Surgeons break down separating conjoined twins
Two contradicting theories exist to explain the origins of conjoined twins. The older and most generally accepted theory is fission, in which the fertilized egg splits partially.
The second theory is fusion, in which a fertilized egg completely separates, but stem cells which search for similar cells find like-stem cells on the other twin and fuse the twins together. However, rather than fission or fusion the defect leading to conjoined twins may well be a coalescence by overlapping of closely contiguous twin embryonic axis formative fields within a single embryonic disc It is presently thought that these factors are responsible for the failure of twins to separate after the 13th day after fertilization.
Conjoined twins can be artificially generated in amphibians by constricting the embryo so that two embryos form, one on each side of the constriction. There are no documented cases of conjoined triplets or quadruplets. Surgery to separate conjoined twins may range from relatively simple to extremely complex, depending on the point of attachment and the internal parts that are shared. Most cases of separation are extremely risky and life-threatening. In many cases, the surgery results in the death of one or both of the twins, particularly if they are joined at the head, craniopagus
It is a multidisciplinary team approach involving extensive medical work-up on patients, multiple meetings and discussions with all the involved specialities and supporting staff, involvement of parents, Psychosocial counselling of parents, rehearsal of the planned surgical procedure, and media contact prior to Surgery. The rationale for deferring surgery should include single heart, major communicating hearts or major anomalies Recommended i.v. doses of anaesthetic agents for the combined body weight of the twins are usually halved and then divided into two equal doses to be administered to each twin.
Reduced incremental doses are titrated against response and help minimize the dangers of compounding drug effects in one twin however, if surgery for separation is planned, careful angiographic or radio isotopic imaging of the cross-circulation is necessary for estimation of the cardiac output percentage which is exchanged, as one of the twins might be dependent on the other’s circulation for survival.
It should also be recognized that the degree of cross-circulation is dynamic and highly dependent on both twins’ relative systemic vascular resistance. Anaesthesia for conjoined twins, either for separation surgery or for MRI or other evaluation procedures is an enormous challenge to the paediatric anesthesiologist. This is an extra challenging surgery because we the anaesthesiologists need to care for two patients at the same time instead of just one.
