Acute Kidney Injury

Question 1

Define acute kidney injury

Answer 1

Sudden loss of renal function, characterised by either abnormal urine output or increased urea and creatinine in the urine.

May be reversible (while CKD is not)

Question 2

What is the KDIGO staging for acute kidney injury

Answer 2

Serum creatinine
1: 1.5-1.9x baseline or 0.3 mg/dl increase
2: 2.0-2.9x baseline
3: 3.0x baseline OR increase >4.0mg/dl

Urine output
1: <0.5ml/kg/h for 6-12 hours
2: <0.5ml/kg/h for >12 hours
3: <0.5ml/kg/h for >24 hours OR anuria >12 hours

Question 3

What are the causes of AKI

Answer 3

Pre-renal (most common):
- Shock or circulatory failure
- Hypovolaemia (sepsis, major haemorrhage, burns, vomiting/diarrhoea e.g. gastroenteritis, HF)
- Trauma
- Nephrotic syndrome
- Renal artery stenosis
- Drugs e.g. NSAIDs, ACEi

Renal:
- Glomerular: Glomerulonephritis
- Interstitial: interstitial nephritis, pyelonephritis
- Tubular: acute tubular necrosis, ischaemia, toxic, obstructive
- Drugs
- Nephrotoxic contrast from imaging
- Vascular: HUS, vasculitis, emboli, renal vein thrombosis

Post-renal:
- Kidney stones,
- Calcified ureter
- Cancer
- Fibrosis
- Urethral stricture, posterior urethral valves

Question 4

What are the most common causes of renal failure in the UK

Answer 4

HUS and acute tubular necrosis

Question 5

Symptoms of AKI

Answer 5

Oliguria/anuria
Oedema (feet, legs, abdomen) → weight gain
Brown/red urine
Fatigue, lethargy, malaise, anorexia
N&V
Pruritus
Dizziness/orthostatic symptoms
Drowsiness, convulsions, coma

Question 6

How does presentation differ between pre-, renal, and post-renal AKI

Answer 6

Pre-renal: tachycardia (hypovolaemia)
Renal: Hx RFs, rash/petechiae/ecchymoses, signs of nephritic syndrome
Post-renal: Urgency, frequency, hesitance, flank pain, haematuria. distended/palpable bladder

Question 7

How do you differentiate between acute and chronic kidney disease

Answer 7

Consider the presentation
Anaemia (Check FBC) will suggest chronic (anaemia of chronic disease)
US: Kidneys smaller than <9cm on USS will suggest chronic
PMH will give clues e.g. HTN, DM
Hypocalcaemia and hyperphosphatemia suggests chronic

Question 8

What investigations should be done for AKI

Answer 8

Bedside:
- Urine dip: protein + haematuria +
- Urinalysis: low fractional Na+ excretion (pre-renal failure)
- Urine output: sustained reduction
- ECG: tented T/flat P/PR prolongation

Bloods:
- U&Es: acute rise in serum creatinine
- FBC: normal Hb, deranged WCC
- ABG/VBG: metabolic acidosis
- Film: exclude MAHA (schistocytes)
- Bone profile
- Albumin

Other:
- US: large, bright kidneys with loss of cortical medullar differentiation + exclude post-renal obstruction
- Bladder scan: <150ml (>150 → bladder obstruction)
- CXR: ?fluid overload

Question 9

What is the management for AKI

Answer 9

1. Find and treat cause (e.g. US scan to check for obstruction)
2. Stop renotoxic drugs
3. IV fluid treatment (depending on severity)
4. Treat any complications e.g. hyperkalaemia, acidosis
5. Consider dialysis

Question 10

Which drugs are renotoxic

Answer 10

Diuretics
Aminoglycosides (gentamicin) and ACE inhibitors
Metformin
NSAIDs.
Spironolactone

Question 11

What is the treatment for the following in AKI:
Metabolic acidosis
Hyperphosphataemia
Hyperkalaemia
Hypovolaemia
Cardiac decompensation

Answer 11

Metabolic acidosis → sodium bicarbonate

Hyperphosphatemia → Calcium carbonate + dietary restriction

Hyperkalaemia → calcium gluconate + salbutamol nebs/IV + dietary restriction + calcium exchange resin + glucose and insulin + renal replacement therapy

Hypovolaemia → IV fluids

Cardiac decompensation → venovenous haemofiltration

Question 12

When should dialysis be given in AKI

Answer 12

A: Severe acidosis (pH<7.2)
E: Persistently high potassium that is refractory to medical treatment | Severe hyponatremia or hypernatremia
I: Drug overdose (e.g. BLAST: barbiturates, lithium, alcohol, salicylates, theophylline)
O: Fluid overload → Refractory pulmonary oedema
U: Symptomatic uraemia (pericarditis, encephalopathy, nausea, pruritis)

Question 13

What is the specific management for pre-renal AKI

Answer 13

Fluid replacement (IV fluids)
Circulatory support

Question 14

What is the specific management for renal AKI

Answer 14

Supportive: Monitor water and electrolyte balance
High calorie, normal protein feed (decreases catabolism, uraemia and hyperkalaemia)

Question 15

What is the specific management for post-renal AKI

Answer 15

Refer if there are complications:
- Pyonephrosis
- Obstructed solitary kidney
- Bilateral upper urinary tract obstruction
- Complications of AKI caused by urological obstruction
Requires assessment of the site of obstruction under nephrostomy or bladder catheterisation
Urology referral, may require surgery

Question 16

What are the complications of AKI

Answer 16

Metabolic acidosis
Water retention: Pulmonary/peripheral oedema, ascites, raised JVP
Hyperkalaemia and check potassium levels every 4 hours
Hyponatraemia
Toxin accumulation e.g. urea
Blood pressure: normal in AKI, raised in CKD
EPO: normal in AKI, raised in CKD
Vitamin D: normal in AKI, raised in CKD

Question 17

What is the prognosis for AKI in children

Answer 17

Generally has a GOOD prognosis unless it is complicating a more serious condition e.g. severe infection, following cardiac surgery