19) Acute Kidney Injury Flashcards
What is oliguria?
Little urine, less than 500ml/day
What is anuria
No urine, less than 100ml/day, indicates blockage
What is acute kidney injury?
Abrupt decline in actual GFR (days to weeks)
What does AKI affect?
Upset in ECF volume, electrolyte and acid base homeostasis
Accumulation of nitrogenous waste products
Why is AKI hard to diagnose?
Serum creatinine has a delayed build up (5 days) after kidney function decline
How is AKI defined? (3 definitions)
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 <0.5 ml/kg/h for 6 hours
How is AKI staged?
3 stages, with each stage a higher increase in serum creatinine
Stage 3 may include initiation of renal replacement therapy
What are the 3 general causes of AKI?
Pre-renal failure
Intrinsic renal failure
Post renal failure (obstruction)
What is pre-renal failure?
Decreased renal perfusion
What can cause pre-renal failure?
Hypovolemia
Heart failure
Systemic vasodilation
Impaired renal autoregulation
How does the kidney maintain renal blood flow normally, when renal perfusion decreases?
Autoregulation to dilate AA and constrict EA, therefore maintaining GFR
What can cause impaired autoregulation?
If BP falls below 80mmHg
Diseases of afferent arteriole
Interfering drugs - NSAIDs and ACEi/ARB
What can occur if pre-renal failure isn’t promptly treated?
Acute tubular necrosis
What can cause intrinsic renal failure?
Acute tubular necrosis - ischaemic, toxic
Glomerular and arteriolar disease
Interstitial disease
What can cause ATN?
Ischemia
Nephrotoxins
Sepsis
Why is ATN a misnomer?
Cells damaged without immediate reversal but not necrosed
What can’t the damaged cells in ATN do?
Cannot reabsorb water and salt
Can’t expel excess water
Why shouldn’t fluid resuscitation be used in ATN?
May get fluid overload due to damaged cell function
What causes ischaemic ATN?
Reduced perfusion
Affects proximal tubule as near hypoxic zone
Where in nephron does ischaemic ATN affect and why?
Proximal tubule as near hypoxic zone and requires lots of O2 to function
How does ischaemic ATN present on microscopy?
Loss of structure on PT
Debris in lumen
How do nephrotoxins cause ATN?
Damage the epithelial cells lining the tubules causing cell death and shedding into lumen
Give some examples of endogenous nephrotoxins:
Myoglobin
Urate (increased in chemo)
Bilirubin
Give some examples of exogenous nephrotoxins:
Endotoxin
X-ray contrast
ACEi, NSAIDs
Weedkiller
What is rhabdomyolysis and how can it cause AKI?
Muscle necrosis due to crush injury - release of myoglobin
Myoglobin filtered and toxic to tubule cells, may cause obstruction and dark urine
How can you tell the difference between pre-renal failure and ATN?
Lower osmolarity in ATN as cells can’t concentrate
Higher urinary Na+ in ATN as cells can’t reabsorb
What causes acute glomerulonephritis?
Primary: IgA nephropathy
Secondary: Lupus, vasculitis
How do haemolytic uraemic syndrome or hypertension cause arteriolar/glomerular damage?
Endothelial damage -> platelet thrombi -> partially obstruct small arteries -> destruction of RBC
What can cause interstitial nephritis?
Infection: acute pyelonephritis
Toxin induced: antibiotics, NSAIDs, PPI
What is seen microscopically in interstitial nephritis?
Lots of lymphocytes and inflammatory infiltrate, wide space between tubules
How does post-renal failure cause AKI?
Obstruction causing rise in intraluminal pressure, dilatation of renal pelvis and decrease in renal function
What can cause obstruction leading to post renal failure?
Within lumen obstruction
From within wall (likely to cause CKD)
Pressure from outside
What can cause obstruction within lumen?
Stones, blood clot, tumour
What can cause obstruction from within the wall?
Congenital megaureter, stricture (post TB)
What can cause obstruction by pressure from outside?
Enlarged prostate, tumour, AAA
What investigations can be carried out in AKI?
Serum biochemistry - urea and creatinine
Urinalysis - blood, protein, leucocytes
Potassium, sodium and calcium
What are symptoms of volume depletion?
Cool peripheries, high pulse, low BP
What are symptoms of volume overload?
Gallop rhythm, raised JVP, oedema
What are the symptoms of sepsis?
Fever, warm peripheries, bounding pulse, low BP
What could you examine if you suspect UT obstruction ?
Anuria
Palpable bladder
Pelvic masses
Enlarge prostate
What imaging may you use to investigate AKI?
Ultrasound
CXR - fluid overload or infection
When would you use a kidney biopsy to investigate AKI?
When pre and post renal AKI ruled out
How can AKI be prevented?
Adequate hydration
Avoid nephrotoxins
Detect early
What are risk factors for AKI?
Advanced age, CKD, dehydration
How is pre-renal AKI treated?
Fluids - restore volume
Diuretics - pump failure
How is intrinsic AKI treated?
Maintain perfusion, avoid nephrotoxins, restrict solutes
How is post-renal AKI treated?
Urological intervention
What can be used if kidneys aren’t functioning after treatment?
Dialysis
What is the prognosis for AKI?
Recovery with 2-3 weeks
Infection and dialysis increase mortality
Increase risk of death for year after
