contrast_reactions

radiologic contrast media precautions and adverse reactions

see also:

Check hydration, renal function, metformin, allergies, and if the patient is pregnant!

introduction

  • iodinated radiocontrast materials are tri-iodinated benzoic acid derivatives that in solution contain a small amount of free iodide and are classified into:
    • ionic agents
      • C/I for intrathecal use
      • iotroxate - binds reversibly to plasma protein promoting biliary excretion and thus approved for iv cholangiography
    • non-ionic agents
      • iopamidol - osmolality twice that of plasma and iodine at 300mg/ml
      • iodixanol - lower osmolality (290mOsm/kg) but due to higher cost, tend to be used when osmolality is important eg. CT coronary angiography and lower limb angiography for severe ischaemia
  • the most important adverse effects include:
    • hypersensitivity reactions
    • contrast-induced nephropathy particularly if impaired renal function and dehydration, or drugs that reduce renal blood flow (eg. non-steroidal anti-inflammatory drugs (NSAIDs))
    • lactic acidosis if on metformin within prior 48hrs
    • contrast media extravasation - risk of skin necrosis, thus early ice for 20min to reduce skin metabolic needs, elevation and crepe.
      • rare, and mainly in those with Grave's disease or multinodular goitre, or with thyrotoxicosis already
      • if subclinical hyperthyroidism, contrast is probably safe but patient should have repeat TFTs 4 weeks post contrast
      • if uncontrolled hyperthyroidism, contrast probably should be avoided as risk of thyroid storm
  • non-iodinated contrast media
    • mainly used in ultrasound (microbubble preparations) and in MRI (eg. gadolinium is paramagnetic and shortens the T1 relaxation time)
      • gadolinium MRI agents have been associated with nephrogenic fibrosing sclerosis in patients with renal dysfunction hence C/I if GFR < 30ml/min
    • carbon dioxide may be used for DSA below the diaphragm in patients with C/I to iodinated contrast media

Mx of patients requiring contrast media

prevention of possible allergic reactions

  • the following is mainly derived from Aust Prescriber Oct 2009 article
  • if PH severe non-immediate cutaneous reaction to contrast media (eg. vasculitis, Stevens-Johnson syndrome, or toxic epidermal necrolysis) then contrast media is contra-indicated.
  • if PH anaphylaxis to contrast media then contrast media is probably contra-indicated.
  • if PH mild-moderate immediate cutaneous reaction to contrast media then use non-ionic low-osmolarity contrast media and give hypersensitivity premedication (see below), closely observe the patient and have a high level of readiness to manage Anaphylaxis.
  • if PH mild-moderate non-immediate cutaneous reaction to contrast media (risk of anaphylaxis is probably NOT increased) then use non-ionic low-osmolarity contrast media and give hypersensitivity premedication (see below).
  • if PH severe food allergy, mod-severe asthma, significant cardiovascular disease or beta adrenergic blockers use, then use non-ionic low-osmolarity contrast media, closely observe the patient and have a high level of readiness to manage Anaphylaxis but pre-medication not needed.

hypersensitivity pre-medications

  • cetirizine 10mg + prednisolone 25mg + ranitidine 150mg
  • give 12 hourly starting the day prior to contrast and including the day of contrast, and if PH delayed reaction, for the day after the contrast.

reducing risk of nephrotoxicity or lactic acidosis

  • avoid in those aged > 70 years
  • reduce dose of, or cease diuretics for 24hours
  • with-hold ACE inhibitors for 24 hours
  • use low osmolal or iso-osmolal agents where possible
  • ensure patient is well hydrated, give adequate hydration prior to contrast:
    • encourage oral intake of 2.5-3.0 litres in the 24 hours prior, or give 1-1.5ml/kg/hr normal saline iv for 12 hours before and 12 hours after contrast if no contra-indication to fluid loading such as cardiac failure.
  • check renal function:
    • contrast is contra-indicated if creatinine > 0.132mmol/L or GFR < 60ml/min per 1.73sq.m
  • for high risk patients who need the examination1):
    • premedication with N-acetylcysteine
      • 4 oral doses (each in 50-100ml diet coke) of 600mg bd NAC starting the night before and ceasing the morning after
    • plus, premedication with bicarbonate:
      • 150ml (150mmol/L) sodium bicarbonate mixed with 850ml 5% dextrose, infuse iv at 3ml/kg/hr for 1 hour prior, and then at 1ml/kg/hr for 6 hours after contrast.
  • if on metformin then:2)
    • check renal function:
      • contrast is contra-indicated if urea > 6.7mmol/L or creatinine > 0.10mmol/L
    • with-hold metformin on day of contrast administration and for a further 48 hours
    • use another hypoglycaemic agent during this period - either insulin or oral hypoglycaemic.
  • check venous access is secured and working well and there is no evidence of extravasation after iv normal saline flush prior to administering contrast - certain contrast procedures require rapid administration mandating a large vein such as a cubital fossa vein.

ensure adequate venous access for the proposed study

always check the patency of the cannula prior to giving contrast, and check that the required infusion rate is deliverable
rapid infusion studies
  • CT scans such as coronary vessel CT angiogram require 5-6ml/sec infusion
  • these patients should have a 16-18G cannula in a cubita fossa
moderately rapid infusion studies
  • CTPA, CT angiograms, CT venograms, CT liver/pancreas require infusion rates of 4-5ml/sec
  • these patients should have a 18-20G cannula in a cubita fossa
slower infusion studies
  • contrast CT brain (not angiographic) or CT abdo/pelvis can be given with infusions 2.5-3.5ml/sec
  • these patients should have a 20-22G cannula in a cubita fossa (if CT abdo/pelvis) but can be on dorsum hand for CT brain.

contrast media reactions

direct toxic or osmolar effects

contrast-induced nephrotoxicity causing acute renal failure

  • defined as an increase in serum creatinine of > 25% within 48 hours of contrast administration
  • usually resolves at least partially within 5 days
    • DDx cholesterol embolisation from intra-arterial catherisation which causes progressive renal failure
  • may be permanent and fatal
  • risk factors include:
    • impaired renal function, especially:
    • total dose of contrast media
    • multiple myeloma
    • age > 70yrs even with normal creatinine

lactic acidosis if on metformin

  • imperative to cease metformin (see above) and ensure adequate renal function prior to and after contrast administration

local tissue necrosis due to extravasation

iodide adverse reactions

  • the only adverse effect of contrast media that can be convincingly ascribed to free iodide is iodide mumps and other manifestations of iodism such as iododerma (acneiform or ulcerative eruption related to iodide ingestion).
  • there is little or no evidence that iodine is a cause of allergic reactions3), and is not responsible for seafood allergy nor contrast allergy nor allergy to iodinated medications or antiseptics such as amiodarone or povidone-iodine (Betadine).

contrast medium idiosyncratic (including allergic) reactions

  • immediate and non-immediate reactions (>1hr post-contrast) to contrast media are common
  • Anaphylaxis has been estimated to occur in 0.1-0.4% with ionic contrast media and in 0.02-0.04% with non-ionic contrast media
    • in the case of hyperosmolar and ionic media, the reaction is thought to be a direct non-immunological effect on mast cells and basophils, or activation of the complement system, hence the preferred term “non-allergic anaphylaxis” (formerly called “anaphylactoid”).
    • a proportion of the rare immediate reactions to non-ionic media is thought to be IgE and intradermal testing or in vitro IgE detection may have a role in detecting patients at risk.

risk factors for hypersensitivity

  • patients with food allergy (not necessarily seafood), or hay fever or asthma have a higher risk
  • presence of cardiovascular disease
  • use of beta adrenergic blockers - odds ratio 7-20 but overall risk is still very low
  • systemic mastocytosis is theoretically a risk factor

Mx of suspected moderate or severe anaphylaxis

  • see also Anaphylaxis
  • cease contrast injection
  • lie flat
  • oxygen 6L/min
  • call a code Blue if patient is not already in a resuscitation area such as ED
  • im 1:1000 adrenaline injection to lateral aspect of thigh as soon as possible:
    • adults and children > 50kg: give 0.5ml
    • adults and children 25-50kg: give 0.25-0.5ml
    • child 25kg (8yrs old): give 0.25ml
    • child 20kg (5yrs old): give 0.2ml
    • child 15kg (3yrs old): give 0.15ml
    • child 10kg (1yr old): give 0.1ml
  • give iv normal saline or Hartmann's at 20ml/kg stat
  • repeat adrenaline dose if needed every 5 minutes if hypotense, cynanosed or severe stridor
  • consider adrenaline infusion if still hypotense despite 2 x adrenaline doses
    • refractory patients on beta blockers may be considered for Rx with glucagon
  • if coma, or respiratory failure, then have an airways expert consider intubation and ventilation
  • adjunctive measures:
    • bronchodilators if wheezing or SOB: eg. salbutamol nebulisers
    • iv corticosteroids eg. hydrocortisone 2-6mg/kg (up to 250mg) or dexamethasone 0.1-0.4mg/kg
    • nebulised adrenaline if stridor eg. 5ml of 1:1000 but do not delay intubation if progressive upper airway obstruction
    • cardiac monitor
    • pulse oximetry
    • transfer to a resuscitation area and observe for at least 4-6 hours (longer if PH asthma or multiple doses of adrenaline needed) after complete resolution as a relapse may occur

Mx of mild reactions

  • if only rash and itch:
  • if severe rash and/or mild SOB/anxiety but still no mod-severe reaction:
contrast_reactions.txt · Last modified: 2020/04/18 14:05 by gary1