Io lo renderei così. "guaina a permanenza" non mi convince.

Vedi ad esempio:
In the present state of the art, concealed hemorrhaging becomes a difficult diagnosis due to the loose areolar tissue in the groin, which can accept significant blood before serious signs become apparent. The hematoma drain according to the invention can be placed in the groin at the end of the procedure and before the sheath is removed by pressing the drain through an area of the skin that has received local anesthesia. The blunt needle can be felt touching the still indwelling sheath and be positioned to one side or immediately below and near by the sheath. The needle component of the drain is then removed and the plastic drain is then connected to a short tubing segment. The tubing is then connected to a collapsible ellipsoid portable vacuum reservoir.