Radiology, contrast and media

Question 1

IV CONTRAST MEDIA

i) what chemical structure is classically used? why?
ii) name three procedures contrast may be used in?
iii) which chemical structure reduces the risk of allergic rection?
iv) what molecule is used in MRI? what is a rare reaction?
v) name four side effects of iodinated contrast? do these indicate allergy?

Answer 1

i) use iodinated hydrocarbon ring - increases abs of xrays
ii) used in contrast enhanced plain film (old), CT scanning (mainstay), angiography, IR procedures
iii) benezene dimer decreases risk of allergy
iv) gadolinium - nephrogenic systemic sclerosis is a rare SE

v) SEs - warm/flushing, headache, nausea, itchy, metallic taste
- dont indicate allergy

Question 2

CONTRAST REACTIONS

i) name four symptoms of allergic reaction to contrast
ii) name two patient groups at risk of contrast reaction? which group is not at inc risk
iii) how should patients be managed if they are having a contrast reaction? (4)
iv) name three reccomendations in place in case contrast allergy occurs

Answer 2

i) urticaria, bronchospasm, laryngeal oedema, hypotension, general anaphylaxis

ii) at risk if had previous contrast reaction
- or have atopic (allergic) asthma > 6x inc risk of reaction
- shellfish or topical iodine allergy does not increase risk

iii) manage with oxygen, IV fluid
anti histamine = chlorphenamine IV 10mg
hydrocortisone 200mg IV
adrenaline IM

iv) recommendations - doctor avail wherever IV contrast injected
patient not left alone for first 5 mins post injection
facilities/drugs for treating are readily available

Question 3

NEPHROTOX POST CONTRAST INJECTION

i) what is it defined as?
ii) what is it a leading cause of?
iii) what are the two main ways it causes nephrotox
iv) give three things that put the patient at increased risk of nephrotox?
v) name three situations where caution should be taken

Answer 3

i) defined as 25% increase in serum creatnine 48-72hrs post injection
ii) leading cause of hospital acquired AKI with increased 1hr mortality

iii) direct cytotox effect on prox renal tubules > exacerbates renal vcontric which causes reduced cr clearance > reduced medullary perfus> reduced GFR and medullary ischaemia
- increased viscosity which reduces tubular flow > reduces GFR

iv) at risk if renal impair, diabetes (more likely to already be in CKD), metformin therapy (met clearance can be reduced therefore nephtox) > stop metformin before injection
v) caution if dehydrated, high dose of contrast or CCF

Question 4

PREVENTING CONTRAST INDUCED AKI

i) what drug should be stopped?
ii) why is pre and post hydration important
iii) give three instances where an eGFR is mandated before contrast is given

Answer 4

i) metformin (until 48hrs post injection)
ii) hydration is important as intravascular volume expansion maintains renal perfusion

iii) need to do eGFR of history of renal disease or DM
- larger dose of contrast than normal
- if given intra arterial > kidneys are directly exposed to a higher conc dose

Question 5

IMAGING IN AKI

i) what needs to be excluded? (3)
ii) what is the mainstay investigation?
iii) what is a nephrostomy used to manage?

Answer 5

i) exclude hydronephrosis (is an obstruction the cause of the AKI),
- stones
- tumour

ii) mainstay investigation is renal US
iii) manage hydronephrosis > decompresses then the cause can be managed

Question 6

RENAL SEPSIS

i) what can be the cause?
ii) what is usually seen on US and CT?
iii) what may be seen on CT?
iv) what may it lead to?

Answer 6

i) pyelonephritis
ii) US and CT can be normal
iii) may see oedema, debris, gas, peinpehric stranding on CT
iv) may get perinephric abscess