Acute Kidney Injury

Question 1

What is AKI?

Answer 1

Acute kidney injury (AKI) is defined as an acute drop in kidney function.

Question 2

How is AKI diagnosed?

Answer 2

It is diagnosed by measuring the serum creatinine.

Question 3

What is the NICE criteria for AKI?

Answer 3

• Rise in creatinine of ≥ 25 micromol/L in 48 hours
• Rise in creatinine of ≥ 50% in 7 days
• Urine output of < 0.5ml/kg/hour for > 6 hours

Question 4

What is the serum creatinine?

Answer 4

The waste product filtered by the kidney, that can be measured.

Question 5

What are the risk factors for AKI?

Answer 5

Consider the possibility of an acute kidney injury in patients that are suffering with an acute illness such as infection or having a surgical operation. Risk factors:

Chronic kidney disease
Heart failure
Diabetes
Liver disease
Older age (above 65 years)
Cognitive impairment
Nephrotoxic medications (NSAIDS and ACE inhibitors e.g. ramipril)
Use of a contrast medium such as during CT scans

Question 6

What are the causes of renal impairment, please categorise them?

Answer 6

Pre renal
Renal
Post-renal

Question 7

What are the pre renal causes of AKI?

Answer 7

Inadequate blood supply may be due to:
Dehydration
Hypotension (shock)
Heart failure

Question 8

What are the renal causes of AKI?

Answer 8

Glomerulonephritis
Interstitial nephritis
Acute tubular necrosis

Question 9

What are the post renal causes of AKI?

Answer 9

Obstruction may be caused by:

Kidney stones
Masses such as cancer in the abdomen or pelvis
Ureter or uretral strictures
Enlarged prostate or prostate cancer

Question 10

What is meant by a pre-renal cause to AKI?

Answer 10

Pre-renal pathology is the most common cause of acute kidney injury. It is due to inadequate blood supply to kidneys reducing the filtration of blood. Inadequate blood supply may be due to several things such as dehydration etc.

Question 11

What is meant by the renal causes of AKI?

Answer 11

This is where intrinsic disease in the kidney is leading to reduced filtration of blood.

Question 12

What is meant by the post renal causes of AKI?

Answer 12

Post renal acute kidney injury is caused by obstruction to outflow of urine from the kidney, causing back-pressure into the kidney and reduced kidney function. This is called an obstructive uropathy.

Question 13

What investigations would you use to investigate an AKI?

Answer 13

1. Urinalysis for protein, blood, leucocytes, nitrites and glucose.
2. Leucocytes and nitrites suggest infection
3. Protein and blood suggest acute nephritis (but can be positive in infection)
4. Glucose suggests diabetes
5. Ultrasound of the urinary tract is used to look for obstruction. It is not necessary if an alternative cause is found for the AKI.

Question 14

How can you AKI be avoided?

Answer 14

By avoiding nephrotoxic medications, ensuring adequate fluid input in unwell patients, including IV fluids if they are not taking enough orally.

Question 15

How would you manage a patient with AKI?

Answer 15

The first step to treating an acute kidney injury is to correct the underlying cause:

• Fluid rehydration with IV fluids in pre-renal AKI
• Stop nephrotoxic medications such as NSAIDS and antihypertensives that reduce the filtration pressure (i.e. ACE inhibitors)
• Relieve obstruction in a post-renal AKI, for example insert a catheter for a patient in retention from an enlarged prostate

Question 16

What are the complications of AKI?

Answer 16

1. Hyperkalaemia
2. Fluid overload, heart failure and pulmonary oedema
3. Metabolic acidosis
4. Uraemia (high urea) can lead to encephalopathy or pericarditis