A self-slitting open lumen cannula (226) may be used with catheter adapters (210) to reduce manufacturing complexity and costs, as well as improve the safety of the catheter adapters against fluid leakage. The open lumen cannula may also include one or more notches to facilitate flashback visualization. The catheter adapters may further include a catheter adapter body (211) formed of a compliant material that houses one or more compression resistant septa (250) with at least one lumen (254) formed by the proximal end of the needle during a self-slitting process as the catheter adapter is assembled. The compression resistant septum may also be coupled to a compression cap (213) that imparts a radial compression force on the one or more compression resistant septa such that the at least one lumen narrows and seals when the cannula is removed.
