Acute Kidney Injury Flashcards
What is oliguria?
Urine output of <400ml/day
What is AKI?
A sudden decline in renal function significant enough to produce uraemia and also often oliguria
What is used to classify a patient as having AKI?
Increased serum creatinine by greater than or equal to 26.5μmol/L within 48 hours
Increased serum creatinine by greater than or equal to 1.5 times the baseline within 7 days
Urine volume <0.5 ml/kg/hr
Pre renal causes of AKI? (General)
Impaired blood flow to the kidneys
Impaired autoregulation
What can impair blood flow to the kidneys causing pre-renal AKI?
- hypovolaemia
- low blood pressure
- low cardiac output
- vascular disease
- systemic vasodilation (sepsis, cirrhosis, anaphylaxis)
- cardiac failure (LV dysfunction, tamponade, valve disease)
What can cause impaired autoregulation causing AKI?
Pre-glomerular vasoconstriction
- sepsis
- hypercalcaemia
- hepatomegaly syndrome
Drugs (NSAIDs)
Post-glomerular vasodilation
- ACE inhibitors
- angiotensin II antagonists
General intrarenal causes of AKI?
Acute tubular necrosis
Glomerular and arteriolar disease
Acute tubule interstitial nephritis
What is acute tubular necrosis caused by?
What happens?
Severe acute ischaemia
Nephrotoxins damage epithelial cells lining the tubules, causing cell death and shedding into the lumen
Can be caused by endogenous or exogenous factors
What are some nephrotoxic drugs which can lead to acute tubular necrosis?
Gentamicin
ACE-inhibitors
Angiotensin receptor blockers
NSAIDs
How can NSAIDs lead to AKI?
Inhibit production of prostaglandins
Prostaglandins normally cause vasodilation of afferent arteriole
Afferent arteriole has unopposed vasoconstriction
Reduced glomerular perfusion pressure
Ischaemia
Acute tubular necrosis
AKI
What is glomerular and arteriolar disease?
An immune disease affecting the glomerulus
Types include
-acute glomerulonephritis
-acute tubulointerstitial nephritis
What happens in acute glomerulonephritis?
Immune disease affecting glomerulus
Primary only affects kidneys
Secondary - kidneys involved as part of a systemic process eg SLE, vasculitis
What happens in acute tubulo-interstitial nephritis?
Inflammation of kidney interstitium
Infection - acute pyelonephritis (ascending bacterial infection)
Toxin induced - drugs
What is post-renal AKI?
Indicates obstruction to urine flow after urine has left tubules
(10% of AKIs)
What can obstruct urine outflow and cause AKI and where?
Within the lumen
- canaliculi - renal pelvis, ureters, neck of bladder, urethra
- blood clot
- papillary necrosis
- tumour of renal pelvis, ureter or bladder
Within the wall
- congential - pelviureteric neuromuscular dysfunction, megaureter neurogenic bladder
- ureteric stricture - usually causes chronic not acute
Pressure from outside
- prostatic hypertrophy
- malignancy
- aortic aneurysm
- diverticulitis
- accidental ligation of ureter in surgery
What is anuria?
No urine - less than 100ml/day
How can sodium be used in diagnosing the type of AKI?
Sodium is reabsorbed in pre-renal AKI to restore volume
Reduced in renal AKI due to tubular cell damage
What is used to calculate sodium for AKI?
FEna (fractional sodium excretion)
(Urine Na ➗ plasma Na)
(Urine Cr ➗ plasma Cr) ✖️100
Pre renal if FEna 1%
What is seen in cardiac failure? (Would indicate pre-renal AKI)
Gallop rhythm Raised BP Raised JVP Pulmonary oedema (basal crackles and dyspnoea) Peripheral oedema (sacral/ankle)
What would indicate sepsis (pre-renal cause)
Pyrexia Rigors Bounding pulse Vasodilation - warm peripheries Rapid capillary refill Hypotension
What would indicate a urinary tract obstruction?
Anuria Single functioning kidney History of renal stones/prostatism/pelvic or abdominal surgery Palpable bladder Pelvic/abdominal mass Enlarged prostate (DRE)
What serum biochemistry markers would indicate AKI?
Raised creatinine
Raised urea
Raised potassium
Raised phosphate
Low sodium
Low calcium
Why would you use an ECG for diagnosis of AKI?
Look for hyperkalaemia
What ECG changes are there in hyperkalaemia?
Tall T waves Small/absent P waves Increased PR interval Wide QRS complex Sine wave pattern Asystole
