Volumetric metering unit for intravenous fluid addition

Abstract

Three embodiments of a metering unit (10, 140, 200) are provided for metering fluid from a container (14) for infusion into a patient. The first embodiment of the metering unit (10) includes a cassette (26) formed of halves (28, 30). The halves (28, 30) each have a concave reservoir portion (36) formed on the inner face (32) thereon. Entry and exit channels (38, 42) extend from the reservoir portions adjacent entry and exit orifices (40, 44). Entry and exit port portions (46, 50) are formed in each half (28, 30). Flexible entry and exit valves (58, 64, 86 and 88) are movable between an open position, permitting fluid to flow through the orifices, to a closed position, preventing fluid from flowing through the orifices. The halves are separated by a flexible diaphragm (70) which divides a reservoir (76) into first and second compartments (78, 80). One entry valve is opened to permit fluid from the entry port (82) to flow into one compartment, the fluid flowing into the compartment moving the flexible diaphragm to force the fluid in the other compartment out to the exit port (84). The position of the valves is then interchanged, permitting fluid to flow into the other compartment and forcing the fluid in the first compartment into the exit port. A cassette (206) in the third embodiment of the unit (200) includes identical halves (208, 210) sonically bonded together. A diaphragm (296) separates parallel channels (218, 222) to reduce head pressure channel volume variations. Grooves (228, 230) are provided in the reservoir portions (216) to prevent fluid trappage between the diaphragm and portion wall. In all cassette embodiments, an activating frame operating the cassette prevents the positioning of all valves in the open position simultaneously.