Week 9 - Acute kidney injury Flashcards
1
Q
What is acute kidney injury?
A
- Clinical syndrome
- Abrupt decline in actual GFR
- – Upset of ECF volume, electrolyte and acid/base homeostasis
- – Accumulation of nitrogenous waste products
- Defined by:
- – Increase in serum creatinine by >= 26.5 μmol/L within 48 hours
- – Increase in serum creatinine by >= 1.5 times baseline within 7 days
- – Urine volume
2
Q
How can pre-renal failure cause AKI?
A
- Volume depletion, heart failure, cirrhosis, etc.
- Mechanism:
- – Actual GFR reduced due to decreased renal blood flow
- – No cell damage so kidneys work harder to restore blood flow
- – Lots of reabsorption of salt and water
- Responds well to fluid resuscitation
- In mild hypoperfusion:
- – Autoregulation ensures renal blood flow is preserved
- If compensatory mechanisms are overwhelmed, AKI occurs
- – May be due to disease of the afferent arteriole can lead to too great or too little response to these stimuli
3
Q
What are some causes of pre-renal failure?
A
- Reduced effective extracellular fluid volume
- – Hypovolaemia (due to blood loss, fluid loss)
- – Cardiac function (due to LV dysfunction, valve disease, tamponade)
- – Systemic vasodilatation (due to sepsis, cirrhosis, anaphylaxis)
- Impaired renal autoregulation
- – Preglomerular vasoconstriction (due to sepsis, hypercalcaemia, hepatorenal syndrome, drugs [NSAIDS])
- – Postglomerular vasodilatation (due to ACEi, AIIR antagonists)
4
Q
What are some causes of intrinsic renal failure?
A
- Intrarenal vascular
- Glomerulonephritis
- – Immune disease affecting the glomeruli
- – Can be primary (only affects kidney) or secondary (a systemic process)
- Ischaemic ATN (acute tubular necrosis)
- Toxin ATN
- Interstitial disease
- Intrarenal obstruction
- Haemolytic uraemic syndrome
- Malignant hypertension
- Pre-eclampsia
- Acute tubulo-interstitial nephritis
- – Infection: acute pyelonephritis
- – Toxin induced: many drugs, most common = antibiotics, NSAIDs, PPIs
5
Q
What are some causes of post-renal failure?
A
- Within the lumen (kidney, ureter, bladder)
- – E.g. stones, blood clot, tumours
- – Stones must be in both renal pelves or ureters, neck of the bladder or urethra
- Within the wall
- – E.g. congenital megaureter, stricture post TB
- Pressure from outside
- – E.g. enlarged prostate, tumour, aortic aneurysm, ligation of ureter
6
Q
What are some causes of acute tubular necrosis?
A
- Ischaemia
- Nephrotoxins
— Damage the epithelial cells lining the tubules
— Cause cell death and shedding into the lumen
— Endogenous = e.g. myoglobin (due to rhabdomyolysis), urate, bilirubin
• Rhabdomyolysis: release of myoglobin due to muscle necrosis, crush injury
• Myoglobin is filtered at the glomerulus and is toxic to tubule cells
— Exogenous = e.g. endotoxin, s-ray contrast, drugs (ACEi, NSAIDs), other poisons (e.g. weedkillers, antifreeze)
— ATN is much more likely if there is reduced perfusion and a nephrotoxin - Sepsis
7
Q
What would you expect to see in blood tests for suspected AKI?
A
- Increased urea
- Increased creatinine
- May or may not be present:
- – Hyperkalaemia
- – Hyponatraemia
- – Hypocalcaemia and hyperphosphataemia
8
Q
What would you look for on an ECG for AKI?
A
To check for signs of hyperkalaemia
- Tall T waves
- Small or absent P waves
- Increased P-R interval
- Wide QRS complex
- Sine wave pattern
- Asystole
9
Q
What signs are there if blood volume is depleted?
A
- Cool peripheries
- Increased pulse
- Low BP/postural hypotension
- Low JVP
- Reduced skin turgor
- Dry axillae
10
Q
What signs are there if blood volume is overloaded?
A
- Gallop rhythm
- BP (may be high, low or normal)
- Raised JVP
- Pulmonary oedema
- Peripheral oedema
11
Q
What are some signs of sepsis?
A
- Pyrexia and rigors
- Vasodilatation, warm peripheries
- Bounding pulse
- Rapid capillary refill
- Hypotension
12
Q
What would you see upon urine testing for AKI?
A
- Detection of blood, protein, leucocytes
- – Intrinsic renal disease = lots of blood and/or protein
- – Pre-renal AKI = normal urinalysis, normal microscopy
- – Glomerulonephritis = proteinuria, haematuria
- – ATN = normal urinalysis
- Culture urine if dipstick is positive
13
Q
If the AKI is due to a urinary tract obstruction, what would you discover from the history and find on examination?
A
- History: (suspect obstruction in patients with: )
- – Anuria
- – Single functioning kidney
- – Loin pain or suprapubic pain
- – History of renal stones
- – History of prostatism or previous pelvic or abdominal surgery
- Examine for:
- – Palpable bladder
- – Pelvic or abdominal masses
- – Enlarged prostate in men – rectal examination
14
Q
What are some susceptibilities for AKI?
A
- Advanced age
- CKD
- Heart disease
- Liver disease
- Diabetes mellitus
- Cancer
- Neurological impairment
- Previous AKI
15
Q
What are some exposures for AKI?
A
- Dehydration or volume depletion
- Sepsis
- Critical illness
- Burns/trauma
- Cardiac surgery
- Emergency surgery
- Neprotoxins
- Radio-iodinated contrast in last week
