Acute Kidney Injury

Question 1

Describe the staging of AKI

Answer 1

• stage 1: serum creation 1.5+ and <2.0 times AKI baseline, or 26.0+ micro-m/l increase above AKI baseline
• stage 2: serum creatinine 2.0+ and <3 times AKI baseline
• stage 3: serum creatinine 3.0 times AKI baseline or 354+ micro-m/l increase above AKI baseline
• requires you to know the patient’s baseline measurement

Question 2

define oliguria

Answer 2

• urine output less than 1ml/kg/hr in infants
• less than 0.5ml/kg/h in children
• less than 400-500ml per 24hr in adults

Question 3

What are the causes of AKI?

Answer 3

• pre-renal: circulatory failure (shock) (eg. hypovolaemia, MI, LVSD, septic shock, renal artery stenosis)
• renal: failure of the cells of the kidney (glomerulonephritis, tubular obstruction/dysfunction, sarcoidosis, drugs)
• post-renal: obstruction to flow of urine (renal papillary necrosis, kidney stones, retroperitoneal stenosis, tumours)

Question 4

What anatomical features must you consider in suspicion of intrinsic AKI?

Answer 4

Things affecting:
* large blood vessels
* small blood vessels and golmeruli
* tubulointerstitium
* acute tubular necrosis (ischaemic, toxic) - 80% think pre-renal!!

Question 5

What can be seen in the histology of ATN?

Answer 5

• debris in the tubules causing occlusion
• mitoses of tubular cells

Question 6

What are the main causes of ATN?

Answer 6

Underperfusion of the tubules and/or direct toxicity:
- hypotension
- sepsis
- toxins (exogenous eg. drugs - gentamicin, contrast, poisons; endogenous eg. myoglobin, haemoglobin, immunoglobulin, Ca

Question 7

What happens in the kidneys as a result of hypovolaemia and how is this affected by NSAIDs and ACEi?

Answer 7

• BP falls, and prostaglandins stimulate afferent arterioles to dilate and efferent arterioles to constrict to maintain GFR
• NSAIDs prevent afferent arteriole dilation
• ACEi prevent efferent arteriole constriction

Question 8

Describe the management of AKI

Answer 8

• airway and breathing
• circulation (shock - restore renal perfusion, address hyperkalaemia and pulmonary oedema if any)
• remove causes (drugs, sepsis)
• exclude obstruction and consider renal causes (or is pre-renal cause enough for diagnosis?)
• nephrology

Question 9

What is the importance of a renal ultrasound when considering AKI?

Answer 9

• allows you to exclude obstruction
• can look at size of kidneys (small kidneys = CKD)
• can see if loss of corticosteroids-medullary differentiation (= CKD)

Question 10

What levels of potassium = medical emergency

Answer 10

6.5 (be aware of possible arrhythmia if 6-6.4)

Question 11

Describe the treatment of hyperkalaemia

Answer 11

• reduce absorption from gut (calcium resonium 15g 4x day orally)
• SHORT ACTING insulin + dextrose (moves K+ into cells) - be aware of hyperglycaemia
• calcium gluconate (cardiac membrane stabiliser)

Question 12

What are the indications for dialysis?

Answer 12

Absolute:
- refractory K+ 6.5+mmol/l (esp if anuric)
- refractory pulmonary oedema

Relative:
- acidosis
- uraemia (esp if >40 - pericarditis, encephalopathy)
- toxins (lithium, ethylene glycol etc.)