Fluid management system

There is disclosed an apparatus for supplying liquid to a body cavity (10) during an endoscopic procedure including a feedback loop-controlled liquid supply device inherently capable of supplying liquid at a substantially constant pressure substantially independent of the flow rate of liquid delivered by the liquid supply device within a relatively wide range of flow rate. Also disclosed are a disposable plastic pump cassette having an inflow pump in a housing, and an operative cannula. The surgical procedure is performed with continuous control over the body cavity pressure, regardless of the outflow flow rate.