Renal Medicine - Acute Kidney Injury Flashcards
What is acute kidney injury?
The acute drop in kidney function, diagnosed by measuring the serum creatinine.
What are the NICE criteria for a diagnosis of AKI?
- rise in creatinine of ≥ 25micromol/L in 48hrs
- rise in creatinine of ≥ 50% in 7 days
- urine output of < 0.5ml/kg/hr for > 6 hours
What are the risk factors for AKI?
- chronic kidney disease
- heart failure
- diabetes
- elderly >75 yrs
- nephrotoxic medications (e.g. ACEi, ARBs, NSAIDs, abx)
- use of contrast medium (e.g. CT scans, PCI)
What are the three broad categories of AKI aetiology?
Pre-renal causes: due to inadequate blood supply to the kidneys, reducing the filtration of blood.
Renal causes: intrinsic disease in the kidney leads to reduced filtration of blood.
Post-renal causes: obstruction to the outflow of urine from the kidney causes back-pressure into the kidney, reducing the filtration of blood.
Give some pre-renal causes of AKI.
- hypovolaemia
- decreased cardiac output
- congestive heart failure
- impaired renal autoregulation (e.g. NSAIDs, ACEi, ARB)
Give some renal causes of AKI.
- glomerulonephritis
- interstitial nephritis
- acute tubular necrosis
Give some post-renal causes of AKI.
- ureteric stones
- masses in the abdomen or pelvis
- uretral strictures
- BPH or prostate cancer
KDIGO defines stage 1 AKI as:
Serum creatinine 1.5-1.9 times baseline
OR
Urine output <0.5ml/kg/hr for <12 hours
KDIGO defines stage 2 AKI as:
Serum creatinine 2.0-2.9 times baseline
OR
Urine output <0.5ml/kg/hr for >12 hours
KDIGO defines stage 3 AKI as:
Serum creatinine >3.0 times baseline
OR
Urine output <0.3ml/kg/hr for >24 hours
OR
Anuria for >12 hours
How is AKI investigated?
Usually an incidental finding upon U&E analysis.
Further investigation should look for the CAUSE of AKI:
- urine dipstick looking for protein and blood (acute nephritis)
- daily FBCs looking for raised WCC (infection)
- ultrasound of the urinary tract to look for obstruction
You perform a urine dipstick on a patient with AKI.
Blood ++
Protein +++
What further investigations should you do?
c-ANCA and p-ANCA to look for vasculitis
anti-GBM, ANA, C3 and C4 to look for lupus nephritis
serum immunoglobulins and electropheresis to look for myeloma
How should AKI be managed?
TREAT UNDERLYING CAUSE
Ensure volume status and perfusion pressure - give IV fluids if dehydrated / give diuretics if overloaded.
Monitor urine output and daily bloods.
Stop nephrotoxic medications (e.g. ACEi, ARBs, NSAIDs)
What are some common complications of AKI?
- hyperkalaemia refractory to medical therapy
- fluid overload refractory to medical therapy
- heart failure
- metabolic acidosis
- uraemia, leading to encephalopathy or pericarditis
What are the options for renal replacement therapy in AKI?
Continuous renal replacement therapy is essentially dialysis.
Renal transplant is other option.
What are the indications for renal replacement therapy for AKI?
- hyperkalaemia
- metabolic acidosis
- fluid overload
- uraemic pericarditis
- uraemic encephalopathy
What is dialysis?
A method for performing the filtration tasks of the kidneys artificially, commonly in patients with end stage renal failure or complications of AKI.
It involved removing excess fluid, solutes and waste products.