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Ann Thorac Surg 2000;69:1499-1504
© 2000 The Society of Thoracic Surgeons
a Service de Chirurgie, Marie Lannelongue Hôpital, Université Paris Sud, Le Plessis-Robinson, France
Address reprint requests to Dr Alkhulaifi, Harefield Hospital, Harefield, Hill End Rd, Middlesex UB9 6JH, United Kingdom
e-mail: abdulalkh{at}talk21.com
| Abstract |
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Methods. Between March 1993 and December 1998, 79 systemic pulmonary shunts were performed in 75 neonates with cyanosis and severely reduced pulmonary blood flow. The mean age was 11.5 days and the mean weight, 3 kg. All neonates were dependent on duct flow and prostaglandin E1 infusion for adequate oxygenation.
Results. The systemic pulmonary shunt was performed through a right thoracotomy in 36 patients, left thoracotomy in 6, and median sternotomy in 33 patients. The 30-day mortality was 3 patients (4%). Univariate and logistic regression analyses revealed a weight less than 2 kg (p = 0.039) and preoperative mechanical ventilation (p = 0.008), to be predictors of early mortality, whereas pulmonary hypoplasia (p = 0.55), diagnostic group (p = 0.79), shunt size (p = 0.2), and surgical approach (p = 0.5) were not. There were seven episodes of shunt-related complications that required early intervention.
Conclusions. Systemic pulmonary shunt remains an effective palliative measure in cyanotic neonates despite specific complications. Both low weight and preoperative ventilation represent significant risk factors for early mortality.
| Introduction |
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This report describes our experience with systemic pulmonary shunting in 75 neonates presenting with severe cyanosis. It also examines the factors that may contribute to morbidity and mortality and also compares the median sternotomy with the conventional thoracotomy approach.
| Material and methods |
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Medical and surgical management
The medical and surgical management consisted of resuscitative measures using oxygen therapy and intravenous prostaglandin E1 infusion. Intravenous bicarbonate was also given and titrated in response to metabolic acidosis. Five neonates (6%) suffered severe oxygen desaturation despite initial resuscitative measures and therefore, required immediate endotracheal intubation and mechanical ventilation before systemic pulmonary shunting.
In all but 1 patient an expanded polytetrafluoroethylene (Gore-Tex, WL Gore & Associés, Evry Cedex, France) graft tube was used. In 1 neonate a classic Blalock-Taussig shunt was performed between the right subclavian and the right PA.
Thirty-six patients (48%) underwent systemic pulmonary shunting through a right thoracotomy, 33 (44%) underwent median sternotomy, and 6 (8%) through a left thoracotomy. The left thoracotomy approach was performed in patients with a right-sided aortic arch and dextrocardia. Of the 33 neonates who underwent median sternotomy 3 had a central aortopulmonary artery shunt using tube graft, whereas 30 neonates underwent either right subclavian or brachycephalic artery to a right PA interposition tube graft.
Technique of median sternotomy
Once the sternum has been vertically split and part of the entire thymus removed, the pericardium is opened in its cephalad portion leaving it intact for a variable length near the diaphragmatic attachment. Leaving part of the pericardium intact over a variable extent of the right ventricle adds protection on resternotomy. The pericardium is then suspended.
Sharp dissection of the right PA and the brachycephalic artery and their branches follows. To enable smooth and unobstructed dissection of these vessels, the aorta must be retracted to the left, the superior caval vein is retracted to the right, and the right atrium is retracted inferiorly (Fig 1). Once isolated these vessels are encircled with Silicone elastomer vascular loops.
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Two marker stitches are placed: one on the undersurface of the selected artery for anastomosis and another, on the superior surface of the right PA very close to the bifurcation of the main PA.
The innominate vein crossing in front of the neck vessels may be retracted superiorly during the innominate arterial anastomosis. It is important to optimize access by adequate and sensible retraction, and to ensure full proximal and distal control of the vessels at all times.
An additional unique feature of the median sternotomy approach is the avoidance of lung compression, which is often encountered during thoracotomy. This is particularly important in the case of the very sick neonate who may not be able to tolerate prolonged lung compression during the procedure.
Data presentation and statistics
Statistical analyses were performed using the SAS software (Statistical Analysis Systems, SAS Software Ltd, Marlow, UK). Summary statistics were presented as either means or proportions with the 95% confidence limits (CL) indicated for means or proportions, respectively. The preoperative and postoperative oxygen saturation and pH measurements were compared using the Wilcoxon matched pairs signed rank sum test.
2 univariate analysis or the Fishers exact test were used initially to assess the following risk factors, with mortality and shunt failure representing, separately, the dependent variable: weight less than 2 kg, the presence of pulmonary hypoplasia (branch PA,
3 mm), the diagnostic group, surgical approach, the size of the shunt used, and preoperative mechanical ventilation. The multivariate nature of the significant risk factors and their importance as isolated or joint predictors of mortality was also assessed using stepwise logistic regression. A p value less than 0.05 was considered significant.
| Results |
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After operation all surviving patients were mechanically ventilated for a variable length of time maintaining peripheral oxygen saturations at more than 85%. Intravenous bicarbonate (8.4%) was titrated against the level of acidosis. On arrival in the intensive care unit all patients underwent echocardiographic examination to visualize the shunt and establish early baseline patency for comparison with subsequent examinations.
Mortality
There were three deaths (4%; 95% CL 0% to 12%) within 30 days of the procedure. One patient, with pulmonary atresia and intact septum, died after a central anastomosis performed on cardiopulmonary bypass through median sternotomy. At the end of cardiopulmonary bypass this patient was unable to maintain adequate oxygen saturations despite a widely patent shunt. Another patient, with pulmonary atresia/ventricular septal defect, had a 5-mm shunt tube between the innominate artery and the right PA, and subsequently developed pulmonary edema due to excessive flow through the shunt. The shunt had to be partially clipped to reduce its size, but the patient died as a result of septicemia. One patient, with univentricular heart, died in the immediate postoperative period of sudden cardiac arrest and unsuccessful resuscitation.
Early shunt-related complications
There were seven episodes (9%; 95% CL 0% to 21%) of early shunt-related complications (Table 1 ), with five episodes in 42 thoracotomies, and two episodes in 33 median sternotomies. Two patients with pulmonary atresia (ventricular septal defect in 1) developed excessive pulmonary blood flow through the shunt and congestive cardiac failure and subsequently required reoperation within 48 hours with reduction of the diameter of the shunt with the use of a metallic clip (Table 1). One patient developed septicemia and died soon after, whereas the second patient made good recovery. In addition there were four episodes (4 of 75, 5%; 95% CL 0% to 14%) of acute thrombosis of the shunt. Two patients with tetralogy of Fallot suffered acute thrombosis of a Blalock-Taussig shunt (3.5 and 4 mm) performed through the right thoracotomy within the first 24 hours after operation. One patient underwent immediate complete correction, whereas the second patient received a second shunt placed at the site of the ductus with subsequent total complete correction performed a month later. Both of these patients made an excellent recovery after the curative procedures.
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The only patient who underwent a classic Blalock-Taussig shunt, with an original diagnosis of DORV with subpulmonary ventricular septal defect, required the insertion of a systemic pulmonary shunt 24 hours later due to increasing cyanosis and inadequate flow through the classic anastomosis. The patient underwent biventricular repair 29 months later with a satisfactory outcome.
Oxygen saturations
The mean time to extubation was 4.1 days (95% CL 2.8 to 5.4 days) and the mean total hospital stay was 12.5 days (95% CL 10.6 to 14.5 days; Table 2). There were no differences in recovery time in relation to the surgical approach (ie, thoracotomy versus median sternotomy).
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Follow-up and duration of palliation
All of the 72 in-hospital survivors were followed up for a mean period of 13.4 months (range, 1 to 29 months). The follow-up was terminated when patients underwent a surgical procedure aimed at establishing a single or two-ventricle hemodynamic physiology, or due to premature death.
There were two deaths during follow-up; 1 patient died suddenly and unexpectedly 17 months after operation and immediately before the construction of a bidirectional Glenn shunt; the second patient died 12 months after operation due to a cerebrovascular accident, the exact nature of which could not be defined because of lack of postmortem examination.
Six patients (7%) required additional systemic pulmonary shunts on the opposite side. Their lesions included tetralogy of Fallot in 2 patients, pulmonary atresia with intact septum in 1 and ventricular septal defect in another, 1 DORV, and 1 patient with double inlet single ventricle. Two of these shunts were performed elsewhere. The mean follow-up period of the patients who underwent a second shunt was 18.2 months (95% CL 7 to 29 months). These patients exhibited increasing cyanosis despite the patency of the systemic pulmonary shunts. Definitive operation was thought to be inappropriate in this selected group of infants on the basis of low weight for age or the presence of multiple stenoses and poor growth of the pulmonary vasculature. These episodes were not classified as shunt failure as shunt patency was demonstrated in all patients by angiography.
Before definitive repair all patients were subjected to cardiac catheterization and angiography. Overall rate of PA distortion, which was defined as significant branch artery lumenal stenosis (50% or more) close to the shunt, was seen in 5 patients (2 tetralogy of Fallot, 1 DORV, 2 pulmonary atresia/ventricular septal defect), 2 patients of which received size 3.5 mm tube whereas 3 patients received size 4 mm tube. This relatively low incidence of severe PA distortion may be related to the smaller tube size used as well as the choice of fine suture material (7-0 and 8-0). Forty patients (55%) completed follow-up either by undergoing biventricular repair (24 patients, 33%) or a univentricular repair (16 patients, 22%). There were no deaths after definitive operation in this group.
The remaining 32 surviving patients (46%), including 5 who underwent a second shunt, are awaiting further operation.
Of the 33 patients who underwent median sternotomy for shunt construction, 20 patients underwent resternotomy for either subsequent univentricular or biventricular repair. There were no complications at the second resternotomy procedure in these patients.
Risk factor analysis
On the basis of univariate analysis weight less than 2 kg (p = 0.02) and preoperative mechanical ventilation status (p = 0.002) were significant risk factors for early mortality. On the other hand pulmonary branch hypoplasia (p = 0.55), diagnostic group (p = 0.79), and shunt size (p = 0.2) had no direct influence on mortality (Table 3).
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| Comment |
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Previous reports have shown that the 4-mm tube graft was associated with inadequate palliation [4]; this was based on data collected from a relatively nonuniform population of patients that included an age range of 1 to 84 days. Additional risk factors, such as pulmonary artery distortion, remain important complications after shunt construction [5], which can be dealt with at the time of the definitive repair.
Although the most common approach for this shunt has been the thoracotomy incision, we have found that median sternotomy offers additional advantages. Median sternotomy enables construction of the anastomosis at the side of the superior caval vein onto the right PA, thus allowing repair of the PA at the time of the bidirectional Glenn, for single ventricle physiology. In addition, anastomosing the shunt closer to the PA bifurcation, allowing even distribution of blood to both lungs, is highly desirable. Preferential flow to one or other lung and unequal growth of the PAs have been observed in shunts constructed through the thoracotomy approach [16].
The median sternotomy remains a less demanding operation for shunt construction, with greater control of the vessels without the risk of lung compression and its attendant respiratory compromise. In a number of patients one is able to institute cardiopulmonary bypass to complete the shunt in small and sick neonates who may not tolerate lung compression through a thoracotomy. The complications rate is significantly lower in patients undergoing median sternotomy. Whether this is due to easier access through the median sternotomy remains to be defined. The finding that the thoracotomy approach is associated with more complications has been noted by other researchers who based their findings on a less homogenous group of patients spanning wider age and weight ranges [17].
During recent years the median sternotomy has become the routine approach for systemic pulmonary shunt construction. The resternotomy has not been associated with an increased incidence of complications. Indeed, the definitive repair with a single scar may provide a significant cosmetic advantage. Coupled with this change in surgical approach we have also found that small shunt sizes of 3.5 mm in neonates are adequate in maintaining blood flow to the pulmonary circulation. More recently we have used size 3 mm in a neonate with satisfactory results.
In conclusion, the significant management of systemic pulmonary shunt in neonates presenting with severely reduced pulmonary blood flow remains controversial. in this series the early mortality was 4%, and shunt-related morbidity 9%; weight less than 2 kg and preoperative mechanical ventilation were significant risk factors. The use of the median sternotomy approach and small shunt size (3 to 5 mm) have been useful to improve the safety of this procedure.
| Acknowledgments |
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| References |
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