Anaesthesia For Radiological Procedures

In most hospitals, the anaesthetic department is called upon to anaesthetize patients for diagnostic and therapeutic radiological procedures. These procedures include angiography, computed tomography (CT) scanning and magnetic resonance imaging (MRI). The major requirement of all these imaging techniques is that the patient remains almost motionless. Thus, anaesthesia may be necessary when these investigations are performed in children, the critically ill or the uncooperative patient. The presence of pain or lengthy procedures may also be an indication for anaesthesia.

Radiological studies may require administration of conscious sedation. This is where medication, often given by a non-anaesthetist, is used to alter perceptions of painful and anxiety-provoking stimuli while maintaining protective airway responses and the ability to respond appropriately to verbal command. Medical personnel responsible for the sedation should be familiar with the effects of the medication and skilled in resuscitation. There should be easy access to a resuscitation kit. A single operator for the radiological procedure and the administration of sedation is at risk of distraction and therefore of missing side-effects. Ideally, different individuals should be responsible for each of these tasks. Guidelines for prescribing, evaluating and monitoring sedation should be readily available.

Intravascular contrast agents are used routinely during angiographic and other radiological investigations. The anaesthetist must always be aware of the risk of adverse reaction to contrast dyes. Over recent years, low-osmolarity contrast media have been introduced. These cause less pain and have fewer toxic effects than the older contrast agents, but are more expensive. Factors contributing to the development of adverse reactions include speed of injection and type and dose of contrast used.

Coronary and cerebral angiography are associated with a high risk of reaction. Other major risk factors are patients with allergies, asthma, extremes of age (under 1 and over 60 years), cardiovascular disease and a history of previous contrast medium reaction. Fatal reactions are rare, occurring in about 1 in 100 000 procedures. Nausea and vomiting are common (consider prophylactic antiemetic), which may progress to urticaria, hypotension and bron-chospasm. Adequate hydration is important, as patients undergoing contrast dye procedures usually have an induced osmotic diuresis which can exacerbate pre-existing renal dysfunction. A urinary catheter may be useful for patients undergoing long procedures.

Treatment of allergic reactions depends on the severity of the reaction. This usually consists of general supportive methods such as fluids, oxygen and careful monitoring. Drugs such as epinephrine, atropine, steroids and antihistamines should be readily available.

Healthcare workers are exposed to X-rays in the radiology and imaging suites. The greatest source is usually from fluoroscopy and digital subtraction angiography. Ionizing radiation from a CT scanner is relatively low because the X-rays are highly focused. Radiation intensity and exposure decrease with the square of the distance from the emitting source. The recommended distance is 1-2 m. This precaution, together with lead aprons and thyroid shields, keep exposure to a safe level.

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