A system for intraosseous access can include an elongated instrument that is positioned within a cannula portion of a cannula assembly. The system can include a shield that is coupled with both the elongated instrument and the cannula assembly when in an unlocked state. The shield can permit proximal movement of the elongated instrument relative thereto when in the unlocked state. The shield can automatically transition to a locked state to attach to a distal end of the elongated instrument to restrict access to a distal tip of the elongated instrument.
