you need to restore renal perfusion e.g. fluid administration
• if urinary tract obstruction then need to re-establish urine flow

Question 19

When would a patient need dialysis?

Answer 19

if the kidneys can no longer adequately excrete salt, water, K+ or other waster products OR if acid base balance can no longer be maintained

Question 20

Why is it clinically important to know difference between renal and pre-renal cause of AKI?

Answer 20

renal cause needs prompt referral to nephrology but pre-renal needs supportive treatment and management of precipitating events

Question 21

What is the best way to diagnose AKI?

Answer 21

Urine dipstick test, USS, microscopy, culture, blood tests

Question 22

What is oliguria?

Answer 22

less than 500ml of urine per day

Question 23

What is anuria and what does it indicate?

Answer 23

less than 100ml of urine per day - indicates a blockage of urine flow or very severe damage to kidneys - less common form of AKI

Question 24

What is uraemia?

Answer 24

the accumulation of nitrogenous metabolic waste produces in the blood - urea and creatinine

Question 25

What is the difference between AKI and CKD in regards to uraemia?

Answer 25

in acute, uraemia develops rapidly within a few days, in chronic there is gradual onset over a few months-years

Question 26

Why are elderly more predisposed to uraemia?

Answer 26

Falls in the elderly - may stay in same position for a while
Muscle breakdown - myoglobin released into blood and filtered by kidney. Myoglobin causes inflammatory reaction causing kidneys to shut down - rhabdomyolysis

Question 27

What are some renal causes of acute renal failure?

Answer 27

• direct damage to kidney
• inflammation
• infection
• drugs
• autoimmune diseases

Question 28

What is acute glomerularnephritis?

Answer 28

Inflammation of the glomerulus most commonly caused by systemic lupus erythromyetusis

Question 29

What is acute tubular necrosis?

Answer 29

Death of cells in the nephron - 50% of ARF have this

Question 30

What is acute interstitial nephritis?

Answer 30

Inflammation of interstitial space in the kidneys - most common due to allergic reaction or infection

Question 31

Why do you get a decreases in GFR in ARF?

Answer 31

• (vascular changes) - vasoconstriction causing increase adhesion of inflammatory cells
• (tubular changes) - necrosis and apoptosis forming necrotic bodies and cause obstruction in the tube so the filtrate cant get through