Session 10: Acute Kidney Injury

Question 1

% of cardiac output the kidney receives.

Answer 1

25%

Question 2

Definition of AKI.

Answer 2

A decline in the GFR that occurs during a short period of time.

Question 3

What is AKI currently measured by?

Answer 3

The GFR is measured by a raise in serum creatinine.

Serum creatinine is however not the ideal marker.

The serum creatinine gives us a way to use a formula that provides an estimated GFR (eGFR)

Question 4

Criteria for AKI.

Answer 4

A rise in serum creatinine of 26 micromol/L or greater within 48 hours.

A 50% of greater rise in serum creatinine where the baseline is known within the past 7 days.

A fall in urine output to less than 0.5 ml/kg/hour for more than 6 hours in adults and more than 8 hours in children and young people.

A 25% or greater fall in eGFR in children and young people within the past 7 days.

Question 5

How is the severity of AKI assessed?

Answer 5

By stages (Stage 1-3)

Question 6

Stage 1 AKI.

Answer 6

1.5-1.9 serum creatinine from baseline or a 26.5 micromol increase.

<0.5 ml/kg/h for 6-12 hours urine output

Question 7

Stage 2 AKI.

Answer 7

2.0-2.9 times serum creatinine of the baseline.

<0.5 ml/kg/h of urine output for >12 hours.

Question 8

Stage 3 AKI.

Answer 8

3.0 times baseline serum creatinine.

Increase in serum creatinine >350 micromol/l

<0.3 ml/kg/h >24 hours or anuria for over 12 hours

Question 9

Why is it important to account for the baseline of serum creatinine when assessing kidney function?

Answer 9

Because serum creatinine can vary a lot in patients.

Muscular black males will have a higher serum creatinine compared to small white elderly women e.g.

Question 10

AKI may be oliguric or non-oliguric.

What is oliguria?

Answer 10

Less than 500 ml of urine per day or less than 20 ml per hour.

Question 11

Definition of anuria.

Answer 11

Defined as less than 100 ml of urine per day.

Question 12

What does anuria usually indicate?

Answer 12

Blockage of urine flow or very severe damage to kidneys.

Question 13

What is uraemia?

Answer 13

Defined as the clinical signs and symptoms of kidney failure.

Results in a lack of secretory and excretory function in the kidneys.

Question 14

Aetiology of AKI can be divided into three major categories.

Which?

Answer 14

Pre-renal

Renal/Intrinsic

Post-renal

Question 15

What is pre-renal disease defined as?

Answer 15

Decreased renal perfusion.

Question 16

Explain why poor renal perfusion leads to pre-renal disease.

Answer 16

As BP declines beneath a threshold level the kidney will be unable to maintain blood flow that is required to maintain an adequate GFR.

This leads a decrease in GFR.

Question 17

Is pre-renal disease reversible?

Answer 17

It is, if it’s recognised quickly enough and hasn’t caused damage to the kidneys.

Question 18

What is most common;

Pre-renal

Renal

Post-renal

Answer 18

Pre-renal (85%)

Question 19

Give causes of pre-renal disease.

Answer 19

Hypovolaemia

Decreased CO

Congestive heart failure

Liver failure

Renal artery stenosis

Medication like NSAIDs, ACE-I and ARB.

Cyclosporine

Question 20

What is the most common cause of renal/intrinsic disease?

Answer 20

Acute tubular injury (ATI)

Question 21

What is the most common cause of ATI?

Answer 21

Pre-renal disease being left untreated.

Question 22

Explain how Pre-renal disease can cause ATI.

Answer 22

Kidney cells are starved of O2. This leads to the cells which have the highest metabolic requirements and the areas which are not well perfused are at risk of damage.

These are the proximal tubules.

Question 23

Give causes of renal/intrinsic kidney disease.

Answer 23

ATI

Drugs like NSAIDs, ACE-inhibitors, Gentamicin etc…

Glomerulonephritis

Ischaemia

Sepsis/Infection

Vasculitis

Nephrotoxins

Rhabdomyolysis

Myeloma

Question 24

What is post-renal disease?

Answer 24

Obstruction to urine flow after urine has left the tubules.

Can lead to hydronephrosis e.g.

Question 25

What does AKI treatment depend on?

Answer 25

Depends on the type.

Pre-renal

Renal

Post-renal

Question 26

Treatment of AKI.

Answer 26

With pre-renal disease restoration of renal perfusion is important.

Treat underlying cause like giving fluids or treating pump failure.

If it is post-renal then looks for stones or other causes.

Question 27

Treatment in case of ATI.

Answer 27

Recovery can take several weeks and treatment is supportive.

Good kidney perfusion

Avoiding nephrotoxins

Restricting various solutes like potassium and phosporous.

Nutritional support

Question 28

If the kidney can no longer adequately excrete salt, water, potassium or other waste products or if the acid-base balance has stopped working

What treatment is suggested?

Answer 28

Dialysis to get rid of these.

Question 29

How does treatment differ in pre-renal vs. intrinsic?

Answer 29

In intrinsic the causes may be more severe and difficult to diagnose. In pre-renal the treatment is usually supportive whereas in intrinsic immunosuppression e.g. might be needed.

Question 30

What investigations are very important in AKI?

Answer 30

Urine dipstick and blood pressure.