Allergic-like or anaphylactoid reactions (not truly IgE mediated) – 1 %
- Including urticaria, pruritus, oedema, throat irritation, nasal congestion
- May be severe – facial oedema, throat swelling, laryngeal oedema, bronchospasm and hypotension
Physiological reactions
- Nausea, headache, altered taste, vomiting, vasovagal episodes
- Very rarely – severe hypertension, arrhythmias
Very rare to have severe reactions with newer low osmolar contrast
Management of reactions – anti-histamines, observe for progression, oxygen and bronchodilators, hydrocortisone and adrenaline as needed.
3 – 5 x increased risk of allergic like reactions in people with multiple allergies (shellfish or betadine allergy is lumped in this – no increased risk cf. other allergies)
Pre-medication:
- Steroids may reduce risk of allergic like reactions in those at risk – 50 mg prednisone 13 hours and 1 hour prior to scan +/- anti-histamines
Hyperthyroidism
- Untreated hyperthyroidism or hyperfunctioning nodule/goitre at risk
Myasthenia gravis
- Worsening of respiratory symptoms reported
Contrast nephropathy / post contrast AKI
- Increase in serum creatinine or drop in urine output after contrast administration
- Large meta-analyses show contrast is not associated with drop in eGFR if > 45, and very rarely associated if eGFR > 30
- IV contrast may be associated with an increase in creatinine if baseline eGFR < 30
- Typically impairs renal function for 3 – 5 days and returns to baseline at 10 – 14 days
RANZCR guideline:
- Give IV contrast if the perceived benefit justifies it in opinion of referrer and radiologist
- Emergency imaging should not be delayed for renal function results
- Risk of contrast related AKI is likely not existent for eGFR > 45
- Risk is very likely to be low or not existent for eGFR 30 – 45 – hydration cannot be recommended unless renal function is actively deteriorating
- In eGFR < 30 or active AKI – risk vs benefit – consider hydration
- Obtain eGFR in patients with known kidney disease, diabetes and taking metformin
- No clear evidence of benefit for N-acetylcysteine or sodium bicarbonate in those at risk of contrast AKI
- The theoretical risk of lactic acidosis being precipitated by iodinated contrast is the same as the theoretical risk of AKI – therefore those with eGFR > 30 are at low to no risk
- Metformin should be stopped 48 hours prior only if eGFR < 30 or deteriorating renal function
Types of contrast
Ionic contrast
- Urografin, gastrografin – there are hyperosmolar
Non-ionic agents
- Iohexol (omnipaque)
Can also be characterised as hyperosmolar or iso-osmolar, or iodinated and non iodinated.
Gadolinium
Gadolinium contains paramagnetic metal ions – these reduce the T1 and T2 relaxation times, increasing intensity in mainly T1 images
May cause pseudohypocalcaemia on bloods for 24 hours
Nephrogenic systemic fibrosis
- Fibrosing disease of the skin, subcutaneous tissues, lungs, oesophagus, heart and skeletal muscle
- Initial symptoms skin thickening and pruritus, progressing to contractures and joint immobility
- Onset between 2 days and 3 months post gadolinium
- 1 – 7 % chance of NSF in CKD with eGFR < 30