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
What are some examples of exogenous nephrotoxins?
Endotoxins
Drugs
What causes high levels of myoglobin in the blood?
Rhabdomyolysis
What is meant by rhabdomyolysis?
Rapid breakdown of skeletal muscle cells
What are some examples of causes of rhabdomyolysis?
Crush injurt
Lack of blood flow to a limb
What is a renal sign of rhabdomyolysis?
Dark urine
What is meant by thrombotic microangiopathy?
Thrombosis in capillaries due to damage to the endothelium
How does thrombotic microangiopathy affect red blood cells?
Passing red blood cells are torn apart
How does thrombotic microangiopathy cause intra-renal kidney failure?
Damage to glomerular capillary membrane
What is meant by acute interstitial nephritis?
Inflammation of the tissue surrounding the nephron tubules
What are the causes of acute interstitial nephritis?
Infections
Drugs e.g. antiobiotics, NSAIDS, proton-pump inhibitors
which both cause inflammation
What is meant a post-renal cause of acute kidney injury?
Acute kidney injury caused by obstruction of urinary tract after kidneys, both kidneys
How does obstruction of the urinary tract cause acute kidney injury?
Increase in tubular pressure
increased hydrostatic pressure in Bowman’s capsule
reduced GFR
What are some examples of post-renal causes of acute kidney injury?
Lumen - stones, tumours,
Wall - stricture
External - enlarged prostate, tumour, aortic aneurysms
Why does a post-renal cause of acute injury have to involve both kidneys?
Because otherwise the other kidney will compensate by increased urine excretion
no change in serum levels of fluid, electrolytes
What age group is post-renal acute kidney injury most common in?
Elderly
How does acute kidney injury affect serum levels?
Increased urea
Increased creatinine
What are the complications of acute kidney injury?
Hyperkalaemia
Metabolic acidosis
Hyponatraemia
Hypocalcaemia
How can acute kidney injury cause metabolic acidosis?
Reduced reabsorption and production of bicarbonate ions in proximal convoluted tubule and later distal convoluted tubule and collecting duct
Reduced secretion of hydrogen ions in later distal convoluted tubule and collecting duct
How can acute kidney injury cause hyperkalaemia?
Tissue damage releases it from cells
Metabolic acidosis causes potassium to move out of cells
Reduced GFR
Reduced distal delivery of sodium ions, reduced secretion in collecting duct
Drugs e.g. RAAS inhibitors, potassium-sparing diuretics,
What are the signs of hyperkalaemia?
Cardiac arrythmias
What does the ECG of a patient with hyperkalaemia look like?
Tall T waves
Small or absent P waves
Increased P-R interval
Wide QRS complex
