Acute Kidney Injury (AKI)

Definition

Acute Kidney Injury (AKI) is a sudden reduction in kidney function, leading to an accumulation of waste products, electrolyte imbalances, and fluid imbalance. It can range from mild to severe and may be reversible or lead to chronic kidney disease.

Aetiology

AKI can result from various causes, typically classified into three categories:

Prerenal: Reduced blood flow to the kidneys due to dehydration, heart failure, or sepsis.
Intrarenal: Direct damage to the kidneys caused by infections, toxins, medications, or autoimmune diseases.
Postrenal: Obstruction of urine flow due to conditions such as kidney stones, tumours, or enlarged prostate.

Pathophysiology

The pathophysiology of AKI involves a sudden decrease in glomerular filtration rate (GFR), leading to the accumulation of nitrogenous waste products (urea and creatinine). Depending on the underlying cause, this can result from hypoperfusion, direct nephrotoxic injury, or obstructive uropathy. The kidneys may suffer from ischaemia, inflammation, or cellular damage, which impairs their ability to filter blood effectively.

Risk Factors

Advanced age.
Pre-existing kidney disease.
Diabetes mellitus.
Hypertension.
Heart failure.
Sepsis.
Use of nephrotoxic drugs (e.g., NSAIDs, aminoglycosides).
Recent surgery or major trauma.
Dehydration or volume depletion.

Signs and Symptoms

Oliguria or anuria (reduced or no urine output).
Fluid retention and oedema.
Fatigue and weakness.
Nausea and vomiting.
Shortness of breath.
Confusion or altered mental status.
Hypertension.

Investigations

Clinical history and physical examination, focusing on fluid status and potential causes.
Blood tests: Serum creatinine, urea, electrolytes, and full blood count.
Urinalysis: To detect proteinuria, haematuria, and urinary sediment abnormalities.
Imaging: Renal ultrasound to assess kidney size, structure, and rule out obstruction.
Additional tests: Depending on suspected cause (e.g., autoimmune markers, drug levels).

Management

Primary Care Management

If the patient is unwell, refer urgently to hospital and then stabilise the patient, ensuring airway, breathing, and circulation (ABCs).
Referral to a specialist (nephrologist) only if symptoms persist and the patient has been assessed in the hospital and told to go to the GP (if they have not already been referred by hospital doctors).
Management of underlying conditions (e.g., rehydration for dehydration, discontinuation of nephrotoxic drugs).
Monitoring of renal function and electrolyte levels.
Patient education on recognising symptoms and avoiding nephrotoxic substances.

Specialist Management

Intravenous fluids: To correct dehydration and improve renal perfusion.
Medications: To manage electrolyte imbalances and treat underlying causes (e.g., antibiotics for infection).
Dialysis: In severe cases to remove waste products and excess fluid.
Close monitoring: Regular assessment of renal function, fluid balance, and electrolyte levels.

Example Management for Acute Kidney Injury

A patient presenting with symptoms of AKI, such as reduced urine output and fluid retention, should be urgently referred to a hospital for immediate evaluation. Initial management may include intravenous fluids to correct dehydration and improve renal perfusion. Blood tests and imaging studies should be performed to identify the underlying cause. If the patient has persistent symptoms and renal dysfunction after initial hospital assessment, they may be referred to a nephrologist for further evaluation and management. Regular follow-up is essential to monitor renal function and manage any complications.

References

NICE. (2024). Acute Kidney Injury: Prevention, Detection and Management. Retrieved from NICE
NHS. (2023). Acute Kidney Injury. Retrieved from NHS
Kidney Disease: Improving Global Outcomes (KDIGO). (2012). Clinical Practice Guideline for Acute Kidney Injury. Kidney International Supplements.
Bellomo, R., et al. (2012). Acute Kidney Injury. The Lancet.
Thomas, M. E., et al. (2015). The Definition of Acute Kidney Injury and Its Use in Practice. Kidney International.