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
What are the broad classifications of renal pathologies
- GN
- Acute tubular necrosis (e.g. contrast induced, THINK endotoxin vs. exotoxin)
- Acute intertistial nephritis
How is a diagnosis of ATN made?
- definitive diagnosis requires a biopsy
- diffuse cellular infiltrate on biopsy
List 4 causes of AIN
- Drug related (e.g. beta lactams, PPIs, NSAIDs, immunotherapy)
- Infection
- Immune-mediate (e.g. Sjogrens, Sarcoidosis, IgG4 disease)
- Idiopathic
List 2 types of acute microvascular diseases that affect the kidney
- thrombotic microangioapthy (includes spectrum of HUS-TTP)
- DIC
- catastrophic anti-phospholipid syndrome
- systemic sclerosis
- cholesterol emboli* (consider cardiac surgery, IABP, angiography)
What are the structures post-renal that need to be considered in a post-renal AKI?
- PUJ
- ureter
- bladder
- prostate
- urethra
*Neurological - can be affected in MS, diabetes
When assessing an AKI, what are the 3 key elements in the clinical work up?
- history
- medication review
- volume assessment
What kidney pathology might be suggestive of fragments on a blood film?
- acute microvascular disease (renal cause)
- consider associated presentation of anaemia, thrombocytopenia
List 2 pathologies an eosinophilia may be suggestive of
- AIN
- Eosinophilic granulomatosis with polyangiitis (EGPA)
- cholestrol emboli
If a patient has a raised CK, what pathology does this suggest related to the kidney?
rhabdomyolysis
What does a high urate suggest?
Tumour lysis syndrome
What is the main purpose of a renal tract USS?
rule out obstruction
If a urine dipstick is +ve for protein, what protein is this specifically?
albumin
If a patient had microscopic haematuria on dipsitck, what might you be concerned about?
- this is suggestive of myoglobin
- need to consider rhabdomyolysis as a possible differential/issue in the presentation
List two types of renal casts
- hyaline casts
- renal tubular epithelial casts // granular casts
If you see hyaline casts of urine microscopy, what might this suggest?
- reduced renal perfusion leading to sluggish flow
- composed of uromodulin, formed in the loop of henle
- NOT associated with tubular injury
- may see this in exercise, dehydration
If you see renal tubular eptihelial cells or casts what might this suggest
- ischaemic injury > suggestive of ATN (but consider other cells present)
What are granular casts and what might this be suggestive of?
Note granular casts = degraded lysosomes within RTECS, muddy brown appearance. THIS is suggestive of ATN
What might White cell casts suggest of?
- note rarely seen in isolation - often hard to distinguish from RTECs
- could be AIN in the appropriate clinical context
What finding in the urine is concerning for glomerular haemorrhage?
- dysmorphic red cells
- RBC casts
> suggest proliferative glomerular lesion
What are the uses of kidney USS?
- obstruction (check for hydronephrosis)
- reduced size, reduced cortical thickness, reduced echoginecity - could point to a chronic cause
- doppler - consider vein thrombosis, stenosis, perfusion
List 3 indications for a kidney biopsy
- active urinary sediment
- heavy proteinuria
- aetiology unclear
- confirm Dx - prognosis, response to treatment
- exclude dual pathologies
List 2 contraindications for a kidney biopsy
- kidney failure
- coagulopathy
- bilateral cysts
- uncontrolled HTN
- hydronephrosis
- UTI
List the five indications for KRT
- Acidaemia
- Electrolyte disturbance
- Intoxicans (toxins)
- Fluid overload - refractory to treatment
- Uraemia - pericarditis, encephalopathy
