Toxins in open heart surgery

Abstract

From the beginning of open heart surgery, there have been sporadic cases in which patients and sometimes groups of patients, have shown signs and symptoms of toxicity. Patients who undergo heart surgery with cardiopulmonary bypass do less well than those who have a similar operation without the use of bypass apparatus. It is common for the patient who has had open heart surgery performed with the use of heart/lung machines to be on the ventilator for 12 hours and to be in the intensive care ward for 24 hours. Postoperative cerebral complications, postoperative bleeding and some degree of multi-organ impairment are all common sequelae of open heart surgery. These complications are not commonly seen in patients operated on without bypass support nor in cases operated on using surface cooling and so-called closed operations, e.g. closed mitral valvotomy. Some of these problems are known to be associated with microemboli¹ but others appear to relate to materials liberated from the bypass apparatus or to some chemical change which occurs in the blood during operation. Blood travels about 20 miles through the tubing during an open heart operation and is thereby in contact with a vast area of potentially bio-incompatibile material. In addition to this, the various circulating and suction pumps will release particulate matter into the circulation from wear of the tubing. The opportunities for toxic materials to be leeched from the extracorporeal apparatus and for the occurrence of mechanical trauma, both to the formed elements of the blood and to the plasma proteins² are considerable. The tubing of the extra-corporeal apparatus is commonly made of polyvinyl chloride (PVC). This heterogenous material consists of pellets of the polymer separated by plasticizers and various fillers. The plasticizers are often complex mixtures. Many of the components of these are themselves highly toxic and some have a significant solubility in an aqueous electrolyte solution. The roughness of the interior wall of a PVC tube is illustrated in Figure 1 in which the size of a red cell is compared with surface irregularities of various materials commonly used in bypass circuits. Because PVC and many of the other plastics used are heat labile they have to be sterilized by methods other than steam autoclaving. The pathologists in charge of sterilization would prefer us to use steam sterilization although we have reservations about this technique as well, since water softeners and other materials are added to the boilers which allow solid materials to pass into the hospital steam rather than furring up the boilers. Deposits of calcium and other materials are shown in Figure 2 on the inside of a heat exchanger viewed under ultra violet light.