Cassette for intravenous delivery system

Claim 1

A cassette for use in an intravenous delivery system of the limited positive displacement type having a reciprocatory pump member, said cassette operating between an upstream portion and a downstream portion of the intravenous delivery system and comprising, a generally elongated cassette body having opposite walls of oval outline having semicircular end configurations, said body defining an elongated main chamber with opposite parallel surfaces of substantially the same outline but of different sizes and with a slanted wall joining said surfaces, said cassette body defining an inlet port to said main chamber proximate one end thereof and passing through said slanted wall, one of said opposite walls defining the larger of said opposite parallel surfaces of said main chamber and having first and second openings therein spaced toward opposite ends thereof, respectively, each of said openings being of substantially smaller area than the area of said larger parallel surface, a membrane spanning said first opening adapted for engaging the reciprocatory pump member for varying the volume of said main chamber in response to movement of said reciprocating pump member, said second opening forming an outlet port arranged proximate the other end of said main chamber from said inlet port, a tongue extending from said elongated wall of said cassette body, said tongue having detent means thereon for coupling said cassette to a pump assembly having a pump element engageable with said membrane, said cassette body having further wall means defining a prechamber arranged above and in communication with said inlet port and extending from said slanted wall, said prechamber having a volume selected to accumulate air from the upstream portion of the intravenous delivery system in an amount sufficient to maintain said main chamber substantially free of air.