Nephrology non-BPT Flashcards
What is the broad definition of an AKI?
- abrupt drop in eGFR
- acute reduction in UO
*note these are markers of reduced function, not injury
In an AKI, which parameter is deranged first - SCr or eGFR?
There may be an acute drop in eGFR before the SCr increases
Describe the broad classifications of an AKI
- pre-renal
- renal
- post-renal
Explain what a pre-renal AKI is
This definition describes a mechanism of reduced renal perfusion
- can be true volume depletion
- reduced effective blood volume (e.g. HF, cirrhosis) [due to overactivation of RAAS]
List 4 causes of pre-renal AKI
- hypovolemia/true volume depletion (acute haemorrhage, diarrhoea, renal ECF depletion, fluid sequestration)
- reduced effective arterial blood volume/hypervolemic state with low effective circulating volume (e.g. severe systolic HF with reduced EF, acutely decompensated liver disease with portal hypertentsion)
- reduced SVR (e.g. sepsis)
- alterations in renal vascular auto-regulation (e.g. afferent arteriole vasoconstriction caused by NSAIDs or contrast, renal artery stenosis)
*note ARB/ACEi alter the kidneys ability to auto-regulate blood flow
Explain the mechanism of pre-renal AKI in hypovolemia
there is low perfusion pressure due to low arterial pressure
Explain the mechanism of pre-renal AKI in HFreF or abdominal compartment syndrome
- perfusion pressure is the difference between arterial and venous pressure
- A patient with HFpEF has elevated venous pressure, so this can lead to a low perfusion pressure
What are the 4 main components of the nephron?
- glomerulus
- tubules
- interistium
- vasculature
What are the two broad sub-types of acute tubular necrosis
- ishcaemic > extension of pre-renal
- toxins
> endo-toxins = myoglobin, casts
> exo-toxins = aminoglycosides, IV contrast, chemotherapy
What are renal casts?
- cylindrical structures formed in the tubular lumen
- matrix composed of Tamm-Horsfall mucoprotein
- within the cast matrix are other elements (e.g. WBCs, RBCs, kidney cells, protein, fat) > this is how casts are defined
Where do renal casts tend to form?
They develop in the distal convoluted tubule or the collecting duct
How do you assess for renal casts?
Do a urinalysis
What is the clinical course of ATN?
- injury pre-dates any changes to SCr
- the SCr will platue once injury is established > if oliguria, consider need for RRT, if polyuria (that occurs at pletau phase) this usually heralds renal recovery
- of note, polyuria occurs BEFORE improvement in SCr
What is a complication of ATN that can make a patient dialysis dependent?
cortical necrosis
What are the risk factors associated with contrast-associated AKI?
- CKD
- established CKD with proteinuria
- Age
- diabetes
List 2 ways a contrast-associated AKI can be prevented
- WH nephrotoxics
> ACE/ARB
> Frusemide
> metformin - Slow IVT prior to imaging
*no benefit in NAC or sodium bicarb