renal Flashcards
5 functions of the kidney
- creating hormones to tell the bone marrow to create their blood cells - erythropeitin
- controls ph
- metabolises vitamin d
- blood volume /fliud management
- waste/toxin/drug extretion
how do we measure how well the kidney is doing?
creatinine -
- can only really be made in the body by muscles
- waste priduct of muscle metabolism
purely excreted by kidneys
- longstanding measure of kidney function
- small increases in creatinine = large changes in eGFR
causes of stepwise decline in GFR
medication
insterstitial cystitis
AKI gfr picture
rapid decline and then level off
newly identified CKD gfr
stable low gfr
what can suggest poor working kidneys
proteinuria/abluminuria
how do you measure proteinuria
problems with it
how to do it more accurately
urine dipstick
problems - just a snapshot, influenced by dilution, have to write it down
accuracy - albumin/creatinine ration
- albumin + creatinine is secreted into urine at constant rate therefore should always be the same ratio
how does kidney failure cause iron-deficiency anaemia
liverproduces hepcidin which is cleared by the kidney.
this doesnt happen as much so you get a build up …
what gfr would make you want to start dialysis
6-8
how does kidney failure cause iron-deficiency anaemia
liver produces toxin hepcidin which is cleared by the kidney.
this doesnt happen as much so you get a build up which inhibits iron absorption by the duodenum
AKI definition
sudden decline in GFR baseline/increase in creatinine with or without oliguria (<0.5ml/kg/hr) / anuria (< 50ml/day)
what is diagnosis of AKI based on
creatinine and urine output
causes of AKI
prerenal - hypovolaemia
- volume depletion - diarrhoea, blod loss, dehydration
- low cardiac output - MI, HF
- sepsis
- drugs - ACE i, NSAIDs
- renal artery stenosis
renal - internal structures
- vascular = vasculitis, malignant hypertension
- tubular = acute tubular necrosis, rhabdomyolysis, myeloma, **radiocontrast (common), drugs (antibiotics)
- glomerular eg glomerulonephritis
- interstitial eg interstitial nephririts
post-renal - obstruction with outflow tract of urine
- stones
- tumours
- strictures
- enlarged prostate
- blood clots
risk factors of AKI
- elderly
- CKD
- chronic conditions eg DM, HF (on eg ACEi, ARB, diuretics), liver disease
- neurological/cognitive impairment (low fluid intake)
- cancer - myeloma (light chains directly affect kidneys)
- previous AKI
- post-op
- medications
- radiocontrast
- sodium retaining states - CHF, cirrhosis, nephrotic syndrome
medications and how they affect the kidney causing AKI
direct effect
- NSAIDs - interstitial nephritis
- antibiotics - toxic effect to tubular cells (penicillin, rimapicin, gold, gentamycin), ATN - aminoglycosides, amphotericin, ciclosporin
accumulation during renal dysfunction
- metformin (can cause hyperglycaemia)
effects on renal/fluid/electrolyte physiology
- ACEi - cause AKI, increase potassium,
- diuretics - overdiuresis (prerenal)
drugs causing GI loss (laxatives - prerenal)
post-renal - causing retention
- anticholinergics
- alc
presentation of AKI
- depends on underlying cause
- incidental finding of raised creatinine
clinically =
- high urea from decreased excretion = nausea, vomiting, decreased consciousness
- hyponatraemia from excess of water relative to sodium = peripheral + pulm oedema, ascites, pleural effusion
- hyperkalaemia from decreased excretion + metabolic acidosis = muscle weakness + ECG changes
- met acidosis from decreased h+ ion secretion = kussmaul breathing
effect an AKI has on body
Impaired clearance and regulation of metabolic homeostasis, impaired acid-base, electrolyte and volume regulation
why is creatinine used as marker of GFR
creatinine
- waste product of normal muscle breakdown
- marker of GFR - used as its only excreted renally, freely filtered at glom, not reabsorbed, generally remains constant
- looking for changes in creatinine if problem
when is eGFR not valid
when creatinine is changing
what affects creatinine levels
muscle mass
ethnicity
gender
age
stages of AKI
KDIGO guidelines for adults
looks at serum creatinine and urine output - both dont need to be present for diagnosis
stage 1 - creatinine increase 1.5x in 7 days OR creatinine >/= 26.5 umol/L in 48 hrs. UO = <0.5ml/kg/hr for 6 hours
stage 2 - creatinine increase 2x in 7 days
UO = <0.5ml/kg/hr for 12 hours
stage 3 - creatinine 3x baseline in 7 days
cr >354
RRT started
UO = <0.3ml/kg/hr for 24 hours or anuria for 12 hours
false positives of AKI alerts from algorithm
causes
recent pregnancy
drugs - trimethoprim (they increase creatinine)
contamination
false negative of AKI alerts from algorithm causes
previous AKI within last year
what is AKI on CKD
when you have sudden decline in renal function with known CKD
normal size of kidneys
11-14cm
GFR normal
120 ml/min/1.73m
20% of CO
eGFR what is it
Predict creatinine generation age, gender, race, sex (n.b. Extreme muscle mass e.g. cachexia/body builder = misleading