Urinary: Acute Kidney Injury Flashcards
What is acute kidney injury?
An abrupt decline in actual GFR - upset of ECF volume, electrolytes, acid base balance and accumulation of nitrogenous waste products
Decreased urine output
How is acute kidney injury staged?
Staged according to how much the serum creatinine has increased from the normal baseline and how low the urine output is
What are the causes of pre-renal acute kidney injury? (general)
Blood supply to the kidney is compromised in some way
- hypovolaemia
- cardiac failure
- systemic vasodilation eg sepsis
- impaired renal autoregulation
How do the kidneys respond to pre-renal AKI?
The actual GFR is reduced due to decreased renal blood flow (there is no cell damage) so the kidneys work hard to restore blood flow so reabsorb lots of salt and water
(responds well to fluid resuscitation)
Which drugs can override the kidneys instrinsic autoregulatory mechanisms to maintain perfusion pressure?
NSAIDs inhibit prostaglandins (normally vasodilate AA)
ACEIs inhibit EA vasoconstrictors
What can cause acute tubular necrosis?
Ischaemia, nephrotoxins or sepsis
The name necrosis is actually a misnomer - there is not tubular necrosis just damaged cells that cannot be immediately reversed
Should treat all drugs the pt is taking as nephrotoxic until proven otherwise
(if not treated promptly AKI leads to ATN)
Which part of the nephron is most vulnerable to acute tubular necrosis?
The PCT and the thick ascending limb because these sit on the brink of hypoxia (medulla) so if blood flow is reduced these are the first places to get damaged
Give some examples of endogenous and exogenous nephrotoxins
Endogenous: myoglobin, urate (can get in tumour lysis syndrome) and bilirubin
Exogenous: drugs eg ACEI, NSAIDs,
Poisons eg weedkiller, antifreeze
Xray contrast
What is rhabdomyolysis?
Better known as ‘crush injury’
It is the release of myoglobin (nephrotoxic) due to muscle necrosis - get ‘coke’ urine
Occurs in drug users when they are unconscious, elderly who fall and cant get back up, wars and natural disasters
What can cause arteriolar/glomerular damage and therefore intrinsic AKI?
Malignant hypertension, pre eclampsia, haemolytic uraemic syndrome
Cause platelet thrombi which partially obstruct small arteries and cause destruction of RBC
How does obstruction cause post-renal AKI?
There is an obstruction to outflow but urine is still be produced
Therefore there is a rise in pressure and the urine backflows up to the kidney causing hydronephrosis
This causes a decrease in renal function
What are some potential obstructions causing post-renal AKI?
Stones, blood clots, tumours, enlarged prostate, aortic aneurysm
What would you look for in a pt potentially presenting with acute kidney injury?
Any signs of hypo/hyperkalaemia, hyponatraemia or hypocalcaemia - emergency!
Volume depletion - cool peripheries, low BP, low JVP, reduced skin turgor, dry axillae
Volume overload - gallop rhythm, raised JVP, peripheral or pulmonary oedema
Signs of sepsis, urinary tract obstruction
What investigations would you if suspecting AKI?
Urinalysis - dipstick and culture if dipstick positive
May measure urine osmolality and urine Na+
Ultrasound scan
Chest xray to look for fluid overload and infection
Renal biopsy
What are some indications that dialysis is required?
- high K+ despite treatment
- metabolic acidosis and NaHCO3- not appropriate
- fluid overload despite diuretics
- presence of a dialysable nephrotoxin eg aspirin overdose
