The invention herein relates to a bubble-type oxygenator of the kind used in thoracic surgery, and more particularly to an oxygenator having improved bubble formation and improved oxygen-carbon dioxide exchange.
The present invention is a further improvement of the devices shown in the Bentley U.S. Pat. No. 3,615,238, issued Oct. 26, 1971, entitled "Oxygenator"; the Bentley, et al. U.S. Pat. No. 3,578,411 issued May 11, 1971, entitled "Bubbler Assembly for Blood Treating Apparatus;" the Bentley, et al. U.S. Pat. No. 3,488,158 issued Jan. 6, 1970, entitled "Bubbler Assembly for Oxygenator;" and applications Ser. Nos. 436,913, now abandoned, and 565,043, now U.S. Pat. No. 4,058,369, entitled "Blood Oxygenator" and "An Improved Oxygenating Device," respectively, the disclosures of which are incorporated by reference herein. These devices each represent important developments in the blood treatment art. However, since these devices temporarily assume the function of the heart and lungs of a patient during certain operations or other treatments of the body, further improvements are desired which will effect within such devices a blood treatment process as equivalent as possible to that natural process effected by the heart and lungs.
One aspect of the human oxygenating process which has heretofore been difficult to duplicate concerns the ratio of oxygen in the blood to carbon dioxide commonly expressed as the physiological ratio of pO.sub.2 to pCO.sub.2. In the past, oxygenating devices were either unable to maintain this pO.sub.2 to pCO.sub.2 ratio or, in an effort to maintain such a ratio over the range of flow rates required during operation of the devices, have operated inefficiently and/or in a manner which may adversely affect the blood. For example, when an increase in pO.sub.2 was desired, it could be effected only by a substantial increase in the flow of oxygen with respect to the flow of blood into the device. A high gas-to-blood-flow ratio represented an inefficient operation of the oxygenator and, more importantly, substantially increased the risk of hemolysis.
The present invention provides features enabling improved blood bubble formation and blood bubble flow which result in substantially improving the oxygenating capabilities of the oxygenator. In particular, the present invention provides for improved flow of blood bubbles along the passageway within the oxygenating chamber as well as improved blood bubble formation. Such improved flow and bubble formation avoid the situation in which relatively few nonuniform blood bubbles are initially generated and then not adequately mixed with free oxygen to effectuate optimum oxygen-carbon dioxide transfer without harm to the blood.
Furthermore, the present invention provides for an improved structure such that the volume of priming liquid for start-up of the oxygenating device can be substantially reduced. This reduction is advantageous in the commonly occurring situations where either blood (not that of the patient) alone, blood mixed with a solution for hemo-dilution, or hemo-dilution solution alone is used for priming the oxygenator. The reason why such reduction is advantageous in the first situation mentioned above, i.e., when blood (not that of the patient) alone is used as priming liquid, is that the less liquid used which is not the blood of the patient, the more physically acceptable is the oxygenating process to the patient. The reason for the advantage in the second situation, i.e., when blood mixed with a solution for hemo-dilution is used as priming liquid, is the one just mentioned, as well as the fact that blood alone is more readily oxygenated than is blood mixed with hemo-dilution solution because of reduced hematocrit of the latter. Therefore, the less mixture used for priming, the better the oxygenating during the initial operation stages. The reasons for the advantage in the third situation, i.e., when hemo-dilution solution alone is used as priming liquid, are the same as those mentioned above for the second.
The present invention contemplates a blood oxygenating device whereby (a) oxygen to blood transfer can be effectively and efficiently achieved with an improved gas-to-blood flow rate, (b) improved blood and blood bubble flow characteristics can be obtained, (c) improved blood bubble formation can be achieved, and (d) the volume of priming liquid can be substantially reduced.
The present oxygenating device in its preferred embodiment comprises an oxygenating chamber and a heat exchange chamber. The oxygenating chamber comprises generally a bubble column including a bubbler chamber and a mixing chamber or passageway. The bubbler chamber is provided with oxygen and blood inlet means and a diffusion cone. Venous blood entering the bubbler chamber is bubbled by a plurality of small jetting streams of oxygen emanating from the diffusion cone in a direction counter to, or parallel with, the flow of blood to form blood bubbles. The blood bubbles then pass into the mixing chamber. The mixing chamber is provided with a plurality of secondary flow-producing means which function to promote a secondary flow of blood bubbles passing therethrough. The passageway, together with the diffusion cone, controls the bubble size and promotes efficient oxygenation of the blood bubbles. The blood bubbles which exit the oxygenating chamber are required to pass through a heat exchange chamber and a defoaming means before exiting the oxygenating device.
In one embodiment of the present invention, the defoaming means is positioned around the oxygenating chamber. The blood bubbles exit the oxygenating chamber and pass down the outside of the oxygenating chamber through an open space provided by a defoamer support member disposed between the oxygenating chamber and layers of defoamer material encompassing said chamber. The bubbles then flow into the reservoired debubbled blood which extends around the lower end of the chamber and are substantially converted to liquid (or debubbled) oxygenated blood and free oxygen and carbon dioxide gases which are vented. The liquid blood then passes through the defoamer material which surrounds the reservoired blood. Bubbles which do not dissipate during their travel down the outside of the bubbler chamber dissipate as they pass laterally through the defoamer material. After the blood passes through the defoamer material, it flows into the heat exchange chamber for the transfer of heat to the blood prior to its return to the patient. In an alternative preferred embodiment, the blood bubbles are passed through the heat exchange chamber prior to being passed through the defoaming means. The defoamer is disposed around the outside of the heat exchanger and is similarly provided with defoamer support members which function to support the defoamer material spaced apart from the heat exchange chamber, thereby similarly providing an open space for the passage of blood bubbles. After passing through the defoamer material, the blood is returned to patient.