Which guideline regarding the use of a coil as an embolic agent is least appropriate?

The guideline that is least appropriate involves the final diameter of the coil matching the target vessel. When it comes to embolization techniques, the choice of coil depends on several factors, including the size of the vessel and the specific clinical scenario. While it is important that the coil fits well within the vessel, stating that the final diameter of the coil should exactly match the target vessel is not accurate. Coils are usually chosen based on their ability to create an effective occlusion and may be intentionally oversized to ensure they adequately fill and occlude the vessel, providing controlled delivery and packing.

In contrast, the other guidelines are well-grounded in practice. For example, matching the diameter of the coil wire to the catheter lumen ensures that the coil can be delivered without difficulty. Applying gentle forward pressure on the catheter can indeed assist in 'packing' the coil properly, which is critical for effective embolization. Additionally, the statement about platinum coils being softer and easier to visualize compared to steel coils is accurate, as platinum is commonly used in coils for its radiopacity and ability to conform better to the vessel shape, thus enhancing visibility during procedures.