ACUTE KIDNEY INJURY Flashcards
What is the definition of acute kidney injury?
An abrupt loss of kidney function that develops within 7 days.
Loss of kidney function is defined as:
Urinary volume of less than 0.5 ml/kg/hour for 6 hours
or
An increase in serum creatinine of more than 0.3 mg/dL over 48 hours or of more than 1.5 baseline over 7 days
How we classify the causes of acute kidney injury?
Pre-renal
Renal
Post-renal
What are the pre-renal causes of acute kidney injury?
Hypovolaemia - eg shock, burns, dehydration, sepsis, haemorrhage
Reduced effective circulating volume - eg heart failure, liver disease
Drugs altering renal haemodynamics - NSAIDs, ACE inhibitors, antihypertensives, ciclosporin
Renal artery stenosis
What are the drugs that can cause pre-renal acute kidney injury?
NSAIDs
ACE inhibitors
Angiotensin receptor blockers
Ciclosporin
What are the renal causes of acute kidney injury?
Acute tubular necrosis - certain drugs and toxins (endogenous and exogenous), prolonged prerenal causes leading to ischaemia, cytokines in response to sepsis
Acute glomerulonephritis
Acute interstitial nephritis - due to drugs, infection (pyelonephritis), hypercalcaemia, multiple myeloma
Vasculitis
Hypertension
Emboli
Acute cortical necrosis - severe shock left untreated
What are the drugs that can lead to acute tubular necrosis and resulting acute kidney injury?
Gentamicin Aciclovir Methotrexate Cimetidine Contrast dye NSAIDs
What are the toxins that can lead to acute tubular necrosis and resulting acute kidney injury?
Myoglobinuria
Lipopolysaccharide in Gram-negative sepsis
What are the drugs that can lead to acute interstitial nephritis and resulting acute kidney injury?
NSAIDs
Ampicillin
Rifampicin
What are the post-renal (obstructive) causes of acute kidney injury?
Bladder outflow obstruction (BPH or urethral strictures)
Retroperitoneal fibrosis
Tumour
Stones
Remember that obstruction must occur in both kidneys or a single functioning kidney for renal failure to occur
What are the clinical features of acute kidney injury?
Uraemia - fatigue, loss of appetite, headache, nausea and vomiting
Flank pain
Hyperkalaemia - dysrhythmias
Fluid imbalance - high or low BP, oedema, pleural effusions, cardiac tamponade
Palpable bladder - obstruction
What investigations might be ordered for someone with suspected acute kidney injury?
Urine tests Blood test - U+Es, creatinine, autoantibodies, complement levels Renal imaging - X-ray and ultrasound ECG Chest X-ray
What might blood tests reveal in someone who presents with acute kidney injury?
Increased plasma urea and creatinine
Increased plasma urate
Increased plasma concentration of potassium
Metabolic acidosis and an increased anion gap
Increased plasma phosphate
Decreased plasma calcium
Decreased plasma sodium
Antinuclear antibodies (ANA)
ANCA
Cryoglobulinaemia
High levels of complement
What might high levels of complement indicate as the underlying cause in someone with acute kidney injury?
SLE-associated nephritis
Type 2 membranoproliferative glomerulonephropathy
Acute glomerulonephritis
In someone with prerenal failure, what is the osmolality of the urine likely to be? Why?
Above 500 mOsm/kg H20 - the renal tubular function is preserved so reabsorption of sodium and water is preserved. ADH also stimulates further uptake of water and hence the osmolality increases.
In someone with acute tubular necrosis, what is the osmolality of the urine likely to be? Why?
Below 350 mOsm/kg H20 - here the renal tubular function is damaged and hence reabsorption of sodium and water is affected so the urine does not become hyperosmolar as in prerenal failure.
In someone with prerenal failure, what is the sodium concentration of the urine likely to be? Why?
Below 20 mmol/L - the renal tubular function is preserved so reabsorption of sodium is preserved and in fact increased.
In someone with acute tubular necrosis, what is the sodium concentration of the urine likely to be? Why?
Above 40 mmol/L - here the renal tubular function is damaged and hence reabsorption of sodium is affected.
In someone with prerenal failure, what is the ratio of urine to serum creatinine likely to be? Why?
Above 40 - the reduced perfusion means that GFR is also reduced and hence the creatinine clearance is reduced. This might make you think that the urine to creatine ratio should go down. However, ADH makes the urine very concentrated. Therefore despite an absolute reduction in creatinine in the urine, the concentration will actually increase substantially.
In someone with acute tubular necrosis, what is the ratio of urine to serum creatinine likely to be? Why?
Less than 20 - damaged renal tubular function means that creatinine clearance is reduced and therefore urine concentration is also reduced.
What about urinalysis might indicate that the cause of the acute kidney injury was prerenal?
High urine osmolality
Low urine sodium
High urine:serum creatinine
What about urinalysis might indicate that the cause of the acute kidney injury was renal (rather than prerenal or postrenal)?
Proteinuria
Haematuria
Renal tubular epithelial cells in urinary sediment
Casts
What about urinalysis might indicate that the cause of the acute kidney injury was postrenal?
Crystalluria
What is the normal range of serum creatinine?
- 6 to 1.2 mg/dL in males
0. 5 to 1.1 mg/dL in females
What is normal eGFR?
90-120 mL/min/1.73m2
How is acute kidney injury (AKI) managed?
Without fluid overload - IV fluids
Monitor renal function with urinary catheter
Treat hyperkalaemia, pulmonary oedema, metabolic acidosis
Treat underlying cause
Stop nephrotoxic drugs
Consider haemodialysis
What is the criteria used to stage acute kidney injury?
RIFLE criteria
What is the R of the RIFLE criteria used to stage acute kidney injury and what does this stage entail?
Risk
1.5-fold increase in the serum creatinine, or glomerular filtration rate (GFR) decrease by 25 percent, or urine output of less than 0.5ml/kg/hour for 6 hours
What is the I of the RIFLE criteria used to stage acute kidney injury and what does this stage entail?
Injury
Two-fold increase in the serum creatinine, or GFR decrease by 50 percent, or urine output of less than 0.5ml/kg/hour for 12 hours
What is the F of the RIFLE criteria used to stage acute kidney injury and what does this stage entail?
Failure
Three-fold increase in the serum creatinine, or GFR decrease by 75 percent, or urine output of 0.5ml/kg/hour for 24 hours or anuria for 12 hours
What is the L of the RIFLE criteria used to stage acute kidney injury and what does this stage entail?
Loss
Complete loss of kidney function (e.g., need for renal replacement therapy) for more than four weeks
What is the E of the RIFLE criteria used to stage acute kidney injury and what does this stage entail?
End-stage renal disease
Complete loss of kidney function (e.g., need for renal replacement therapy) for more than three months
Why is eGFR not useful in a patient with acute kidney injury?
Because the eGFR is only useful if the creatinine is pretty stable. In acute kidney injury the rate of deterioration means that the creatinine level will still be rising. So if actual GFR is 0 the eGFR might not be 0 because the creatinine hasn’t had time to fully rise yet.
What are the indications for renal replacement therapy in the acute kidney injury?
Metabolic acidosis / Hyperkalaemia which is not responsive to medication
Fluid overload (pulmonary oedema) which is not responsive to medication (diuretics, GTN)
How do we definitively make the diagnosis of post renal acute kidney injury?
Renal imaging normal ultrasound
How can you tell looking at a red cell whether the blood in the urine is from the upper urinary tract or lower urinary tract?
Shape of the red. From lower urine red cell will maintain biconcave shape. From upper end cell will form casts or look different.
