Background: Achieving a reliable venous access in a particular subset of patients and/or in emergency settings can be challenging and time-consuming. Furthermore, many hospitalized patients do not meet the criteria for central venous catheter positioning, unless an upgrade of the treatment is further needed. The mini-midline catheter has already showed to be reliable and safe as a stand-alone device, since it is easily and rapidly inserted and can indwell up to 1 month. Methods: In this further case series, we retrospectively evaluated data from 63 patients where a previously inserted mini-midline catheter was upgraded to a central venous catheter (the devices inserted in the arm replaced by peripherally inserted central catheter and others inserted “off-label” in the internal jugular replaced by single lumen centrally inserted central catheter), being used as introducer for the Seldinger guidewire. Results: The guidewire replacement was been made even early (after 1 day) or late (more than 10 days), usually following a need for an upgrade in treatment. No early or late complications were reported. Conclusion: According to the preliminary data we collected, this converting procedure seems to be feasible and risk-free, since neither infectious nor thrombotic complications were reported.