This invention relates to the field of medical fluid collection devices for receiving fluids from patients and particularly to those devices having removable and/or disposable liners (line-in-canister devices). Medical fluid collection devices are used for suctioning wounds or abscesses or during surgery areas filling with blood or other fluids or for the collection of blood from donors.
There are three types of liner-in-canister suction devices. One, devices in which there is no communication between the inside of the liner and the void space between the outside of the liner and the inside of the canister housing. In these devices vacuum drawn on the void space (as by a hospital's vacuum system) causes the liner to expand. The resulting reduced pressure in the liner draws the fluid to be suctioned into the liner. Neither air nor liquid pulled into the liner will enter the void space or the hospital's vacuum system unless the liner fails. See, e.g., U.S. Pat. Nos. 2,597,715, 2,999,500, and 3,032,037.
Two, devices in which there is extensive communication between the liner and the void space so that the pressure is the same in both (excluding hydrostatic pressure of any liquid in the liner). With this type of unit, air is constantly drawn out of the liner when vacuum is applied and unless an internal safety device is provided, liquid can easily overflow the liner into the void space and may be drawn into the hospital's vacuum system. See, e.g., U.S. Pat. No. 3,704,709.
Three, suction devices in which there is limited communication between the void space and the liner. These devices have small openings in the liner and in some cases the openings have flow retarders to make the pressure in the liner higher than that in the void only when vacuum is first applied so that the liner will expand, after which the pressures equalize. See. e.g., U.S. Pat. Nos. 3,556,101, 3,680,560, and 3,848,628.
A problem with the devices of the first type (no communication) is that if air is sucked into the liner (as when used with an open wound), it cannot escape. A problem with the devices of the second and third types (full- and limited-communication, respectively) is that air normally contacts the fluid collected in the liner and, thus, aseptic and/or air-free collection of fluid is impossible.
A further problem with some of the devices of the third type (e.g., U.S. Pat. No. 3,680,560) is that certain operating upsets (for instance, blockage of the patient or vacuum source tube) tend to make the liner collapse. Such collapse makes it difficult to tell how much liquid has been suctioned into the liner because the walls of the liner are not in their normal position adjacent the walls of the canister, which often has volumetric markings.