Intravenous Contrast

Intravenous contrast may be divided into:

  • X-ray Contrast
    These agents are all based on a tri-iodinated benzene ring, which absorbs x-ray radiation. Alterations to this ring alter toxicity, lipophilicity, and elimination.
    • Agents are classified by these structural differences into:
      • Ionic
        Ionic substances are strong acids and are water soluble due to ionisation. They are further divided into:
        • Monomers
          Typically high molecular weight.
        • Dimers
      • Non-Ionic
        Water soluble due to hydrophilic side chains. Lower molecular weight than ionic contrast agents.
        • Monomer
          Agent of choice for angiography.
          • Easy to inject
          • Water soluble at physiologic pH
        • Dimer
          Harder to inject than monomers due to higher viscosity. Typically used for urography.
    • All are renally eliminated, and may be retained in renal dysfunction
  • Gadolinium Contrast
    Gd3+, due to its seven unpaired electrons, is paramagetic and will alters the magnetic field of an MRI machine.
    • Free gadolinium is nephrotoxic and must be chelated
    • This increases its solubility and allows it to be renally eliminated
    • Gadolinuim also attenuates x-rays, but is not used as x-ray contrast as doses required would be toxic

Adverse Reactions

Adverse reactions to low-osmolarity agents are uncommon (3%), with severe reactions being very rare (0.04%) and fatal reactions being extremely rare (1:170,000).

General Adverse Reactions

Adverse ractions include:

  • Chemotoxicity
    • Platelet inhibition
    • Increased vagal tone
      • Negative inotropy
      • Negative chromotropy
  • Ionic toxicity
    • Cellular membrane dysfunction
      May worsen myasthenia gravis.
  • Osmotoxicity
    • Pain
    • Emesis
    • Increased PAP
    • Decreased PVR
  • Hypersensitivity reaction
    Typically occur within 20 minutes of injection.

Risk factors include:

  • Asthma or atopy
  • Critically ill
  • Cardiac disease
  • Renal disease

Contrast Nephropathy

Defined as an increase in creatinine by 25% above baseline within three days of IV contrast administration.

  • It is theorised that osmotic stress and direct tubular toxic effects lead to renal tubular injury, and may cause acute tubular necrosis
  • Typically is benign, with creatinine returning to baseline within 10-14 days
  • Significant uncertainty as to whether contrast media do cause acute kidney injury
    IF this risk is present, it is probably only relevant in patients who have:
    • Impaired renal function
    • Arterial contrast
  • Rehydration and volume correction are effective in preventing a rise in creatinine

References

  1. Dickinson MC, Kam PC. Intravascular iodinated contrast media and the anaesthetist. Anaesthesia. 2008 Jun;63(6):626-34.
  2. The Royal Australian and New Zealand College of Radiologists. Iodinated Contrast Media Guideline. Sydney: RANZCR; 2016.
Last updated 2017-10-04

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