1. Acute kidney injury
Vivian Phan

2. Acute kidney injury = Acute renal failure
A sudden (within 48h) deterioration in renal function, that is potentially reversible
Absolute increase in:
↑SCr ≥ 0.3 mg/dL (26.4 micromol/L) from baseline
↑SCr ≥ 50%
Oliguria < 0.5 mL/kg/h for > 6h

3. RIFLE criteria Creatinine GFR Urine Risk Injury Failure Loss ESRD
1.5x ↑
↓ 25%
<0.5ml/kg for 6h
Injury
2x ↑
↓ 50%
<0.5ml/kg for 12h
Failure
3x ↑
↓ 75%
<0.5ml/kg for 24h or anuria for 12h
Loss
Need for RRT for >4 weeks
ESRD
Need for RRT for >3 months
Crit Care 2004; 8:R204.

4. AKI: KDIGO Classification
Stage
SCr criteria
UOP criteria (duration of oliguria)
Stage 1
increase ≥ 26 μmol/L within 48hrs or
increase ≥ BL
<0.5 mL/kg/hr for > 6 consecutive hrs
Stage 2
increase ≥ BL
<0.5 mL/kg/ hr for > 12 hrs
Stage 3
Increase ≥3 BL or
increase ≥ 354 μmol/L or commenced on RRT
<0.3 mL/kg/ hr for > 24 hrs or anuria for 12 hrs
BL = Base line: the lowest creatinine value recorded within 3 months of the event.
≥ 1.5 = ≥ 50%; ≥ 2 = ≥ 100%; ≥ 3 = ≥ 200% increase in Scr; (or 150%; 200%; 300% of BL SCr level)
SCr and UOP remains the best biomarkers for AKI (RA, AKI Guidelines )
Stage 1 = AKIN/ (KDIGO) definition of AKI

5. Causes Pre-renal failure Intrinsic renal failure Post-renal failure
Hypoperfusion
Intrinsic renal failure
Many causes
Acute tubular necrosis
Post-renal failure
Obstruction
Mostly pre-renal due to hypoperfusion – during surgery, on the wards, due to systemic illness etc.
Other than that, obstruction – good to USS regardless of symptoms

6. Pre-renal causes Renal hypoperfusion Systemic hypotension
- Hypovolaemia, hypotension (bleeding, dehydration)
Sepsis
Anaphylatic shock
Local = hypoperfusion of the gromerulus
- Renal artery stenosis (reduced gromerular pressure)
- Drugs: ACE inhibitors, NSAIDs

7. Intrinsic renal causes
Primary renal disease
Glomerulonephritis
Interstitial nephritis – usually caused by drugs e.g. NSAIDs, Gentamicin
Secondary renal disease
Diabetes, SLE, myeloma, etc.
Secondary ATN (acute tubular necrosis)
Established after pre-renal injury
ATN happens after shock e.g. sepsis, haemorrhage – brief ischaemia to kidney causes damage that takes a while to recover. Symptoms = low Na, high K, high urea (uraemia), oliguria, high urine osmolality (not excreting). Treatment = USS, fix K, urgent dialysis. Likely to recover within 6-8 weeks following dialysis.

8. Post-renal causes Obstruction Intrinsic Extrinsic
Urinary tumours e.g. RCC
Stones
Extrinsic
Pelvic tumours (prostate, cervix, ovaries)
TB strictures
Retroperitoneal tumours & fibrosis

10. Investigations History & examination Bedside Bloods Imaging
Rate of onset, urinary symptoms, PMH, DH
Fluid status, signs of sepsis
Bedside
Urine tests: dipstick, MSU, ACR/PCR
Urine output
ECG: K+, arrhythmia
Bloods
Kidney function: U+E, Creat, GFR
Markers of CKD: Ca, PO4, PTH, HCO3
Imaging
USS – if find problems -> CT KUB, biopsy
CXR to monitor fluid overload
Fluid status: skin turgor, mucous membrane/tongue, pulse rate/volume, BP, JVP, peripheral perfusion, peripheral oedema
ACR = albumin:creatinine ratio; PCR = protein:creatinine ratio

11. Treatment Treat underlying cause Generic AKI management
Pre-renal: IV fluids
Intrinsic: Treat medically
Post-renal: Relieve obstruction
Percutaneous nephrostomy (drain pus/urine from kidneys)
Stents: antegrade (kidneys to bladder) vs retrograde (bladder to kidneys)
Monitor: EWS (early warning score)
BP, pulse, sats, U+E, weight (= fluid level)
Fluid input vs output

12. Hyperkalaemia: K+ > 6mmol/L
Very common complication of AKI
ECG changes (in this sequence)
Peaked “tented” T waves
Prolonged P-R interval
Prolonged QRS duration
Loss of P waves
VF/asystole
Treatment (at once!)
Stabilise myocardium: Ca Gluconate
Shift K+ into cells: IV Insulin+Dextrose, Salbutamol nebuliser, NaHCO3 if acidotic
Diuresis, Ca Resonium, (RRT/Dialysis)

13. Look at V3
Next step: any higher K+ will cause asystole

14. Indications for RRT
Starting RRT is a clinical decision RA Guidelines, AKI, :
AKI and the AEIOU
Acidaemia (PH <7.1) when correction would cause fluid overload
Electrolyte abnormalities e.g. K > 7
Intoxication with certain substances (salicylic acid, lithium, etc.)
Overload of fluid when diuretics are of no use
Uraemic effects: seizure and coma (encephalopathy); Pericardititis