Acute Kidney Injury (AKI)

Question 1

Define Acute Kidney Injury (AKI) and Acute Renal Failure (ARF)

Answer 1

Acute Renal Failure

• A rapid decline in renal excretory function, acid-base balance and removal of solutes and water

Acute Kidney Injury

• Abrupt reduction in kidney function
• Determined by an absolute increase in serum creatinine of
  
  • >=26.4umol/L within 48hr
  • >=50% (1.5xbaseline) within 7 days
  • Reduction in urine output documented as oliguria <0.5mL/kg for 6hrs

Question 2

Outline the staging of AKI

Answer 2

1. Stage 1
   
   • Creatinine clearance
     
     • Inc >=26.4umol/L within 48hr
     • 1.5-2 fold increase from baseline
   • Urine output
     
     • <0.5mL/kg for 6hrs
2. Stage 2
   
   • Creatinine clearance
     
     • >2-3 fold increase from baseline
   • Urine output
     
     • <0.5mL/kg for >12hr
3. Stage 3
   
   • Creatinine clearance
     
     • >3 fold increase
     • Or serum >350umol/L with an acute rise of 1.5 fold within 7days
   • Urine output
     
     • <0.3mL/kg for 24hr or anuria for 12hr

Question 3

Outline the risk factors for AKI

Answer 3

• Old septic heart failing diabetic with CKD & PVD

Question 4

Outline the causes of AKI

Answer 4

1. Pre-renal (perfusion)
   
   • Volume depletion (hypovolaemia)
   • Hypotension, pump failure
   • Sepsis
   • Cirrhosis
   • Renal artery stenosis
   • NSAID’s or ACE-i
2. Renal (organ)
   
   • Established acute tubular necrosis - ischaemic or toxic
   • Glomerulonephritis/ vasculitis
   • Tubulointerstitial nephritis
   • Nephrotoxins (aminoglycosides, amphotericin B, tetracyclines)
3. Post-renal (obstruction)

Question 5

How would you assess and investigate AKI?

Answer 5

Assessment

• Drug history
• Acute or chronic?
  
  • Chronic → comorbidities, previous U&E
  • Small kidneys on US (<9cm) with inc. echogenicity
  • Anaemia: low Ca²⁺, high PO₄^3- occur in days (so may be chronic or acute) but absence indicates acute
• UT obstruction?
  
  • Suspect if; 1 kidney functioning, history of renal stones, BPH, previous pelvic/ retroperitoneal surgery
  • Examine for palpable bladder, pelvic or abdo mass, enlarged prostate
  • Complete anuria suggests obstruction
  • US for renal pelvic and calyces dilating
• Rare cause of AKI?
  
  • eg Glomerulonephritis

Investigations;

• Urine dipstick (presence of haemat/proteinuria may indicate GN, vasculitis)
• U&Es (beware of inc K⁺)
• FBC
• ABG
• CRP
• ESR
• ECG - hyperkalaemia?
• Renal US - size/ obstruction
• LFT - is albumin falling? Consider GN
• Clotting
• CK - rhabdomyolysis [damaged muscle breaks down & breakdown products damage kidneys]
• Blood cultures & urine MC&S (sepsis screen)
• Serum protein & urine electrophoresis

Question 6

How would you treat AKI?

Answer 6

Immediate treatment;

• Treat underlying causes OBVIOUSLY.
• Fluid balance
  
  • Resus with crystalloids to achieve appropriate physiological targets
• Drugs
  
  • Stop nephrotoxins (eg NSAIDS, ACE-i, AG2 receptor antagonists)
  • Stop metformin
• Renale replacement therapy
  
  • Intermittent or continuous dialysis if;
    
    • Fluid overloaded
    • Potassium >6.5mmol/L
    • Uraemia
    • Sever acidosis