Acute Kidney Injury

Question 1

What is AKI?

Answer 1

AKI is decreased renal function following insult to the kidney
Measured by serum creatinine or urine output
Occurs over hours-days

Question 2

Define AKI

Answer 2

AKI is defined as:

Rise in creatinine > 26umol/L within 48h
Rise in creatine > 1.5x baseline within 7 days
Urine output < 0.5ml/kg/hr for > 6 hours

Question 3

What is stage 1 AKI?

Answer 3

Rise in creatinine > 26umol/L (0.3mg/dL) within 48h or
Rise in creatine 1.5 - 1.9x baseline within 7 days
Urine output < 0.5ml/kg/hr for 6-12 hours

Question 4

What is stage 2 AKI?

Answer 4

Rise in creatine 2.0-2.9x baseline within 7 days

Urine output < 0.5ml/kg/hr for > 12 hours

Question 5

What is stage 3 AKI?

Answer 5

Rise in creatinine > 353.6umol/L (4mg/dL) within 48h or
Rise in creatine >3.0x baseline within 7 days or
RRT
Urine output < 0.3ml/kg/hr for >24hours or anuria for >12h

Question 6

What are causes of AKI?

Answer 6

Pre-renal

• reduced perfusion of the kidneys
• reduced vascular volume
• reduced CO
• systemic vasodilation
• renal vasoconstriction

Renal

• intrinsic kidney disease
• glomerular
• interstitial
• vessels

Post-renal

• obstruction to the urine
• renal tract
• extrinsic compression

Question 7

What are prerenal causes of AKI?

Answer 7

Reduced vascular volume
- Haemorrhage, diarrhoea & vomiting, burns, pancreatitis

Cardiac output reduced
- Cariogenic shock, MI

Systemic vasodilation
- Sepsis, drugs

Renal vasoconstriction
- NSAIDs, ACE-i, ARB, hepatorenal syndrome

Question 8

What are renal causes of AKI?

Answer 8

Glomerular
-Glomerulonephritis, acute tubular necrosis (prolonged renal hypo perfusion causing intrinsic renal damage)

Interstitial
- Drug reaction, infection, infiltration

Vessels
- Vasculitis, DIC

Question 9

What are post renal causes of AKI?

Answer 9

Within renal tract
- stones, malignancy, stricture, clot

Extrinsic compression
- pelvic malignancy, prostatic hypertrophy, retro-peritoneal fibrosis

Question 10

What are risk factors for AKI?

Answer 10

CKD
Organ failure - heart failure, liver disease
DM
Hx of AKI
Nephrotoxic drug use (NSAIDs, ACEi ARB, diuretics, ahminoglycosides) in past week
Contrast agents in past week
Age 65+

Question 11

What happens when the kidneys stop working? Clinical features? Complications?

Answer 11

Reduced urine output
Fluid overload –> pulmonary, peripheral oedema
Rise in molecules that kidney normally excretes –> hyperkalaemia, acid base imbalance, acidosis, arrhythmias
Uraemia –> pericarditis, encephalopathy

Question 12

When should you treat hyperkalaemia?

Answer 12

Treat if >6.5mmol/L or any ECG changes

Question 13

What investigations for AKI?

Answer 13

Bedside:
Urinalysis - dipstick for proteinuria/haematuria suggesting intrinsic renal disease

Bloods:
U&E
LFT
FBC - platelets

Imaging:
USS - small kidneys suggest CKD, asymmetric kidneys suggest renal vascular disease

Other:
Vasculitis screen if indicated

Question 14

How do you differentiate between acute and chronic renal failure?

Answer 14

Kidneys are small bilaterally in CKD

Question 15

When should you refer to the renal team?

Answer 15

Unresponsive AKI
Complications - hyperkalaemia, acidosis, fluid overload
Stage 3
Fluid balance difficult
Intrinsic renal disease
AKI + HTN

Question 16

What are some nephrotoxins?

Answer 16

Radiological contrast dye
Aminoglycosides
NSAIDs
ARBs
ACEi
Diuretics - especially potassium sparing
Metformin