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.
What are the indications for acute dialysis?
AEIOU
Acidosis
Electrolyte abnormalities (e.g. hyperkalaemia)
Intoxication (overdose of medications)
Oedema (pulmonary)
Uraemia (e.g. seizures, reduced consciousness)
What are the indications for long term dialysis?
- end stage renal failure (CKD stage 5)
- any acute indication continuing long term
What are the three main options for dialysis in patients requiring it long term?
- continuous ambulatory peritoneal dialysis
- automated peritoneal dialysis
- haemodialysis
Outline the physiology of peritoneal dialysis.
Peritoneal dialysis used the peritoneal membrane as the filtration membrane with a dialysis solution containing dextrose added to the peritoneal cavity.
Ultrafiltration occurs from the blood, across the peritoneal membrane, into the dialysis solution. This is then replaced, taking away the waste products.
Which catheter is used to perform peritoneal dialysis?
Tenckhoff catheter
What is continuous ambulatory peritoneal dialysis?
The dialysis solution is in the peritoneum at all times, consisting of 4-5 dialysis exchanges per day.
Exchanges are performed at regular intervals throughout the day, with a long overnight dwell.
What is automated peritoneal dialysis?
Peritoneal dialysis performed via an automated cycler machine at night, continuously replacing dialysis fluid in the abdomen to optimise ultrafiltration.
What are the advantages of peritoneal dialysis?
- maintains quality of life
- designed on individualised basis
What are the disadvantages of peritoneal dialysis?
- patients need to manage technical aspects of dialysis
- unsuitable in patients with stoma
- risk of infection
What are some complications of peritoneal dialysis?
Bacterial peritonitis. Infusions of glucose solution make the peritoneum a great place for bacterial growth. Bacterial infection is a common and potentially serious complication of peritoneal dialysis.
Peritoneal sclerosis involves thickening and scarring of the peritoneal membrane.
Ultrafiltration failure can develop. This occurs when the patient starts to absorb the dextrose in the filtration solution. This reduces the filtration gradient making ultrafiltration less effective. This becomes more prominent over time.
Weight gain can occur as they absorb the carbohydrates in the dextrose solution.
Psychosocial effects. There are huge social and psychological effects of having to change dialysis solution and sleep with a machine every night.
What is haemodialysis?
Patients have their blood filtered by a haemodialysis machine, removing waste solute, salt and excess fluid.
In order for haemodialysis to be successful, there must be abundant blood supply. How is this ensured?
- tunnelled cuffed catheter
- aterio-venous fistula
What is tunnelled cuffed catheter?
A tunnelled cuffed catheter is inserted into the subclavian or jugular vein, providing a route of access for haemodialysis.
These can stay in long term and be used for regular haemodialysis, however there is a risk of infection and blood clots.
What are the commonest types of arterio-venous fistula?
- radio-cephalic fistula
- brachio-cephalic fistula
- brachio-basilic fistula
Provides an artificial connection between an artery to the bein, allowing blood to flow under high pressure from the artery directly into the vein. This provides a permanent, large, easy access blood vessel.
What are the common complications of arterio-venous fistulas?
- STEAL syndrome
- high output heart failure
- aneurysm
- infection
- thrombosis
What is STEAL syndrome?
Occurs when there is inadequate blood flow to the limb distal to the AV fistula, as it ‘steals’ blood from the limb.
The blood is diverted away straight into the venous system, causing distal ischaemia.
How does AV fistula complicate to high output heart failure?
Where there is an A-V fistula blood is flowing very quickly from the arterial to the venous system through the fistula. This means there is rapid return of blood to the heart. This increases the pre-load in the heart (how full the heart is before it pumps). This leads to hypertrophy of the heart muscle and heart failure.
What are the advantages of haemodialysis?
- efficient
- unit-based so good staff support
What are the disadvantages of haemodialysis?
- dialysis access must be secured
- haemodynamic instability
- complications with AV fistula or tunnelled cuffed catheter
- greater disruption to life
What is acute tubular necrosis?
The most common cause of AKI, whereby damage to the kidney parenchyma by ischaemia or toxins causes acute tubular necrosis.
What are the causes of ATN?
- shock
- sepsis
- dehydration
- radiology contrast dye
- NSAIDs
What is the typical urinalysis finding of ATN?
Muddy brown casts
What is haemolytic uraemic syndrome (HUS)?
Thrombosis within the small blood vessels throughout the body, triggered by shiga toxin, leads to the following triad of:
- haemolytic anaemia
- AKI
- thrombocytopenia
What is the cause of haemolytic uraemic syndrome?
Shiga toxin from shigella or E. coli 0157
Presentation of haemolytic uraemic syndrome?
E. coli 0157 causes a brief gastroenteritis with blood diarrhoea.
Around 5 days later, the patient will display sx of HUS:
- oligouria
- haematuria
- abdominal pain
- lethargy
- confusion
- hypertension
- bruising
What is the management of haemolytic uraemic syndrome?
HUS is a medical emergency and has up to 10% mortality. The condition is self limiting and supportive management is the mainstay of treatment:
Antihypertensives
Blood transfusions
Dialysis
