Acute Kidney Injury (AKI) for PLAB 1
Acute Kidney Injury (AKI) is a sudden, rapid decline in kidney function. It's a critical topic for PLAB 1, as it can arise from various medical conditions and requires prompt recognition and management. Understanding the causes, pathophysiology, and clinical presentation is essential for patient care.
Defining AKI: The KDIGO Criteria
AKI is defined by a rapid increase in serum creatinine or a decrease in urine output. The Kidney Disease: Improving Global Outcomes (KDIGO) guidelines provide a standardized definition, categorizing AKI into three stages based on the severity of creatinine rise and urine output reduction.
| Stage | Serum Creatinine Increase | Urine Output Reduction | |
|---|---|---|---|
| Stage 1 | ≥ 0.3 mg/dL (≥ 26.5 µmol/L) within 48 hours OR | < 0.5 mL/kg/h for more than 6 hours | |
| Stage 2 | 1.5- to 2.0-fold increase from baseline within 7 days | < 0.5 mL/kg/h for more than 12 hours | |
| Stage 3 | 3.0-fold increase from baseline within 7 days OR | < 0.3 mL/kg/h for more than 24 hours OR | Anuria for more than 12 hours |
Causes of AKI: The 'R.I.F.L.E.' Framework
A useful mnemonic for remembering the causes of AKI is R.I.F.L.E., which stands for Risk, Injury, Failure, Loss, and End-stage renal disease. However, a more practical clinical classification divides AKI into three main categories based on the location of the insult:
Clinical Presentation and Diagnosis
The clinical presentation of AKI can be subtle or dramatic, depending on the underlying cause and severity. Patients may present with symptoms related to fluid overload (edema, dyspnea), electrolyte imbalances (nausea, vomiting, arrhythmias), or the underlying condition causing the AKI.
Serum creatinine, blood urea nitrogen (BUN), electrolytes (sodium, potassium, chloride, bicarbonate), urine output, urinalysis (for casts, protein, blood), and sometimes renal ultrasound.
Urinalysis is crucial. For pre-renal AKI, the urine is typically concentrated with a high BUN:creatinine ratio (>20:1) and low fractional excretion of sodium (FENa <1%). In intrinsic AKI, especially ATN, the urine may be dilute, with a lower BUN:creatinine ratio (<10:1) and a high FENa (>2%). The presence of red blood cell casts suggests glomerulonephritis, while white blood cell casts may indicate interstitial nephritis.
Management of AKI
Management focuses on identifying and treating the underlying cause, supporting kidney function, and preventing complications. This includes fluid management, electrolyte correction, and addressing any reversible factors.
In pre-renal AKI, prompt fluid resuscitation is paramount. In intrinsic AKI, fluid management can be complex, requiring careful monitoring to avoid overload.
For patients with severe AKI, fluid overload, or refractory electrolyte abnormalities, renal replacement therapy (dialysis) may be necessary. This can be intermittent hemodialysis or continuous venovenous hemofiltration (CVVH).
Prognosis and Prevention
The prognosis of AKI depends heavily on the underlying cause, the severity of the injury, and the presence of comorbidities. Early recognition and intervention significantly improve outcomes. Prevention strategies include maintaining adequate hydration, avoiding nephrotoxic agents where possible, and promptly managing conditions that can lead to AKI, such as sepsis and heart failure.
Acute Tubular Necrosis (ATN), often due to ischemia or nephrotoxins.
Learning Resources
Provides a clear overview of AKI, its causes, symptoms, and treatment from a UK healthcare perspective, suitable for PLAB preparation.
A comprehensive and detailed medical resource covering the pathophysiology, diagnosis, and management of AKI, offering in-depth knowledge.
Offers evidence-based recommendations for the recognition, management, and prevention of AKI in adults, crucial for UK clinical practice.
A detailed clinical overview of AKI, including epidemiology, etiology, pathophysiology, and diagnostic approaches, with a focus on clinical management.
A review article that provides a practical approach to diagnosing and managing AKI, covering key aspects relevant to clinical decision-making.
A visual explanation of AKI, its causes, and mechanisms, which can aid in understanding complex physiological processes.
Osmosis provides clear, concise video explanations of medical topics, including AKI, with a focus on understanding the underlying science.
Offers patient-focused information on AKI, which can help understand the patient experience and common concerns, useful for communication skills in PLAB.
The official guidelines from KDIGO, providing the definitive criteria and recommendations for AKI diagnosis and management.
A comprehensive review article from a reputable medical journal, offering in-depth insights into AKI for advanced understanding.