Extrauterine Twin-to-Twin Transfusion Syndrome: A Critical Variable in the Anesthetic Management of Omphalopagus Twin Separation

INTRODUCTION

Conjoined twinning is a rare embryological anomaly, occurring in approximately 1 in 50,000–1 in 100,000 births, with a marked female predominance.^[1] This condition results in the formation of anatomically connected fetuses with varying degrees of shared organs and structures. Omphalopagus, accounting for about 5.5% of all conjoined twins, most commonly involves hepatic fusion in approximately 80% of cases and intestinal connection in around 30%.^[2,3]

From an anesthetic perspective, the separation of conjoined twins represents a paradigmatic scenario of shared physiology, in which conventional pharmacologic and hemodynamic assumptions may not apply. Among the principal anesthetic challenges are the evaluation of shared circulation, adjustment of anesthetic drug dosing, synchronized induction, airway management, and vigilant intraoperative monitoring. These challenges are amplified when significant cross-circulation exists, as it may profoundly alter pharmacokinetics, pharmacodynamics, and cardiovascular responses in a non-linear and asymmetric manner.^[4]

Although classical descriptions of anesthetic management in conjoined twins exist, most reports emphasize anatomical considerations and logistical organization, with limited focus on the functional consequences of persistent intertwin hemodynamic coupling.^[2] In the present case, the unique hemodynamic pattern resulting from substantial cross-circulation demanded individualized adaptations, directly influencing drug titration, monitoring strategies, and the maintenance of inter-twin stability.

Notably, this complexity was already suggested during the initial pre-operative evaluation, when the twins still exhibited asymmetric perfusion: One presented lower body weight and cutaneous pallor, while the other showed relative hyperemia and better peripheral perfusion. Although their weights equalized by the time of surgery, these earlier findings were suggestive of extrauterine twin-to-twin transfusion syndrome (EUTTTS) and likely reflected a preexisting donor–recipient physiology. This antecedent imbalance proved clinically relevant, as it translated into divergent anesthetic requirements and distinct intraoperative cardiovascular responses during separation, despite apparent pre-operative normalization.

The anesthetic goals in this case were to maintain hemodynamic stability during separation, ensure balanced drug delivery despite cross-circulation, and secure both airways under challenging positioning. Key challenges included unpredictable pharmacokinetics, asymmetric cardiovascular responses, difficult airway management, and instability during hepatic vascular division, requiring continuous invasive monitoring and coordinated dual-team management.

CASE REPORT

We report the case of 49-day-old female omphalopagus conjoined twins, delivered late preterm by cesarean section with low birth weight. Pre-operative assessment demonstrated asymmetric perfusion: Twin A appeared smaller and pale, while Twin B was larger and hyperemic [Figure 1]. These findings raised early concern for a functional circulatory imbalance. By the time of surgery, both twins had achieved similar body weights (approximately 3.5 kg each).

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Figure 1: 49-day-old-female omphalopagus conjoined twins. Twin A (on the left) appeared smaller and pale, while Twin B (on the right) appeared larger and hyperemic.

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Extensive pre-operative planning was undertaken. Two separate anesthesia workstations were prepared, with complete duplication of all anesthetic equipment, medications, and monitoring devices. A strict color-coding system was implemented (blue for Twin A and red for Twin B) to minimize the risk of medication or line misidentification. Two independent anesthesia teams managed each twin simultaneously, maintaining constant verbal communication.

Continuous monitoring included cardioscopy, pulse oximetry, and invasive arterial blood pressure measurement, allowing real-time assessment of cardiovascular stability throughout the procedure. Arterial access was prioritized early due to the anticipated hemodynamic volatility associated with cross-circulation and surgical separation.

Before induction, both patients were hemodynamically stable. Twin A presented with a heart rate (HR) of 132 bpm, respiratory rate (RR) of 44 breaths/min, oxygen saturation (SpO₂) of 97%, and a mean arterial pressure (MAP) of 48 mmHg. Twin B had HR 145 bpm, RR 46 breaths/min, and MAP 46 mmHg. Hemodynamic and respiratory stability were maintained following induction.

Inhalational induction with sevoflurane was performed while maintaining spontaneous ventilation. This strategy was chosen to preserve airway reflexes and reduce the risk of abrupt hemodynamic compromise in the setting of shared circulation. Airway management was technically more difficult, primarily due to restricted access, limited alignment of airway axes, and the requirement to maintain both patients in lateral decubitus.

Drug doses were calculated based on the combined body weight divided equally between the twins. Identical doses of fentanyl (10mcg), propofol (15mg), and rocuronium (2mg) were administered to each. During sequential intravenous induction, transient hypoventilation was observed in the non-induced twin, consistent with cross-circulation and intertwin drug transfer.

After initiation of mechanical ventilation, invasive arterial blood pressure monitoring was established via right upper limb arterial cannulation in both twins, using 22-gauge catheters, chosen due to greater anatomical accessibility. Subsequently, central venous access was obtained in the brachiocephalic trunk under ultrasound guidance by the surgical team. The twins were then positioned for separation, and anesthesia was maintained with sevoflurane.

From the onset of hepatic resection, Twin A exhibited persistent hypotension and tachycardia, necessitating repeated fluid boluses and escalating doses of vasoactive agents (adrenaline 0.5, noradrenaline 0.3 mcg/kg/min). Serial arterial blood gas analyses revealed metabolic acidosis and elevated lactate levels (pH 7.24 and lactate 4.2 mmol/L), consistent with relative hypoperfusion.

Concurrently, hemoglobin and hematocrit decreased to 8.2 g/dL and 25.4% in Twin A and 8.0 g/dL and 24.6% in Twin B, prompting red blood cell transfusion. Following transfusion, values increased to 11.8 g/dL and 36.2% in Twin A and 11.7 g/dL and 35.8% in Twin B.

Twin B remained comparatively more hemodynamically stable throughout this phase, requiring lower vasoactive support (epinephrine up to 0.2 µg/kg/min). Notably, administration of vasoactive agents to one twin elicited measurable hemodynamic responses in the other, confirming clinically significant cross-circulation.

The surgical team identified shared hepatic structures, with multiple venous interconnections confirming functional cross-circulation. There was no duodenal continuity. Vascular connections were ligated and divided in a stepwise and controlled manner.

At the end of the procedure, both twins were transferred to the neonatal intensive care unit, intubated and sedated, requiring ongoing vasoactive support. Final vasopressor doses were adrenaline 0.3 mcg/kg/min and norepinephrine 0.1 mcg/kg/min for Twin A, and adrenaline 0.2 mcg/kg/min for Twin B. Vasoactive support was progressively weaned and discontinued on post-operative day 1, and successful extubation was achieved on post-operative day 2.

Key intraoperative hemodynamic changes, vasoactive requirements, and metabolic findings are summarized in Table 1.

DISCUSSION

The anesthetic separation of omphalopagus twins with substantial cross-circulation represents one of the most complex scenarios in contemporary perioperative practice, as it challenges standard physiological models and requires continuous reinterpretation of hemodynamic data. This case demonstrates that even when traditional clinical parameters appear stable, shared physiology may preserve concealed patterns of cardiovascular and pharmacologic coupling that fundamentally reshape anesthetic management.^[5-7] In the present report, these challenges were largely attributable to EUTTTS, a rare and under-recognized condition.

Unlike classic intrauterine twin-to-twin transfusion syndrome, EUTTTS results from persistent postnatal vascular shunting through shared organs, most commonly the liver, leading to sustained donor–recipient physiology after birth.^[5-7] From an anesthetic perspective, this condition is characterized by asymmetric intravascular volume status, divergent myocardial reserve, and altered pharmacokinetics due to ongoing cross-circulation. Importantly, apparent normalization of clinical parameters, such as body weight equalization or baseline vital signs, does not necessarily reflect normalization of underlying physiology, as also observed in previously reported cases.^[5]

In this context, although pre-operative imaging confirmed vascular communication, the functional impact of cross-circulation was greater than anticipated, directly affecting drug responses and hemodynamic stability. This discrepancy highlights the limited ability of static imaging to predict effective shunt flow.^[5,6]

In this context, anesthetic induction and maintenance require particular caution. Sevoflurane allowed controlled anesthetic titration in the presence of cross-circulation, minimizing abrupt cardiorespiratory effects. This approach is especially advantageous in twins with shared circulation, as inhalational agents provide more predictable effects within each patient, whereas intravenous drugs may lead to unintended systemic effects in the co-twin depending on the extent of cross-circulation.^[8,9] The presumed donor twin was intubated first to secure the airway and ensure hemodynamic control before proceeding with the second twin.

Given that vascular communication had already been demonstrated by computed tomography and magnetic resonance imaging, additional pharmacologic cross-circulation testing was deemed unnecessary and potentially destabilizing. Instead, management relied on detailed anatomical imaging, continuous invasive monitoring, and dynamic assessment of intertwin responses to anesthetic and vasoactive agents.^[4]

The clinical presentation was compatible with EUTTTS, with one twin exhibiting features of relative hypoperfusion and the other demonstrating recipient hypervolemic physiology.^[10] Despite similar pre-operative body weights, the presumed donor twin consistently showed hypotension, tachycardia, metabolic acidosis, and increased vasoactive requirements, while the recipient twin remained comparatively stable. This pattern closely parallels previously described cases in which, during the pre-operative period, laboratory parameters may appear deceptively similar between twins as a result of blood mixing, thereby masking true disparities in end-organ perfusion.^[5-7]

Beyond baseline hemodynamic differences, this case highlights the broader implications of shared physiology. Cross-circulation resulted in altered pharmacokinetics, reciprocal cardiovascular effects, and heightened vulnerability during the transition from shared to independent circulation. Hepatic dissection and vascular clampage represented critical intraoperative moments, during which abrupt redistribution of preload and afterload could precipitate cardiovascular instability, as reported in other cases of EUTTTS.^[5-7] Anticipatory adjustment of vasoactive infusions and close inter-team communication were therefore essential to maintain stability during separation.

The most distinctive contribution of this report lies in demonstrating that functional consequences of EUTTTS may persist despite apparent pre-operative clinical normalization, an aspect that remains insufficiently emphasized in the anesthetic literature on conjoined twins.^[8,9] Conventional metrics such as weight, baseline vital signs, and routine laboratory tests proved insufficient predictors of intraoperative behavior. In contrast, dynamic indicators, such as perfusion asymmetry, lactate trends, and differential drug responses, were more informative and clinically actionable.

As a limitation, this report reflects a single clinical experience, and its findings cannot be generalized to all conjoined twins due to the wide anatomical and physiological heterogeneity inherent to this condition. In addition, the absence of quantitative pre-operative flow measurements limits objective correlation between anatomical communication and functional cross-circulation.

CONCLUSION

This case underscores that apparent pre-operative stability does not exclude persistent intertwin physiological coupling. Residual donor–recipient dynamics may result in asymmetric hemodynamic responses and clinically significant pharmacologic interactions, despite similar baseline parameters. Recognition of this pattern is critical for anticipating instability and guiding anesthetic management. Early identification of EUTTTS and reliance on dynamic intraoperative indicators may improve safety in complex conjoined twin separations.