Anesthetic Strategies and Challenges in the Separation of Pygopagus Conjoined Twins: A Case Report

Introduction

Conjoined twins are a rare phenomenon [1,2], which is thought to be the result of an aberrant embryogenesis, where the bodies of 2 identical twins are connected in utero [1]. The incidence is estimated to be 1 in 50 000 births; however, since approximately half of the cases result in stillbirth, the true incidence is around 1 in 200 000. The literature suggests a higher occurrence of live births in females, with a ratio of 3: 1 [2]. The attachment site is used for classification. Sacral union is referred to as pygopagus and accounts for 19% of conjoined twins [3,4]. Diagnosis of pygopagous conjoined twins happens primarily via prenatal ultrasound, which can be performed as early as 12 weeks of gestation. This can be followed by a detailed scan that presents a reasonable evaluation of the degree of the fusion or any other possible issues at 20 weeks of gestation [2]. The spine, rectum, urinary tract, and reproductive organs can be connected in variable degrees [5]. The complex anatomy of pygopagus twins makes the separation procedure a challenging one, necessitating the highest degree of medical and surgical expertise.

Several prior case reports have discussed the importance of coordination and communication among multidisciplinary specialists in different types of conjoined twin cases [1,3,6]. Careful preoperative planning and the availability of well-trained teams for complex intraoperative and postoperative care are essential [1]. Anesthesiologists face one of their most challenging tasks when providing anesthesia for 2 interconnected infants. The site of the junction, position, and presence of a shared circulation pose multiple technical issues that require early insight and proper planning [1,6].

This report provides a detailed description of the anesthetic strategies and challenges of pygopagous conjoined female twins who underwent 2 surgeries before separation at 17 weeks of age.

Case Report

Female conjoined twins were delivered at a gestational age of 37 weeks by an urgent cesarean delivery under spinal anesthesia, due to suspected maternal preeclampsia. The diagnosis of conjoined twins was made at 25 weeks of gestation by ultrasound. Radiologic imaging revealed sacral fusion at the S4 level, fusion of thecal sacs at the L5 level, and cord tethering, with the conus terminating below the L3 level in both patients. The twins had 2 separate rectal ampullae that merged in a Y configuration, forming a single anal canal in the midline (Figures 1–3). Clinical examination showed a common anal canal with a functional sphincter positioned toward 1 side of the external genitalia and fused only at the inferior fornixes of the vulvae, with separate vaginal openings. The twins had separate urinary tracts with normal kidney function and normal acid-base and electrolytes ranges. On physical examination, the babies exhibited retrognathia (Figure 2). Baseline comorbidities are summarized in Table 1.

The babies underwent 2 surgeries prior to separation. Following multiple multidisciplinary meetings, on October 6, 2022, at 20 days of life, twin B underwent meningocele repair. Under the same anesthesia, both twins underwent dilation of the anal canal with mapping of the anal sphincter. Twin A had an estimated body weight of 3255 g, while twin B weighed 2074 g.

They presented to the operating room (OR), each having a 24G intravenous (i.v.) catheter in place. Care was provided by 2 anesthesia teams, each consisting of 2 attending anesthesiologists, 1 resident physician, and 1 anesthesia nurse. All anesthesia equipment was duplicated, and medications were color-coded to avoid confusion. The plan was to induce general anesthesia in twin B first, followed by twin A, given the relative critical status of twin B. Standard American Society of Anesthesiologists monitors were applied for each baby, and no premedication was provided.

Both twins were simultaneously preoxygenated with 100% oxygen. Before induction, twin B received 0.1 mg i.v. atropine to check for cross circulation, and no tachycardia was noted in twin A. Twin B was induced with sevoflurane, followed by the administration of propofol 15 mg i.v. as an adjuvant to optimize intubating conditions. Meanwhile, twin A was closely monitored and remained awake and spontaneously breathing. Two failed intubation attempts with direct laryngoscopy in twin B using the Oxford blade #1 showed a Cormack and Lehane view of III. Subsequently, intubation was successfully achieved using a 3-mm cuffed endotracheal tube (ETT) and a #1 blade Glidescope with a hockey stick-shaped stylet. Twin A was then similarly induced and successfully intubated at the first attempt using a 3-mm cuffed ETT and video laryngoscopy. Both babies were easy to ventilate, and they were successfully extubated at the end of the operation.

In the neonatal intensive care unit (NICU), it was observed that twin B experienced episodes of inspiratory stridor associated with transient desaturation that improved with nasal cannula. Flexible fiberoptic laryngoscopy showed erythema of the arytenoids with prolapse, consistent with laryngomalacia.

After the first surgery, twin B developed ex-vacuo hydrocephalus, necessitating the insertion of a ventriculoperitoneal shunt at the age of 10 weeks and 4 days. The surgery was performed on November 28, 2022, under general anesthesia, following the same anesthesia setup as in the previous operation. The induction protocol included the use of sevoflurane and rocuronium 5 mg i.v. However, this time, immediately after administering rocuronium to twin B, twin A developed apnea. Ventilation was difficult in twin B, and higher positive pressures were needed to achieve adequate tidal volumes. Both twins were successfully intubated from the first attempt, using video laryngoscopy and a 3-mm cuffed ETT. The surgery was performed successfully, and the babies were extubated at the end of the procedure.

The separation surgery was scheduled on January 18, 2023, at the age of 17 weeks and 4 days. At that time, twin A weighed 5568 g, and twin B weighed 4556 g. Both twins had a thicker neck and retrognathia, more pronounced in twin B. The same OR and anesthesia setup were used, and each twin had a 24G i.v. catheter in place. Glycopyrrolate 0.1 mg i.v. was administered to twin B as an anti-sialagogue. Anesthesia induction for twin B involved inhaled sevoflurane and propofol 20 mg i.v. Twin B was successfully intubated using a 3.5-mm cuffed ETT, after 3 attempts of video laryngoscopy with blade #1 Glidescope and an intubating hockey stick-shaped stylet. Twin A was similarly induced and intubated successfully with a 3.5-mm cuffed ETT using the Oxford direct laryngoscopy blade. Both twins were easy to ventilate this time.

Ultrasound guidance was used for line insertion in both twins. In twin A, a right arterial catheter was inserted at the first attempt, while a left subclavian venous line was inserted after an unsuccessful attempt to insert a left internal jugular venous catheter. In twin B, a left arterial line and a right internal jugular venous line were simultaneously inserted at the first attempt.

During surgery, the twins were maintained with sevoflurane (end-tidal concentration of 2%) and remifentanil i.v. infusion ranging between 0.05 and 0.1 mcg/kg/min. Fluid maintenance included dextrose 10%, lactated Ringer’s solution, and normal saline. Dexamethasone 0.5 mg/kg i.v., vancomycin 15 mg/kg i.v., and meropenem 20 mg/kg i.v. were given. Rocuronium was administered to both twins before incision, and pressure-controlled ventilation was applied throughout the procedure.

The separation process involved 3 surgical teams, specializing in neurosurgery, pediatric surgery, and plastic surgery. The plastic surgery team initiated the separation by creating lumbosacral fasciocutaneous axial advancement flaps at the point where the twins joined, without using tissue expanders. The neurosurgery team then separated the bony vertebral fusions and dural sacs, untangled the spinal cords and nerves, and formed distinct dural sacs without using grafts. The pediatric surgery team identified and separated the 2 rectal vaults, which were fused and shared a single anal canal about 3.5 to 4 cm proximal to the common anal verge, forming a Y-shaped configuration. A direct muscle stimulator was used to locate and dissect the sphincter muscles along the midline. The rectal vaults were separated, resulting in a natural rectum-anal canal structure, with sufficient circumferential sphincter muscle in twin A, which was then reconstructed with the perineal body and a floating rectum with a band of sphincter muscle in twin B, which was threaded through the sphincter complex. The separation was completed by dissecting the vagina from the hindgut in both twins and finalizing the flaps on the posterior aspect of their junction. The procedure was concluded with the insertion of negative suction drains and the closure of skin flaps by the plastic surgery team. The intraoperative course was uneventful, and an arterial blood gas analysis was performed approximately every 2 h. A summary of the results is illustrated in Table 2. The separation of the twins was achieved approximately 5 h after the incision. Intraoperative characteristics are presented in Table 3. Each child experienced an estimated blood loss of around 100 mL, and normothermia was maintained.

The surgery was successful, and the twins were transferred intubated to the NICU for continuity of care. Twin A was extubated in the NICU on postoperative day 1 and twin B on day 3. Twin A had an uneventful recovery, while twin B required prolonged hospital care, due to her preexisting neurological defects and laryngomalacia, including tracheostomy and gastrostomy.

Discussion

In the case of conjoined twins, multidisciplinary meetings and thorough planning are essential to determine the ideal course of action. A team with a high level of expertise is needed to navigate through all the unique considerations of such a rare and complicated case. Major considerations should be accounted for, namely separation timing, cross circulation assessment, vascular access, and anesthesia-specific considerations, in addition to ethical considerations.

Conjoined twins are a rare occurrence in which monozygotic and monochorionic twins are born physically connected to each other. Among conjoined twins, pygopagus twins, who are joined at the perineal area, account for approximately 19% of cases [3,4]. Due to the low incidence of conjoined twins, it is exceedingly uncommon for an anesthesiologist to gain sufficient exposure and familiarity with the unique perioperative challenges associated with such cases.

The diagnosis of conjoined twins and the recognition of any associated comorbidity can be made prenatally using ultrasound and magnetic resonance imaging, enabling the planning of their delivery and perinatal care [7]. In our case, the twins were diagnosed by ultrasound at 25 weeks of gestation. The individual weights of the babies were estimated during prenatal ultrasound, with twin A accounting for 55% and twin B for 45% of the total weight. This weight proportion was used for medication dose adjustment after birth.

Due to the rarity and complexity of the case, several multidisciplinary meetings were conducted from the initial diagnosis until the successful separation of the twins. The team consisted of anesthesiologists, general pediatricians, neonatal intensivists, neurosurgeons, pediatric surgeons, plastic surgeons, obstetricians, and other consultants. The discussion covered various aspects, including the anatomy of the conjunction, extent of cross circulation, concomitant comorbidities, required investigative procedures, and interventions. The optimal timing of neurosurgery for twin B, timing of separation, surgical teams involved, intraoperative logistics, and risk mitigation plans were all addressed.

In the case of conjoined twins, the separation can be either elective or emergent, depending on factors such as the type of conjunction, associated comorbidities, and hemodynamics of each baby. In cases in which a delayed separation is feasible, allowing the twins to grow and thus surpass the critical neonatal period is advantageous. The optimal time for delayed separation typically falls between 4 and 11 months of age [8]. However, as observed in our case, it is possible for the twins to require anesthesia for multiple surgical or investigative procedures prior to the separation surgery. Thus, it is imperative for the anesthesia team to be readily available and have a well-documented plan in place for pre-separation surgeries or in the event of emergency surgery right from the beginning.

In the OR, it is essential to consider the twins as 2 separate individuals and treat them accordingly. Therefore, 2 separate anesthesia teams, each consisting of 2 anesthesiologists – 1 resident and 1 anesthesia nurse – were assigned to each baby. Additionally, all equipment, medications, and blood products were duplicated and color-coded to ensure clear differentiation. The position of the anesthesia machines is usually tailored to the specific type of conjunction and separation [9]. In our case, the anesthesia machines were positioned at the heads of the pygopagus twins. As this was the first surgery of this kind performed at our institution, a rehearsal session was conducted 1 day before the scheduled surgery, to ensure preparedness and coordination.

It is important to assess the cross circulation between the twin members, given its potential impact on the drug pharmacokinetics, pharmacodynamics, and fluid and blood management strategies. It can be quantified using contrast and radioisotopes and can be assessed as well via administration of an anticholinergic medication to one twin and monitoring the hemodynamics of the other twin [6–9]. However, it is important to note that the accuracy of the atropine test can be compromised, particularly in cases in which baseline tachycardia is present. In our case, during the first surgery, the administration of atropine to twin B did not result in tachycardia in twin A. Additionally, when twin B was induced with sevoflurane and propofol, twin A remained awake. In the subsequent surgery, the administration of rocuronium to twin B resulted in immediate apnea in twin A. This could be explained by the difference in pharmacokinetic models among the medications used, leading to different effects within the same cross circulation. For instance, due to its low lipid solubility, rocuronium has a small volume of distribution, compared with propofol. Consequently, the dose of rocuronium adjusted to the weight of twin B resulted in paralysis in twin A, whereas propofol adjusted for the weight of twin B had no noticeable effect on twin A. It is important to calculate the anesthesia drug doses based on the estimated body weight of each twin. Furthermore, it is crucial to administer general anesthesia to both twins, even if only one of them is undergoing surgery. This is necessary because emergency control of the airway for the nonsurgical twin under the surgical drapes can be hazardous and difficult.

Additionally, securing vascular access is challenging due to different anatomical variations, small body weight, complex surgical positions, and prolonged admission period that necessitates the use of all possible access points. Peripheral lines are suitable for simple procedures, while major procedures require the placement of central venous and arterial lines. In our case, i.v. vascular access sites were limited to the upper right side in twin B and the left upper side in twin A. The other sides were inaccessible due to the connection between the twins. Additionally, the lower extremities could not be accessed, as they were within the operative fields. To increase the chance of success, we used ultrasound guidance, since it is well known to reduce the number of attempts and decrease the time to vascular access, with reduced rate of complications [10].

When it comes to the anesthetic management, several key considerations arise in the case of conjoined twins. Performing an airway assessment upon the initial presentation is essential. It is important to avoid emergency intubation and instead anticipate and perform intubation in a controlled manner [8,9].

Generally, the sicker twin is induced and intubated first [8]. Airway management in conjoined twins can be challenging due to the varying anatomical presentations, complex positions, and concomitant head and neck abnormalities [9]. Our twins had short necks and retrognathia. Their heads and bodies faced opposite directions, making vascular and airway access difficult. Advanced airway equipment should be available, particularly videolaryngoscopy. Both i.v. and inhalational anesthesia induction techniques have been described in conjoined twins [8]. We used inhaled sevoflurane in conjunction with propofol to optimize intubating conditions during the first surgery and during the separation surgery. However, during the second surgery, the induction protocol included rocuronium, which resulted in high positive airway pressures being required in twin B to achieve adequate tidal volumes through the face mask. Rocuronium may have worsened airway collapse in laryngomalacia [11]. During the separation surgery, we maintained airway patency during induction by omitting rocuronium, resulting in smooth face mask ventilation. All these factors rendered airway management in our twins extremely challenging. Videolaryngoscopy proved to be a valuable tool in navigating the complex airway anatomy.

The fluid/blood replacement strategy is determined based on perioperative hemodynamics, estimated blood loss, hematological studies, and urine output. Massive blood loss should be anticipated in separation surgeries involving the heart, liver, and fused bones. Blood products should be prepared in advance for each child individually and should be readily available within the OR premises [8]. Normothermia should be maintained by adjusting the OR temperature, administering warm fluids, applying air convection devices, and taking preventive measures during transportation [8].

For such complicated cases, teams with a high level of expertise are crucial to ensure a smooth and uneventful process. Compared with hospitals with no or infrequent previous encounters, referral centers offer many advantages, including superior expertise and multidisciplinary collaboration and access to evolving technological adjuncts and diagnostic imaging. The surgical outcome can be optimized by applying visual interactive modeling and simulation sessions. Presurgical planning helps identify space requirements and determine the optimal patient and equipment positions. Additionally, rehearsals focusing on the management of common intraoperative scenarios and emergencies are beneficial [12].

Another important part of conjoined twin case management is the ethical considerations that come with it. The survival rate of conjoined twins greatly depends on the circumstances of their separation [13]. The elective separation survival rate is reported to be around 90%, while emergency separation drops the survival rate to 50% [14]. The decision to attempt separation involves complex ethical challenges. An attempt of separation should be proposed when the death of a twin threatens the life of the other, or in the case of presence of congenital anomalies rendering a member not compatible with life [15]. In such cases, shared organs and/or tissues from the dead member can be used for the surviving one. The twins’ and family’s wishes should be considered in extensive multidisciplinary meetings that involve the hospital ethics committee [16].

It is important to note that several case reports have been published in the literature describing the anesthetic management of conjoined twin separation cases. While the step-by-step management, from positioning of the monitors, drugs used, and interventions needed, among other things, differ from case to case, the key takeaway points and general approach remain the same. Sato et al reported the importance of multidisciplinary meetings and planning, need for rehearsal sessions, importance of color-coding and equipment duplication, and cross circulation assessments [6]. Similarly, Kaniyil et al emphasized the need for a multidisciplinary approach, thorough preoperative evaluation to guide planning, and anticipation of complications, such as massive blood loss and hemodynamic instability [1].

Conclusions

In conclusion, the anesthetic management for pygopagus twins presents complex challenges. Despite limited experience with similar cases, successful management was achieved through planning, effective communication, and rehearsal of unfamiliar setups. Attention to detail and involvement of highly experienced teams were crucial to the success of the procedures.