Acute Kidney Injury Flashcards
What is acute kidney injury?
Rapid reduction in kidney function
What is acute kidney injury based on?
- Rise in creatinine (reduction in removal by kidneys)
- Decreases in urine output
What is the serum creatinine criteria for stage 1 AKI?
SCr increase ≥26 µmol/L within 48 hrs
or
SCr increase 1.5–1.9 fold from baseline
What is the urine output for stage 1 AKI?
<0.5 mL/kg/hr for 6 consecutive hrs
What is the serum creatinine criteria for stage 2 AKI?
SCr increase 2–2.9 fold from baseline
What is the urine output for stage 2 AKI?
<0.5 mL/kg/hr for 12 hrs
What is the serum creatinine criteria for stage 3 AKI?
SCr increase ≥3 fold from baseline
or
SCr increase ≥354 µmol/L
or
initiated on RRT (irrespective of stage at time of initiation)
What is the urine output for stage 3 AKI?
<0.3 mL/kg/hr for 24 hr
or
anuria for 12 hr
What are the 3 broad types of AKI?
- Pre-renal
- Post-renal
- Intrinsic
According to which part of the renal system is primarily affected
What is pre-renal AKI?
Drop in blood flow to kidneys so kidneys cannot remove creatinine (in health, around 20% of cardiac output is directed to kidneys)
No cellular injury unless left untreated
What are the common causes of pre-renal AKI?
- Severe sepsis (vasodilation)
- Toxins
- Haemorrhage
- Hypotension (vomiting, diuretics, haemorrhage, diarrhoea, medication)
- Over diuresis with diuretics
- Burns (excessive fluid loss through skin)
What is intrinsic AKI?
Structural damage to the kidney tissue (glomeruli/tubules/interstitium). Cellular injury (necrosis) can release intracellular contents that damages surrounding cells
This is commonly 2ary to pre-renal AKI
What are the most common causes of intrinsic AKI?
- Prolonged pre-renal AKI
- Acute tubular injury
- Nephrotoxins (e.g. gentamicin, contrast media)
- Interstitial nephritis (e.g. NSAIDs)
- Vasculitis
- Glomerulonephritis
What is post-renal AKI?
Occurs after an acute obstruction of urinary flow. This increases intra-tubular pressure and decreases GFR
Examples:
- Kidney stones
- Prostatic hypertrophy
- Tumours (bladder carcinoma, cervical carcinoma)
- Retroperitoneal fibrosis
What are common causes of post-renal AKI?
Caused by obstruction to the renal tract - this can be anywhere from the renal pelvis to the urethra.
If the kidney’s drainage is blocked this will lead to damage of kidney tissue
Where are 80% of the glomeruli found?
In the cortex
What structures are found in the outer medulla?
Proximal straight tubule
Describe the proximal straight tubule?
Very dense network of blood vessels (25% of cardiac output)
Filtrate being produced
When blood pressure drops, where do kidneys divert blood? What does this pose risk to?
To the cortex to preserve the glomeruli (glomeruli cannot recover after injury)
Poses risk to outer medulla (proximal straight tubule)
What is reperfusion injury?
Tissue damage (exacerbation of cellular death) following restoration of blood flow and oxygen after a period of ischaemia or lack of oxygen (anoxia or hypoxia)
How is apoptosis unique?
When cells die, their contents are not released so do not damage surroundings
How might a patient present acutely ill / post-major surgery?
- Hypovolaemia / hypotensive
- Sepsis (infection)
What are the risk factors for AKI?
- Age
- Pre existing CKD
- Previous AKI
- Heart failure
- Liver diseases
- Diabetes
- Hypotension
- Sepsis
- Nephrotoxins
What are the complications of AKI?
- Hyperkalaemia
- Acidaemia
- Pulmonary oedema
- Uraemia
- GI effects
- Haematological effects