There are 3 main risks associated with using contrast:
1) Allergic reactions
- Reactions occur in 0.15% of cases. These are classified as 'severe' in just 0.04% of cases.
- Allergic reactions are 6 to 10 times more common in asthmatics; non ionic low or iso-osmolar agents should be used for these patients.
2) Contrast nephropathy
- This is defined as an impairment in renal function (an increase in serum creatinine by more than 25% or 44micromol/l) within 3 days of administration of IV contrast in the absence of an alternative aetiology
- Risk of contrast nephropathy is increased in patients with:
- eGFR <60
- dehydration
- CCF
- gout
- age >70
- concurrent use of nephrotoxic drugs, eg NSAIDs or gentamycin
- The risk of contrast nephropathy can be reduced by:
- using the smallest possible dose of contrast
- ensuring the patient is well hydrated before and after the procedure either orally or, if the contrast is to be given arterially or at high dose, by IV fluids
- there is currently insufficient evidence to support the use of n-acetyl cysteine in prevention of contrast-induced nephropathy
- There is no need for metformin to be stopped routinely for contrast investigations as long as the eGFR is >60. If it is below this level, stopping for 48 hrs before and after the investigation should be considered.
3) Extravasation
- Conservative management is sufficient in most cases - elevate limb and apply ice packs.
- Plastic surgeon input may occassionally be required.
Other points:
- Contrast can be used in breastfeeding mums with no special precautions.
- Contrast cannot be used in patients who are hyperthyroid.
- There is a specific risk of a delayed skin rash if contrast is given to patients on interleukin-2 therapy.
