Anesthesia for conjoined twins

Introduction

Anesthesia for conjoined twins may range from a very straightforward pediatric anesthetic procedure to one of the most daunting and challenging procedures faced by any pediatric anesthesiologist.

This rare but fascinating congenital problem is of considerable importance to anesthesiologists. In medical literature, there are ever-increasing reports of anesthesia for conjoined twins, both general and regional. From the twins’ initial admission, anesthesiologists should be involved in the care and decision-making procedures planned for these infants. At any stage of the hospitalization, anesthesiologists may be called on to provide resuscitation for the infants or to anesthetize them for investigations or procedures. These may be related to their conjoined state or for some other pathology in one or the other twin, such as pyloric stenosis, or adenoidectomy for upper-airway obstruction ( ). Management of conjoined twins is a multidisciplinary exercise involving many specialties, and the anesthesiologist is an integral part of this team. Likewise, it is essential that anesthesiologists establish a team approach within their own discipline, so that each specialist knows precisely the roles of all individuals at the various stages of the procedures. The separation of a set of conjoined twins is the best example of teamwork that any hospital staff will experience.

Four major centers in the world have described their experiences and outcomes in their management of conjoined twins ( ; ; ; ; ) ( Table 39.1 ). Many of the cases and examples used and described in this chapter are from the Red Cross War Memorial Children’s Hospital in Cape Town, South Africa, where 49 sets of symmetric and asymmetric conjoined twins have been managed over 45 years (1964 to 2009).

Incidence

Because of the significant number of conjoined twins who are aborted or who are stillborn, the exact incidence is not known, but the reported incidence worldwide is estimated at 1:50,000 to 1:100,000 live births, with a higher incidence of 1:14,000 to 1:25,000 experienced in Africa and Asia ( ). Of those that are born, many may have congenital abnormalities that are incompatible with life. The presence of associated congenital anomalies in live twins is common. Congenital diaphragmatic hernia, pulmonary hypoplasia, congenital heart disease, anomalous hepatic arterial and venous drainage, biliary tree anomalies, bowel atresia, Meckel’s diverticulum, complex urogenital anatomy, and spinal dysraphism have all been reported.

Historical perspectives

Conjoined twins are one of nature’s greatest enigmas. Cave drawings, pottery, figurines, and folklore indicate that conjoined twins have occurred since prehistoric times. Embryonic duplication also occurs in plant and other animal forms of life ( Fig. 39.1 ) ( ). The famous and most celebrated pair of conjoined twins, Chang and Eng Bunker, who were joined at their xiphisterna, was born in Siam (now Thailand) in 1811. Because of their fame and the rarity of this pathology, the term Siamese twins has become synonymous with conjoined twins. Over time, the bridge of skin and tissue between them stretched, and they were able to stand side by side. The twins were taken to the United States, where they were on display by Phineas T. Barnum in his circus. Surgery for separation was deemed too risky unless one of the twins was to die. The Bunker twins lived very interesting lives—they married sisters and fathered 22 children between them. They died within hours of each other at 63 years of age ( ). Interestingly, the twins who have become most famous have all remained conjoined, whereas there is very little literature on the lives of those who have been separated. reported on the long-term results of ten separations, as have , with their experiences studying ischiopagus twins over 23 years. The first set of omphalopagus twins separated at the Red Cross Children’s Hospital now each has children of their own ( ; ).

The first successful separation of conjoined twins was performed by Konig in 1689, when he separated omphalopagus twins by slowly tightening an encircling band around the connection until it necrosed the connecting bridge. The first successful separation of thoracopagus twins with a conjoined heart was reported in 1979 when, after the interatrial bridge was interrupted, there was a single survivor ( ).

During the 1960s and 1970s, emphasis in the perioperative management of conjoined twins was on preoperative discussions and planning, dress rehearsals, and on the then-new techniques of invasive intraoperative monitoring for blood loss and hemodynamic status ( ). From the 1980s onward, most improvements have occurred in obstetric and fetal ultrasound; fetal and neonatal surgery; magnetic resonance imaging (MRI); contrast computed tomography (CT); numerous radiographic technologic options to help delineate anatomic variations in different twins; anesthetic advances of oximetry, capnography, and agent analysis; and techniques for monitoring brain oxygenation and blood flow.

For the induction of omphalopagus twins, Allen and colleagues described the use of cyclopropane and oxygen, supplemented by ether via the open-drop method ( ). He describes the attempts at intubation by holding one infant above the other to facilitate easier intubation as a “near-fatal mistake.” In this position, the upper twin became pale and apneic, whereas the condition of the lower infant rapidly deteriorated, and it became plethoric. Once they were returned to their normal position, they were successfully intubated. He comments that “there are few vital signs available for monitoring infants of this size. The most important signs are respirations, color, and muscle tone.” Both infants survived the surgical separation.

The anesthesia provided to separate the first set of twins in 1967 in Cape Town, South Africa, was described as “uneventful” ( ). Preoperative investigations in these omphalopagus twins indicated that there was no cross-circulation between the infants, and this was confirmed at the induction of anesthesia, when the pancuronium given to one infant had no effect on the other.

In Furman’s report ( ), intubation on a set of xiphopagus twins was performed when both infants were awake, and vascular cannulation was done when they were under local anesthetic. In Jarem’s classic paper, he describes the double breathing circuit fashioned from readily available parts of anesthetic equipment ( ).

described his experience with craniopagus twins. His group used two anesthetic teams, but only one anesthetic machine with a nonrebreathing Jackson-Rees breathing system from the gas outlet leading to two T pieces. Monitoring included electrocardiogram (ECG), Doppler arm-cuff pressures, esophageal stethoscopes, and rectal telethermometers. Each infant received preoperative atropine, and they were induced simultaneously with halothane, nitrous oxide, and oxygen. He continued to describe the 15-month preparation time before their separation. This was successfully achieved, but he describes the anesthetic challenges as severe hemorrhage and maintenance of a clear airway with obstruction from secretions, kinking, or accidental extubation. commented on the need for modification of the breathing circuit to accommodate the process of ventilating neonatal conjoined twins simultaneously and stated that adequate intravascular fluid replacement was essential to prevent hypotension at separation. They also commented on the intraoperative challenges of these infants.

Diaz and Furman, in their well-known paper on the perioperative management of conjoined twins, highlighted many factors that are now integral to the care of these patients ( ). Advances in anesthetic equipment, monitoring, and drugs (inhalational or intravenous) provide options for anesthesia that earlier anesthetic specialists did not have. Similarly, outcomes for surgical procedures in these patients have improved. The developments in pediatric intensive care have had a positive effect on both the preoperative and postoperative care and outcomes of these children.

Embryology

Two theories have been proposed as to the etiology of conjoined twins: fusion and fission. Although the differences between these theories have yet to be resolved, fission is the generally accepted and older theory, where the fertilized egg fails to split completely ( ). Spencer proposed the theory of fusion, which suggests that the fertilized egg splits completely, but a secondary union of two separate embryonic discs at the dorsal neural tube or ventral yolk sac takes place at 3 to 4 weeks’ gestation ( ). Aristotle also held this theory ( ).

Monozygotic twins are the result of one ovum being fertilized by one sperm and then dividing into two embryos. In conjoined twins, this division, at the thirteenth to seventeenth day of the blastocyst stage, is incomplete.

Conjoined twins are identical, with what has always been thought to be an identical chromosomal pattern. With new molecular genetics, this has been shown to not necessarily be the case, and the twins may neither be completely identical nor have the same chromosome pattern ( ). It has been hypothesized that monozygotic twinning occurs at four possible phases: up to 3 days’ postconception, after 4 to 6 days, after 7 to 12 days, and finally after 13 to 17 days. It is during this latter period that conjoined twins, fetus-in-fetu, or a teratoma may arise ( ). Parasitic twins are thought to result from the embryonic death of one twin, with the remaining parts of the body vascularized by the surviving autocyte. Fetus-in-fetu are asymmetric monozygotic diamniotic intraparasitic twins ( ). Conjoined triplets and quadruplets have been documented, although all have been aborted ( ; ). These cases are exceptionally rare, with an even more obscure pathogenesis.

Conjoined twins are always the same gender. There is a 3:1 female-to-male incidence in live births, but more males are stillborn ( ; ). They are monozygotic, monoamniotic, and monochorionic. Despite this, the infants usually vary in size, appearance, personality, internal anatomy, and degree of organ-sharing and duplication. Many of the challenges for all disciplines relate to the vast diversity in the anatomic variations that may possibly occur. Organs may be conjoined, duplicated, or absent. Investigations are crucial to clarifying these differences in order to make decisions about surgery, interventions, and survival. Even then, surprises occur at the time of surgery, and innovative techniques may be necessary.

Survival depends on the site and complexity of conjunction, the degree of organ sharing, and the presence of other congenital anomalies, with the extent of cardiac fusion and lung development being major determining factors ( ).

Classification, nomenclature, and terminology

Conjoined twins are typically classified by the anatomic site of conjunction (which may be complex) followed by the suffix -pagus— the Greek word meaning “that which is joined” ( Box 39.1 ). There is an international collaboration attempting to create a more uniform classification of conjoined twins ( ). This considers a ventral (front, caudal, or lateral) or dorsal (back-to-back, sacrum-to-sacrum, or head-to-head) fusion, with further classification described in the following paragraphs ( Fig. 39.2 ).

Twins are described as being symmetric or asymmetric, although these terms are often misleading, because even when the twins are fully formed they are seldom truly symmetric. According to the most prominent site of conjunction, the following sites of conjunction are the most common: the chest ( thoracopagus twins), the abdomen ( omphalopagus twins), sacrum ( pygopagus twins), pelvis ( ischiopagus twins), and back ( rachipagus twins) ( Table 39.2 ).

Symmetric twins are two anatomically identifiable infants with a physical appearance suggestive of two possible survivors. With asymmetric, or parasitic, twins, one twin is a potential survivor and usually appears normal, but the other is incomplete and attached as a parasite. This may be externally visible, or it may be internal. Where there is an attachment of an anatomically identifiable part, but not of a total individual, the term heteropagus is used. It is in this group that regional anesthesia is particularly useful. Within a classified group, especially with complex conjunctions, the external physical appearance and spatial arrangement of the infants may be very different ( Figs. 39.3 and 39.4 ).

Conjoined twins are further classified by the number of limbs present and the internal organs that are involved in the conjunction. The following list shows this classification system:

• Two arms: dibrachius

• Three arms: tribrachius

• Four arms: tetrabrachius

• Two legs: bipus

• Three legs: tripus

• Four legs: tetrapus

The degree of cardiac fusion, or degree of cardiopagus, can be considered as follows ( ):

• Group A: Separate hearts and pericardium

• Group B: Separate hearts and a common/shared pericardium

• Group C: Fused atria and separate ventricles

• Group D: Fused atria and ventricles

Outcomes for separation in groups C and D are poor.

Ethics

In broad terms, ethics are a set of standards of professional conduct ( ). Whenever planned separation of conjoined twins takes place, and when there is a possibility or probability that one twin may not survive the procedure, moral, ethical, and legal arguments are raised. Many of these issues have been addressed in the literature ( ; ; ; ). The Hastings report identified three cardinal issues ( ):

• If one twin would not (be able to) survive, surgical separation is justified to provide life for the other twin.

• Survival is determined by the premorbid condition and not by surgery.

• Parents have the right to refuse separation.

In a review of this subject, Atkinson commented that the birth of a handicapped child is an immense burden to all parents ( ). If they are to avoid greater challenges, the clinicians require sensitivity and patience as they steer the family along a pathway to survival. The question most often asked is whether it is justified to sacrifice one life to save another, or should both infants be allowed to die? Answers are seldom simple, and each case should be assessed on its own merit. Decisions depend on the type and complexity of the conjunction, the overall health of both infants, the laws of the country, and the religion and beliefs of the parents. If the sacrifice of one twin is necessary for the other twin to survive, it is important to recognize that both would die without separation. If they were separated, at least one would live ( ).

Especially in centers where these operations are done more often, the medical staff is more confident in their ability to provide insightful management decisions pertaining to the care of conjoined twins. They are supported by investigations that provide valuable information, allowing rational decisions to be made about the immediate and long-term futures of these infants. These investigations, performed to clarify anatomic structures, include radiologic imaging, ultrasonography, CT, MRI, radioisotope studies, echocardiography, cardiac catheterization, and neuroradiologic imaging. As a consequence, in the perioperative period the pediatric surgeons and anesthesiologists in these centers have reported much higher rates of success in operating on these infants. Developments in intensive care also have a positive effect on these improved outcomes.

Ian Aird wrote that surgery should be performed if there is a possibility of at least one twin surviving ( ). The operation does not decide which twin will survive; this is determined by their relative conditions ( ).

A number of units have adopted the Great Ormond Street Ethical Guidelines for Conjoined Twin Separation. When separation is feasible with a reasonable chance of success, it should be carried out. When surgery is not possible, custodial care should be offered, and nature should be allowed to take its course. When one twin is dead or has a lethal abnormality and cannot survive independently from its normal twin, and if there is no surgery both twins would die, separation to save the healthy twin should be attempted ( ; ).

Perinatal considerations

Improved techniques of antenatal diagnosis and fetal imaging have allowed the diagnosis of conjoined twins to be made during pregnancy, so that counseling of the parents may allow them the option to have the pregnancy terminated. Conjoined twins can be identified as early as 11 weeks’ gestation and, in a case series studied by Sebire and colleagues, all parents opted for termination ( ). Complex craniopagus and cardiopagus anatomy in particular may tilt the decision in this direction. Conjoined hearts are easier to study via ultrasound in utero, because the amniotic fluid acts as a buffer, whereas after birth the lungs inflate with air and prevent optimal visibility ( ).

Obstructed labor with difficult vaginal delivery may necessitate an emergency cesarean section, but this can be avoided by antenatal diagnosis and elective cesarean section at 36 to 38 weeks’ gestation ( ). In many developing countries, the birth of conjoined twins may come as a surprise to the mother and the attending midwife or medical practitioner ( ; ).

Perinatal management of conjoined twins involves close collaboration among anesthesiologists, obstetricians, and pediatricians so that birth trauma for both the mother and infants can be minimized. Unborn conjoined twins may be referred to pediatric surgeons for advice in order to plan the delivery and the immediate perinatal management.

Careful prenatal investigations may identify cases in which emergency separation at birth is life-saving ( ). Advances in prenatal ultrasound, as well as the use of color-flow Doppler and prenatal MRI, have improved the antenatal diagnosis of conjoined twins. In particular, prenatal and postnatal echocardiography has been shown to accurately delineate the extent of cardiac fusion, the intracardiac anatomy, and the ventricular function ( ). Planning of the antenatal course and the perinatal management of twins can be facilitated by identifying those twins at particular risk, such as twins with twin reversed–arterial perfusion sequence. In this situation, vascular communications between the two fetuses allows deoxygenated blood from one fetus (the pump twin) to perfuse the other fetus (the perfused twin), resulting in reversed flow in the umbilical vessels and the development of multiple anomalies, including acardia, in the perfused twin ( ). Antenatal surgical intervention, removing the acardiac twin in utero, may allow for the survival of the remaining (pump) twin. If they are conjoined, however, this is not possible, and immediate surgical intervention at birth is necessary. In order to make rational and sound decisions as to the anesthetic management, anesthesia for fetoscopic fetal surgery requires knowledge of the pathophysiology of the fetus, the fetoplacental unit, and the condition of the mother ( ).

Plans may be necessary for an ex utero intrapartum treatment (EXIT) procedure in units providing that option ( ). In this operation, access to the fetus is achieved when the fetus is brought into the surgical field while it is still attached to the mother’s placenta. The planned procedure, whether for access to the fetal airway in the case of an airway tumor or to allow separation of a conjoined twin from its nonsurvivable twin, is then carried out. Once it has been completed, the infant is then delivered from the mother and separated from its placenta. This procedure was also used for airway control of both twins when the antenatal airway and cardiopulmonary status of the twins was not known ( ).

At delivery, it is optimal to have two sets of all neonatal resuscitation equipment available and a pediatrician (or anesthesiologist) present for each infant. A conventional open incubator usually provides a large enough surface area to accommodate both infants. If one twin is doing poorly, it should be attended to first. Especially with thoracopagus twins, overvigorous ventilation of one may compromise the other because of the chest contents moving across into the chest cavity of the other. If intubation is necessary, this should be performed on one infant at a time, with the other twin being supported, if necessary, with bag-mask oxygen and ventilation. A T piece and small mask is easier to use than an Ambu bag. While laryngoscopy is being performed on one twin, care must be taken to protect the infant who is not being intubated from trauma to the face and eyes by the laryngoscope. The aim of immediate postnatal management should be the resuscitation and stabilization of both infants, thorough physical examination and special investigations that will allow for definition of the relevant anatomy, and subsequent medical and surgical management.

Cardiopulmonary resuscitation (CPR) in conjoined twins has significant limitations. Not only can it be physically challenging, but it may also be unreliable because the anatomy is distorted and access to the heart is limited, especially in thoracopagus twins. Damage to other organs may occur, particularly to the upper gastrointestinal tract and the liver ( ). The basics of neonatal and pediatric resuscitation should be followed. Although no national or international guidelines exist for resuscitation of conjoined twins, have prepared a neonatal resuscitation program algorithm for conjoined twins. The algorithm addresses the challenges with ventilation, chest compression, and medication administration of conjoined twins in the delivery room.

Medical and surgical management

Spitz and Kiely describe the management of conjoined twins in the prenatal and postnatal stages. When complex thoracopagus or craniopagus twins are diagnosed, termination of pregnancy is recommended ( ). The postnatal management involves the following options:

• Nonoperative care: palliative care until the twins die, or raise the twins in their conjoined status (i.e., no attempt is made to separate them).

• Emergency operative care: surgery that may include separation is performed.

• Operative or surgical management aimed at elective separation: elective separation may be performed as a staged procedure, or separation may occur with a single operation.

Some overlap occurs when the twins arrive for emergency surgery before the results of all the investigations have enabled decisions around survival to be made (e.g., when intestinal obstruction develops). Emergency surgery is then performed, but later findings may indicate that other anomalies that are incompatible with life are present. In all studies, emergency surgery for separation is associated with poor prognosis.

Indications for emergency separation include the following ( ; ; ; ):

• When there is damage to a connecting bridge (e.g., omphalopagus). This may occur at the time of delivery.

• When the condition of one twin threatens the survival of the other (e.g., complex congenital heart disease, cardiomyopathy, sepsis).

• When there is deterioration of both twins because of hemodynamic and respiratory compromise. This occurs typically in thoracopagus twins.

• When the condition of one twin is incompatible with life (e.g., anencephalic, acardiac, stillborn, or complex congenital anomalies) but the other twin has a good chance of survival.

Elective separation for simple conjunctions can be performed in the neonatal period with minimal problems. No benefit is gained from waiting for the infants to grow or for further investigations to be done. The maternal hormonal influences are still present; thus the skin is more pliable to cover the wound defect. In general, separation is planned for some time between 4 and 11 months of age when the infants are bigger and their investigations are more meaningful and when they have had adequate tissue expansion to allow closure of the skin defect ( ). highlights the role of technology in the preparation and planning of elective separation. Teleconferencing between the patient and international teams with experience separating twins can facilitate the identification and selection process of some of these patients. Volumetric computed tomography with 3-D imaging and 3-D printing ( Fig. 39.5 ) are becoming essential aspects of the planning process. In addition, simulation and virtual reality have been used to plan for the surgical approach and to augment team concepts.

Investigations

Accurate preoperative imaging is essential to surgical planning and prognosis, and the area(s) of fusion determines the imaging modality used. MRI and CT provide very good anatomic and bone detail and show organ positions, shared structures, and limited vascular anatomy ( ). Radiography with contrast material provides excellent gastrointestinal and urogenital evaluation. When there is liver conjunction, its anatomy, the vascular supply, and assessment of the biliary tree are required. Angiography helps clarify the vascular supply of organs and determine blood supply between the twins. Careful use of contrast material is important, because there may be overenthusiastic administration of this in an attempt to achieve better views. Evaluation of vascular shunts and cross-circulation is vital for anesthesiologists; loss of blood from these during surgery can be catastrophic.

Cardiac catheterization is required to identify intracardiac connections and to clarify cardiac chambers. Echocardiographic technology is constantly improving, so the need for catheterization (and therefore anesthesia) is becoming less common. When cardiac surgery is required, however, this is the preferred investigation ( Fig. 39.6 ).

Results of these tests clarify anatomic variations in each infant. Understanding the complexity of organ conjunctions enables investigators to identify the structures that are present or missing. The results of complex investigations are best evaluated by a multidisciplinary team, because many factors are raised that anesthesiologists do not consider but that are important for both anesthetic management and good overall care of the infants. Each test has its own role for all of these requirements. Box 39.2 details investigations for craniopagus twins. The order in which procedures occur is also determined by the results of the investigations.

Planning before surgery