Acute Kidney Injury Flashcards
How much of the the CO does the kidney receive?
25%
How can you define AKI?
a decline in the GFR that occurs during a short period of time (2-7 days)
How is GFR measured?
Creatinine - endogenous product in muscle cells at a constant rate e.g if excretion rate drops your kidney function has dropped (whole lecture on this)
Whats the difference between AKI stage 1, 2 and 3 on blood tests?
Stage 1 - serum creatine increased by 50%
Stage 2 - serum creatine increased 2 fold
Stage 3 - serum creatinine increased 3 fold
What are some issues with serum creatinine testing?
As creatinine is a marker of muscle breakdown, if you don’t eat enough, your serum creatinine will be low - same as if low muscle mass
What are the 3 causes of AKI?
Pre-renal, renal and post-renal
What does pre-renal causes include?
Perfusion problems - the kidneys not receiving a lot of blood;
- hypovolaemia due to shock, burns, dehydration, sepsis, haemorrhage
- reduced effective circulating volume e.g. congestive cardiac failure and liver disease
- Drugs
- Renal artery stenosis
How does hypovolaemia cause AKI?
there is decreased effective circulating volume so less blood reaches the kidney so less blood is filtered so GFR decreases
What kind of drugs cause AKI and how do they do this?
NSAIDS, ACE inhibitors and antihypertensives
-they alter the renal haemodynamics - imparted renal auto regulation
Is pre-renal disease reversible?
Yes because kidney injury has not occurred yet, they are just unable to maintain the blood flow and hence GFR but it has to be recognised quickly
What is ATI?
Acute tubular injury - this is when the kidney cells get damaged and stop working - ischaemia or toxin damage
In what case does ATI develop from pre-renal AKI?
if pre-renal AKI is sustained for long enough, ATI can occur. The kidney cells can become starved of oxygen and the cells with the highest metabolic requirements and those in the areas that are less well perfused are at risk i.e. PCT
What other renal causes are there of AKI?,
- drug toxicity - NSAIDS, antibiotics, ACE inhibitors (cause low blood pressure as hypotension leads to hypo perfusion of kidneys)
- Sepsis
- Hypertension
- vasculitis
- emboli
- kidney stones?
What is vasculitis?
inflammation of the blood vessels - can cause AKI as protein and blood can leak into the urine caused by decreased kidney function
What are the post-renal causes or AKI?
post-renal indicates an obstruction of urine flow after urine has left the tubules
- bladder outflow obstruction (BPH, urethral strictures)
- retroperitoneal fibrosis
- tumours
- stones
What is significant about renal stones in renal failure and AKI?
For renal stones to cause AKI/renal failure, they must occur in both kidneys or in a single functioning kidney
What is the difference between AKI and CKD?
AKI is an acute change in renal function whereas CKD is a decline in GFR that occurs over months to years
What is the treatment for AKI?
Depends on the cause;
- with pre-renal you need to restore renal perfusion e.g. fluid administration
- if urinary tract obstruction then need to re-establish urine flow
When would a patient need dialysis?
if the kidneys can no longer adequately excrete salt, water, K+ or other waster products OR if acid base balance can no longer be maintained
Why is it clinically important to know difference between renal and pre-renal cause of AKI?
renal cause needs prompt referral to nephrology but pre-renal needs supportive treatment and management of precipitating events
What is the best way to diagnose AKI?
Urine dipstick test, USS, microscopy, culture, blood tests
What is oliguria?
less than 500ml of urine per day
What is anuria and what does it indicate?
less than 100ml of urine per day - indicates a blockage of urine flow or very severe damage to kidneys - less common form of AKI
What is uraemia?
the accumulation of nitrogenous metabolic waste produces in the blood - urea and creatinine
What is the difference between AKI and CKD in regards to uraemia?
in acute, uraemia develops rapidly within a few days, in chronic there is gradual onset over a few months-years
Why are elderly more predisposed to uraemia?
Falls in the elderly - may stay in same position for a while
Muscle breakdown - myoglobin released into blood and filtered by kidney. Myoglobin causes inflammatory reaction causing kidneys to shut down - rhabdomyolysis
What are some renal causes of acute renal failure?
- direct damage to kidney
- inflammation
- infection
- drugs
- autoimmune diseases
What is acute glomerularnephritis?
Inflammation of the glomerulus most commonly caused by systemic lupus erythromyetusis
What is acute tubular necrosis?
Death of cells in the nephron - 50% of ARF have this
What is acute interstitial nephritis?
Inflammation of interstitial space in the kidneys - most common due to allergic reaction or infection
Why do you get a decreases in GFR in ARF?
- (vascular changes) - vasoconstriction causing increase adhesion of inflammatory cells
- (tubular changes) - necrosis and apoptosis forming necrotic bodies and cause obstruction in the tube so the filtrate cant get through
