Acute Kidney Injury

Question 1

Define acute kidney injury (AKI) [1]

Answer 1

syndrome of decreased renal function, measured by serum creatinine or urine output, occuring over hours-days

Question 2

Describe the staging system for AKI severity [3]

Answer 2

• Stage 1
  
  • serum creatinine 1.5-1.9 x AKI baseline
• Stage 2
  
  • serum creatinine 2.0-2.9 x AKI baseline
• Stage 3
  
  • serum creatinine ≥3.0 x AKI baseline

Question 3

What is oliguria?

1. in infants? [1]
2. in children? [1]
3. in adults? [1]

Answer 3

1. in infants = urine output that is less than 1 mL/kg/h
2. in children = less than 0.5 mL/kg/h
3. in adults = less than 400 mL or 500 mL per 24hr

Question 4

Aetiology of AKI can be classified according to site.

List the pre-renal ​causes of AKI [15]

Answer 4

1. hypovolaemia & hypotension
   
   • acute haemorrhage
   • GI losses → diarrhoea/vomiting
   • dermal losses → burns
   • renal losses → diuretics/osmotic diuresis
2. reduced effective circulating volume - systemic vasodilation
   
   • cardiac failure
   • septic shock
   • cirrhosis
3. drugs causing renal vasoconstriction
   
   • ACE inhibitors
   • NSAIDs
4. renal artery stenosis
5. hypoperfusion
6. hypoxia

Question 5

Aetiology of AKI can be classified according to site.

List the intrinsic renal ​causes of AKI affecting the…

1. glomerulus? [2]
2. tubules (obstruction & dysfunction)? [3]
3. interstitium? [3]
4. vessels? [1]

Answer 5

1. glomerular:
   
   • glomerulonephritis
   • drugs - e.g. gentamicin
2. tubules:
   
   • tubulo-interstitial nephritis
   • ischaemic or nephrotoxic acute tubular necrosis
   • rhabdomyolysis
3. interstitium:
   
   • drugs
   • myeloma
   • sarcoid
4. vessels:
   
   • vasculitis

Question 6

Aetiology of AKI can be classified according to site.

List the post-renal ​causes of AKI [9]

Answer 6

1. within the renal tract - obstructive causes
   
   • renal papillary necrosis
   • kidney stones
   • renal tract malignancy
   • retroperitoneal fibrosis
   • urethral stricture
   • blood clots
2. extrinsic compression
   
   • pelvic malignancy
   • carcinoma of the cervix
   • prostatic hypertrophy/malignancy

Question 7

If blood pressure falls, how does the kidney respond?

1. how does the afferent arteriole respond and what is this mediated by? [3]
2. how does the efferent arteriole respond and what is this mediated by? [4]

Answer 7

1. afferent arteriole dilates to increase GFR
   
   • mediated by ANP and prostaglandins
2. efferent arteriole constricts to increase GFR
   
   • mediated by ANP, angiotensin II and sodium

Question 8

What drugs act on the glomerular arterioles and what do they result in?

1. on afferent arteriole? [3]
2. on efferent arteriole? [3]

Answer 8

1. NSAIDs target the afferent arteriole
   
   • block prostaglandins, hence causing vasoconstriction
2. ACE inhibitors/ARB target the efferent arteriole
   
   • block Angiotensin II, hence causing vasodilation

Question 9

What are the causes of acute tubular necrosis? [4]

Answer 9

• ATN is always due to under perfusion of the tubules and/or direct toxicity:
  
  • Hypotension
  • Sepsis
  • Toxins
  • or often, all 3

Question 10

Describe the treatment strategy for AKI [6]

Answer 10

1. Immediate
2. Airway and Breathing
3. Circulation – shock - restore renal perfusion and check for:
   
   • hyperkalaemia
   • pulmonary oedema
4. Remove causes
   
   • drugs
   • sepsis
5. Exclude obstruction & consider ‘renal’ causes
   
   • are the pre-renal causes sufficient to account for AKI?
6. Ask for help: ICU or renal unit

Question 11

What are the typical ECG changes in hyperkalaemia? [6]

Answer 11

1. tall “tented” T waves
2. increased PR interval
3. small or absent P wave
4. widened QRS complex
5. “sine wave” pattern
6. asystole

Question 12

Classify degrees of severity of hyperkalaemia based on figures [3]

Answer 12

1. K⁺ <6.0
   
   • abnormal but no immediate concern
2. K⁺ 6.0-6.4
   
   • risk of arrhythmia
   • needs treatment especially if ECG changes present
3. K⁺ >6.5
   
   • medical emergency

Question 13

How do you treat hyperkalaemia? [3]

Answer 13

1. Reduce absorption from gut
   
   • calcium resonium 15g 4x day orally (or enema)
2. Insulin 10-15units actrapid+ 50ml 50%
   
   • dextrose moves potassium into cells (watch BM)
3. Calcium gluconate 10ml 10%
   
   • cardiac membrane stabiliser

Question 14

Under what circumstances would you classify acidosis and how would you treat it? [3]

Answer 14

1. if raised potassium & HCO₃ <16
2. treat with IV bicarb supplementation

Question 15

What are the indications for dialysis?

1. the absolute indications? [2]
2. the relative indications? [5]

Answer 15

1. the absolute indications:
   
   • refractory potassium ≥6.5mmol/l
   • refractory pulmonary oedema
2. the relative indications:
   
   • acidosis (pH <7.1)
   • uraemia (esp. if urea >40)
     
     • can result in pericarditis & encephalopathy
   • toxins (e.g. lithium)