Acute Kidney Injury

75yo John presents to the hospital with a lower respiratory tract infection. His blood test show eGFR is 40 and creatinine >100. His previous blood test earlier in the year eGFR 79 and creatinine 65. You diagnose him with acute kidney injury.

Overview Acute kidney injury (AKI) is the syndrome arising from a rapid fall in GFR (over hours to days). It is characterised by retention of both nitrogenous (including Urea and Creatinine) and non-nitrogenous waste products of metabolism, as well as disordered electrolyte, acid–base, and fluid homeostasis.

Remember AKI is neither a diagnosis nor a disease. Rather, it is a clinical syndrome that is caused by, or complicates, a wide range of disorders

Definition
Acute Kidney Injury: Rapid reduction in kidney function over hours to days, as measured by serum urea and creatinine and leading to a failure to maintain fluid, electrolyte and acid-base homeostasis.
Chronic Kidney Disease: Impaired renal function >3months based on abnormal structure or function, or GFR <60 for >3months.
Oliguria: A urine output of <400ml/day may be the earlier sign of impaired renal function

Classification The aetiology of acute kidney injury can be simply divided into pre-renal, renal and post renal causes.

Pre-renal – Sepsis and hypotension
- Severe sepsis
- Haemorrhage
- Dehydration
- Cardiac failure
- Liver failure
- Renovascular insult
Intrarenal
- Toxicity
  - Nephrotoxic drugs
  - Iodinated radiological contrast
- Parenchymal kidney disease
  - Glomerulonephritis
  - Tubulointerstitial nephritis
  - Rhabdomyolysis
  - Haemolytic uraemic syndrome
  - Myeloma
  - Malignant hypertension
Post renal Obstruction
- Bladder outflow
- Stones
- Tumour
- Surgical ligation of ureters
- Extrinsic compression (lymph nodes)
- Retroperitoneal fibrosis

Approach to Acute Kidney Injury

History

Prerenal causes
- Vomiting, diarrhoea, polyuria?
- Use of diuretics
- Dry mucosal membranes, low JVP, reduced skin turgor
Renal causes
- Diuretics and other nephrotoxins (NSAIDs, ARBs, ACEI)
- Palpable purpura, pulmonary haemorrhage or sinusitis raises suspicion of systemic vasculitis with glomerulonepritis
- Polyarthralgia, rash suggests rheumatological cause such as SLE
- Recent injury, limb ischaemia suggest rhabdomyalsis
Postrenal obstruction
- Nocturia, hesitancy and urgency suggest prostate issues
- Severe flank pain with history of stones suggest nephrolithiasis
- Suprapubic discomfort may suggest urinary retention
Other questions
- Haematuria?
- Fevers night sweat and chills

Examination

Stable or unstable patient
Vitals signs
Catheter in situ? – Haematuria
Urine output chart

Bedside test

Urine analysis
Urine sediment examination and microscopy
- Urine that has been centrifuged to concentrate the substances in it at the bottom of a tube

Drawing for urine sediment examination….

Investigations

Overview of Acute Kidney Injury

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