Session 10: Acute Kidney Injury Flashcards
% of cardiac output the kidney receives.
25%
Definition of AKI.
A decline in the GFR that occurs during a short period of time.
What is AKI currently measured by?
The GFR is measured by a raise in serum creatinine.
Serum creatinine is however not the ideal marker.
The serum creatinine gives us a way to use a formula that provides an estimated GFR (eGFR)
Criteria for AKI.
A rise in serum creatinine of 26 micromol/L or greater within 48 hours.
A 50% of greater rise in serum creatinine where the baseline is known within the past 7 days.
A fall in urine output to less than 0.5 ml/kg/hour for more than 6 hours in adults and more than 8 hours in children and young people.
A 25% or greater fall in eGFR in children and young people within the past 7 days.
How is the severity of AKI assessed?
By stages (Stage 1-3)
Stage 1 AKI.
1.5-1.9 serum creatinine from baseline or a 26.5 micromol increase.
<0.5 ml/kg/h for 6-12 hours urine output
Stage 2 AKI.
2.0-2.9 times serum creatinine of the baseline.
<0.5 ml/kg/h of urine output for >12 hours.
Stage 3 AKI.
3.0 times baseline serum creatinine.
Increase in serum creatinine >350 micromol/l
<0.3 ml/kg/h >24 hours or anuria for over 12 hours
Why is it important to account for the baseline of serum creatinine when assessing kidney function?
Because serum creatinine can vary a lot in patients.
Muscular black males will have a higher serum creatinine compared to small white elderly women e.g.
AKI may be oliguric or non-oliguric.
What is oliguria?
Less than 500 ml of urine per day or less than 20 ml per hour.
Definition of anuria.
Defined as less than 100 ml of urine per day.
What does anuria usually indicate?
Blockage of urine flow or very severe damage to kidneys.
What is uraemia?
Defined as the clinical signs and symptoms of kidney failure.
Results in a lack of secretory and excretory function in the kidneys.
Aetiology of AKI can be divided into three major categories.
Which?
Pre-renal
Renal/Intrinsic
Post-renal
What is pre-renal disease defined as?
Decreased renal perfusion.
Explain why poor renal perfusion leads to pre-renal disease.
As BP declines beneath a threshold level the kidney will be unable to maintain blood flow that is required to maintain an adequate GFR.
This leads a decrease in GFR.
Is pre-renal disease reversible?
It is, if it’s recognised quickly enough and hasn’t caused damage to the kidneys.
What is most common;
Pre-renal
Renal
Post-renal
Pre-renal (85%)
Give causes of pre-renal disease.
Hypovolaemia
Decreased CO
Congestive heart failure
Liver failure
Renal artery stenosis
Medication like NSAIDs, ACE-I and ARB.
Cyclosporine
What is the most common cause of renal/intrinsic disease?
Acute tubular injury (ATI)
What is the most common cause of ATI?
Pre-renal disease being left untreated.
Explain how Pre-renal disease can cause ATI.
Kidney cells are starved of O2. This leads to the cells which have the highest metabolic requirements and the areas which are not well perfused are at risk of damage.
These are the proximal tubules.
Give causes of renal/intrinsic kidney disease.
ATI
Drugs like NSAIDs, ACE-inhibitors, Gentamicin etc…
Glomerulonephritis
Ischaemia
Sepsis/Infection
Vasculitis
Nephrotoxins
Rhabdomyolysis
Myeloma
What is post-renal disease?
Obstruction to urine flow after urine has left the tubules.
Can lead to hydronephrosis e.g.
