The invention relates generally to pump mechanisms, and more particularly, to a method an apparatus for protecting a pump mechanism used in an infusion pump from possible adverse effects caused by the entrance of extraneous fluid into the pump mechanism, such as adhesion of mechanism parts.
An infusion system typically includes a reservoir, such as a bottle or bag, for holding infusion fluid, a drip chamber for monitoring the flow of fluid from the reservoir, infusion tubing for carrying the fluid to an injection needle, and an infusion pump for precisely controlling the flow rate of fluid through the infusion tubing. One conventional infusion pump, known as a linear peristaltic pump, comprises finger members that move into and out of contact with the tubing in a peristaltic manner so that they compress the infusion tube in a wavelike motion, squeezing the fluid as the wave progresses and thereby carry out the infusion. The finger members and the drive mechanism controlling the movement of the finger members are collectively referred to as a pump mechanism. The pump mechanism and a control processor with ancillary power and display systems comprises an infusion pump. A typical infusion pump as such is described in Japanese patent publication No. Sho-62-8763.
In some cases during operation, infusion fluid, such as a liquid containing a sugar, leaks out of the bottle or bag and travels down the outer surface of the infusion tube and may enter the pump mechanism area. If the pump is constructed so that leaking infusion fluid is not diverted out of the pump, the leaking infusion fluid may accumulate in the pump mechanism, dry, and adhere to the pump mechanism and cause the finger members to stick to the driving mechanism and to each other. This sticking can cause the pump mechanism to malfunction and not be available when needed.
In a typical infusion pump, adjacent finger members contact each other in a face-to-face manner, i. e., the upper and lower surfaces of the finger members rub against each other as the finger members move. As infusion fluid accumulates on the face-to-face surfaces of the finger members and begins to dry, the finger members may stick to each other and a malfunction of the pump mechanism may occur if the driving mechanism does not have sufficient power to overcome the adhesion of the fingers to one another. A remarkably large force may be required, depending on the nature of the leaking fluid, to break the face-to-face adhesive bond. This is especially so when an attempt is made to break the bond by moving the finger members in the direction parallel to the face, which is the direction of movement during pump operation.
One method to eliminate this adhesive problem involves covering, with a rubber sheet, the portion of the finger members which compresses the infusion tube. Essentially the rubber sheet blocks infusion fluid from entering the pump mechanism. However, as the rubber sheet is continuously pressed against the infusion tube by the finger members, the rubber sheet may become swelled by the plasticizer from the infusion tube and may become soft and eventually break. Accordingly, the rubber sheet must be periodically replaced.
A second method involves making the clearances between the finger members as narrow as possible so that infusion fluid is unlikely to enter the pump mechanism. To further ensure that fluid does not enter, a grease like repellent filler such as silicon may be placed in the clearances. There is, however, a limitation in the mechanical accuracy, and it is very difficult to completely block the entrance of infusion fluids. In addition, an upgrading of the mechanical accuracy results in higher production costs. Furthermore, when a repellent filler is used, there is a possibility that the filler may leak into other regions of the pump mechanism and a pump mechanism malfunction may result.
A third method involves unitizing a cleanable and removable pump mechanism. When infusion fluid adheres to the inside of the pump mechanism, the unitary pump mechanism may be removed, cleaned and reinstalled. In unitary pump mechanisms, however, the mechanical connection is often times loose and produces high noise levels during operation. Furthermore, it is inconvenient for a nurse, who is very busy with daily business, to remove and wash the pump mechanism.
Hence, those skilled in the art have recognized a need for a pump mechanism that conveniently and effectively reduces or eliminates the entrance of infusion fluid into the pump mechanism and reduces the detrimental effects of any fluid which does enter the pump mechanism. The invention fulfills these needs and others.