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Flashcards in Acute Kidney Injury Deck (26):

What is AKI?

AKI is defined as decline in GFR that occurs during a short period of time. Acute change in renal function. Decline in GFR is measured by an increase in serum creatinine.


Describe the management of AKI

Treatment is dictated by the cause of AKI. Usually involved managing fluid balance.


How would you confirm a distinguish between pre-renal AKI and tubular necrosis?

Specific gravity >1.018
Osmolality >500mosm/kg
Urinary Na+ <10mmol/L

Specific gravity <1.012
Osmolality <250 mosm/kg
Urinary Na+ >20mmol/L


What is post renal AKI?

An obstruction to urine flow after it has left the tubules.


How do you treat pre-renal AKI?

Restore renal perfusion by restoring volume or treating pump failure.


How do you treat post renal AKI?

Urological intervention is necessary to remove obstruction/ re-establish urine flow.


How do you treat acute tubular necrosis?

Recovery can take weeks. Treatment is supportive hence, maintaining renal perfusion, avoiding nephrotoxins, restricting various solutes (K+) and providing nutritional support.


When might you use dialysis to treat a patient with AKI?

If the kidneys are unable to excrete salt, water, potassium or other waste products or if the acid-base balance can no longer be maintained. Also in signs of uraemia.


What are the causes of prerenal AKI?

1. Reduced BP (hypervolemia, systemic vasodilation, cardiac failure)
2. Impaired renal autoregulation (pre-glomerular vasoconstriction, post glomerular vasodilation)


What is acute tubular necrosis?

Pre-renal disease leads to ischemia of kidney tubule cells (highest metabolic requirement). Cells become damaged and non functional. Cannot reabsorb salt and water efficiently or expel excess water. Much more likely if there has been reduced renal perfusion and nephrotoxin presence.


What are the causes of pre-glomerular vasoconstriction?

Sepsis, NSAIDS


What are the causes of post-glomerular vasodilation?

ACE inhibitors


What are the causes of acute tubular necrosis?

Ischemia, nephrotoxins, sepsis


Why is aggressive fluid resuscitation in acute tubular necrosis potentially damaging?

Risks fluid overload. Damaged tubular cells cannot expel water efficiently.


Give an example of an endogenous nephrotoxin

Myoglobin, urate, bilirubin


Give an example of an exogenous nephrotoxin

Endotoxin, X-ray contrast, drugs (NSAIDS, gentamicin) and certain poisons


What is rhabdomyolysis?

Rhabdomyolysis is the breakdown of damaged skeletal muscle due to muscle necrosis causing the release of myoglobin into the bloodstream. Nephrotoxic but may also cause obstruction.


Who is more likely to get rhabdomyolysis?

- Drug users (unconscious so don't move)
- Elderly people (fall and can't get up)


Describe the appearance of urine in myoglobinuria

Coca cola urine - very dark brown


What is thrombotic microangiopathy?

Thrombotic microangiopathy (TMA) is a pathology that results in thrombosis in capillaries and arterioles, due to an endothelial injury. It may be seen in association with thrombocytopenia, anemia, purpura and renal failure.


Describe the pathophysiology of post-renal AKI

Obstruction in ureter causes a rise in intraluminal pressure and dilation of the renal pelvis(hydronephrosis) causing a decrease in renal function.


What are the causes of post-renal failure?

Stones, blood clots and tumours within the lumen, strictures, enlarged prostate etc


What are the causes of hyperkalaemia?

Excess intake, movement out of cells (acidosis, hyper tonicity, tissue damage), reduced urine loss and certain drugs


Describe the ECG changes seen in hyperkalaemia

Tall t waves, small or absent P waves, increased PR intervals, wide QRS complex, sin wave pattern, asystole.


How do you investigate patients with AKI?

Every patient with AKI must have a urinalysis for detection of blood, protein, leucocytes and a urine microscopy/culture if dipstick is positive.

USS imaging within 24 hours of presentation of suspected obstruction or unknown cause.

CXR to look for fluid overload and infection


When would you obtain a renal biopsy?

When pre-renal and post-renal AKI have been ruled out. A confident ATN diagnosis cannot be made and systemic inflammatory symptoms/signs aren't present.