Abstract: A trocar device, comprising a trocar cutting element, a surrounding insulating sheath, and a cannula surrounding the sheath, also includes an arrangement providing a substantially smooth transition between the sheath and cannula at the distal end of the cannula during the insertion of the trocar device into a patient so as to reduce drag on the device at the transition. In one embodiment, the sheath includes a shaped portion of enlarged diameter, and the cannula includes, at the distal end thereof, inwardly directed slits forming corresponding resilient leaf members which engage the shaped portion to provide the smooth transition. The shaped portion includes oppositely tapered surfaces meeting at a common apex. In another embodiment, an expandable section, when expanded, provides the smooth transition.

Abstract: A trocar assembly includes an elongate trocar device and a surrounding cannula. The trocar device incorporates an electrosurgical cutting element which is used to make a guide hole for the cannula and thus enables the remainder of the trocar assembly to enlarge the puncture. The cutting element comprises a bi-polar electrode assembly. An electronic control circuit senses the current flow to the cutting element and, when the trocar device breaks through the wall of the body cavity being cut into, this circuit cuts off the connection to the associated electrosurgical generator. Further control circuitry prevents a surgeon from resuming electrosurgery until a predetermined time period has elapsed. Multiple trocars of different diameters are provided for the same assembly.