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Operation of a Bubble Type Pump-Oxygenator
Operation of a Bubble Type Pump-Oxygenator RODMAN E. TABER, M.D., F.A.C.S. * LUIS A. TOMATIS, M.D.**
ALTHOUGH no one claims that the currently available pump-oxygenators for extracorporeal circulation are perfect, there are several types which have been shown to be safe and reliable if operated by an experienced team. With but few exceptions, morbidity and mortality are related to the complexity of the cardiac lesion and the degree of pulmonary and myocardial damage rather than to the perfusion itself. Extracorporeal oxygenation may be accomplished across a liquid-gas interface by the film,! disc 2 or bubble dispersion 3 methods or through a membrane permeable to gases. 4 Each of these carry out the two functions of an artificial lung, the adding of oxygen to the blood and the removal of carbon dioxide. Our experience in the field of extracorporeal circulation consists of over 300 perfusions with the pump-oxygenator of the bubble type (DeWallLillehei). Since our first clinical perfusion in April 1956, a number of modifications have been made in the apparatus and its mode of operation. The most important change was the gradual increase in the perfusion rate from the low rate of 35 cc./kg. of body weight per minute (azygos flow principle) to flows of 70 to 100 cc./kg./min. Instead of pump aspiration of the vena cavas, the blood is now allowed to flow into a reservoir by gravity. A third modification and an important one has been the reduction in the amount of oxygen per cubic centimeter of blood passed into the oxygenating column of the apparatus. This has had the effect of not supersaturating the plasma with oxygen which might result in the formation of microbubbles in the blood and central nervous system damage. 6 The experimental work was supported by a grant from the Michigan Heart Association.
* Associate Surgeon, Division of Thoracic Surgery, Henry Ford Hosp1:tal, Detroit, Michigan.
** Resident Surgeon, Division of Thoracic Surgery, Henry Ford Hospital, Detroit, Michigan. 1539
Rodman E. Taber, Luis A. Tomatis
1540
Fig. 425. Photograph of bubble oxygenator of the DeWall-Lillehei type, with dual oxygenator columns and debubbling chambers. A, Venous reservoir for receiving caval drainage by gravity. B, Sigmamotor pump, Model TM2. C, Oxygenator columns. D, Debubbling chambers. E, Helix in water bath. F, Reservoir for cardiotomy drainage, which is removed periodically by pump head G of Sigmamotor Model TMI and passed into venous reservoir A.
ASSEMBLY OF THE BUBBLE OXYGENATOR
The following description concerns the assembly of the original allplastic pump-oxygenator of DeWall and Lillehei (Figs. 425 and 426). Only slight modification would be required if the newly developed vertical debubbling canister were to be substituted for the inclined plastic de- . bubbler. The sizes and lengths of the disposable vinyl tubing* used for one patient are as follows (To agree with the diagram in Figure 426, the inside diameter of the tubes is given in inches and the length in centimeters): The oxygenator column is of lY2 inch tubing, and is 75 cm. in length. The debubbling chamber is of 2Y2 inch tubing and is 55 cm. in length. For flows up to 2500 cc./min., the helix which is of ~ inch tubing is 250 cm. in length. For flows in excess of 2500 cc./min., two oxgenator columns and two debubblers are necessary and the helix tubing is lengthened to 600 cm. (as in Fig. 426). Tubing of % inch internal diameter is used to connect the patient to the pump in all cases. The use of this size rather than U inch tubing in small patients facilitates venous outflow and requires only a relatively small increase in the priming blood volume (8 cc. for each 10 cm. of tubing).
* Available from
Mayon Plastics, 45 Seventeenth Avenue, Hopkins, Minnesota.
Operation of a Bubble Type Pump-Oxygenator
1541
Venous catheters
c:::D
Mayo" lub;ng
=Metal -
Rubber
Fig. 426. Diagra m of the tube connections for bubble oxygenator shown in Figure 425 . (Courtesy of Dr. C. Walton Lillehei.)
Fig. 427. Stainless steel cannula for arterialized blood passing into the femoral artery. The femoral artery is now used more frequently than the left subclavian for the pump return. Also shown is a short length of vinyl tubing and a low resistance stainless stPel connector.
1542
Rodman E. Taber, Luis A. Tomatis
A
B
Fig. 428. Defoaming device placed in the dependent end of the debubbling chamber. The stainless steel wire frame (A) is covered with plastic mesh (B) which is sprayed with Antifoam before autoclaving.
The new tubing stock is washed with a detergent (Alconox), rinsed with distilled water and wrapped in heavy cloth in a manner to prevent kinking during sterilization in the autoclave. The oxygenator is assembled the morning of operation with sterile precautions. Connectors and reducers are of stainless steel with mirror polished inner surfaces (Fig. 427). The debubbling chamber is coated with a thin layer of Dow-Corning Antifoam A before sterilization. The device shown in Figure 428 is inserted in the debubbling chamber. This consists of a stainless steel frame over which is stretched a plastic net consisting of an unfolded household plastic sponge (Tuffy Sponge). This device has served admirably to increase the area of contact between the blood bubbles and the Antifoam, permitting flows of up to 2500 cc./min. through one unit. A filter is placed between the helix and the arterial pump. For this purpose, we have constructed a low resistance filter of stainless steel, nylon and vinyl tubing (Fig. 429). Although probably not essential in every perfusion, we have preferred to retain a low resistance filter as a regular part of the extracorporeal circuit. In addition to removing fibrin, it catches bits of calcium, suture material and fragments of !valon prostheses which may be introduced into the system by the cardiotomy suction. The cardiotomy blood reservoir is fitted with a spare inlet connection for receiving an accessory line if separate atrial drainage is desired. A right atrial catheter has proved useful to remove coronary sinus blood when the heart is not arrested during procedures on the mitral valve. Left atrial decompression is of value during the period of resuscitation following direct operations on the aortic valve. Cardiotomy suction is not allowed to exceed 2.5 cm. of mercury. As indicated, the cardiotomy
Operation of.a Bubble Type Pump-Oxygenator
1543
Fig. 429. Arterial filter of low resistance. The stainless steel wire frame is covered with nylon fabric, 80 mesh. The wire frame prevents whipping action during perfusion.
reservoir is emptied into the venous reservoir with the auxiliary Sigmamotor pump. When the tubing connections have been made, the arterial head of the Sigmamotor pump is calibrated with warm saline solution, passing it through the arterial cannula of the size predicted for the patient. Calibrations are determined for flow rates of 50, 70 andllOO cc./kg. of body weight per minute. Flow rates for small patients are probably better calculated on the basis of surface area in which case the settings are for 1.5, 2.0, 2.3 and 2.5Iiters/M.2 per minute. Maintenance of a satisfactory mean arterial pressure during by-pass is a more reliable indication of a satisfactory perfusion than the predetermined pump calibrations. The saline solution used for the calibration is circulated through the debubbling chamber to wash away any excess Antifoam. Not infrequently, small amounts of oily film due to Antifoam may be seen on the surface of this washing solution. Heparinized blood warmed to 40° C. is used to prime the system. It is comforting to have about one minute's supply of blood in the helix. The quantities of heparinized and citrated blood ordered for various sized patients is indicated in Table 1. The venous lines may be filled by elevating the blood-filled venous reservoir, and this permits gravity siphon drainage to start as soon as the tubes are opened at the beginning of the perfusion. Oxygen flow rates of two to three times the blood flow rate are used. If the blood in the arterial line appears dark, the larger flow of oxygen is indicated. Experimental studies have demonstrated that satisfactory arterial oxygenation and the
1544
Rodman E. Taber, Luis A. Tomatis Table 1
QUANTITIES OF BLOOD PREPARED FOR EXTRACORPOREAL CIRCULATION PATIENT'S WEIGHT IN KG.
10 15 20 25 30 35 40 45 and over
HEPARINIZED
CITRATED
5 6 7 9 10 11
2 2 2 3 3 3 3 4
12 13
avoidance of oxygen debt during prolonged perfusions can be accomplished with these oxygen flow rates. 5 . MANAGEMENT OF THE PERFUSION WITH THE BUBBLE OXYGENATOR
Experience has demonstrated that the responsibility for the management of the perfusion is best vested in one member of the surgical team who is assisted by a technician. A check list of potential sites of difficulty such as loose connections, kinked tubing (easily prevented with a wire spring over the tubing) and improper assembly of the debubbler should be covered before starting the perfusion. Provided blood replacement has been adequate up to this point and vessel cannulas are of sufficient size and are correctly positioned, the oxygenator blood level will rapidly stabilize. The arterial inflow rate which began at 50 cc./kg.jmin. or 1.5 liters/M.2/min. may now be increased progressively up to 100 cc./kg.j min. or 2.3 liters. The surgeon may then be notified that the perfusion is satisfactory and cardiotomy with or without induced cardiac arrest follows. Four matters demand the constant and alert attention of the pump operator and his assistant: 1. It is obvious that the helix must not be allowed to run dry due to output exceeding venous return, or fatal air will be introduced into the arterial system. The arterial pump must be slowed until the venous drainage problem is rectified by repositioning of the cannulas, the straightening out of a kink or the replacement of lost blood. 2. The defoaming activity demands frequent observation. Inadequate debubbling may result from improper assembly of the defoaming chamber or from prolonged use of the apparatus at high flow rates. The solution to this problem is to have a spare sterile debubbling chamber ready and:this can replace the faulty one with only a minute or two of interruption of the perfusion. Obviously, the situation is less acute when the dual debubbling chambers are being used.
Operation of a Bubble Type Pump-Oxygenator
1545
3. The third matter requiring constant evaluation is the patient's blood volume. Assuming that the venous cannulas are not obstructed, a blood deficit in the gravity and helix reservoirs may be interpreted as indicating hypovolemia. Information about the need for additional blood can be gained by inspection of the conjunctivae and the rapidity of capillary refill after pressure on the skin of the face (done by the anesthesiologist). Monitoring the aortic pressure is of obvious value. We frequently measure this pressure through a small polyethylene tube which has been passed through a needle. Intermittent transfusions of 50 to 100 cc. are given to replace any operative loss during the perfusion. When extracorporeal circulation is discontinued, the blood in the pleural spaces is removed and measured along with any other blood which has been previously removed by aspiration. Obviously, saline irrigations should be avoided up to this point. Blood loss on the drapes is estimated, and the deficit in the helix if any is noted. This blood loss is balanced against the amount given by transfusion into the saphenous vein and into the extracorporeal system. If there is a net deficit, it may be replaced at this time by transfusion from the system into the arterial cannula. Overloading is immediately evident by inspection and palpation of the right auricle or by the caval pressure monitoring device. A final check consists of the weighing of the patient and comparing the postperfusion weight with the preperfusion weight. 4. The fourth aspect of the perfusion requiring frequent checking is the amount of oxygen which is passed into the oxygenating column. The amount is varied between two and three times the blood flow rate depending on the color of the arterial and caval blood lines. With flow rates of 70 to 100 cc./kg./min. and well maintained patient blood volume, satisfactory oxygen supply will be manifested by a red arterial line as well as vena caval blood which is not markedly desaturated. It is advantageous to monitor the superior vena caval pressure because unsuspected elevations in this pressure may occur with possible detrimental effects on the brain. This pressure may be conveniently measured continuously through a small polyethylene tube passed into the innominate vein from an antecubital vein. The patient's temperature is monitored by a rectal telethermometer. During a good perfusion, the temperature will not fall more than a degree, if the helix water bath temperature has been maintained properly. A NEW MODEL VERTICAL STAINLESS STEEL BUBBLE OXYGENATOR
The original plastic bubble oxygenator has a limited debubbling capacity which has necessitated the use of dual oxygen columns and debubbling chambers for high flow perfusions (Fig. 425). This arrangement is usually satisfactory but debubbling remains a problem in high flow runs over extended periods. The use of a steel debubbling canister at the
1546
Rodman E. Taber, Luis A. Tomatis
Fig. 430. Vertical stainless steel bubble oxygenator for high flow rates. The defoaming chamber at the top contains steel sponges coated with Antifoam. See diagram, Figure 431.
top of the oxygenating column by the Minneapolis group is one solution to the problem. To satisfy the demands of extended high flow perfusions, we have constructed a vertical stainless steel oxygenator (Figs. 430 and 431). This is similar in many respects to that devised by Cooley and his associates. 6 The main components are a vertical column surmounted by a debubbling canister in which is placed stainless steel sponges coated with Dow Antifoam. Oxygenated blood flows from the debubbling canister into the reservoir through the vinyl plastic helix. The helix serves to complete the defoaming and also as a gauge to the amount of blood in the reservoir. A filter of stainless steel mesh is provided at the bottom of the reservoir. A perforated nylon disc in the base of the oxygenation column serves as an oxygen dispersion plate. Steel surfaces in contact with blood are coated with baked-on Teflon. All components are sterilized byautoclaving. Venous blood may be pumped into the oxygenating column from a gravity reservoir or the oxygenator may be placed on the floor and the venous blood can be allowed to drain directly into it, thus eliminating a pump. At the present time, the perfusion blood is warmed by placing the lower two-thirds of the oxygenator in a water bath. Investigations are in progress to see if the heating can be done safely electrically with a coil or jacket around the reservoir. Flow rates of 5000 cc./min. have been handled satisfactorily with this oxygenator.
Operation of a Bubble Type Pump-Oxygenator
Defoamer
1547
, . III III III
III III III
Oxygenating Column
Reserv~/
Helix
', __ ---
s
Telethermolmet'er~-=:=== ~
A rterial ~~~~ _ _-J.c!J;r~
Fig. 431. Diagram of vertical oxygenator shown in Figure 430. The oxygenating column (black) is 75 cm. in length and 5 cm. in internal diameter. For children, the capacity of the reservoir may be decreased by inserting an oxygenating column of greater diameter. Teflon gaskets (black) are placed between the oxygenating column and the base, and between the reservoir and the base, ROTATING DISC OXYGENATOR
Although our own experience has been only with oxygenators of the bubble type, another popular oxygenator deserves discussion. This is the disc oxygenator of the Bjork type which has been modified and popularized by the Cleveland surgeons Kay and Cross (Figs. 432 and 433). The initial limitations in oxygenating capacity have been overcome with the availability of 9, 13, 17 and 21 inch units. In a recent communication, Cross 7 stated that he was satisfied with the oxygenation in blood flow rates up to 4500 cc./min. Blood priming volumes are reasonable. A 20 kg. child requires 1500 cc. with a 17 inch oxygenator reservoir, and an adult of 70 kg. requires 2000 cc. of blood with a 21 inch unit. In theory, the multiplicity of moving parts and the lack of disposability requiring a tedious cleaning operation are drawbacks, but those who have the apparatus do not seem to object to these difficulties. The entire
Rodman E. Taber, Luis A. Tomatis
1648
Fig. 432. Photograph of pump-oxygenator apparatus, utilizing the Kay-Cross disc oxygenator and the Pemco pumping unit. (Courtesy of Dr. Frederick S. Cross.)
OXYGEN-C02 INLET ~ ~~~~~~ ARTERIAL LINE ~:::;;;,,--..::~== ~
VENOUS LINE
KAY-CROSS ROTATING DISC OXYGENATOR PUMP
PUMP GRAVITY TO RESERVOIR FROM VENA CAVA PUMPING TO OXYGENATOR PEMCO 3 OR 4 PUMP UNIT
Fig. 433. Diagram of circuits in the disc oxygenator unit. (Courtesy of Pemco, Inc., 5663 Brecksville Road, Cleveland 31, Ohio.)
Operation oj a Bubble Type Pump-Oxygenator
1549
oxygenator may be sterilized by autoclaving and hence may be assembled, sterilized and maintained ready for use. SOME REMARKS ABOUT THE SIGMAMOTOR PUMP
Since the beginning of our experience in extracorporeal circulation, we have contiuned to use the Sigmamotor Pump for the propulsion of the blood. The original physically unattractive model (Fig. 425) can now be replaced with the Model TM2 which is enclosed in a case more in keeping with the decor of the operating room. The milking-like action of the steel fingers in the pump have not produced undue trauma to the blood. Even after runs of approximately an hour, it is unusual to find plasma hemoglobin levels of more than 100 mg. per 100 cc. Other types of pumps utilize the roller principle of DeBakey (Fig. 432). A Note on the Calibration of the Sigmamotor Pump. It is of fundamental importance properly to adjust the plates opposite the fingers in the Sigmamotor pump before calibration, in order to secure delivery of the desired flow. This is done by holding the arterial line filled with saline 2 feet above the pump and adjusting the plate until the level is maintained during the complete revolution. The screw is then given an additional quarter of a turn to assure occlusion. This maneuver has the effect of making the plate parallel to the axis of the fingers so that uniform pressure will be produced by all the fingers. Even the properly adjusted occlusive pump may fail to deliver the full anticipated flow if the arterial cannula used for the perfusion is smaller than that used for the calibration. Mechanical Failure of the Pump. Obviously, failure of the pumpoxygenator for any reason during a perfusion could be disastrous. Electrical failure is unlikely, because of the stand-by source provided in most modern operating rooms. The old model Sigmamotor pump, like the Model T Ford, had a hand crank which could be used in the event of power failure. The new model has no crank. Even with the power supply intact, an apparatus as complicated as the Sigmamotor pump may fail for a mechanical reason. The group at Mount Sinai HospitalS of New York reported one instance of mechanical failure of their Model TM2 and they mentioned that in 1700 cases of cardiopulmonary by-pass in this country, there had been another failure. Mechanical failure has occurred once in our series of 300 perfusions, due to uncoupling of the venous pump from the motor. In this instance, the heart had been stopped with acetycholine, but fortunately the cardiotomy had not been made. The heart was massaged and it resumed its beat. In the meantime, a Model TM2 was brought in from an adjoining room and the latex tubes of the pumping arrangement were quickly transferred. The operation continued and the patient suffered no ill effects. The patient of Zaroff, Kreel, Kavee and Baronofsky, 8 who was being operated on for mitral insufficiency, did not survive after the pump fail-
Rodman E. Taber, Luis A. Tomatis
1550
.j...... ••••-;y. From Venous Reservoir
y
!
Arterial Line To Patient
Fig. 434. Diagram of Y-connectors for parallel arrangement of Sigmamotor pumps for stand-by purposes. (Courtesy of Zaroff et al. 8 and Surgery.)
ure mentioned above. To prevent this catastrophe, they have suggested that two Sigmamotor pumps be placed in parallel (Fig. 434). The venous and arterial lines are connected by Y connectors as indicated. The arterial side of the nonfunctioning pump is primed before the perfusion begins and the usual calibration is carried out. Because the pumps are occlusive, it is possible to maintain perfusion with either pump merely by stopping one pump and turning on the other. Only about 100 cc. of blood is needed for the priming of the stand-by pump. These authors have suggested the following in the prevention of failure during perfusion with the Sigmamotor pump: (1) adequate fusing, (2) lock type of electrical outlet plugs, (3) frequent check of oil levels in motor, gear box and pump heads, (4) avoidance of overloading the torque capacity (the Venier dials should not be pushed past the maximum setting) and (5) careful investigation by a factory representative of overheating or any unusual noises coming from the gear box or pump heads. SUMMARY
The assembly and operation of a bubble oxygenator of the DeWallLillehei type has been described, and some lessons learned in 300 perfusions have been reported. A compact stainless steel model of a bubble oxygenator is undergoing clinical trial. Some data about a practical disc type oxygenator are presented. REFERENCES l. Jones, R. E., Donald, D. E., Swan, H. J. C., Harshbarger, H. G., Kirklin, J. W. and Wood, E. H.: Apparatus of Gibbon Type for Mechanical Bypass of
Operation of a Bubble Type Pump-Oxygenator 2. 3. 4. 5. 6. 7. 8.
1551
Heart and Lungs: Preliminary Report. Proc. Staff Meet. Mayo Clin. 30: 105, 1955. Cross, F. S., Berne, R. M., Hirose, Y., Jones, R. D. and Kay, E. B.: Evaluation of a Rotating Disc Type Reservoir-Oxygenator. Proc. Exper. BioI. & Med. 93: 210, 1956. Lillehei, C. W., DeWall, R. A., Read, R. C., Warden, H. E. and Varco, R. L.: Direct Vision Intracardiac Surgery in Man Using a Simple Disposable Artificial Oxygenator. Dis. of Chest 29: 1, 1956. Clowes, G. H. A. Jr., Hopkins, A. L. and Neville, W. E.: An Artificial Lung Dependent upon Diffusion of Oxygen and Carbon Dioxide Through Plastic Membranes. J. Thoracic Surg. 32: 630, 1956. Tomatis, Luis, Taber, R. E., Lam, C. R. and Green, Edward: Experimental Studies with Low Oxygen Flow Rates in Bubble Oxygenator. Henry Ford Hospital Bull. 6: 341, 1958. Cooley, D. A., Belmonte, B. A., Latson, J. R. and Pierce, James: Bubble Diffusion Oxygenator for Cardio-Pulmonary By-Pass. J. Thoracic Surg. 35: 131, 1958. Cross, F. S.: Personal communication to the authors, June, 1959. Zaroff, L. I., Kreel, Isadore, Kavee, D. J. and Baronofsky, I. D.: Mechanical Failure During Extracorporeal Circulation: A Method for Prevention. Surgery 45: 645, 1959.
Henry Ford Hospital Detroit 2, Michigan
ALTHOUGH no one claims that the currently available pump-oxygenators for extracorporeal circulation are perfect, there are several types which have been shown to be safe and reliable if operated by an experienced team. With but few exceptions, morbidity and mortality are related to the complexity of the cardiac lesion and the degree of pulmonary and myocardial damage rather than to the perfusion itself. Extracorporeal oxygenation may be accomplished across a liquid-gas interface by the film,! disc 2 or bubble dispersion 3 methods or through a membrane permeable to gases. 4 Each of these carry out the two functions of an artificial lung, the adding of oxygen to the blood and the removal of carbon dioxide. Our experience in the field of extracorporeal circulation consists of over 300 perfusions with the pump-oxygenator of the bubble type (DeWallLillehei). Since our first clinical perfusion in April 1956, a number of modifications have been made in the apparatus and its mode of operation. The most important change was the gradual increase in the perfusion rate from the low rate of 35 cc./kg. of body weight per minute (azygos flow principle) to flows of 70 to 100 cc./kg./min. Instead of pump aspiration of the vena cavas, the blood is now allowed to flow into a reservoir by gravity. A third modification and an important one has been the reduction in the amount of oxygen per cubic centimeter of blood passed into the oxygenating column of the apparatus. This has had the effect of not supersaturating the plasma with oxygen which might result in the formation of microbubbles in the blood and central nervous system damage. 6 The experimental work was supported by a grant from the Michigan Heart Association.
* Associate Surgeon, Division of Thoracic Surgery, Henry Ford Hosp1:tal, Detroit, Michigan.
** Resident Surgeon, Division of Thoracic Surgery, Henry Ford Hospital, Detroit, Michigan. 1539
Rodman E. Taber, Luis A. Tomatis
1540
Fig. 425. Photograph of bubble oxygenator of the DeWall-Lillehei type, with dual oxygenator columns and debubbling chambers. A, Venous reservoir for receiving caval drainage by gravity. B, Sigmamotor pump, Model TM2. C, Oxygenator columns. D, Debubbling chambers. E, Helix in water bath. F, Reservoir for cardiotomy drainage, which is removed periodically by pump head G of Sigmamotor Model TMI and passed into venous reservoir A.
ASSEMBLY OF THE BUBBLE OXYGENATOR
The following description concerns the assembly of the original allplastic pump-oxygenator of DeWall and Lillehei (Figs. 425 and 426). Only slight modification would be required if the newly developed vertical debubbling canister were to be substituted for the inclined plastic de- . bubbler. The sizes and lengths of the disposable vinyl tubing* used for one patient are as follows (To agree with the diagram in Figure 426, the inside diameter of the tubes is given in inches and the length in centimeters): The oxygenator column is of lY2 inch tubing, and is 75 cm. in length. The debubbling chamber is of 2Y2 inch tubing and is 55 cm. in length. For flows up to 2500 cc./min., the helix which is of ~ inch tubing is 250 cm. in length. For flows in excess of 2500 cc./min., two oxgenator columns and two debubblers are necessary and the helix tubing is lengthened to 600 cm. (as in Fig. 426). Tubing of % inch internal diameter is used to connect the patient to the pump in all cases. The use of this size rather than U inch tubing in small patients facilitates venous outflow and requires only a relatively small increase in the priming blood volume (8 cc. for each 10 cm. of tubing).
* Available from
Mayon Plastics, 45 Seventeenth Avenue, Hopkins, Minnesota.
Operation of a Bubble Type Pump-Oxygenator
1541
Venous catheters
c:::D
Mayo" lub;ng
=Metal -
Rubber
Fig. 426. Diagra m of the tube connections for bubble oxygenator shown in Figure 425 . (Courtesy of Dr. C. Walton Lillehei.)
Fig. 427. Stainless steel cannula for arterialized blood passing into the femoral artery. The femoral artery is now used more frequently than the left subclavian for the pump return. Also shown is a short length of vinyl tubing and a low resistance stainless stPel connector.
1542
Rodman E. Taber, Luis A. Tomatis
A
B
Fig. 428. Defoaming device placed in the dependent end of the debubbling chamber. The stainless steel wire frame (A) is covered with plastic mesh (B) which is sprayed with Antifoam before autoclaving.
The new tubing stock is washed with a detergent (Alconox), rinsed with distilled water and wrapped in heavy cloth in a manner to prevent kinking during sterilization in the autoclave. The oxygenator is assembled the morning of operation with sterile precautions. Connectors and reducers are of stainless steel with mirror polished inner surfaces (Fig. 427). The debubbling chamber is coated with a thin layer of Dow-Corning Antifoam A before sterilization. The device shown in Figure 428 is inserted in the debubbling chamber. This consists of a stainless steel frame over which is stretched a plastic net consisting of an unfolded household plastic sponge (Tuffy Sponge). This device has served admirably to increase the area of contact between the blood bubbles and the Antifoam, permitting flows of up to 2500 cc./min. through one unit. A filter is placed between the helix and the arterial pump. For this purpose, we have constructed a low resistance filter of stainless steel, nylon and vinyl tubing (Fig. 429). Although probably not essential in every perfusion, we have preferred to retain a low resistance filter as a regular part of the extracorporeal circuit. In addition to removing fibrin, it catches bits of calcium, suture material and fragments of !valon prostheses which may be introduced into the system by the cardiotomy suction. The cardiotomy blood reservoir is fitted with a spare inlet connection for receiving an accessory line if separate atrial drainage is desired. A right atrial catheter has proved useful to remove coronary sinus blood when the heart is not arrested during procedures on the mitral valve. Left atrial decompression is of value during the period of resuscitation following direct operations on the aortic valve. Cardiotomy suction is not allowed to exceed 2.5 cm. of mercury. As indicated, the cardiotomy
Operation of.a Bubble Type Pump-Oxygenator
1543
Fig. 429. Arterial filter of low resistance. The stainless steel wire frame is covered with nylon fabric, 80 mesh. The wire frame prevents whipping action during perfusion.
reservoir is emptied into the venous reservoir with the auxiliary Sigmamotor pump. When the tubing connections have been made, the arterial head of the Sigmamotor pump is calibrated with warm saline solution, passing it through the arterial cannula of the size predicted for the patient. Calibrations are determined for flow rates of 50, 70 andllOO cc./kg. of body weight per minute. Flow rates for small patients are probably better calculated on the basis of surface area in which case the settings are for 1.5, 2.0, 2.3 and 2.5Iiters/M.2 per minute. Maintenance of a satisfactory mean arterial pressure during by-pass is a more reliable indication of a satisfactory perfusion than the predetermined pump calibrations. The saline solution used for the calibration is circulated through the debubbling chamber to wash away any excess Antifoam. Not infrequently, small amounts of oily film due to Antifoam may be seen on the surface of this washing solution. Heparinized blood warmed to 40° C. is used to prime the system. It is comforting to have about one minute's supply of blood in the helix. The quantities of heparinized and citrated blood ordered for various sized patients is indicated in Table 1. The venous lines may be filled by elevating the blood-filled venous reservoir, and this permits gravity siphon drainage to start as soon as the tubes are opened at the beginning of the perfusion. Oxygen flow rates of two to three times the blood flow rate are used. If the blood in the arterial line appears dark, the larger flow of oxygen is indicated. Experimental studies have demonstrated that satisfactory arterial oxygenation and the
1544
Rodman E. Taber, Luis A. Tomatis Table 1
QUANTITIES OF BLOOD PREPARED FOR EXTRACORPOREAL CIRCULATION PATIENT'S WEIGHT IN KG.
10 15 20 25 30 35 40 45 and over
HEPARINIZED
CITRATED
5 6 7 9 10 11
2 2 2 3 3 3 3 4
12 13
avoidance of oxygen debt during prolonged perfusions can be accomplished with these oxygen flow rates. 5 . MANAGEMENT OF THE PERFUSION WITH THE BUBBLE OXYGENATOR
Experience has demonstrated that the responsibility for the management of the perfusion is best vested in one member of the surgical team who is assisted by a technician. A check list of potential sites of difficulty such as loose connections, kinked tubing (easily prevented with a wire spring over the tubing) and improper assembly of the debubbler should be covered before starting the perfusion. Provided blood replacement has been adequate up to this point and vessel cannulas are of sufficient size and are correctly positioned, the oxygenator blood level will rapidly stabilize. The arterial inflow rate which began at 50 cc./kg.jmin. or 1.5 liters/M.2/min. may now be increased progressively up to 100 cc./kg.j min. or 2.3 liters. The surgeon may then be notified that the perfusion is satisfactory and cardiotomy with or without induced cardiac arrest follows. Four matters demand the constant and alert attention of the pump operator and his assistant: 1. It is obvious that the helix must not be allowed to run dry due to output exceeding venous return, or fatal air will be introduced into the arterial system. The arterial pump must be slowed until the venous drainage problem is rectified by repositioning of the cannulas, the straightening out of a kink or the replacement of lost blood. 2. The defoaming activity demands frequent observation. Inadequate debubbling may result from improper assembly of the defoaming chamber or from prolonged use of the apparatus at high flow rates. The solution to this problem is to have a spare sterile debubbling chamber ready and:this can replace the faulty one with only a minute or two of interruption of the perfusion. Obviously, the situation is less acute when the dual debubbling chambers are being used.
Operation of a Bubble Type Pump-Oxygenator
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3. The third matter requiring constant evaluation is the patient's blood volume. Assuming that the venous cannulas are not obstructed, a blood deficit in the gravity and helix reservoirs may be interpreted as indicating hypovolemia. Information about the need for additional blood can be gained by inspection of the conjunctivae and the rapidity of capillary refill after pressure on the skin of the face (done by the anesthesiologist). Monitoring the aortic pressure is of obvious value. We frequently measure this pressure through a small polyethylene tube which has been passed through a needle. Intermittent transfusions of 50 to 100 cc. are given to replace any operative loss during the perfusion. When extracorporeal circulation is discontinued, the blood in the pleural spaces is removed and measured along with any other blood which has been previously removed by aspiration. Obviously, saline irrigations should be avoided up to this point. Blood loss on the drapes is estimated, and the deficit in the helix if any is noted. This blood loss is balanced against the amount given by transfusion into the saphenous vein and into the extracorporeal system. If there is a net deficit, it may be replaced at this time by transfusion from the system into the arterial cannula. Overloading is immediately evident by inspection and palpation of the right auricle or by the caval pressure monitoring device. A final check consists of the weighing of the patient and comparing the postperfusion weight with the preperfusion weight. 4. The fourth aspect of the perfusion requiring frequent checking is the amount of oxygen which is passed into the oxygenating column. The amount is varied between two and three times the blood flow rate depending on the color of the arterial and caval blood lines. With flow rates of 70 to 100 cc./kg./min. and well maintained patient blood volume, satisfactory oxygen supply will be manifested by a red arterial line as well as vena caval blood which is not markedly desaturated. It is advantageous to monitor the superior vena caval pressure because unsuspected elevations in this pressure may occur with possible detrimental effects on the brain. This pressure may be conveniently measured continuously through a small polyethylene tube passed into the innominate vein from an antecubital vein. The patient's temperature is monitored by a rectal telethermometer. During a good perfusion, the temperature will not fall more than a degree, if the helix water bath temperature has been maintained properly. A NEW MODEL VERTICAL STAINLESS STEEL BUBBLE OXYGENATOR
The original plastic bubble oxygenator has a limited debubbling capacity which has necessitated the use of dual oxygen columns and debubbling chambers for high flow perfusions (Fig. 425). This arrangement is usually satisfactory but debubbling remains a problem in high flow runs over extended periods. The use of a steel debubbling canister at the
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Rodman E. Taber, Luis A. Tomatis
Fig. 430. Vertical stainless steel bubble oxygenator for high flow rates. The defoaming chamber at the top contains steel sponges coated with Antifoam. See diagram, Figure 431.
top of the oxygenating column by the Minneapolis group is one solution to the problem. To satisfy the demands of extended high flow perfusions, we have constructed a vertical stainless steel oxygenator (Figs. 430 and 431). This is similar in many respects to that devised by Cooley and his associates. 6 The main components are a vertical column surmounted by a debubbling canister in which is placed stainless steel sponges coated with Dow Antifoam. Oxygenated blood flows from the debubbling canister into the reservoir through the vinyl plastic helix. The helix serves to complete the defoaming and also as a gauge to the amount of blood in the reservoir. A filter of stainless steel mesh is provided at the bottom of the reservoir. A perforated nylon disc in the base of the oxygenation column serves as an oxygen dispersion plate. Steel surfaces in contact with blood are coated with baked-on Teflon. All components are sterilized byautoclaving. Venous blood may be pumped into the oxygenating column from a gravity reservoir or the oxygenator may be placed on the floor and the venous blood can be allowed to drain directly into it, thus eliminating a pump. At the present time, the perfusion blood is warmed by placing the lower two-thirds of the oxygenator in a water bath. Investigations are in progress to see if the heating can be done safely electrically with a coil or jacket around the reservoir. Flow rates of 5000 cc./min. have been handled satisfactorily with this oxygenator.
Operation of a Bubble Type Pump-Oxygenator
Defoamer
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, . III III III
III III III
Oxygenating Column
Reserv~/
Helix
', __ ---
s
Telethermolmet'er~-=:=== ~
A rterial ~~~~ _ _-J.c!J;r~
Fig. 431. Diagram of vertical oxygenator shown in Figure 430. The oxygenating column (black) is 75 cm. in length and 5 cm. in internal diameter. For children, the capacity of the reservoir may be decreased by inserting an oxygenating column of greater diameter. Teflon gaskets (black) are placed between the oxygenating column and the base, and between the reservoir and the base, ROTATING DISC OXYGENATOR
Although our own experience has been only with oxygenators of the bubble type, another popular oxygenator deserves discussion. This is the disc oxygenator of the Bjork type which has been modified and popularized by the Cleveland surgeons Kay and Cross (Figs. 432 and 433). The initial limitations in oxygenating capacity have been overcome with the availability of 9, 13, 17 and 21 inch units. In a recent communication, Cross 7 stated that he was satisfied with the oxygenation in blood flow rates up to 4500 cc./min. Blood priming volumes are reasonable. A 20 kg. child requires 1500 cc. with a 17 inch oxygenator reservoir, and an adult of 70 kg. requires 2000 cc. of blood with a 21 inch unit. In theory, the multiplicity of moving parts and the lack of disposability requiring a tedious cleaning operation are drawbacks, but those who have the apparatus do not seem to object to these difficulties. The entire
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Fig. 432. Photograph of pump-oxygenator apparatus, utilizing the Kay-Cross disc oxygenator and the Pemco pumping unit. (Courtesy of Dr. Frederick S. Cross.)
OXYGEN-C02 INLET ~ ~~~~~~ ARTERIAL LINE ~:::;;;,,--..::~== ~
VENOUS LINE
KAY-CROSS ROTATING DISC OXYGENATOR PUMP
PUMP GRAVITY TO RESERVOIR FROM VENA CAVA PUMPING TO OXYGENATOR PEMCO 3 OR 4 PUMP UNIT
Fig. 433. Diagram of circuits in the disc oxygenator unit. (Courtesy of Pemco, Inc., 5663 Brecksville Road, Cleveland 31, Ohio.)
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oxygenator may be sterilized by autoclaving and hence may be assembled, sterilized and maintained ready for use. SOME REMARKS ABOUT THE SIGMAMOTOR PUMP
Since the beginning of our experience in extracorporeal circulation, we have contiuned to use the Sigmamotor Pump for the propulsion of the blood. The original physically unattractive model (Fig. 425) can now be replaced with the Model TM2 which is enclosed in a case more in keeping with the decor of the operating room. The milking-like action of the steel fingers in the pump have not produced undue trauma to the blood. Even after runs of approximately an hour, it is unusual to find plasma hemoglobin levels of more than 100 mg. per 100 cc. Other types of pumps utilize the roller principle of DeBakey (Fig. 432). A Note on the Calibration of the Sigmamotor Pump. It is of fundamental importance properly to adjust the plates opposite the fingers in the Sigmamotor pump before calibration, in order to secure delivery of the desired flow. This is done by holding the arterial line filled with saline 2 feet above the pump and adjusting the plate until the level is maintained during the complete revolution. The screw is then given an additional quarter of a turn to assure occlusion. This maneuver has the effect of making the plate parallel to the axis of the fingers so that uniform pressure will be produced by all the fingers. Even the properly adjusted occlusive pump may fail to deliver the full anticipated flow if the arterial cannula used for the perfusion is smaller than that used for the calibration. Mechanical Failure of the Pump. Obviously, failure of the pumpoxygenator for any reason during a perfusion could be disastrous. Electrical failure is unlikely, because of the stand-by source provided in most modern operating rooms. The old model Sigmamotor pump, like the Model T Ford, had a hand crank which could be used in the event of power failure. The new model has no crank. Even with the power supply intact, an apparatus as complicated as the Sigmamotor pump may fail for a mechanical reason. The group at Mount Sinai HospitalS of New York reported one instance of mechanical failure of their Model TM2 and they mentioned that in 1700 cases of cardiopulmonary by-pass in this country, there had been another failure. Mechanical failure has occurred once in our series of 300 perfusions, due to uncoupling of the venous pump from the motor. In this instance, the heart had been stopped with acetycholine, but fortunately the cardiotomy had not been made. The heart was massaged and it resumed its beat. In the meantime, a Model TM2 was brought in from an adjoining room and the latex tubes of the pumping arrangement were quickly transferred. The operation continued and the patient suffered no ill effects. The patient of Zaroff, Kreel, Kavee and Baronofsky, 8 who was being operated on for mitral insufficiency, did not survive after the pump fail-
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.j...... ••••-;y. From Venous Reservoir
y
!
Arterial Line To Patient
Fig. 434. Diagram of Y-connectors for parallel arrangement of Sigmamotor pumps for stand-by purposes. (Courtesy of Zaroff et al. 8 and Surgery.)
ure mentioned above. To prevent this catastrophe, they have suggested that two Sigmamotor pumps be placed in parallel (Fig. 434). The venous and arterial lines are connected by Y connectors as indicated. The arterial side of the nonfunctioning pump is primed before the perfusion begins and the usual calibration is carried out. Because the pumps are occlusive, it is possible to maintain perfusion with either pump merely by stopping one pump and turning on the other. Only about 100 cc. of blood is needed for the priming of the stand-by pump. These authors have suggested the following in the prevention of failure during perfusion with the Sigmamotor pump: (1) adequate fusing, (2) lock type of electrical outlet plugs, (3) frequent check of oil levels in motor, gear box and pump heads, (4) avoidance of overloading the torque capacity (the Venier dials should not be pushed past the maximum setting) and (5) careful investigation by a factory representative of overheating or any unusual noises coming from the gear box or pump heads. SUMMARY
The assembly and operation of a bubble oxygenator of the DeWallLillehei type has been described, and some lessons learned in 300 perfusions have been reported. A compact stainless steel model of a bubble oxygenator is undergoing clinical trial. Some data about a practical disc type oxygenator are presented. REFERENCES l. Jones, R. E., Donald, D. E., Swan, H. J. C., Harshbarger, H. G., Kirklin, J. W. and Wood, E. H.: Apparatus of Gibbon Type for Mechanical Bypass of
Operation of a Bubble Type Pump-Oxygenator 2. 3. 4. 5. 6. 7. 8.
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Heart and Lungs: Preliminary Report. Proc. Staff Meet. Mayo Clin. 30: 105, 1955. Cross, F. S., Berne, R. M., Hirose, Y., Jones, R. D. and Kay, E. B.: Evaluation of a Rotating Disc Type Reservoir-Oxygenator. Proc. Exper. BioI. & Med. 93: 210, 1956. Lillehei, C. W., DeWall, R. A., Read, R. C., Warden, H. E. and Varco, R. L.: Direct Vision Intracardiac Surgery in Man Using a Simple Disposable Artificial Oxygenator. Dis. of Chest 29: 1, 1956. Clowes, G. H. A. Jr., Hopkins, A. L. and Neville, W. E.: An Artificial Lung Dependent upon Diffusion of Oxygen and Carbon Dioxide Through Plastic Membranes. J. Thoracic Surg. 32: 630, 1956. Tomatis, Luis, Taber, R. E., Lam, C. R. and Green, Edward: Experimental Studies with Low Oxygen Flow Rates in Bubble Oxygenator. Henry Ford Hospital Bull. 6: 341, 1958. Cooley, D. A., Belmonte, B. A., Latson, J. R. and Pierce, James: Bubble Diffusion Oxygenator for Cardio-Pulmonary By-Pass. J. Thoracic Surg. 35: 131, 1958. Cross, F. S.: Personal communication to the authors, June, 1959. Zaroff, L. I., Kreel, Isadore, Kavee, D. J. and Baronofsky, I. D.: Mechanical Failure During Extracorporeal Circulation: A Method for Prevention. Surgery 45: 645, 1959.
Henry Ford Hospital Detroit 2, Michigan