1. Field of the Invention
The present invention relates to methods and apparatus in the field of cardiotomy perfusion, and in particular, it is directed to cardiotomy reservoirs which are used in extracorporeal blood circuits.
2. The Prior Art
There are a wide variety of medical and surgical procedures in which a patient's blood is conducted extracorporeally through a blood circuit for treatment and thereafter returned to the patient. Typical extracorporeal blood circuits include, for example, cardiopulmonary bypass and extracorporeal hemodialysis.
Effective circulation and control of a patient's blood are essential to successful heart surgery. In modern surgical procedures, blood is circulatd through the patient mechanically by establishing a cardiopulmonary bypass circuit in which the blood is forced through a bloodline or tube with a blood pump. This circuit removes blood from the patient, oxygenates the blood, and then returns the blood to the patient.
In addition, blood which accumulates in the patient's pericardium or heat cavities during the course of surgery is transported away from the surgical site. This is generally accomplished by means of a "cardiotomy sucker" which aspirates the blood from the areas of accumulation. During an operation of only thirty minutes, as much as 250,000 cubic centimeters of blood may be aspirated from the patient through the "cardiotomy sucker." Consequently, unless it can be successfully returned to the patient, this aspirated blood must be replaced by blood from other sources. In attempting to return this aspirated blood to the patient, however, one encounters of number of obstacles.
Blood removed from the surgical site through a "cardiotomy sucker" invariably contains tissue fragments, blood clots and other debris which prevent the blood from being returned directly to the patient through the cardiopulmonary bypass circuit. This difficulty can generally be minized by allowing the blood to pass through filters which remove all particles larger than a predetermined size, for example, twenty (20) microns. However, this filter will sometimes become occluded and must, consequently, be replaced.
A somewhat more difficult obstacle to recycling aspirated blood is due to the fact that blood which is removed from the surgical site through a "cardiotomy sucker" has a substantial amount of air bubbles suspended within it, thereby resulting in a foam-like solution. Oxygenators which are used in the cardiopulmonary bypass circuit have traditionally had some limited defoaming capability, because small air bubbles remain in the blood after the oxygenating process. However, aspirated blood differs greatly from oxygenator blood for which the oxygenator defoamer was designed. Although bubbles are present in both oxygenator and aspirated blood, the bubbles contained in oxygenator blood are typically within the same, specific micron range as the bubbles produced by the oxygenator. Aspirated blood, on the other hand, contains bubbles with no such size uniformity, and the quantity of bubbles may vary from a steady stream to a froth. As a result, defoaming aspirated blood is significantly more difficult than defoaming oxygenator blood and has provided a significant challenge to those skilled in the art.
In order to more effectively prepare aspirated blood for return to the patient, a device known as a cardiotomy reservoir has been used. Cardiotomy reservoirs currently in use have the capability of holding large volumes of blood separate from the main extracorporeal cardiopulmonary bypass circuit. Many of the cardiotomy reservoirs currently in use also include internal filters which separate out the above-mentioned debris. Typical prior art cardiotomy reservoirs also contain a small defoaming element which defoams the blood as it passes through the cardiotomy reservoir. After the blood has been so treated, it is then recycled to the patient through the cardiopulmonary bypass circuit.
Although the cardiotomy reservoirs presently in use have greatly improved the quality of the blood which is returned to the patient, current cardiotomy reservoirs have proven inadequate in many respects. Current cardiotomy reservoirs use a defoaming substance which is composed of the same material used in the defoamer within the oxygenator. This defoamer, which is a uniform single density defoamer, cannot effectively defoam aspirated blood where there are a wide variety of sizes and quantities of air bubbles suspended within the blood.
Additionally, the design of present cardiotomy reservoirs allows blood to pass quite rapidly through the reservoir. That blood is, therefore, not in contact with the defoaming element for any significant length of time and this results in inadequate defoaming of the blood. Even if the outflow of blood from current cardiotomy reservoirs is intentionally interrupted, significant volumes of blood are held in the lower portion of the cardiotomy reservoir and are not in contact with the defoamer element at all. Consequently, the temporary interruption of blood outflow from present cardiotomy reservoirs does significantly improve their defoaming capability.
Finally, cardiotomy reservoirs which include internal filters occasionally clog due to excessive debris and/or blood clots resulting from inadequate heparinization, accelerated metabolism of the heparin, or blood coagulopathy. When the internal filtr of the cardiotomy reservoir becomes clogged, the entire cardiotomy reservoir must be changed. This interrupts and disrupts the cardiotomy reservoir circuit. Equally important, the blood trapped within the clogged cardiotomy reservoir cannot always be recovered and returned to the extracorporeal circuit; hence, significant volumes of blood must sometimes be discarded. Even if the trapped blood is recovered, it will often not be used because there is an insufficient guarantee of sterility. In addition, there is often even no attempt to recover this trapped blood, because the time needed to recover the blood to the extracorporeal circuit may be too lengthy. Each of the above-mentioned situations adds significantly and dangerously to the normal risk involved in heart surgery.
Accordingly, it would be a significant improvement in the art to provide a cardiotomy reservoir having a defoamer which is specifically designed to handle blood containing suspended air bubbles of many sizes, such as blood aspirated during heart surgery, Additionally, it would be an improvement in the art to provide a cardiotomy reservoir in which the defoamer is always in substantial contact with the blood which is located within the reservoir. Further, it would be an improvement in the art to provide a cardiotomy reservoir which would allow for the rapid replacement of a clogged filter, without compromising asepsis or blood recoverability. Finally, it would be an improvement in the art to provide a method for defoaming aspirated blood which adequately separates the air from the blood while minimizing the risk to the patient incident to the defoaming process. Such a novel cardiotomy reservoir apparatus and method is described and claimed herein.