AKI Flashcards
define AKI
rapid reduction in kidney function from hours to days, as measured by serum urea and creatinine, and leading to failure to maintain fluid, electrolyte and acid-base balance homeostasis.
time frame
<48 hours
diagnosis criteria
Diagnosis: abrupt (<48hrs) reduction in kidney function:
- Rise in serum creatinine >26.4umol/L
- Rise in creatinine >50% baseline
- Reduction in urine output
Must follow adequate fluid resuscitation and exclusion of obstruction.
KDIGO staging system
patient risk factors
- Older age (≥65)
- CKD
- DM
- Cardiac failure
- Liver disease
- PVD
- Previous AKI
exposure risk factors
- Hypotension, hypovolaemia
- Sepsis
- Deteriorating NEWS
- Recent contrast
- Exposure to certain medications
- History of urinary symptoms
what investigation should be carried out within 24 hours of assessment
- US
- check for obstruction
- check size of kidneys - can indicate acute or chronic damage
UCR in pre renal AKI
Decreased renal perfusion lead to a reduction in GFR – this decreases both urea and creatinine filtration (increases serum concentration) as they accumulate. Urea is also reabsorbed more in the proximal tubule because it is flowing slower à increased urea:creatinine ratio.
UCR in intra renal AKI
Ratio becomes closer to 1 as urea is unable to be reabsorbed.
how much of CO do kidneys receive
20% even though they are 0.5% of body weight
causes of decreased blood flow to kidneys
- Absolute loss of fluid:
- Major haemorrhage, vomiting, diarrhoea, severe burns (body fluid evaporates really fast without protective skin)
- Relative loss of fluid (total stays the same):
- Distributive shock – fluids moves from vessels into tissues
- Congestive heart failure – blood pooled in venous side
- Hypotension
- Cardiogenic shock
- Distributive shock (e.g. sepsis, anaphylaxis)
- Local to renal artery
- Narrowed in renal artery stenosis
- Blocked by embolus
- Renal hypoperfusion:
- Hepatorenal syndrome
- Drugs
- E.g. NSAIDs
how do NSAIDs cause pre renal AKI
- NSAIDs inhibit COX (and PG production) and may precipitate acute renal failure in conditions where renal blood flow is dependent upon vasodilatory PG (no effect on renal function in healthy people), e.g. CHF, cirrhosis, nephrotic syndrome
- Cause afferent arteriole vasoconstriction.
assessing fluid status
- Mucous membranes, skin turgor, E+S, BP, JVP, (creps in chest), CRP
- Bloods: urea, haematocrit, osmolarity + urine osmolarity
- Peripheral oedema indicates fluid in the wrong place, not necessarily intravascular volume status
pre renal AKI
- the kidneys are v sensitive to low blood flow - decrease in GFR
- oliguria and a rise in UCR (rise in urea (++) and creatinine)
- increase in salt and water retention
- decreased blood flow for a prolonged period of time leads to intrinsic renal failure due to acute tubular necrosis
distinguishing pre renal and renal causes of AKI: urine sodium
low in pre renal - kidneys are holding on to sodium to preseve volume
high in renal
distinguishing pre renal and renal causes of AKI: urine specific gravity
- a measure of the concentrating ability of the kidneys
distinguishing pre renal and renal causes of AKI: urine osmolality
signs of uremia
- yellow tinge
- uremic frost
- involuntary muscle twitching
- bleeding
- metabolic acidosis - Kussmaul breathing
- pericardial rub or haemorrhagic pericarial effusion
- encephalopathic: flapping tremor and confusion
why is there a metabolic acidosis in renal failure
kidney normally excretes H+ ions
how does urea cause bleeding
uremia acts as an antiplatelet, less clot formation which means patients bleed and bruise more easily
uremic frost
- occurs in those who have had established renal failure for years, trying to excrete/secrete toxins through skin pores – urea concentration increases in sweat. Evaporation of sweat with high urea concentration causes urea to crystallize and deposit on the skin.
- stale urine smell to skin
- rarely seen now due to RRT
intra renal causes of AKI
- vascular eg vasculitis
- GN
- interstitial nephritis
- tubular injury
which drugs cause IN
(inflammation of the space between renal tubules)
- NSAIDs
- diuretics
- sulphonamides
- rifampicin
- PPIs
- allopurinol
infection and immune causes of IN
- infection eg TB
- immune reactions eg sarcoidosis and SLE
what haematological thing may drug reactions cause
peripheral eosinophilia and allergic picture: fever and rash
what will a biopsy of IN show
inflammatory cell infiltrate
causes of tubular injury
- ischaemia due to prolonged renal hypoperfusion etc
- drugs eg gentamicin
- radio contrast dye
- massive haemolysis
- rhabdomyolysis
what damage do aminoglycosides do to the kidneys
- they are nephrotoxic - cause ATN
- typically presents as a mild non-oliguric AKI 1-2 weeks into therapy
- there is a high output of watery urine and high creatinine