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Department of Anesthesia and Critical Care, Massachusetts General Hospital, Boston, Massachusetts
Address correspondence and reprint requests to Erik Shank, MD, Department of Anesthesia and Critical Care, Massachusetts General Hospital, Boston, MA 02114. Address e-mail to eshank{at}etherdome.mgh.harvard.edu.
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Introduction |
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Case Report |
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26 wk gestational age. They weighed 3.95 kg. Apgar scores were 7 for Twin 1 and 8 for Twin 2. They were observed for a week in the neonatal intensive care unit (ICU), where they displayed no issues with feeding, voiding, or bowel movements. Both twins had oxygen saturations of 70%–80% on 4 L/min of blow-by oxygen. Diagnostic computed tomographic studies indicated two sets of lungs, kidneys, intestines, and gallbladders. There appeared to be one shared liver and one pericardial sac containing two hearts and four chambers.
They were transferred to our hospital for further evaluation for potential separation surgery. On arrival, they were 1.5 mo old. Their combined weight was 4.75 kg. Besides blow-by oxygen supplementation at 4 L/min, neither twin was receiving any medications. Both twins were tachypneic with transient respiratory rates as frequent as 80 breaths/min. Vital signs were as follows: Twin 1 had an arterial blood pressure of 79/41 mm Hg, a heart rate of 125 bpm, a respiratory rate of 60–80 breaths/min, and an oxygen saturation of 85% and was afebrile. Twin 2 had an arterial blood pressure of 65/29 mm Hg, a heart rate of 125 bpm, a respiratory rate of 60–80 breaths/min, and an oxygen saturation of 78% and was also afebrile. Visually, their electrocardiograms (ECGs) appeared identical. Both twins would desaturate into the mid 60s with feeding.
Echocardiography of the twins revealed the following complex circulation (Fig. 1): the twins were anatomically joined at the atrial and ventricular level but maintained independent inflow and outflow tracts. The systemic venous return from both infants pooled in a common atrium. There was mixing of pulmonary venous return from both twins with their systemic venous return at the shared atrial level. Twin 1’s left ventricle and Twin 2’s right ventricle were fused to form a common shared ventricle. The common ventricle ejected through Twin 2’s pulmonary artery and Twin 1’s slightly hypoplastic aorta. Twin 1’s outflow tract was proximal to her mitral inflow tract, which enabled her to maintain a higher saturation than her sister.
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Cardiac angiography and hepatic cholangiography were planned via MRI in anticipation of future surgical separation. Because of the expected length of the procedure (>5 h) and the need for relative immobility of the patients, general anesthesia was requested.
The setup for anesthesia consisted of two In Vivo Millennia (In Vivo Research, Orlando, FL) MRI monitors and two MRI-compatible Narkomed MRI-2 anesthesia machines (Dräger Medical AG, Lubeck, Germany) (Fig. 2). Additionally, two Harvard 2 infusion pumps (Harvard Clinical, Boston, MA) were used. Because pumps are not MRI compatible, they remained outside the MRI room, and tubing was run through ports in the wall. The In Vivo monitors display pulse oximetry, end-tidal capnography, ECG, and noninvasive blood pressure.
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Routine noninvasive monitors (noninvasive blood pressure, ECG, and pulse oximetry) were applied to each twin, and 24-gauge peripheral IV access was established in one of each twin’s lower extremities. Each twin was administered oxygen (fraction of inspired oxygen [Fio2], 1.0) via face mask. Atropine 40 µg was administered simultaneously to each twin, followed by 10 mg of ketamine IV (4 mg/kg), also injected simultaneously to each twin. Both infants remained hemodynamically stable; thus, once easy mask ventilation was demonstrated, succinylcholine was administered parenterally to each twin (5.0 mg; 2 mg/kg).
At this point, orotracheal intubation was attempted, first on Twin 2, without success. The twins’ position (facing each other, attached chest to chest; Fig. 3) made direct laryngoscopy very awkward. As the heads were turned to give more room for direct laryngoscopy, the laryngeal anatomy became severely distorted. A No. 1 laryngeal mask airway (LMA) was successfully placed in Twin 2, and this yielded ideal ventilating conditions. Direct laryngoscopy was then attempted in Twin 1. These attempts also failed and resulted in laryngospasm in Twin 1. Remarkably, neither twin desaturated during the period of laryngospasm; the ventilation of Twin 2 was adequate to maintain both twins with saturations more than 90%. Once the laryngospasm resolved, a No. 1 LMA was also placed in Twin 1 (Fig. 3). The twins were then placed in the MRI scanner for their studies (Fig. 4). They were maintained on air, positive-pressure hand ventilation (by manually attempting to ventilate both twins in synchrony), a nondepolarizing muscle relaxant (mostly because of concerns of further episodes of laryngospasm), and a remifentanil infusion administered to only one twin at 0.05 µg · kg–1 · min–1 (the weight was set at their combined weight: 4.75 kg).
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Heart rates were essentially identical throughout the procedure (150–160 bpm), as were arterial blood pressures; however, oxygen saturations were not identical. Twin 1 frequently had a saturation of 90%, whereas twin 2 was at 80%. We found that both twins had better saturations and arterial blood pressures while they were ventilated with an oxygen fraction (Fio2) of 30%. When one twin was ventilated with a higher Fio2, the other twin would tend to decrease her saturation, suggesting some form of steal. Consequently, we maintained both twins with the same Fio2.
The procedures lasted 6 h. Upon completion of the scans, the remifentanil infusion was discontinued, the twins’ muscle relaxation was reversed with neostigmine and atropine, and they breathed spontaneously. Twin 1’s LMA was removed. Once spontaneous ventilation in Twin 1 was reconfirmed by auscultation and end-tidal CO2 production, Twin 2’s LMA was removed. The twins were then returned to the pediatric ICU, awake (they awoke during transport), spontaneously breathing on blow-by oxygen, and in stable condition.
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Sedation without the induction of general anesthesia has been successfully performed in children (7–9) for MRI studies. However, general anesthesia is often required in high-risk patients, in extremely long studies, or in procedures in which maneuvers such as breath holding (e.g., MRI angiography) are necessary (8,9). Accordingly, we chose to provide general anesthesia for our patients with their airways secured with endotracheal tubes. Because we were unable to perform endotracheal intubation, the airways were managed with LMAs. LMAs have been widely used for pediatric airway management in MRI (8), and, because they were providing a stable airway in both infants, we believed it appropriate to continue with the MRI. The authors do not routinely use LMAs in small infants and neonates having prolonged diagnostic procedures because of the possibility of LMA dislodgment, atelectasis development, or aspiration. These concerns had to be balanced with the complexity of the infants’ cardiac physiology, the risk of laryngospasm with further laryngeal instrumentation, and an anatomy which precluded direct laryngoscopy.
Echocardiographic studies revealed that the twins shared a very complex cardiac circulation. Both twins had been hemodynamically stable and oxygenating satisfactorily with blow-by oxygen. However, we did not know how anesthesia would affect hemodynamics in each twin. In addition, it was unclear to what extent one twin’s hemodynamic status would affect the other twin. Finally, we were unsure how the twins would respond to positive-pressure ventilation changes and did not know whether ventilation in synchrony was warranted.
In general, anesthesia for MRI should provide easy titration to a reliable sedation state and rapid induction and emergence. Both inhaled and IV anesthetics may fulfill these requirements (10). In addition to the demands of the MRI environment, we needed to consider the complex cardiac physiology of the twins. Rivenes et al. (11) reported the effects of different anesthetic management in children with complex cardiac lesions. In their study, sevoflurane and isoflurane maintained cardiac output, but both anesthetics decreased cardiac contractility (11). Propofol has been shown to act as a vasodilator in clinically relevant concentrations (12). Opioids, as a result of their hemodynamic stability, have been the mainstay of pediatric cardiac anesthesia for the last few decades (13). Ketamine also has a long history of use in pediatric patients with heart disease and has been successfully used in anesthetic management of conjoined twins with complex cardiac anomalies (14). We therefore chose ketamine as the induction drug because of its ability to provide hemodynamic stability. However, neither ketamine nor most opioids allow rapid emergence. In contrast, remifentanil provides the advantage of easy titration and rapid emergence with hemodynamic stability. A remifentanil infusion was therefore chosen for the maintenance of anesthesia.
Throughout the case, the twins remained hemodynamically stable. Because both twins required high respiratory rates, it was necessary to hand-ventilate both twins throughout the procedure. We attempted to ventilate the twins in synchrony, believing that this would decrease the likelihood of untoward shunting or steal.
In conclusion, we have reported a case of thoracopagus conjoined twins requiring general anesthesia for MRI. Meticulous planning and teamwork are necessary for a positive outcome in complex cases (1,14). We followed these principles, and the conjoined twins were returned to the pediatric ICU spontaneously breathing and in stable condition.
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This article has been cited by other articles:
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  P. Szmuk, M. F. Rabb, B. Curry, K. J. Smith, M. R. Lantin-Hermoso, and T. Ezri Anaesthetic management of thoracopagus twins with complex cyanotic heart disease for cardiac assessment: special considerations related to ventilation and cross-circulation Br. J. Anaesth., March 1, 2006; 96(3): 341 - 345. [Abstract] [Full Text] [PDF]
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 P. Szmuk, O. Ghelber, and T. Ezri Difficult Intubation in Thoracopagus Twins in MRI Suite Anesth. Analg., October 1, 2005; 101(4): 1246 - 1246. [Full Text] [PDF]
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