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Ann Thorac Surg 1995;59:1120-1125
© 1995 The Society of Thoracic Surgeons
Division of Cardiothoracic Surgery, University of California, San Francisco, California
Accepted for publication December 23, 1994.
| Abstract |
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| Introduction |
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The bidirectional superior cavopulmonary shunt (BSCPS) procedure has become a well-established intermediate-stage palliative procedure en route to a Fontan operation in patients with a single ventricle [16]. It is generally performed as a second-stage procedure following the take-down of an arterial shunt or a pulmonary artery (PA) band, or sometimes it is performed as the first procedure in older infants or children who have a naturally balanced pulmonary blood flow. The benefits of a BSCPS procedure are (1) it avoids volume overload of the single ventricle and its attendant sequelae; (2) it prevents the PA distortion seen with systemic-to-PA shunts and PA bands; (3) it prevents the development of pulmonary vascular obstructive disease; and (4) it provides an opportunity to perform other required surgical procedures (eg, PA plasty, atrioventricular valve repair, bulboventricular foramen enlargement, the Damus-Kaye-Stansel procedure, or repair of other coexisting lesions) before a Fontan operation. These benefits are likely to promote a better early and possibly a better late outcome from the Fontan procedure. Despite its wide application and an increasing number of reports in the literature documenting its benefits [16], there has been a general reluctance to perform a BSCPS procedure in very young infants. The possible reasons for this include concerns over elevated or labile pulmonary vascular resistance in very young infants, poor outcomes reported for classic Glenn shunts in infants [710], and possibly fixed notions relating to reluctance to perform Fontan operations in very young infants. Albanese and associates [6] describe a successful outcome from BSCPS in 1 patient who underwent it as the primary procedure. There is only one study reported in the literature that explored the outcome from BSCPS in infants between 4 to 6 months of age, mostly done as a second-stage procedure [11]. The feasibility of performing BSCPS as the primary procedure in infants within the first several months of life has not been explored systematically, even though well-established concepts regarding the timing of maturation of the pulmonary vasculature [12] would support its use at this time. Encouraged by the potential benefits of early primary BSCPS procedures already mentioned, and by the chance to reduce the total number of operations in patients who will ultimately undergo a Fontan operation, we have adopted a policy of performing the BSCPS procedure in selected very young infants.
| Material and Methods |
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The azygos vein (and hemiazygos vein) was ligated in all cases. The SVC was transected at the level of the branch (right/left) PA and the cardiac end was oversewn. An adequate longitudinal pulmonary arteriotomy was made on the superior surface of the branch PA, and the cavopulmonary anastomosis was made with 7-0 Maxon suture (D & G Monofil Inc, Manati, Puerto Rico) using the continuous suture technique. When deep hypothermia was employed for any additional surgical procedures, the BSCPS procedure was performed during rewarming. If atrial septectomy was the only additional intracardiac procedure, the heart was fibrillated for a brief period to accomplish this.
After completion of the procedure, a temporary pressure monitoring line was placed into the PA by way of the right SVC. The PA pressure, pull-back gradient across the cavopulmonary anastomosis, and SVC pressures were then obtained and the catheter was removed. A right atrial catheter was placed simultaneously for measuring atrial pressure. This was left in situ until the patient was extubated.
| Results |
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Pressure Data
The immediate postbypass SVC pressure ranged from 8 to 12 mm Hg (mean ± standard deviation [SD], 10.1 ± 1.45 mm Hg). In 4 patients the PA pressure increased from a mean ± SD of 10.75 ± 1.5 mm Hg (range, 9 to 12 mm Hg) to a mean ± SD of 14.25 ± 3.3 mm Hg (range, 11 to 18 mm Hg) after the new source of pulmonary blood flow was added. The PA pressures were identical to the SVC pressures in all patients, indicating that there was no anastomotic gradient. The atrial pressure ranged from 3 to 6 mm Hg (mean ± SD, 3.9 ± 1.17 mm Hg). The transpulmonary gradient ranged from 5 to 13 mm Hg (mean ± SD, 7.78 ± 2.44 mm Hg), with the higher gradients present in those patients with an extra source of pulmonary blood flow.
Arterial Oxygen Tension Trends
In 4 of our first 5 patients, the PaO2 was low (21 to 26 mm Hg) despite a low SVC and PA pressure (9 to 12 mm Hg) immediately after the discontinuation of CPB. Because of this relative hypoxia, an extra source of pulmonary blood flow was added (see Table 2
). The PaO2 gradually improved during the ensuing few hours after bypass and continued to improve over the first 24 to 48 postoperative hours. Based on this observation, we changed our strategy in the next 4 patients. The BSCPS procedure was performed without CPB if technically feasible, and if no other intracardiac procedures were necessary. If CPB was necessary, a low postbypass PaO2 was accepted without providing an additional source of pulmonary blood flow, with the expectation that the PaO2 would rise during the convalescent phase, as it had in the initial 5 patients. In our last 3 patients, the BSCPS procedure was performed without bypass and the early postoperative PaO2 in these patients was higher (see Fig 1
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Postoperative Course
There was no hospital mortality and 6 patients (67%) had an uncomplicated hospital course (see Table 2
). The 9 patients were ventilated for a median duration of 30 hours, required a median intensive care unit stay of 4 days, and were discharged after a median hospital stay of 10 days. Three patients required a prolonged hospital stay. Bacterial pneumonia developed in patient 5; this was treated with appropriate antibiotics and the patient was extubated 8 days after operation. Patient 4 had the asplenia syndrome, a single ventricle with pulmonary atresia, a total anomalous pulmonary venous connection, severe central PA hypoplasia, and bilateral SVCs. In addition to undergoing bilateral BSCPS procedures, this patient required deep hypothermic circulatory arrest to allow for repair of the total anomalous pulmonary venous return. This patient, who was in the first half of our experience, also received a 2-mm right, modified Blalock-Taussig shunt because of concerns about early postbypass hypoxia. The patient was extubated 10 days after operation, but she required an intensive care unit stay of 45 days and was discharged from the hospital after 74 days. During the early postoperative period, placement of a left axillary artery line was attempted and caused left subclavian vein thrombosis. Decompression of the left upper body venous return through venous chest wall collaterals into the inferior vena cava system developed because of the left subclavian vein thrombosis, causing chronic hypoxia. Because of this, she remained dependent on her right modified Blalock-Taussig shunt. Chronic pleural effusions developed related to her hemodynamic status, which amounted to the combination of a Glenn plus a systemic-to-PA shunt.
Patient 8 underwent a successful BSCPS procedure without CPB. The early postoperative PaO2 was 45 mm Hg and the SVC pressure was 10 mm Hg. Viral pneumonia developed in this patient postoperatively and she became progressively more hypoxic. The patient underwent reexploration on the third postoperative day. The BSCPS was found to be functioning normally, but the pulmonary venous saturation was 86%. To relieve the severe hypoxia, the BSCPS had to be taken down to a classic Glenn shunt and antegrade blood flow from the right ventricle to the left lung was allowed by removing the main PA ligature. This patient was extubated 9 days after operation, required an intensive care unit stay of 32 days, and was discharged from the hospital 40 days after the BSCPS procedure.
Patient 2 was readmitted with bilateral pleural effusion 2 weeks after discharge from the hospital. This patient had initially received an extra source of pulmonary blood flow and the PaO2 at discharge exceeded 55 mm Hg. The pleural effusions resolved within 2 days of removing the extra source of pulmonary blood flow by completely ligating the main pulmonary artery. The PaO2 stabilized above 40 mm Hg.
Follow-up
All 9 patients were followed up from 3 to 16 months (median, 11 months; mean ± SD, 9.22 ± 4.5 months). There were two deaths (22%) on follow-up. Patient 4, who had the asplenia syndrome and suffered left subclavian vein thrombosis postoperatively, was eventually discharged on postoperative day 74. However, she never thrived and suffered from numerous problems typically related to a full-blown heterotaxy syndrome. She required several general surgical operations to relieve gut malrotation and gastroesophageal reflux, and also required multiple hospitalizations for the treatment of episodes of moderate hypoxia and pleural effusions. Because of her thrombosed left subclavian vein and subsequent venous collateralization combined with relatively higher PA pressures due to the Blalock-Taussig shunt, the only real option for the patient was conversion to a complete Fontan shunt. This was planned somewhat arbitrarily to be done when she was a year old, but she died of an undiagnosed pulmonary illness at a local hospital at 11 months. As no autopsy was performed, the exact cause of death could not be ascertained. Another patient (No. 7), who had the polysplenia syndrome with an interrupted inferior vena cava and hemiazygos continuation and bilateral SVCs, underwent bilateral BSCPS procedures (Kawashima procedure) at 60 days of life, and had an uncomplicated postoperative course. At 5 months after operation he was evaluated because of increasing cyanosis, and was found to have extensive pulmonary arteriovenous fistulas on the basis of cardiac catheterization and contrast echocardiography findings. He died 2 days after cardiac catheterization with profound and progressive hypoxia.
In patient 8, who had suffered viral pneumonia requiring take-down of the BSCPS to a classic Glenn shunt with antegrade flow to the left PA, the viral lung injury resolved gradually and she was left with excessive left lung blood flow. She had a 3.5-mm central shunt placed to the left PA and underwent main PA ligation 2 months after her original procedure. She was reevaluated 3 months later with cardiac catheterization, which showed an aortic saturation of 84% and both a right and left PA pressure of 12 mm Hg. At the present time she and the remaining 6 patients are doing well clinically. Ongoing evaluation is planned in these 7 patients, followed by an elective Fontan procedure at 3 to 4 years of age.
| Comment |
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There has been a general reluctance to perform or a failure to consider performing the BSCPS operation in young infants, and there are several probable reasons for this: (1) it is likened to a Fontan operation, in that both provide systemic venous blood directly to the lungs, and in general there is a great reluctance to performing a Fontan operation in younger infants; (2) there have been concerns over the pulmonary vasculature being reactive and labile in very young infants; and (3) there were early reports of poor outcome in young infants after a classic Glenn shunt procedure [710].
In a recent report Chang and associates [11] have shown that the BSCPS procedure can be safely performed with good results in infants as young as 4 to 6 months, usually as a second-stage procedure after a standard neonatal palliative procedure. The present study shows that the BSCPS operation can be performed as a primary procedure in selected patients as early as 5 weeks of age with excellent hemodynamic results. This approach has a number of advantages. It eliminates the need for the traditional first-stage procedures, such as systemic arterial shunting and PA banding. This minimizes PA manipulation and subsequent distortion. The reduction in the number of procedures will also have a favorable impact on cost. It also decreases to a minimum the length of time the single ventricle is volume overloaded. Excessive shear force on the pulmonary vasculature is also reduced. Recent evidence suggests that increased shear force can cause endothelial dysfunction within weeks in a neonatal animal model [15].
The most general benefit of our experience is that it demonstrates the feasibility of the procedure and thereby expands the limits of the procedure. Even if a particular institution does not choose to adopt this approach as a routine one, it can use this information in specific circumstances, such as in the infant with a regurgitant common atrioventricular valve that is sensitive to volume overload or the young infant with pulmonary atresia with an intact ventricular septum and marked coronary abnormalities who demonstrates poor left ventricular function. These infants would benefit from the reduced left ventricular work and higher diastolic coronary blood pressure brought about by conversion of a systemic shunt to a BSCPS.
It can be argued that 4 of the 9 patients in the present series required an extra source of pulmonary blood flow, thereby negating some of the benefits. However, our surgical approach has evolved with experience and we no longer believe that an extra source is necessary. The early postoperative hypoxia seems to be best explained by the well-known transient effects of CPB on the lungs [16]. An early postoperative PaO2 of 100 to 150 mm Hg on a fraction of inspired oxygen of 100% in the neonate who has undergone a two-ventricle repair (such as an arterial switch) is not a concern, but clearly lung dysfunction is present. In the setting of BSCPS physiology, however, the equivalent lung injury results in a concerning, albeit transient, hypoxia.
Our present approach is to perform the BSCPS procedure without CPB if feasible. If CPB is used for additional procedures, we accept the initial hypoxia with the knowledge that the PaO2 will reliably improve in the postoperative period. Any neonatal patient who is not ``duct-dependent'' for pulmonary blood flow can theoretically be managed by a primary BSCPS procedure as early as 4 to 6 weeks of age. Such patients will either have relatively low pulmonary blood flow or pulmonary overcirculation, or the flow may be naturally balanced. All of these conditions are relatively well tolerated using medical management techniques for the limited period of time before the primary BSCPS procedure.
The pleural effusions in 2 patients were related to an extra source of pulmonary blood flow. This association has also been recently reported by Mainwarning and associates [17]. The onset was delayed in 1 patient, and removal of the extra source of pulmonary blood flow resulted in prompt resolution of the effusions. The extra source in the second patient, a Blalock-Taussig shunt, could not be ligated completely because of subclavian vein thrombosis and venous collateralization. The iatrogenic complications in this patient were preventable. This patient and 1 other patient (with postoperative viral pneumonia) required prolonged (>3 weeks) hospitalization.
Medium-term follow-up has revealed that 7 patients are doing extremely well. The 2 patients who died had complex conditions, each a form of heterotaxy syndrome. One patient had all of the cardiac and abdominal malformations of asplenia syndrome. Although this patient had a poor prognosis simply on the basis of her disease, she nevertheless suffered principally from iatrogenic and preventable complications during her prolonged hospital course. The patient with polysplenia who had an uncomplicated early course, had extensive pulmonary arteriovenous fistulas develop in both lungs (left more than right) and died of hypoxia 5 months after operation. Although the development of pulmonary arteriovenous fistulas after BSCPS and classic Glenn shunt procedures is a known but unusual complication, it is generally seen a few years after these venous shunt procedures are performed [18, 19]. We are unaware of any patients reported in the literature in whom pulmonary arteriovenous fistulas developed this rapidly. Whether cavopulmonary shunts in young infants expedite the development of such fistulas is not clear. The incidence of this problem is also markedly higher in patients with polysplenia, compared with that in other morphologic subsets of patients with single ventricles [20].
It is important to know that there are some theoretic disadvantages to doing very early cavopulmonary shunt procedures. Because the ratio of pulmonary flow to systemic flow in the setting of BSCPSs is 0.4 to 0.5, there is a concern that low flow into a maturing lung may adversely affect the growth of PAs and pulmonary parenchyma. This question can only be answered by critical follow-up evaluation of the PA anatomic characteristics by echocardiography, angiography, and intraoperative lung biopsy. Animal models of cavopulmonary shunts may also be helpful.
The number of patients in this report is too small to permit any meaningful statistical comparisons to be done. Therefore it is inappropriate to make any firm recommendations based on our experience. However, some important inferences can be drawn from our findings. A BSCPS operation can be accomplished as the primary procedure in very young infants with excellent hemodynamic results. Pulmonary vascular resistance was not an issue in any of these patients. Excellent pulmonary gas exchange is critical to the success of this approach. The relative early hypoxia is reversible, and is most likely due to CPB-related pulmonary dysfunction. Therefore avoiding the use of CPB when possible and avoiding an extra source of pulmonary blood flow when CPB is required are recommended.
| Footnotes |
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Presented at the Forty-third Annual Meeting of the American College of Cardiology, Atlanta, GA, March 1317, 1994.
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