Acute Kidney Injury

Question 1

Define AKI

Answer 1

Rapid decline in renal function: ↓GFR, ↑ creatinine or ↓ urine output (<5ml/kg/hr)

Question 2

What are the causes/risk factors of AKI?

Answer 2

Pre-renal
Impaired renal perfusion: 
• Hypovolaemia –
dehydration e.g. D&V
• Haemorrhage
• Sepsis
• Third space losses
• Heart failure/cardiogenic
shock
• Renal artery stenosis
• Renal artery thrombosis

Renal
Direct injury to renal
parenchyma:
• Acute tubular necrosis
(45-70% of AKI)
- Toxic – drugs,
rhabdomyolysis,
myeloma
- Ischaemic
• Acute interstitial nephritis
– drugs, infection
• Glomerulonephritis
• Nephrotoxins
• Vascular e.g. vasculitis,
HUS/TTP, thrombosis

Post-renal
Obstruction of urinary flow: 
• Retroperitoneal fibrosis
• Lymphoma
• Tumour
• BPH
• Strictures – post-surgical,
post-infection
• Urinary tract calculi
• Pyelonephritis
• Urinary retention

Risk Factors:
• Increasing age
• Diabetes
• Heart failure
• Nephrotoxins e.g. radiocontrast, gentamicin, NSAIDs
• Trauma
• Surgery
• Connective tissue disease e.g. SLE

Question 3

What are the symptoms of AKI?

Answer 3

• Nausea
• Vomiting
• Orthopnoea
• PND
• Pulmonary oedema
• Malaise
• Anorexia
• Pruritus
• Drowsiness
• Convulsions
• Coma

Pre-renal
• Dizziness
• Thirst

Renal
• Haematuria
• Fever
• Flank pain

Post-renal
• Haematuria
• Flank pain
• Urgency
• Frequency
• Hesitancy

Question 4

What are the signs of AKI?

Answer 4

• Oliguria/anuria
• Peripheral oedema

Pre-renal
• Hypotension
• Tachycardia
• Dehydration

Question 5

What investigations are carried out for AKI?

Answer 5

• Bloods
- U&Es – ↑ urea, ↑creatinine, ↑K, metabolic acidosis, CK (rhabdomyolysis)
- FBC – anaemia (CKD, blood loss), ↑WCC (infection)
- Serum electrophoresis
• Urine
- Osmolality – high in pre-renal failure
- Output – low
- Urinalysis – RBCs, WBCs, cellular casts, proteinuria, bacteriuria, nitrites,
myoglobin (infection, nephritides, rhabdomyolysis)
- Culture – exclude infection
• Renal screen e.g. ANA, ANCA, anti-GBM, HIV, hepatitis serology, complement
• Bladder catheterisation – diagnostic and therapeutic in urinary retention
• Renal USS – post-renal obstructive causes, small kidneys in CKD, RAS
• Renal biopsy – identify renal cause
• CXR – fluid overload
• ECG – hyperkalaemia

Question 6

What is the management for AKI?

Answer 6

Assess hydration and fluid balance
• Pulse, BP, JVP, CVP
• Skin turgor
• Pulmonary/peripheral oedema
• Fluid (input/output) and weight charts

Treat complications
Metabolic acidosis (if pH <7.2)
• 50-100ml bicarbonate
Hyperkalaemia (ECG changes or K >7mmol/l)
• 10ml of 10% calcium gluconate IV (cardioprotective)
• 50ml of 50% dextrose
• 5U insulin
• Nebulised salbutamol
• PO/PR calcium resonium (reduces bowel absorption)
Pulmonary oedema
• O2 – consider CPAP or BiPAP
• IV GTN
• IV furosemide
• IV diamorphine (respiratory depression relieves anxiety and breathlessness)

Pre-renal
• Volume expansion with normal saline or RBC transfusion
• Inotropes if persistent hypotension
• Diuretics if volume overloaded

Renal
• Treat the underlying cause!

Post-renal
• Bladder catheterisation
• Relieve obstruction e.g. stricture with stenting, calculi
Indications for haemofiltration or dialysis
• Acidosis (pH <7.1, bicarbonate <12mmol/l)
• Electrolyte imbalance – intractable hyperkalaemia (>7mmol/l)
• Intoxication – bleomycin, lithium, alcohol, salicylates, theophylline
• Oedema – refractory e.g. pulmonary oedema
• Uraemia – pericarditis, encephalopathy

Question 7

What are the complications of AKI?

Answer 7

• Metabolic Acidosis
• Electrolyte imbalance – hyperkalaemia, hyperphosphataemia
• Volume Overload – pulmonary oedema, peripheral oedema
• Uraemia
• Chronic kidney disease
• End-stage renal disease