Informed consent should be acquired before undertaking any interventional procedures, with the patient advised of all relevant risks. The risk of bleeding from the procedure should be assessed—patients with low platelet counts or who have a coagulopathy are at higher risk of bleeding. However, a precise 'safe' level for any given procedure is difficult to define and the risks will need to be balanced against the urgency of the case and the exact nature of the procedure. It is important to bear in mind that a 'normal' coagulation screen does not exclude a clotting disorder, e.g. von Willebrand disease, and simply asking the patient if they have had any bleeding problems after previous minor procedures is invaluable.

The images, ideally contrast-enhanced, should be viewed to establish the safest approach. Deviating from either a horizontal or vertical approach, or crossing axial planes, significantly increases the complexity of a procedure and should be avoided wherever possible. The patient should be placed in a comfortable position suited to the chosen approach, ideally with the arms extended to avoid artefacts. The patient should often be positioned slightly off-centre so that there is adequate space for the needle between the patient and the gantry. The skin entry site should be localised, marked and cleaned; all procedures should be performed under aseptic conditions. Local anaesthetic should be injected as required, but key sites for infiltration are skin, pleura, peritoneum and periosteum. A topical anaesthetic should be applied before the procedure in children.

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