Acute Kidney Injury Flashcards
Define acute kidney injury
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)
What is the KDIGO staging for acute kidney injury
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
What are the causes of AKI
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
What are the most common causes of renal failure in the UK
HUS and acute tubular necrosis
Symptoms of AKI
Oliguria/anuria
Oedema (feet, legs, abdomen) → weight gain
Brown/red urine
Fatigue, lethargy, malaise, anorexia
N&V
Pruritus
Dizziness/orthostatic symptoms
Drowsiness, convulsions, coma
How does presentation differ between pre-, renal, and post-renal AKI
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
How do you differentiate between acute and chronic kidney disease
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
What investigations should be done for AKI
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
What is the management for AKI
- Find and treat cause (e.g. US scan to check for obstruction)
- Stop renotoxic drugs
- IV fluid treatment (depending on severity)
- Treat any complications e.g. hyperkalaemia, acidosis
- Consider dialysis
Which drugs are renotoxic
Diuretics
Aminoglycosides (gentamicin) and ACE inhibitors
Metformin
NSAIDs.
Spironolactone
What is the treatment for the following in AKI:
Metabolic acidosis
Hyperphosphataemia
Hyperkalaemia
Hypovolaemia
Cardiac decompensation
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
When should dialysis be given in AKI
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)
What is the specific management for pre-renal AKI
Fluid replacement (IV fluids)
Circulatory support
What is the specific management for renal AKI
Supportive: Monitor water and electrolyte balance
High calorie, normal protein feed (decreases catabolism, uraemia and hyperkalaemia)
What is the specific management for post-renal AKI
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