PUMP AND OXYGENATOR

By W. T. Mustard, M.D. The Hospitalfor Sick Children, Toronto

T ms PAPER is a general review of the ing effect of protamine on was ap- development of the artificial heart- preciated that many dogs survived a simple to facilitate open-heart surgery. At the close bypass for any length of time without bleed- of World War II many centers began in- ing to death. This postoperative bleeding, vestigating the possibility of total cardiac due both to hepaninization and perhaps to bypass. Oven the past decade, pump oxy- the reduction of platelets from prolonged generators of various types have become extracorporeal pumping, was overcome by popular and recent clinical successes administration of protamine and successes throughout the world have given further were achieved. impetus to the study of problems posed by The problem of delivering the to the artificial heart-lung apparatus. the experimental animal is relatively simple. The subject divides itself into three sepa- It can be delivered into a subclavian artery rate parts, the first two being concerned where it passes centrally, closes the aontic with the maintenance of life in an expeni- valves and is redistributed to the body. This mental animal during a total cardiac by- is the common practice with most surgeons pass. One must take all the blood from the in both experimental and clinical apphica- animal and return it to the animal by tion at the present time. The actual removal means of a pump. Secondly, one must oxy- of the blood from the dog constituted a genate the blood before returning it. The major problem in the early phases of study. third pant of the problem confronting the It was not until catheters were inserted surgeon is the selection of cases and con- through the right aunicubar appendage rection of defects in human subjects. into the superior and inferior vena cavae The pumping mechanism must duplicate that the removal of the blood was adequate. as nearly as possible the action of the Even this presents occasional hazards and chambers of the heart. Pumping action some controversy exists as to whether one must be smooth so as to prevent hemolysis should remove this blood by a vacuum and to avoid turbulence with thrombosis. pump or by gravity. Certainly, if one in- It is not difficult to construct a pump with creases the pressure slightly the cannulae which hemolysis can be kept to relatively are apt to become blocked, and it may be negligible amounts. Most of the pumps in that suction through the vena cavae causes use throughout the world give an hemolysis some deleterious effect on both liven and of less than 50 mg of hemoglobin pen 100 brain. Gravity methods of removal are not ml of blood, which is perfectly safe. Tunbu- always certain although in use in some hence with thrombosis can be overcome by centers. removing valves inside the stream and plac- The oxygenation of the blood proved at ing valves outside of, rather than within the first to be a most difficult stumbling block. stream of blood. Furthermore, hepaniniza- It was felt that large quantities of blood tion of the blood lessens the tendency to would have to be oxygenated to approach thrombosis. It was the experience of all the normal flow, that is, somewhere in the the early investigators, including ourselves, neighborhood of 4 to 6 1/mm, and a tre- that postoperative bleeding was a serious mendous surface must be created to oxy- complication. It was not until the neutrahiz- genate such a large quantity of blood. It

Presented at the Annual Meeting, October 8, 1956. ADDRESS: 555 University Avenue, Toronto, Ontario, Canada. 1124

Downloaded from www.aappublications.org/news by guest on October 2, 2021 AMERICAN ACADEMY OF PEDIATRICS - PROCEEDINGS 1125 was probably for this reason that most the most significant change and this can be oxygenators were inadequate during the overcome by the administration of appno- early years and the contribution by An- pniate alkali at the termination of a cardiac dreason (as applied by the Minneapolis bypass. group) of the azygos flow principle lessened At this time it would be appropriate to the need for oxygenatons with such large give a brief description of the various types surface and for such large quantities of of artificial heart-hung machines which are blood to be oxygenated. Life can be main- in use clinically at the present time. Gibbon, tamed in the experimental animals for a in 1937, carried out experiments on animals2 few moments on the return flow through designed to determine whether the circu- the azygos vein when the vena cavae are lation could be aided by artificial means in clamped. Periods up to 3 hour of the total the presence of partial occlusion of the venous occlusion are compatible with life . The means employed if two and one-half times the azygos flow were the withdrawal of blood from a pe- are used-about one-third of the normal ripherab vein, the introduction of oxygen venous return. into the blood and the neinjection of the The use of low rates of flow reduced the blood into a peripheral artery in a central necessity for very large oxygenators and as direction. The present modified apparatus a result numerous types of oxygenators are of the Gibbon type is being used success- now being used experimentally and chini- fully by Kirklin at the Mayo Clinic.3 cahhy. These oxygenatons can be divided into The basic hemodynamic feature of the four groups : The first group films out a Gibbon type apparatus is automatic main- thin layer of blood to come in contact with tenance of a constant volume of blood in oxygen. Examples are the Jongbboed oxy- the extraconporeal circuit during the pen- genaton1 which was one of the first, the oxy- fusion. This is accomplished by the corn- genaton of the Swedish group now being bined action of three mechanisms : A level- used in Stockholm, and that of Gibbon,2 sensing device which maintains a constant now being used successfully in the Mayo volume within the venous reservoir; a sec- Clinic.3 A second method of oxygenation ond level-sensing device which maintains a of blood is the bubbling of oxygen through constant volume in the bower oxygenator the blood. Removal of the bubbles by anti- reservoir; a constant rate of flow of blood foam preparation and a specially designed across the screens of the oxygenator, thus helix such as in DeWahl’s oxygenator is insuring constant volume of blood within now being used successfully in Minneapolis. the oxygenator proper. The components of Other bubble oxygenatons are those of Dod- the machine are as follows : Flow circuit of nill and Kaplan, where finer bubbles of oxy- tygon tubing; pumps of the nonocciusive gen are used with less foaming. Membrane DeBakey nobler type; venous and coronary dialysis would seem a physiologic approach sinus reservoirs; occiuder mechanisms; high to oxygenation of blood and such an oxy- pressure stops; the oxygenator composed genator has been constructed by Kohff.4 of 14 wire mesh screens measuring 12 by 18 The use of a biologic oxygenator as advo- inches enclosed in a lucite case and arterial cated by our center many years ago has filter (Fig. 1). the disadvantage of the possibility of in- Jongbboed’s oxygenator1 was also a pio- troducing into the circulation organisms neer apparatus in the field. The artificial and proteins foreign to the patient. heart-lung consists of six parts, each part In surveying in a broad way the bio- consisting of a rigid tube of some suitable chemistry of the blood after cardiac by- plastic material bent into the shape of a pass for 15 to 60 minutes, it appears that spiral. The six spirals are mounted in a none of the constituents are seriously al- frame with their axes pointing slightly tered. A lowering of the pH appears to be downward. They turn about this axis

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FIG. 1. The Gibbon pump in use at the Mayo Clinic. synchronously with the pumps. As the venous blood circulating through the mix- blood passes through the spiral tube it will ing tube. The bubbles present the large adhere to the wall and form a thin layer. surface area necessary for efficient uptake Streams of oxygen and carbon dioxide con- of oxygen and elimination of carbon dioxide stantly pass through the tube and the ex- without the intervention of a foreign sub- change of gases takes place. stance for filming. The bubbles are then The artificial bubble-oxygenator of De- largely dissipated by momentary contact Wall has no moving pants. It is assembled with a patent nontoxic silicone antifoam entirely from commercially available plastic substance sprayed on or painted on the (pure polyvinyl) food hose, and is sterilized distal portion of the walls of the mixing by autoclaving. The pump used extensively tube and the smaller plastic connecting is the milking type of sigmamotor available tube. Any remaining bubbles rapidly rise commercially. Oxygenation of the venous to the surface and are eliminated, carrying blood occurs by the direct introduction of off carbon dioxide as well, as the blood 100% oxygen in the form of large bubbles descends by flow of gravity in a plastic set- in a vertical plastic mixing tube. The blood thing tube (helix). From the settling tube and oxygen make contact at the surface of the now artenialized blood enters the cen- these bubbles as they rise in the column of trab collecting reservoir from which it is

Downloaded from www.aappublications.org/news by guest on October 2, 2021 AMERICAN ACADEMY OF PEDIATRICS - PROCEEDINGS 1127 perfused through the patient after passing ably carries out some detoxifying function. through standard blood filters (Fig. 2). In the remainder of the extraconporeab sys- In the artificial lung of Kolff4 oxygenation tem there is included a bubble trap to safe- occurs through a polyethylene membrane. guard against air embolism and a water bath The membrane consists of three layers of to maintain perfusing fluid at body tempera- fiberglass window screen, two polyethylene tune. All tubing is of plastic material with tubes and three pairs of spacers (to allow plastic connections. space for the tubes to become distended We must now return to the third pant of with blood). The plastic coated fiberglass the problem, namely, the selection of cases strips 7 m long are wound around a can for direct intracardiac surgery and must and the completed coil is placed in a plastic also consider the complications of this type bag. Oxygen is blown into the bottom of of surgery. It is without question that the the artificial at a rate of 30 1/mm daring and boldness of Lilhehei6 provided (for eight lungs). the answer to the batten problem. His group Experimentally and clinically our group in Minneapolis used a human donor as a has used a pump designed by Cowan.5 The perfect physiologic pump-oxygenator and advantages listed for this pump are ade- were able to perform intracardiac surgery quate output, easy regulation by hand con- under direct vision. They opened the field tnol, easy sterilization, absence of internal for the actual surgical technique and the valves and negligible hemolysis. The oxyge- selection of cases for operation. After initial nator is a biologic one. The advantages of a success with the human donor, the Minne- biologic oxygenator of this type are that it apobis group returned to the bubble oxy- allows a massive surface area for oxygena- genaton and sigmamoton type of pump, and tion of blood, causes minimal trauma to con- have continued with their successes. stituents of the blood, is a filter, and prob- The artificial heart-lung type of bypass

FIG. 2. The DeWall bubble oxygenator and sigmamotor pump in use at Minneapolis.

Downloaded from www.aappublications.org/news by guest on October 2, 2021 1128 MUSTARD - HEART PUMP AND OXYGENATOR is most useful in operations requiring in- hypothermia, as introduced by Bigelow, terruption of cardiac flow for more than was receiving wide recognition and used for 8 or 10 minutes. For interruption of cardiac short-term cardiac bypasses. It was felt by flow of shorten duration, protection could many investigators, including ourselves, that be afforded with hypothermia. The inter- a combination of hypothermia and artificial ventricular septal defect requires use of an heart-lung, might reduce the rate of flow to extracorponal circulation and successful such an extent that oxygenation would not surgery in such cases is being reported all be necessary and that one could simply oven the world. use preoxygenated blood. The idea is in- Coronary and cerebral air embolism has triguing but from our experimental studies not proven hazardous in the presence of an has not proved feasible. Irreversible yen- extracorporeal circulation. The reverse flow triculan fibrillation occurred frequently. from the pump appears effective in closing There may be some promise in the future if the aortic valves, and air in the left ventricle this can be overcome. With the use of re- escapes through the defect during closure. duced rates of flow the added hazard of Flow through bronchial arteries with re- ventricular fibrillation due to hypothermia turn to the left side of the heart is sufficient did not seem warranted. to fill and expel air from the left ventricle. In conclusion, it seems justifiable to state Indeed, this flow, particularly in cases of that after one decade of trial and tribulation tetrad of Falbot, is considerable and must be the artificial heart-lung is here to stay as returned to the extracorporeal system. pant of the anmamentarium of the cardiac Experience is being gained in many cen- surgeon. tens with different methods of closure of REFERENCES intenventnicular septal defects either by direct suture or by the use of some form of 1. Jongbhoed, J. : The mechanical heart-lung system. Surg., Gynec. & Obst., 89:684, plastic material. Further experience is being 1949. gained in the selection of cases and in the 2. Gibbon, J. H. : Artificial maintenance of problem of the reversibility of pulmonary circulation during experimental occlusion hypertension. It would appear that the of pulmonary artery. Arch. Sung., 34: younger the patient at the time of opera- 1105, 1937. 3. Jones, R. E., Donald, D. E., Swan, H. J. C., tion, the greaten the possibility of albeviat- Harshbarger, H. G., Kirklin, J. W., and ing pulmonary hypertension. It has been Wood, E. H. : Apparatus of the Gibbon our experience and that of many others that type for mechanical bypass of the heart the infant is a poor operative risk for extra- and lungs. Proc. Staff Meet., Mayo Chin., corporeal circulation because of the fre- 30:105, 1955. 4. Kolif, W. J., Effler, D. B., Groves, L. K., quency of postoperative complications. Peereboom, G., and Moraca, P. P. : Dis- However, progress is being made and, as posable membrane oxygenator (heart- each center gains more experience with hung machine) and its use in experimental the connection of interventnicular septal de- surgery. Cleveland Clin. Quart., 23:69, fects, the artificial heart-lung will be used 1956. 5. Mustard, W. T., and Chute, A. L. : Experi- for correction of tetrad of Fahlot and for mental intracardiac surgery with extra- certain cases of infundibular stenosis with corporeal circulation. Surgery, 30:684, normal outflow tract. It is still very hazard- 1951. ous to attempt connection of atrioventricu- 6. Lillehei, C. W., DeWahh, R. A., Read, R. C., Warden, H. E., and Vanco, R. L. : Direct bans communis. vision intracardiac surgery in man using During the time the pump-oxygenators a simple, disposable artificial oxygenator. were being developed in various centers, Dis. Chest, 29: 1, 1956.

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Pediatrics is the official journal of the American Academy of Pediatrics. A monthly publication, it has been published continuously since 1948. Pediatrics is owned, published, and trademarked by the American Academy of Pediatrics, 345 Park Avenue, Itasca, Illinois, 60143. Copyright © 1957 by the American Academy of Pediatrics. All rights reserved. Print ISSN: 1073-0397.

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