Access & devices
Sheath and dilator
A short conduit, introduced over a wire after the tract has been dilated, that holds an access site open for repeated instrument exchange.
- Owner
- WIRS education committee
Overview
A vascular or non-vascular sheath is a short tube with a valved hub, introduced over a guidewire once a dilator (or a graduated series of dilators) has gradually enlarged the puncture tract. The valve limits back-bleeding and allows catheters, wires and other devices to be exchanged through the same sheath without a fresh puncture each time, and a side-arm is usually present for flushing or contrast injection. Dilators themselves are solid or tapered devices used only to enlarge the tract; they are withdrawn once the sheath (or, in some techniques, the working catheter) is in place.
Sizing and compatibility
- Sheath size is described on the French (Fr) scale, referring to the outer diameter of the sheath — by convention, 1 Fr is roughly a third of a millimetre.
- A sheath's stated French size describes its outer diameter, but what determines compatibility with the next device is the sheath's inner lumen — the two are related but not identical, which is why compatibility is checked rather than assumed from the outer size alone.