A cannula adapter for converting a trocar insufflator into a two-phase or two-mode insufflation system. In the needle insufflation mode the insufflation gas flows through a trocar cannula, a cannula adapter and an insufflation needle before entering a body cavity and in the trocar insufflation mode gas flows directly into the body cavity from the trocar cannula. The cannula adapter although sealingly attachable to the trocar cannula during the needle insufflation mode is removable therefrom for a seamless transfer between the needle insufflation mode and the trocar insufflation mode.