Acute kidney failure is also known as acute renal failure (ARF) or acute kidney injury (AKI), is a sudden kidney’s inability to filter waste products from the blood. It develops over a few hours or days. It is characterized by decreased urine output (oliguria <400ml/24hrs or <0.5ml/kg/hr), edema (due to fluid retention), elevated blood urea nitrogen (BUN) and creatinine (Azotemia).
What are kidneys?
Kidneys are two bean-shaped organs that are positioned on each side of the spine, just below the rib cage. They receive blood from the renal arteries, and the glomeruli filter this blood. After filtration, the essential substances are absorbed back into the blood, and the leftover waste is transferred to the bladder as urine through the ureter. Then the bladder releases the urine through the urethra, which we excrete out of our bodies.
The kidneys have seven functions and have a popular mnemonic called A WET BED:
- A – Acids base balance(maintaining the PH of the body’s extracellular fluid)
- W – Water balance maintenance
- E – Electrolyte balance
- T – Toxin removal
- B – Blood pressure control
- E – Erythropoietin formation
- D – vitamin D metabolism
The sudden problems with filtration can be caused by disorders that decrease blood flow to the kidneys (prerenal), diseases that damage the kidney (renal/intrinsic), and issues with the ureter, bladder, prostate, or the urethra (post-renal).
What are the main causes of acute kidney failure?
The chief causes of acute kidney failure may be
1. Prerenal causes (decrease blood flow to the kidneys):
- Hypovolemia (e.g., Dehydration) due to bleeding, severe vomiting or diarrhea
- Hypotension (low blood pressure)
- Heart failure
- Liver cirrhosis
- Renal vein thrombosis
- Renal artery stenosis
- Nephrotoxic drugs ( e.g., NSAIDs, gentamycin, streptomycin, iodinated contrast agents)
- Restrictive cardiomyopathy
- Constrictive pericarditis
2. Renal/intrinsic causes (direct damage to the kidneys):
- Acute tubular necrosis
- Acute interstitial nephritis
- Tumor lysis syndrome(is the release of the contents of killed cancer cells into the bloodstream as a result of chemotherapy. This causes a metabolic shutdown. Tumor lysis syndrome can be treated with allopurinol and rasburicase).
- Diabetes mellitus
- Malignant hypertension
- Disseminated intravascular coagulopathy(DIC)
- Medications such as Tacrolimus (an immunosuppressive drugs that can damage the tubular cells of the kidney).
3. Post renal causes (disorders of that affect flow of urine, ureter, bladder or urethra):
- Kidney stones
- Benign prostate hyperplasia (BPH)
- Prostate cancer
- Bladder stone
- Obstructed urinary catheter
- Bladder neck stenosis
- Bladder cancer
- Cancer of the ureters
- Advanced cancer of the cervix
How is acute kidney failure diagnosed?
The diagnosis of acute kidney failure is based on risk, injury, failure, loss, and end-stage renal disease (RIFLE). It was introduced in 2012 by KDIGO (a global non-profit foundation dedicated to improving care and outcome of kidney disease patients worldwide).
Definition by KDIGO: acute kidney failure is diagnosed in the presence of any one of the following:
- Increase in serum creatinine of greater or equal to 0.3mg/dL within 48hrs compared to baseline.
- Increase in serum creatinine of greater or equal to 50% (known to have occurred within the last seven days)
- Urine volume <0.5ml/kg/h for 6 hours.
- Normal Blood urea nitrogen(BUN) is 7 – 20mg/dL (2.5 – 7.1mmol/L).
- Normal blood creatinine level is 0.6-1.2mg/dL in adult males and 0.5-1.1mg/dL in adult female.
RIFLE: Risk, Injury, failure, loss, and end stage renal disease diagnostic methods
| ||GFR CRITERIA||URINE OUTPUT CRITERIA|
|RISK||1.5 fold increase in serum creatinine or GFR decrease by 25%.||Urine output<0.5 ml/kg/hr for 6hrs.|
|INJURY||2 – fold increase in serum creatinine or GFR decrease by 50%.||Urine output<0.5ml/kg/hr for 12hrs|
|FAILURE||3 – fold increase in serum creatinine or GFR decrease by 75%.||Urine output<0.3ml/kg/hr for 24hours or no urine output (anuria) for 12hrs.|
|LOSS||Complete loss of kidney function for more than 4weeks( need for renal replacement therapy).|
|END STAGE KIDNEY DISEASE||Complete loss of kidney function for more than 3 months( need for renal replacement therapy)|
Other diagnostic methods of Acute Kidney Failure are:
- BUN/Serum Creatinine ratio
- Renal ultrasound
- Kidney biopsy
- CT Scan
NOTE: IV contrast is a contrast agent that is contraindicated in AKI because it is a nephrotoxic agent.
What are the treatment options for acute kidney failure?
Treat the underlying cause and supportive therapy:
1. Prerenal management
- Without fluid overload: give IV fluids and monitor fluids with a central venous catheter to avoid an overdose
- Vasopressor (norepinephrine) to raise BP
- Dobutamine to improve renal blood flow by increasing the heart’s pumping ability.
- Remove nephrotoxic drugs
- With fluid overload: give diuretics(furosemide).
Post renal management
- A urinary catheter for obstruction
- Radiation therapy
- Surgery (proctectomy)
- Alpha-blockers such as Doxazosin
- 5 alpha-reductase inhibitors(5ARIs) such as Finasteride and dutasteride.
Renal replacement therapy: Dialysis.