FRCA Notes

Anaesthesia in the Radiology Department

Resources

  • Patients may require anaesthesia in order to undergo diagnostic and/or interventional procedures in the radiology department
  • There is a growing number of medical procedures utilising radiation
  • As such, there is an obligation on the part of those involved to understand the risks to staff and patients, and minimise harm

Procedures requiring ionising radiation

  • Nuclear medicine: administration of unsealed radioactive pharmaceuticals for diagnosis or treatment
  • Radiotherapy: using either external or internal radioactive sources, typically in the treatment of cancer
  • Radiology: using simple XR, CT or fluoroscopically-guided procedures in either a diagnostic or interventional fashion

Levels of exposure

  • Safe radiation exposure limits are specified by the International Committee on Radiological Protection (ICRP)
  • They specify exposure in terms of:
    • Equivalent doses, for individual organs or tissues
    • Effective doses, for whole body exposure
  • NB both X-ray and gamma rays have similar carcinogenic potential
Category Dose (mSv/yr)
Average background radiation 6
Effective dose 20 (averaged over 5yrs)
50 (in any single year)
Lens (equivalent dose) 150
Skin 500
Hands & feet 500

Occupational exposure

  • The degree of exposure ranges from almost negligible (simple CXR) to significant (complex interventional procedure)
  • The two sources of occupational exposure are:
  1. From the X-ray beam itself; either the primary beam or 'leakage' X-rays from other areas

  2. From scattered radiation
    • The X-ray beam interacts with the patient's body surface to produce scattered radiation
    • This emanates from the patient in all directions
    • The degree of scatter is related to the dose the patient receives

    • Scattered radiation is the main determinant of occupational exposure
      • The degree of exposure is related to the proximity to the patient
      • Radiation intensity falls off rapidly with distance, according to the inverse-square law

Stochastic vs. deterministic effects

  • Stochastic effects refer to the development of cancer occurring due to DNA damage
    • They are cumulative and have a long latency period
    • There is no 'safe' dose below which induced-neoplasia does not occur
    • There is a linear relationship between radiation dose and excess cancer risk

  • Deterministic effects
    • These produce cellular death at tissue level following high-dose absorption
    • Typically manifests as skin erythema, but may induce more severe effects

Ocular effects

  • The eye may be the most sensitive organ to radiation damage, particularly to scatter radiation
  • The radiation dose to anaesthetists' eyes can be up to 3x greater than interventional radiologists
  • In practice, eye damage may be more important than other effects of radiation exposure
  • Radiation-induced posterior lens opacification occurs, which may be either a deterministic or stochastic effect
  • Protective eyewear reduces lens exposure to scatter by ≥90%

Teratogenicity

  • The recommended lower limit for foetal occupational radiation exposure is 1 - 5mSv
    • Standard protection measures result in negligible foetal risk
  • The effects of higher doses are deterministic
  • The effect of ionising radiation exposure in utero at any dose is associated with increased risk of childhood malignancy
  • At doses >0.5Gy, excess risk of leukaemia is 6%

  • Education and training of staff involved with ionising radiation

  • Monitoring of radiation doses
    • Fluoroscopy devices record both peak skin dose and total screening time
    • Personal dosimeters should be worn by personnel regularly exposed to radiation

  • Structural barriers e.g. shielding within the wall and window of a control room
  • Protective clothing e.g. aprons, thyroid shields, spectacles
  • Protective screens

  • Reduce exposure time where possible
  • Maintain physical distance from patient and/or radiation source

  • IR procedures are becoming more common, both electively and in the emergency setting
  • Examples include:
    • Interventional neuroradiology e.g. for coiling of aneurysm, stroke thrombectomy
    • Management of AAA i.e. EVAR
    • Management of emergency bleeding e.g. upper GI bleeding, MOH