Thorax: first published as 10.1136/thx.20.6.540 on 1 November 1965. Downloaded from Thorax (1965), 20, 540. A low priming volume oxygenator for bloodless priming in cardiopulmonary bypass E. PROCTOR AND A. H. DE BONO' From tl/e Thoracic Research Department, Guy's Hospital, London The oxygenator described here arose out of the need to dispense with homologous blood in animal perfusions. It was considered that this could best be attained with an oxygenator having a priming volume sufficiently small to allow the use of isotonic solutions without undue dilution and consistent with full gas exchange and adequate temperature control. It was recognized that modifications to existing machines were unlikely to reduce the priming volume sufficiently to allow of total haemodilution without a significant reduction in their perform- ance. As a result the following design was evolved (Figs I and 2). copyright. An annular bubble column was devised as the most practical method of attaining efficient gas exchange with a small amount of blood. The annulus increases 'lift' and mixing in the vertical tube and allows of full oxygenation at flows of up to 2 5 1./min. (in the small model shown here) http://thorax.bmj.com/ at normal temperature with only 300 ml. of blood in transit through the annular column. Since temperature control is an essential func- tion of cardiopulmonary bypass, both in normo- thermic and hypothermic perfusions, an appreci- able volume of priming blood is usually involved in heat exchange. This volume was eliminated by using the inner surface of the annulus for heat on September 24, 2021 by guest. Protected exchange. The efficiency of the bubble type of oxygenator is usually offset by the large volume of blood re- quired for debubbling by settling reservoirs after antifoaming. This volume was considerably reduced by efficient antifoaming, by low-pressure filtration, and by the use of a sump reservoir with an additional filter which together prevent vortex formation in the reservoir. 'Present adcdress: Department of Experimental Surgery, Hammer- smith Hospital, London, W.12 FIG. 1. Side view of oxygenator showirg stainless steel heat exchanger in vertical buibbling column. 540 Thorax: first published as 10.1136/thx.20.6.540 on 1 November 1965. Downloaded from A low priming volume oxygenator for bloodless priming in cardiopiulmonary bypass 541 - From water bath Heat Anti-foamed stainless steel wool Silastic valve .I. Detachable cartridge - ; 1-~ = Reservir Filter A ......Sump Recirculating tube .........-Filter 'B' FIG. 2. Diagram of oxygenator showing path offoam up the vertical annulus and into the horizontal defoaming copyright. cartridge. To arterial pump http://thorax.bmj.com/ on September 24, 2021 by guest. Protected FIG. 3. View of oxygenator showing valve control mechanism. The.far side valve is open into the far cartridge. Thorax: first published as 10.1136/thx.20.6.540 on 1 November 1965. Downloaded from 542 E. Proctor and A. H. De Bono SVE SILASTIC WASHER VALVE CLOSED VALVE OPEN GAS OUTLE.T FIG. 4. Diagram of twin cartridges from above showing path of foam from annulus into one of the defoaming cartridges. The valve mechanism allows only one cartridge to be used at a time and permits of the replacement of a used cartridge without stopping the blood flow by releasing the screw at the distal end of the cartridge. A theoretical disadvantage of bubble oxygen- As a result of these features the oxygenator hascopyright. ators has been the limited life of the antifoaming a priming volume of 500 ml. plus 250 ml. in the apparatus in extended perfusions. This problem arterial and venous lines, a total of 750 ml. This is has been overcome in two ways: (1) An improve- sufficient to initiate and maintain total bypass of ment in antifoaming properties and adhesion due up to 2-5 1./min. in dogs of 20 to 30 kg. The to baking 20°o Antifoam A on to the surface of system can therefore be primed with buffered scrupulously clean stainless steel wool at a electrolyte solutions (Ringer-Locke, Ringer- http://thorax.bmj.com/ temperature of 2000 C. for four to six hours. This Lactate), low molecular weight dextran, or com- gives a 'rubbery' texture to the silicone surface binations of these while maintaining full gas and improves both the antifoaming and adhesive exchange and adequate temperature control for qualities of the surface. The usual technique of normothermia, mild hypothermia, and slow dipping, drying, and autoclaving (McGregor, profound hypothermia. 1960) imparts a less adherent, greasy surface. It As an approximate guide to the degree of should be noted, however, that this improvement haemodilution involved, the average haematocrit is not sustained at higher temperatures, since at values for the usual one to two hours' total per- 3200 C. and above the silicone surface becomes fusion are: pre-bypass. 4400 ; during bypass, on September 24, 2021 by guest. Protected brittle and fragments with movement. The surface 330%; and 24 hours after bypass, 41 %. At no time resulting from baking at 2000 C. is sufficient for has it been necessary to add blood either during up to six hours' efficient antifoaming with the bypass or post-operatively. type of cartridge described. (2) By using twin anti- Although the oxygenator has so far been used foaming cartridges (Figs 3 and 4) which can be only for animal perfusions, a larger model switched alternately into the foam path, the anti- designed for flows of 4 to 5 1. /min. with an foaming time can be simply doubled to 12 hours. estimated priming volume of 12 to 1 5 1. Ringer- Should the need arise for extended perfusions Locke, etc., is in hand. beyond 12 hours as in long-term, partial, closed- chest perfusions for circulatory support the DESCRIPTION cartridges can be replaced without stopping the perfusion, thereby conferring an indefinite running The annulus for oxygenation and heat exchange is time limited only by the trauma to the blood. formed by the insertion of a thin-walled stainless steel Our experience in this field is as yet limited to tube into a vertical perspex tube. It is centralized and 10 hours. supported by the gas sinter at the bottom and a silastic Thorax: first published as 10.1136/thx.20.6.540 on 1 November 1965. Downloaded from A low priming volume oxygenator for bloodless priming in cardiopulmonary bypass 543 washer at the top. Sucker reservoir and venous lines Reservoir enter at the bottom of the tube. Length, 11-5 in. Width at upper end, 6 in. OXYGENATION Gas, usually 97 % oxygen and 3 % Width at sump, 2-5 in. carbon dioxide, enters through a sinter to give bubbles Depth, 2 5 in. of approximately 3 mm. diameter which foam and Volume, 1 litre. lift the blood up the annulus to a large port at the Sump top of the column where it is directed by the valves Depth, 4 in. into one of the antifoaming cartridges. With a ratio Internal diameter. 1-25 in. of 4 to 5 litres of gas flow per litre of blood flow the Filters oxygen saturations are 97 to 99% (arterial) and 70 to 80 gauge mesh stainless steel. 74% (venous) at flows up to 2 5 1./min. in 20-30 kg. Cartridges dogs at normothermia. Length, 11 in. HEAT EXCHANGE The stainless steel tube forms the Internal diameter, 2-5 in. inner surface of the annulus, and water from the Sinter appropriate water-bath emerges at the bottom via the 50 holes 0-021 in. diameter. narrow central tube and flows up between it and the inner surface. The efficiency of heat exchange METHOD OF USE obviously depends on a variety of factors-water flow, blood flow, temperature gradient, size of animal, etc. The reservoir is primed with 750 ml. of fluid, Ringer- -but with a dog weighing 20 kg., 2 1./min. blood Locke, Ringer-Lactate, or low molecular weight flow, and a water-bath temperature of 1-3° C. the dextran (Rheomacrodex5). The pH at 200 C. of temperature of the blood drops approximately 70 C. Ringer-Locke is 7-52; of Ringer-Lactate, 6-55; and in transit through the annulus in the range 200 C. of 10% low molecular weight dextran in dextrose, to 360 C. This will result in cooling the animal at 5x35 (mainly due to the dextrose). We normally use a 0.70 C./min. over the same range. Equally, a water- mixture of 550 ml. Ringer-Lactate and 200 ml. dextran. The pH of this mixture is 6-39 at 200 C. and bath temperature of 38.50 C. will maintain normo- copyright. thermia. 1 mEq of sodium bicarbonate converts this to 7-39. Since the liver is less able to metabolize lactate at ANTIFOAMING This occurs in the sloping cylindrical low temperatures, we tend to use Ringer-Locke in cartridges. The cylindrical shape allows of a good fit place of Ringer-Lactate for profound hypothermia. for the balls of stainless steel wool, a constant area of The arteriovenous loop is filled by attaching the silicone in contact with the blood, and no 'short-cuts' venous end of the loop to the re-circulating tube at for the foam. The rate of advance of the foam through the side of the reservoir and pumping the fluid http://thorax.bmj.com/ the cartridge is about 1 inch per hour. through the lines and back into the reservoir. The venous line is then connected to the bottom of the RESERVOIR The defoamed blood enters the reservoir bubbling tube. With the gas line, sucker reservoir line, at the distal end. This reservoir has a sloping floor and heat exchanger lines appropriately connected, the and is narrower at the lower end.