A Compact Single-Unit Oxygenator,

Transcription

1 A Compact Single-Unit Oxygenator, Reservoir, and Heat Exchanger for Emergency Cardiopulmonary Bypass R. D. Sautter, M.D. T he apparatus described in this paper was designed for use in the hypothertnic low-flow hemodilutioti technique of total body perfusion.* It had been originally intended for use only in emergency cardiopulmonary bypass, such as would be required for pulmonary embolectomy. However, because of its efficiency and ease of operation, it has now been adopted for use whenever cardiopulmonary bypass is necessary. The unit has proved completely satisfactory both experinientally and in fifteen consecutive clinical perfusions at St. Joseph's Hospital, Marshfield, Wisconsin. The instrument has the following advantages: (1) it can be assembled in 15 minutes, and the entire unit-heat exchanger, reservoir, and oxygenator-with the defoaming canister is sterilized assembled; (2) it is compact and far less cumbersome in the operating room than most heart-lung machines (Fig. 1); (3) it is easily cleaned and requires very little maintenance: and (4) there are fewer disposable supplies necessary than in most heart-lung machines, thus the cost of each perfusion is lower. DESCRIPTION General Specifications. The entire unit is constructed of stainless steel. All joints are silver-brazed, and the surfaces in contact with the blood are highly polished to reduce trauma to the red blood cells. Table 1 shows the volume of the various chatnbers of the unit. The capacity of the defoaming canister? is 1,300 ml.; however, when the unit is in operation it contains only 0 cc. of blood. Water is circulated through the heat-exchanging jacket and canister at 8,000 cc. per minute. Kimray$ tubs supply the water at three temperatures: 4"C., 22"C., or 45 C. From the Marshfield Clinic and Marshfield Clinic Foundation, Marshfield, Wis. Received for publication June 1, 'Available from Arthur D. Little, Inc., Cambridge, Mass. +Available from the Phelan Manufacturing Corp., Minneapolis, Minn. $Available from Kimray, Inc., Oklahoma City, Okla. 760 THE ANNALS OF THORACIC SURGERY

2 NOTE: Oxygenator for Emergency Bypass FIG. 1. The single-unit oxygenator, reservoir, and heat exchanger assembled and ready for operation. A, uenotis inlet; B, oxygenating column; C, jacket d ~ - foaming canister; L), column delivery line; E, helical reservoir; F, arterial outlet; G, arterial line; H, cardiotomy sucker reservoirs; 1, sticker lines; J, oxygen line; K, vacuum line for suckers; I-, canister level indicator; M, column vent; N, ruater inlet; 0, water outlet; P, water jacket. TABLE 1. VOLUME OF CH.4MBERS OF UNIT Chamber Volume (cc.) Reservoir (blood) 750 Canister (full) (blood) 1,300 Heat exchange jacket of unit (water) Heat exchange jacket of canister (water) VOL. I, NO. 6, NOV.,

3 SAUTTER Assembly. A 16-inch length of Mayon tubing with an internal diameter of 2.5 inches is slipped over the unit and made blood-tight with hose clamps. Although the tubing fits snugly over the unit, it may be properly positioned without difficulty. The stainless-steel helix will indent the Mayon tubing after autoclaving and form a watertight seal. This, in effect, functions as any other helical bubble trap. A 4-inch length of Mayon tubing with an internal diameter of 1.5 inches connects the oxygenating column to the bottom of the defoaming canister. Hose clamps are used to insure a blood-tight seal. A 24-inch length of 3/8- inch-internal-diameter Mayon tubing is connected to the outlet at the bottom of the canister and taped to the canister side. This serves to indicate the level of blood within the canister. A 12-inch length of 1 /4-inch-internal-diameter Mayon tubing is connected to the vent in the upper part of the unit and is also taped to the side of the canister. This vent,balances the air pressure within the reservoir when the blood level fluctuates. Before autoclaving, the blood outlet, the two blood inlets, and the oxygen delivery tube are covered with gauze held in place with masking tape. The gauze is removed just before connection of the appropriate lines. The pump technician need not be gowned or gloved to preserve sterility when making these connections. Cultures done before and after each pump run have shown no growth. The water connections to thc heat exchanger are made after all other connections are secure. The water enters the heat exchanger via the water inlet at the bottom of the unit and leaves via the outlet at the upper end. A connection is made between this upper outlet and the water inlet at the lower part of the canister. Water then circulates through the jacket on the defoaming canister and is discharged from the upper water outlet and returned to the source. The canister is assembled in the manner described by DeWall et nl. [ll. OPERATION Figure 2 shows the internal construction of the apparatus. Blood from the venae cavae, or right side of the heart, enters the oxygenator via one of the two blood inlets (the remaining blood inlet is used for the cardiotomy suction return). This venous blood is mixed in the oxygenating column with a stream of oxygen delivered at between 5 and 10 liters per minute, depending on the flow rate. The oxygen is disbursed by a perforated Mylar disc. The release of carbon dioxide and saturation of the hemoglobin occur as in all bubble oxygenators. Oxygen saturation of the blood ranges from 9OY0 to 1o4yO, and averages 96.5%. This mixture of blood and gas is carried to the defoani- 762 THE ANNALS OF THORACIC SURGERY

4 NOTE: Oxygenator for Emergency Bypass V FIG. 2. Internal construction of the apparatzis. ing canister, where the blood is defoamed by silicone-coated stainlesssteel sponges which are enclosed in a fine mesh nylon screen [ll. The oxygenated blood is delivered to the unit through Mayon tubing, which contains a dependent loop. This loop provides a,bubble-free stream of blood from the canister to the reservoir. This is an additional protection against gas embolism, and during a normal operation there are no bubbles within the reservoir. In the laboratory, bubbles have been allowed to enter the reservoir via this tubing, and always have been quickly disbursed at the blood interphase, even though the reservoir is not coated with silicone. After entering the.blood inlet, the blood is gently carried down the helix to the blood level in the reservoir. Saturated blood is withdrawn from the reservoir through the blood outlet and returned to the patient by any appropriate pumping mechanism. Heat Exchange. Heat is exchanged in two areas of the unit and, to a lesser degree, in the jacketed defoaming canister. As the venous blood and oxygen mixture ascends the oxygenating column, the blood VOL. I, NO. 6, NoV.,

5 SAUTTER is in contact with the inner surface of the heat exchanger. After being defoamed, the blood is in contact with the heat-exchanging surface of the canister. The blood is then delivered to the unit and contacts the outer surface of the heat exchanger as it travels down the helix. As the blood accumulates in the reservoir before being returned to the patient, heat is again exchanged. The heat exchanger is an integral part of the oxygenator and reservoir; thus, there are no parts to assemble. Its cost is about onefourth the total price of the unit, and it fulfills all the characteristics of an ideal heat exchanger as descri,bed by Peirce [2] (Table 2). TABLE 2. COMPARISON OF PRESENT UNIT WITH CH..\RACTERISTICSa OF AN IDEAL HEAT EXCHANGER Safety Characteristics, Ideal Heat Exchanger No internal leaks Visibly clean Atraumatic to blood Efficiency Minimum surface area Low priming volume Adaptable to size of patient Easy to assemble Low in cost Present Unit Fail-safe: all joints external Yes; all surfaces easily inspected Blood not exposed to additional trauma Blood not exposed to any additional surface area for purpose of heat exchange No prime used See text Integral part of unit; no assembly necessary Yes "As designated by Pcirce t21 Safety. Internal leaks (mixing of blood and coolant) are not possible with this heat exchanger, as all joints on the heat jacket are external. The unit is therefore fail-safe. The heat exchanger causes no additional trauma to the blood. The unit is visibly clean. The inner wall of the heat exchanger is the oxygenating column; the outer wall forms the inner wall of the reservoir. All these surfaces can be easily inspected and exposed for cleaning. Eficiency. Since the heat exchanger is an integral part of the 764 THE ANNALS OF THORACIC SURGERY

6 NOTE: Oxygenator for Emergency Bypass I K) IS S SI LENGTH OF PUMP RUN IN MINUTES FIG. 3. Mean cooling and warming temperatiire curves in fifteen clinical perfusions done with the single-mit oxygenator, reservoir, and heat exchanger. oxygenator and reservoir, it is not necessary to expose the blood to any additional surface for the purpose of heat exchange. For the same reason, the priming volume of the heat exchanger is zero. The priming volume in the reservoir is precooled to about 4"C., which increases the efficiency of cooling. The unit is usually primed with 16 ml. of 5% glucose in water per kilogram of body weight, as suggested by Zuhdi, Carey, and Greer 141. The heat exchanger is adaptable to the size of the patients. They receive an amount of 5% glucose in water at the beginning of the perfusion which is in proportion to their weight. Figure 3 demonstrates the mean cooling and warming curves of patients in whom this unit has been used. The average time to cool to 30 C. was six minutes, even though the patients were of varying weight. In patients weighing 25 kg. or less, 500 cc. of freshly drawn beparinized blood is added to the usual priming volume of 5% glucose in water. The proportionally larger volume of precooled fluid infused accounts for the more rapid fall in body temperature. Rewarming occurs at a slower rate than does cooling, due to the thermal limits to which blood may be heated without damage. TECHNIQUE FOR CLINICAL PERFUSION We employ the low-flow hemodilution hypothermic technique of total body perfusion. After the proper connection of the arterial and venous lines coming from the patient are made, partial perfusion is started at a rate of cc. per kilogram of body weight per minute. The VOI.. I, NO. 6, NOV.,

7 SAUTTER arterial pressure is closely monitored on an oscilloscope during this period to insure that an excess amount of blood is not being withdrawn and that a partial perfusion pressure is being maintained. When the midesophageal temperature reaches 30 C., total cardiopulmonary bypass is started, and the arterial flow is balanced against the available venous return. The arterial pressure ranges from 25 to 60 mm. Hg and averages about 40 mm. Hg. We do not become concerned unless the arterial pressure rises above 100 mm. Hg, for at this point the vascular space being perfused has,become smaller. This has occurred in two of our patients, and in these patients the acidosis was more severe than in similar circumstances when the perfusion pressure was below 100 mm. Hg. The midesophageal temperature is maintained between 25 C. to 30 C. in most instances. As the perfusion progresses and the peripheral tissues cool, there is a gradual decrease in the available venous return and therefore a decrease in the arterial pump flow. The flow has varied from 15 to 75 cc. per kilogram per minute, but averages about 40 cc. per kilogram per minute. Although the flow rate decreases, it has never been necessary for us to add fluid to the unit. Blood is replaced as it is lost. A total flow of 3,500 cc. per minute is seldom exceeded, but we have maintained flows of 7,000 cc. per minute for short periods of time and encountered no difficulty with oxygenation or defoaming. In the laboratory we have not encountered a large enough animal to exceed the limits of this unit. We are now in the process of accurately determining the maximum flows for this unit. CLINICAL RESULTS Table 3 summarizes the physiological data concerning the fifteen consecutive clinical perfusions done using this apparatus. Seven of the patients had congenital heart disease and eight had acquired heart disease. The severity of their lesions varied. Among those having acquired lesions were three patients who had had pulmonary embolectomies, two of whom are still alive and well without disability. The success of one of the pulmonary embolectomies [3] was directly related to the fact that this apparatus can be ready for use in fifteen minutes. The patients' body weights varied from 7.6 to 93 kilograms and averaged approximately 50 kilograms. The longest perfusion time with a surviving patient was 132 minutes, the shortest time was 21 minutes, and the average perfusion time was 58 minutes. The plasma hemoglobin rose approximately 1.6 mg. per minute of perfusion. This level of plasma hemoglobin is greater than desirable but is probably not 766 THE ANNALS OF THORACIC SURGERY

8 I ~~ TABLE 3. PHYSIOLOGICAL DATA, 15 CONSECUTIVE CLINICAL PERFIJSIOSS Pt. Lesion (kg.) in water) Partial Perfusion Cool to Priming Flow 30 C. Length Volume During (startof Warm of (cc. of 5% Cooling total to Pumo Weight glucose 1 c.c.ikg. ni in. ) bypass1 10 C. Run (min.) (min.) (min.) Base Excess Highest at Time Plasma of De- Hemo- cannuglobin lation (mg.1 cmeq.1 I00 cc.) I..) Results A. C. IASD B. S. Aortic stenosis , K. M. IASD; anomalous venous 300~ return P. s. Aortic stenosis (Starr-Edwards valve, K. L. Mitral stenosis B. G. Pulmonary embolus R. R. IASD ~ <:. D. IASD; anomaloiis venous return T. M. lotal anomalous venous , drainage J. S. IASD v. IASD; pulmonary stenosis ). M. Left ventricular aneurysm C. J. Pulmonary embolus J. F. Pulmonary embolus A. P. Aortic stenosis (Gott valve) nplus 500 cc. blood. bplus 475 cc. blood > 5 ) I4 42 X 21 I I Alivc Dead.\live ;\li\e ;\live ;\live.lli\ e ;\live Dead -_

9 SAUTTER related to this unit but to the type of cardiotoiiiy suction aid pump used. We have not, however, encountered difficulty with oliguria or anuria. All patients had a iioriiial plasma hemoglobin level six hours following the procedure. The acid-base status of each patient was measured by the Xstrup method before bypass, every 30 minutes during bypass, at the termination of bypass, and at six and twenty-four hours following the procedure. Nearly all of the patients had mild acidosis at the termination of bypass. The average base excess was -3. All patients were given appropriate amounts of sodium bicarbonate when the base excess was -5. The question as to whether air eiiibolization occurs during the use of this apparatus is answered by the fact that all of the surviving patients were awake and verbalizing on the operating table immediately following the procedure. Neither of the two deaths in the series were related to the perfusion. A CK N 0 IYLEDGMEN TS The author wishes'to thank Mr. R. Biechler, Mr. L. Ferries, Mr. J. Illatson, and Mr. F. Wenzel for their assistance in the development of this apparatus. REFERENCES 1. DeWall, R., Lillehei, C. W., Hodges, P., Long, D., Wade, J., antl Cartlozo, R. Description of the helical reservoir bubble-type pump oxygenation for hemodilution hypothermic perfusion. Ilk. Chat. 44: 1 IS, Peirce, E. C. A simplified heat exchanger for perfusion hypothermia. Arch. Siirg. (Chicago) 84:329, Sautter, R. D., antl Emanuel, D. A. Pulmonary embolectomy utiliing cardiopulmonary bypass. Amer. J. Surg. 109:493, Zuhdi, N., Carey, J., and Greer, A. Hemotlilution for body perfusion. Arkansas Med. J., p. 88, THE ANNALS OF THORACIC SURGERY