Acute Kidney Injury

Question 1

What is acute kidney injury?

Answer 1

• Decline in renal excretory function over hours or days, recognised by the rise in serum urea and creatinine

Question 2

What are the criteria for AKI?

Answer 2

• Stage 1 - ↑serum creatinine ≥0.3mg/dL or ↑ 1.5-2 fold from baseline, urine output <0.5ml/kg for >6hrs
• Stage 2 - ↑serum creatinine 2-3 fold from baseline, urine output <0.5mg/kg for >12hrs
• Stage 3 - ↑serum creatinine >3 fold from baseline or >4mg/dL with an acute increase of at least 0.5mg/dL, urine output <0.3mg/kg for 24 hrs or anuria for 12hrs

Question 3

What are the pre-renal (circulatory) causes of AKI?

Answer 3

• Hypotension
• Hypovolaemia (i.e. dehydration, burns, diarrhoea, haemorrhage)
• Hypoperfusion
• Heart failure
• Hypoxia
• Sepsis (vasodilation so effective prefusion reduced)
• Drugs, toxins

Question 4

What are the renal (cells of the kidney) causes of AKI?

Answer 4

• Acute tubular necrosis
• Obstructive
• GN (primary and secondary)
• Acute tubulointerstitial nephritis
• Vasculitis
• Atheroembolic

Question 5

What are the post-renal (obstruction) causes of AKI?

Answer 5

• Calculi
• Tumours (ureter, bladder, prostate, cervix, ovarian, can be extrinsic)
• Ureter or urethral strictures
• Lymph nodes (compression)
• Prostate enlargement

Question 6

What is the process of recovery from AKI?

Answer 6

• Often polyuric phase for 48-72hrs
• May be up to 6l urine/day
• Often subsequent low K, Ca, Mg as low urine quality
• Tubules fail to concentrate urine

Question 7

What is involved in the emergency management of AKI?

Answer 7

• ABCs (restore renal perfusion, treat hyperkalaemia and pulmonary oedema)
• Remove causes (drugs, sepsis)
• Exclude obstruction and consider renal causes
• ICU or renal unit
• Dialysis may be required

Question 8

How is hyperkalaemia treated?

Answer 8

• K<6.0 abnormal but no immediate concern
• K 6.0-6.4 risk of arrhythmia – needs treatment especially if ECG changes
• K>6.5 medical emergency
• Give calcium resonium to reduce absorption from the gut
• Insulin and dextrose to move potassium into cells (watch BM)
• Calcium gluconate as cardiac membrane stabiliser
• If HCO3 <16 give bicarbonate supplementation

Question 9

What are the indications for dialysis in AKI?

Answer 9

• Refractory potassium ≥6.5 mmol/l
• Refractory pulmonary oedema
• Acidosis (pH <7.1)
• Uraemia (especially is urea >40)
• Toxins (lithium, ethylene glycol)

Question 10

What are the risk factors for AKI?

Answer 10

• CKD
• HF
• DM
• Liver disease
• Age >65 years
• Cognitive impairment
• Nephrotoxic medications
• Use of contrast medium

Question 11

Investigation in AKI

Answer 11

• Urinalysis
  
  • Leukocytes and nitrates suggest infection
  • Protein and blood suggest acute nephritis
  • Glucose suggests diabetes
• US of urinary tract to rule out obstruction

Question 12

Management of AKI

Answer 12

• Treat underlying cause
• Fluid rehydration with IV fluids in pre-renal AKI
• Stop nephrotoxic medications
• Relieve obstruction in post-renal AKI

Question 13

Complications of AKI

Answer 13

• Hyperkalaemia
• Fluid overload, heart failure and pulmonary oedema
• Metabolic acidosis
• Uraemia (can lead to encephalopathy or pericarditis)