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
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
- Dehydration
- Assess for comorbidities which may reduce renal perfusion – heart failure, shock
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
- Fevers night sweat and chills may suggest vasculitis or urine infection
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

Examination

Stable or unstable patient
Vitals signs
Catheter in situ? – Haematuria
Urine output chart
Assess fluid status – hypovolaemia, normovolemic or hypervolaemic
- Hypovolaemic – reduced skin turgor, dry mucus membranes
- Hypervolaemic – JVP elevated, peripheral oedema, pulmonary coarse inspiratory crackles (pulmonary oedema)

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