This invention pertains to blood filters. It relates particularly to continuous high volume blood filtering devices of the class employed principally in making blood transfusions.
It presently is routine medical practice when making blood transfusions to employ blood bank blood. As is well known, this is prepared by withdrawing blood from donors, adding heparin and other preservatives, and then storing the blood under carefully controlled conditions until its use is required.
In the use of the blood, there have been observed in the patient complications, sometimes serious, which have been recognized as being a function of blood storage duration. Accordingly, it has been common practice to discard blood bank blood after it has been stored for a predetermined time.
It has been discovered that when blood bank blood is stored, its leukocyte and platelet components are altered, developing characteristics which are responsible for the transfusion complications referred to above. The alteration is evidenced in two ways.
First, some of the platelets become adhesive. Second, some of the platelets form aggregates with some of the leukocytes. The aggregates primarily are responsible for the adverse results occurring when old blood is used in blood transfusions. In addition, when carrying out auto transfusions, the blood becomes contaminated with extraneous material such as epithelium, pieces of muscle, fat emboli, fragments of suture material and the like.
The importance of removing foreign material such as the above from the blood before introducing it into the patient is obvious.
My U.S. Pat. No. 3,593,854 describes and illustrates a blood treating and filtering apparatus overcoming the foregoing problem which has been used widely and successfully. However, continued surgical experience with the unit has shown that the fibrous filter mat used in it tends to become clogged at its upstream, or presenting surface before the filtering capacity of the filter is reached. This materially shortens the life of the filter and adds expense and inconvenience to the blood filtering operation.
The causes of clogging of the filter are two-fold; First, the comparatively high density of the filter material at the presenting surface provides relatively small filter surface openings which rapidly become plugged with debris. Second, the construction of the filter is such that a relatively small filter surface area is presented to the incoming blood.
The first of the foregoing disadvantages has been overcome in my co-pending application Ser. No. 807,378 of which the present application is a continuation-in-part. This application describes and illustrates a blood filter having a filamentous or fibrous filtering component arranged within the filter in such a manner that the filter body is of graduated density i.e. has a lesser density at its presenting surface than it does at its exit surface with the density progressively increasing throughout the body of the filter. As a result of this arrangement, the presenting surface of the filter filters out the larger particles while the exiting surface filters out the minute particles, thereby putting to work the entire body of the filter, rather than just the presenting surface portion thereof.
The filter of my patent application Ser. No. 807,378 aforesaid is, however, particularly suited for application in the technique of open heart surgery and related operations and is not so well suited for use in blood transfusions.
It accordingly is the general purpose of the present invention to provide a high capacity, rapid, blood filter for use in making blood transfusions and auto transfusions.
It is another principal object of the present invention to provide a blood transfusion micro filter of comparatively small size which retains a relatively small amount of the blood being transfused, with the consequent advantage to the patient.
Still another object of the present invention is the provision of a blood transfusion micro filter characterized by rapid flow.
A further object of the present invention is the provision of a transfusion type micro filter simple in construction, low in cost, efficient in operation (with particular regard to freedom from channeling) and well adapted for use in present day operating procedures without extensive modification thereof.
Generally stated, the high capacity blood transfusion micro filter of my invention broadly comprises a substantially vertically arranged case terminating at its upper and lower ends in inlet and outlet ports, respectively. A plurality of radially spaced ribs or other projections extend inwardly from the inner surface of the upper portion of the case. Perforate blood filter material support means is positioned across the lower portion of the case a spaced distance below the projections to form a chamber. A quantity of woolly or filamentous blood filter material is contained in the chamber, fluffed into the spaces between the projections to provide filter areas of decreased filter material density.
Preferably, the case is divided into two chambers: An upper chamber containing filter material of decreased density and a lower chamber containing filter material of relatively greater density.
Combination baffle means and filter material densifying means is provided in the interior of the case for directing the flow of blood inwardly through the filter material.