AKI Flashcards
What are the risk factors for developing an AKI?
Age >75 Chronic kidney disease Other organ failure/chronic disease Drugs Use of iodinated contrast agents Sepsis Poor fluid intake/increased losses History of renal symptoms/past AKIs
What drugs are associated with increased risk of AKI?
NSAIDs, aminoglycosides, ACE inhibitors, angiotensin II receptor antagonists [ARBs] and diuretics
What can the causes of AKI be split up into?
Pre-renal
Intrinsic/Intrarenal
Post-renal
What are some causes of pre-renal AKI?
Absolute loss of fluid – major haemorrhage, vomiting, diarrhoea, severe burns
Relative loss of fluid – distributive shock, congestive heart failure
Renal Artery – stenosis or embolus
ACE inhibitors
What is the underlying mechanism of pre-renal AKI?
Decreased blood flow into kidney
What are the consequences of reduced blood flow in pre-renal AKI?
↓blood filtered =↓GFR = ↑creatinine and urea in blood and less urine
RAAS system activates reabsorbs sodium
Increased sodium and water retention
What happens to the UOsm in pre-renal AKI?
> 500 Osm/kg
What are some causes of Intra-renal AKI?
Acute tubular necrosis
Glomerulonephritis
Acute Interstitial Nephritis
how does acute tubular necrosis cause an AKI?
when cells die they build up and pug renal tubules = creates higher pressure in renal tubules = reduces pressure gradient = less urea and creatinine is filtered out of blood = ↑creatinine and urea in blood and less urine produced = azotaemia and oliguria
what are the causes of acute tubular necrosis?
ischaemia, pre-renal AKI, nephrotoxins – aminoglycosides, lead, myoglobin, ethylene glycol, radiocontrast dye, uric acid – tumour lysis syndrome
How does glomerulonephritis cause AKI?
damaged membrane permeability increases – large molecules are filtered into urine – proteinuria and haematuria
Fluid leakage reduces pressure difference – lower GFR – oliguria, more circulating fluid – edema and hypertension
what are the biochemical affects of acute interisitial nephritis AKI?
BUN:creatinine <15:1
Una > 40, FEna>2%, or water Uosm < 350
what is the pathophysiology of acute interstitial nephritis
infiltration of immune cells - Type 1 or 4 hypersensitivity leading to renal papillary necrosis
what is the mechanism of an intrarenal AKI?
damage to tubules, glomerulus or interstium
What is the mechanism of post renal AKI?
obstruction to outflow
what are the causes of post-renal AKI?
Compression – intra-abdominal tumours, Benign prostatic hyperplasia
Blockage – kidney stones
What does obstruction of outflow in post-renal AKI cause?
increases renal tubule pressure – reduces pressure gradient = ↓GFR = less urea and creatinine is filtered out of blood = ↑creatinine and urea in blood and less urine produced = azotaemia and oliguria
what are the biochemical affects of post-renal AKIs?
Initially high pressure causes more Na, urea and water to be reabsorbed
BUN: Creatinine >15:1, urine concentrated
Over time epithelial cells damaged - less urea and Na BUN:creatinine <15, Una>40, FEna >1-2%
Clinical Features of AKI
Asymptomatic reduced urine output Oedema (pulm, peri) arrhythmias (acid/base balance) Uraemia - anorexia, lethargy, pericarditis, encephalopathy
what is the diagnositic criterai of a AKI?
a rise in serum creatinine of 26 micromol/litre or greater within 48 hours
a 50% or greater rise in serum creatinine known or presumed to have occurred within the past 7 days
a fall in urine output to less than 0.5 ml/kg/hour for more than 6 hours in adults and more than
What features of examination could exist in AKIs?
palpable bladder, palpable kidneys, abdominal/pelvic masses, renal bruits, rashes
What aspects of urinalysis should be looked at in AKI?
infection, glomerular disease, microscopy, culture, BJ proteins
Which routine bloods should be done in AKI?
U&Es, FBC, LFT, clotting, CK, ESR, CRP
Which additional bloods should be done in AKI?
blood film, renal immunology: immunoglobulins, paraprotein electrophoresis, complement, autoantibodies
what is the serum creatinine criteria for stage 1 AKI?
Increase >26μmol/L in 48hr OR increase > 1.5 x baseline
what is the serum creatinine criteria for stage 2 AKI?
Increase 2-2.9 x baseline
what is the serum creatinine criteria for stage 3 AKI?
Increase >3 x baseline OR >354μmol/L OR commenced on RRT irrespective of stage
what is the urine output criteria for stage 1 AKI?
<0.5mL/kg/h for >6 consecutive hours
what is the urine output criteria for stage 2 AKI?
<0.5mL/kg/h for >12h
what is the urine output criteria for stage 3 AKI?
<0.3mL/kg/h for 24h or anuria for 12h
What is the urine specific gravity of pre-renal and intrarenal AKI?
Pre-renal >1.020
Intrarenal <1.020
What is the urine osmolarity of pre-renal and intrarenal AKI?
Pre-renal >500
Intrarenal <350
What is the urine sodium of pre-renal and intrarenal AKI?
Pre-renal <20
Intrarenal >40
what are the complications of AKI?
- Hyperkalaemia
- Pulmonary Oedema
- Uraemia
- Acidaemia
what is the general management of an AKI?
Assess volume states: aim for euvolemia
Stop nephrotoxic drugs
monitor
nutrition
what are the features of management in pre-renal AKIs?
correct volume depletion
what are the features of management in intrarenal AKIs?
refer
what are the features of management in post-renal AKIs?
catheterise and CT of renal tract
consider cystoscopy and stents or nephrostomy
What are the indications for renal replacement therapy?
fluid overload, hyperkalaemia, hypocalcaemia, metabolic acidosis, pericarditis, uremic symptoms, GFR <15ml/min/1.73 m2, or poisoning.
