Acute kidney injury Flashcards
What are the types of kidney failure?
Acute kidney injury (AKI)
Chronic kidney disease (CKD)
What is meant by acute kidney injury?
Abrupt decrease in actual GFR, reduced kidney function over a few days
What is the clinical definition of acute kidney injury?
Increase in serum creatinine, decrease in eGFR
Decrease in urine volume
What is the disadvantage of using serum creatinine to define acute kidney injury?
Takes a few days for serum creatinine levels to increase after decrease in actual GFR and kidney function
What are the groups of causes of acute kidney injury?
Pre-renal
Intra-renal
Post-renal
What is meant by a pre-renal cause of acute kidney injury?
Acute kidney injury due to decreased blood supply to kidneys
What are some examples of pre-renal causes of acute kidney injury?
Hypovolaemia - haemorrhage, vomiting and diarrhoea, severe burns
Hypotension - anaphylactic shock, septic shock, congestive heart failure
Renal artery stenosis, embolism
Impaired renal autoregulation
What can cause impaired renal autoregulation?
Drugs
- NSAIDS
- ACE inhibitors
- Angiotensin2 receptor antagonists
How do ACE inhibitors cause impaired renal autoregulation?
Inhibit angiotensin 2
which vasoconstricts efferent arteriole
loss of this gives vasodilation of efferent arteriole
How do angiotensin 2 receptor antagonists cause impaired renal autoregulation?
Inhibit angiotensin 2
which vasoconstricts the efferent arteriole
loss of this gives vasodilation of efferent arteriole
How does the kidney respond to pre-renal acute kidney injury?
RAAS
How is pre-renal acute kidney injury treated?
Fluids
How well does pre-renal acute kidney injury respond to fluid treatment?
If blood supply to kidney was high enough to keep cells alive
then responds well
What can pre-renal acute kidney injury develop into?
Intra-renal acute kidney injury
acute tubular necrosis
What is meant by an intra-renal cause of acute kidney injury?
Acute kidney injury due to abnormality of kidney itself
What are some examples of intra-renal causes of acute kidney injury?
Acute glomerulonephritis
Acute tubular necrosis
Acute interstitial nephritis
Acute pyelonephritis
What is the most common cause of acute kidney injury?
Intra-renal acute tubular necrosis
What is acute tubular necrosis?
Cell damage but not cell necrosis
damaged cells cannot reabsorb
What are the causes of acute tubular necrosis?
Ischaemic hypoxia - severe pre-renal acute kidney injury
Nephrotoxins
Sepsis
What parts of the nephron are most affected by ischaemic hypoxia? Why?
Proximal convoluted tubule S3
Loop of Henle thick ascending limb
Lots of reabsorption occurs here so have high metabolic demand
but are deeper in medulla where pO2 is lower
What is the difference between pre-renal acute kidney injury and acute tubular necrosis caused by ischaemic hypoxia? What is the exception to this?
Pre-renal acute kidney injury, still have some cell function, some reabsorption
Acute tubular necrosis due to ischaemic hypoxia, cells too damaged to function, reduced reabsorption
Exception is patient on diuretic, itself gives reduced reabsorption
How is pre-renal acute kidney injury differentiated from acute tubular necrosis caused by ischaemic hypoxia clinically?
Pre-renal acute kidney injury - high urine osmolality, low urine sodium
Acute tubular necrosis caused by ischaemic hypoxia - low urine osmolality, high urine sodium
What is meant by a nephrotoxin?
Substance that damages epithelial cells lining the nephron tubules
What are some examples of endogenous nephrotoxins?
Myoglobin
Bilirubin
Urate
