In various embodiments, an improved catheter insertion device is described that provides an improved flashback response and use for deep vein access. In various embodiments, the improved flashback response comprises two separate and distinct flash events, the first indicating insertion of a cannula in a blood vessel, and a second indicating insertion of a catheter in the blood vessel. The two flash responses are made possible by a combination of features provided on the cannula, such as including a view window in the cannula and a flat relief portion on the outer surface of the cannula at the distal opening.
