A system for delivering gas during a surgical procedure performed within a patient's body cavity or through a patient's body lumen, comprising: a) a gas delivery device having a main housing including a port for receiving insufflation gas from a gas source and enclosing a pump assembly for circulating gas throughout the system; and b) a gas conditioning unit configured for operative association with the gas delivery device and defining: i) an insufflation gas flow path for delivering insufflation gas to the body cavity or lumen and for facilitating periodic static pressure measurements from the body cavity or lumen; ii) a pressurized gas flow path for delivering pressurized gas from the pump to an internal nozzle assembly configured to accelerate the pressurized gas and thereby generate a continuous pressure barrier contained within the gas conditioning unit that inhibits egress of insufflation gas from the body cavity or lumen; iii) a vacuum return flow path for returning depressurized gas spent by the internal nozzle assembly back to the pump under vacuum; iv) an air entrainment flow path for drawing air into the body cavity or lumen to maintain a given pressure therein under certain abnormal operating conditions; and v) a smoke evacuation flow path for conveying smoke and debris from the body cavity or lumen, wherein the air entrainment flow path and the smoke evacuation flow path comprise a common bi-directional flow path that is open to the atmosphere when the gas conditioning unit is installed in the gas delivery device and the insufflation gas flow path, the pressurized gas flow path and the vacuum return flow path are in fluid communication with the patient's body cavity. a) a gas delivery device having a main housing including a port for receiving insufflation gas from a gas source and enclosing a pump assembly for circulating gas throughout the system; and b) a gas conditioning unit configured for operative association with the gas delivery device and defining: i) an insufflation gas flow path for delivering insufflation gas to the body cavity or lumen and for facilitating periodic static pressure measurements from the body cavity or lumen; ii) a pressurized gas flow path for delivering pressurized gas from the pump to an internal nozzle assembly configured to accelerate the pressurized gas and thereby generate a continuous pressure barrier contained within the gas conditioning unit that inhibits egress of insufflation gas from the body cavity or lumen; iii) a vacuum return flow path for returning depressurized gas spent by the internal nozzle assembly back to the pump under vacuum; iv) an air entrainment flow path for drawing air into the body cavity or lumen to maintain a given pressure therein under certain abnormal operating conditions; and v) a smoke evacuation flow path for conveying smoke and debris from the body cavity or lumen, wherein the air entrainment flow path and the smoke evacuation flow path comprise a common bi-directional flow path that is open to the atmosphere when the gas conditioning unit is installed in the gas delivery device and the insufflation gas flow path, the pressurized gas flow path and the vacuum return flow path are in fluid communication with the patient's body cavity. i) an insufflation gas flow path for delivering insufflation gas to the body cavity or lumen and for facilitating periodic static pressure measurements from the body cavity or lumen; ii) a pressurized gas flow path for delivering pressurized gas from the pump to an internal nozzle assembly configured to accelerate the pressurized gas and thereby generate a continuous pressure barrier contained within the gas conditioning unit that inhibits egress of insufflation gas from the body cavity or lumen; iii) a vacuum return flow path for returning depressurized gas spent by the internal nozzle assembly back to the pump under vacuum; iv) an air entrainment flow path for drawing air into the body cavity or lumen to maintain a given pressure therein under certain abnormal operating conditions; and v) a smoke evacuation flow path for conveying smoke and debris from the body cavity or lumen, wherein the air entrainment flow path and the smoke evacuation flow path comprise a common bi-directional flow path that is open to the atmosphere when the gas conditioning unit is installed in the gas delivery device and the insufflation gas flow path, the pressurized gas flow path and the vacuum return flow path are in fluid communication with the patient's body cavity.