AKI

Question 1

Define AKI

Answer 1

An abrupt (<48hrs) reduction in kidney function defined as:

• An absolute increase in serum creatinine by >26.4µmol/l or by > 50%
• OR a reduction in UO to < 0.5ml/kg/h for >6hrs

Question 2

How is AKI staged ?

Answer 2

Using KDIGO

Serum creatinine is used in practice as urine output is not measured well

• Stage 1 AKI - Serum Cr Increase >26µmol/L or Increase > 1.5-1.9 x reference Cr
• Stage 2 AKI - Increase > 2 to 2.9 x reference SCr
• Stage 3 AKI - Increase > 3 x reference SCr or increase to > 354µmol/L or need for RRT

Question 3

What are the 3 main categories for AKI ?

Answer 3

• Pre-renal - anything that reduces the blood supply to the kidney
• Renal - these are intrinsic renal causes
• Post-renal - anything obstructive

Question 4

What are the pre-renal causes of AKI ?

Answer 4

Essentially renal hypoperfusion

This can be caused by:

• Haemorrhage
• Volume depletion (e.g. D&V, burns)
• Shock - e.g. sepsis, anaphylaxis
• NSAIDs / COX-2, ACEi / ARBs

Question 5

Outline the pathophysiology of AKI

Answer 5

1. Hypoperfusion - due to volume depletion, sepsis etc
2. Causes decreased intravascular volume
3. In response to this ADH and aldosterone is secreted
4. This results in Na+ and water retention
5. Therefore oliguria (reduced urine output)
6. AKI insuses

Question 6

Describe the mechanism by which ACEi can caused reduced GFR ?

Answer 6

1. ACEi inhibit Angiotensin II
2. Angiotensin controls mediates vasoconstriction of the afferent arterioles so if this is inhibited there will be vasodilatation of the arterioles
3. This will reduce the pressure in the afferent arteriole coming to the glomerular capillary which will result in a smaller NET pressure difference ==> reduced GFR

Question 7

How can ACEi’s cause AKI ?

Answer 7

• Due to lowering the GFR if a patient becomes unwell with vomiting or diarrhoea, or they have bilateral renal artery stenosis reducing the perfusion of the kidneys
• Then they run the risk of causing a major decrease in GFR which can result in AKI

Question 8

When should ACEi be stopped then ?

Answer 8

If someone on them is unwell with diarrhoea/vomiting, or dehydrated

Question 9

What is the other class of drug which can cause hypoperfusion to the kidneys so should be stopped during the times ACEi’s would be stopped ?

Answer 9

• NSAID’s
• They are COX2 inhibitors

Question 10

What does untreated pre-renal AKI lead to ?

Answer 10

Acute tubular necrosis - a condition involving the death of tubular epithelial cells that form the renal tubules of the kidneys

Question 11

What are the causes of acute tubular necrosis ?

Answer 11

• sepsis and severe dehydration
• rhabdomyolysis and drug toxicity

Question 12

What is the treatment of pre-renal and renal AKI ?

Answer 12

• Fluid Challenge for hypovolaemia (so give saline solution)
• If they still have low BP then could give vasopressors – e.g. adrenaline, dopamine, noradrenaline
• Treat underlying cause
• If patient uraemia, severe metabolic acidosis, hyperkalaemia refractory to medical management, or volume overload unresponsive to diuretics the do dialysis

Question 13

What is the general mechanism of renal AKI ?

Answer 13

Diseases causing inflammation or damage to cells causing AKI

Question 14

What are the different structures within the kidney which can be damaged to result in renal AKI ?

Answer 14

• Blood vessels
• Glomerular disease
• Interstitial Injury
• Tubular Injury

Question 15

So building on what structures could be damaged in the kidney to cause renal AKI, what are the specific causes of renal AKI ?

Answer 15

• Vascular - vasculitis, renovascular disease
• Glomerular - GN
• Interstitial Nephritis - usually due to drugs
• Tubular Injury - Ischaemia—prolonged renal hypoperfusion, Drugs (gentamicin), Contrast, Rhabdomyolysis

Question 16

What is rhabdomyolysis and who is usually affected by this causing AKI ?

Answer 16

Rhabdomyolysis is a serious syndrome due to a direct or indirect muscle injury. It results from the death of muscle fibers and release of their contents into the bloodstream, these contents can cause damage to the kidneys.

IVDU are commonly affected by this - they get things like compartment syndrome which can cause the death of muscle ==> AKI

Question 17

What are the signs/symptoms of AKI ?

Answer 17

Non specific symptoms:

• Anorexia, weight loss, fatigue, lethargy
• Nausea & Vomiting
• Itch
• Fluid overload
• Oedema, SOB

Signs:

• Fluid overload incl HTN, Oedema, Pul oedema, effusions (pleural & pulmonary)
• Uraemia incl itch, sign is pericarditis (a pericardial rub)
• Oliguria

Question 18

What are some of the clues which can point you to the renal cause of the AKI ?

Answer 18

• Rash ==> vasculitis, lupus
• Haemoptysis ==> goodpastures
• Sore throat ==> post streptococcal GN, IgA nephropathy
• Urinanalysis ==> Blood and protein in the urine will indicate intrinsic cause e.g. a vasculitis
• On any drugs e.g. Gentamicin
• Have they had an angiogram recently ==> contrast causing AKI

Question 19

What are the different investigations done to try and figure out the cause of AKI ?

Answer 19

U&Es - check renal function

FBC & Coagulation Screen:

• Low plateletes - HUS? TTP?
• Abnormal clotting - DIC, Septic?
• Anaemia - CKD ? Myeloma?

Urinalysis - Haematoproteinuria suggesting active GN

USS - Obstruction ?Size

Immunology - ANA (SLE), ANCA (Vasculitis), GBM (Goodpastures)

Protein electrophoresis & BJP - myeloma (everyone over 50yrs)

Question 20

What is the definite test done to diagnosis a renal cause of AKI ?

Answer 20

Renal biopsy

Question 21

What are some of the urgent indications to do a renal biopsy ?

Answer 21

• Suspected rapidly progressive GN
• Positive Immunology & AKI

Question 22

What are some of the contraindications for a renal biopsy ?

Answer 22

• Uncontrolled hypertension increases the risk of bleeding so needs to be controlled prior to biopsy
• Coagulation defects or thrombocytopaenia – these needs to be corrected before biopsy
• On warfarin, aspirin
• Untreated urine infection