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Eur J Cardiothorac Surg 2001;19:294-301
© 2001 Elsevier Science NL
Nemours Cardiac Center, Alfred I. DuPont Children Hospital, 1600 Rockland Road, Wilmington, DE 19899, USA
Received 8 October 2000; received in revised form 1 December 2000; accepted 29 December 2000.
Corresponding author. Nemours Cardiac Center, 85 West Miller Street, Suite 306, Orlando, FL 32806407, USA. Tel.: +1-407-237-6373; fax: +1-407-999-5126
e-mail: cpizarro{at}nemours.org
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Abstract |
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 Top Abstract 1. Introduction2. Materials and methods3. Results4. Discussion5. Summary6. LimitationsAppendix A. Clinical variables...Appendix B. Conference...References |
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Key Words: Hypoplastic left heart syndrome • Norwood procedure • Extracorporeal support • Pediatric • Cardiac surgery
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1. Introduction |
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TopAbstract1. Introduction2. Materials and methods3. Results4. Discussion5. Summary6. LimitationsAppendix A. Clinical variables...Appendix B. Conference...References |
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Due to the limited experience with extracorporeal support and the poorer overall outcome with this particular patient population, single ventricle physiology has been considered a relative contraindication for post-cardiotomy support [6,7]. In this review, we report our experience with ECMO support after the stage I Norwood procedure.
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2. Materials and methods |
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TopAbstract1. Introduction2. Materials and methods3. Results4. Discussion5. Summary6. LimitationsAppendix A. Clinical variables...Appendix B. Conference...References |
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The decision to initiate extracorporeal support was based on the presence of low cardiac output, persistent acidosis, difficulty to balance pulmonary/systemic circulation (Qp/Qs), severe hypoxemia, the presence of arrhythmia, and/or cardiac arrest in the perioperative period. We did not use a specific algorithm or clinical pathway to dictate when extracorporeal support would be employed. Our practice was to employ intravenous (dopamine and sodium nitroprusside) and/or inhalational (CO2/N2) therapies to either redistribute or improve the cardiac output. When these maneuvers were insufficient, then extracorporeal support was provided to the patient. All patients are represented in Table 1.
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2.1.2. Priming components
The priming volume is approximately 450 cc, consisting of Plasma-lyte A which is displaced by fresh whole blood (approximately 24–48-h-old) to achieve a pump hematocrit of 20%. Additional medications include heparin (100 units/kg), solumedrol (30 mg/kg), lasix (1 mg/kg), mannitol (0.5 g/kg), NaHCO3 (10 mEq), oxacillin (25 mg/kg), and gentamycin (2.5 mg/kg). In addition, 100 units/kg of heparin are administered to the patient just prior to cannulation.
2.1.3. Perfusate pathway
Fig. 1 illustrates the pathway for blood during conventional CPB in the operating room. From the venous cannulation, blood drains by gravity to the venous reservoir, then is pumped by the arterial roller pump to the integrated heat exchanger and oxygenator which has ports for laboratory sampling and volume administration. From the oxygenator, blood travels to the arterial cannula; this line includes an arterial to venous bridge which allows recirculation of the A–V loop. This bridge is configured with straight 0.25-inch tubing connectors with luer adapters, stopcocks and 0.25-inch perfusion adapters. This allows the bridge to remain closed to the A–V loop and crystalloid primed until needed, negating the need to ‘flash’ the bridge routinely.
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2.3. Cannulation
All patients received cannulation via median sternotomy using a single right atrial cannula and an arterial cannula in the main pulmonary artery or reconstructed neo aorta. No left atrial cannula was placed for additional drainage if there was an unobstructed intra-atrial communication. In the case of intraoperative institution of support, the patient was kept on the same circuit used for the surgery. The cannulae were kept in place, the pursestrings were controlled with a tourniquet and surgical clips, the chest was closed with a silastic patch, and a direct wall suction catheter was used to evacuate shed mediastinal blood. Adequate cardiac decompression was evaluated by direct inspection and/or echocardiogram. If the patient left the operating room without support, but was considered likely to require it in the immediate postoperative period, then the pursestrings and tourniquets were secured with a surgical clip and left in the chest. This action would facilitate rapid recannulation and the institution of extracorporeal support when needed.
2.4. Flows
The primary goal of the extracorporeal support in this patient population with their parallel circulations was to maintain adequate tissue perfusion, minimize pulmonary overcirculation, and provide time for the myocardial and/or lung dysfunction to recover. The flows (which ranged between 50 and 150 ml/kg per min) were titrated according to each patient's needs, maintaining adequate gas exchange, tissue perfusion and acceptable acid base status. Accordingly, the mechanical ventilatory support and the gas flow through the oxygenator were adjusted to achieve acceptable levels of alveolar gas exchange. While on extracorporeal support, all inotropic medications were discontinued.
2.5. Ventilator
After the initiation of the circulatory support, manipulations in the inspired gas mixture on the ventilator were made to achieve acceptable arterial blood gases. The mechanical ventilatory support was titrated according to the amount of extracorporeal support. If the baby was on greater than 75 cc/kg flow per min, the ventilator would typically be set to provide a 20 cc/kg tidal volume at ten breaths/min with an attendant end expiratory pressure of 10 cm of H2O. The patients received a remifentanil infusion for sedation.
2.6. Shunt management
The prevailing strategy during this experience was to leave the aorta–pulmonary shunt open during the period of support, unless there was a significant degree of run-off towards the pulmonary circuit. If there was a significant fall in the mean arterial pressure (particularly diastolic pressure) and/or significant cardiac distention, the shunt was partially occluded until hemodynamic recovery occurred, at which point the shunt was reopened. The size of the shunt was 4.0 mm, unless the baby was prematurely born, in which case, the shunt was 3.5 mm in size.
2.7. Fluid management
Depending on their fluid status and renal function, these patients were managed with fluid restriction, diuretics and/or ultrafiltration in an effort to decrease interstitial edema and improve cardiopulmonary function. Electrolytes were kept within the normal range and nutritional support was provided.
2.8. Weaning
Once signs of cardiopulmonary recovery were evident as judged by improved hemodynamic parameters, an increase in arterial override, improved cardiac contractility by direct inspection, a well balanced Qp/Qs, and adequate alveolar gas exchange, the extracorporeal support was lowered. The ventilator support was increased and inspired carbon dioxide, low dose dopamine and sodium nitroprusside may have been administered in order to achieve a balance in systemic and pulmonary circulations. This process was monitored by frequent clinical observation and arterial blood gas analysis. Delayed sternal closure was usually performed 24 h after decannulation.
2.9. Statistical analysis
Data analysis was performed using SPSS (SPSS, Inc., Chicago, IL). The cross-tabulation procedure and Fisher's exact test were used for all the discrete variables. The continuous variables were analyzed with a Mann–Whitney test. Statistical significance was determined at P<0.05.
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3. Results |
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TopAbstract1. Introduction2. Materials and methods3. Results4. Discussion5. Summary6. LimitationsAppendix A. Clinical variables...Appendix B. Conference...References |
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There were three patients with a weight of 2 kg or less. Four patients had gestational ages of less than 35 weeks at birth, and two of these patients were products of multiple pregnancy (twins and triplets, respectively). Another patient in this group had a diagnosis of congenital diaphragmatic hernia, hypoplastic left lung and scimitar syndrome, in addition to hypoplastic left heart syndrome. This patient underwent stage I Norwood palliation 3 days after his diaphragmatic hernia repair.
The most common cardiac diagnosis was hypoplastic left heart syndrome of the mitral atresia, aortic atresia variant. One patient with critical aortic stenosis underwent a failed balloon valvuloplasty and had stage I Norwood 2 days later. Another patient had a prenatal diagnosis of severely dilated and poorly functioning left ventricle, associated with mitral valve hypoplasia and mitral regurgitation. The aortic arch was unobstructed but there was retrograde flow via the ductus into the arch. This baby had a stage I palliation at 5 days of age [9].
Other associated cardiac anomalies were present in five patients and included cor triatriatum, dilated myopathy, scimitar syndrome and partial and total anomalous pulmonary venous connection. Additional surgical procedures were performed in two of these patients: a partial ventriculectomy and the repair of total anomalous pulmonary venous drainage, respectively.
Associated non-cardiac diagnoses included: Turner syndrome in one patient, chromosome 11 deletion in another patient, renal dysplasia in a third, and a congenital diaphragmatic hernia as well as scimitar syndrome in the fourth patient.
The mean duration of deep hypothermic circulatory arrest was 56 min, with a range between 46 and 63 min. A comparison of the pre-support variables is shown in Table 2.
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All of the patients who were hospital survivors had initiation of support in the operating room. Subsequently, five of these patients are known to have completed their second stage (hemifontan or bi-directional Glenn). Unfortunately, one of them died at home after his second stage.
There were no hospital survivors in the group of patients who underwent institution of extracorporeal support outside the operating room, either in the pre- or postoperative period (Table 3).
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Four patients required partial closure or total shunt occlusion at the initiation of the support due to the excessive pulmonary overcirculation and inadequate systemic perfusion pressure despite high flows. Only one patient was weaned successfully after 48 h of support, and was eventually discharged from the hospital.
Two patients had a devastating neurological complication and were taken off support. A third patient had no recovery of cardiac function after 5 days on the circuit and was similarly removed from support.
The incidence and comparison of major complications between survivors and non-survivors is shown in Table 4. Non-survivors were more likely to have sustained renal, neurologic, respiratory and bleeding complications, although renal dysfunction was the only event associated with poor outcome (P<0.05). All of the neurologic events were present in the non-survivor group, however, this factor did not reach statistical significance. Sepsis was evenly distributed among survivors and non-survivors.
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4. Discussion |
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TopAbstract1. Introduction2. Materials and methods3. Results4. Discussion5. Summary6. LimitationsAppendix A. Clinical variables...Appendix B. Conference...References |
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Our results demonstrate that in the group of patients who required extracorporeal support after stage I Norwood palliation, 66% (8/12) of them could be successfully weaned from extracorporeal support, and 50% (6/12) were discharged home in good condition. The presence of a residual hemodynamic defect determined a poor outcome in one of our patients. This is consistent with the ECMO literature [5,6,8] that states that extracorporeal support cannot overcome the handicap of an inadequate repair. If the patients with residual surgical defects were excluded, then the overall success rate to hospital discharge was improved to over 50% in our series.
These results may be directly related to the indications, timing and threshold for the initiation of extracorporeal support. Contrary to the experience of other centers, where the intraoperative initiation of support was associated with worse outcomes [3,6,11], our experience revealed the opposite. In fact, we had a lack of survivors when patients were placed on extracorporeal support out of the operating room, and a much better outcome in those patients placed on support in the operating room. This experience is similar to that reported by Jaggers et al. [12], where the early institution of extracorporeal support in the operating room was associated with a better chance of survival to hospital discharge in a cohort of patients, including ten patients with single ventricle. There is little doubt that patients with single ventricle physiology are more vulnerable to myocardial damage and tolerate dysfunction less than other patients who do not have the added demands of balancing two circulations and adapting to an increased volume burden. Therefore, it is not surprising that these patients would require some cardiac support postoperatively. By providing mechanical circulatory support in a timely way, this patient population is afforded time to adjust to the increased demands to its ventricle.
Our strategy of maintaining the shunt open during the extracorporeal support is based on clinical and laboratory evidence that antegrade pulmonary blood flow is beneficial [12,13]. Of course, it is difficult to conclude that leaving a shunt patent during extracorporeal support is the cause of the improved outcome in our patients. Perhaps those patients who were able to have their shunts open had more favorable hemodynamics and that is the explanation for their improved outcome. In fact, those with the worse hemodynamics and the most significant myocardial dysfunction, had low perfusion pressures and significant compromise of their coronary perfusion. In this scenario, closure of the shunt provided temporary improvement of the hemodynamic conditions by increasing the systemic perfusion pressure and coronary blood flow, and decreased the amount of pulmonary overcirculation and cardiac distension. Not surprisingly, in our experience, the patients who required shunt occlusion at the institution of extracorporeal support had the worse hemodynamic profile and required the highest amount of support. We had only one survivor in the group of patients who had their shunts occluded during their support and this patient had his shunt only temporarily occluded. This patient was eventually weaned off and discharged home. Despite the fact that it appeared that occluding the shunt would be associated with a poor outcome, this variable did not reach statistical significance as a risk factor for mortality.
Although not used in our particular patient population, the VAD device is another form of circulatory support to be used when only myocardial dysfunction is present. A recent report by Thuys et al. [14] included 12 patients with hypoplastic left heart syndrome who were managed with this form of support. Although their report only had a 25% hospital survival rate (3/12), it demonstrated the advantages of this form of support: effective reduction in preload and wall stress, decrease in anticoagulation needs, decrease in inflammatory effects related to the device and simplicity [14,15]. This is an attractive modality assuming the lung function and the ability to balance the systemic and pulmonary circulations are adequate.
Despite our reported improvement in survival in this patient population, the morbidity in these patients remains quite high. When looking at different potential risk factors for poor outcome, renal dysfunction was the only factor that reached statistical significance. This is consistent with other reports [5,12]. Bleeding was not a common problem in our experience as opposed to most series [3,5,8,12]. This finding may be related to the use of fresh whole blood in the immediate postoperative period and the use of a heparin-coated circuit, which allowed the maintenance of lower activated clotting times. Consequently, the need for mediastinal exploration was infrequent.
Neurologic complications were mostly related to intracranial bleeding, which is not surprising given this younger aged group. Those infants with neurologic complications were also the ones who had their support instituted after having had a cardiac arrest. The presence of neurologic dysfunction showed a tendency towards a poor outcome, but it did not reach statistical significance, perhaps because of a small sample size.
In reviewing our experience, we believe that satisfactory results can be achieved when using ECMO support for patients after stage I Norwood palliation. It is clear that failure to wean from CPB after the procedure is not a contraindication to this therapy, assuming there are no residual hemodynamic defects. The institution of support after cardiovascular collapse has occurred, unfortunately, remains a significant factor for poor outcome. Early initiation of mechanical circulatory support should be considered when signs of hemodynamic instability are developing. Utilizing the same circuit during surgery or having a circuit primed and ready in case it is needed in the intensive care unit, are some of the techniques that allow for the prompt utilization of this therapy. Unfortunately, in our series of patients, although this plan has minimized the time to cannulation in an emergency situation, the survival for post-arrest support remains poor.
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5. Summary |
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TopAbstract1. Introduction2. Materials and methods3. Results4. Discussion5. Summary6. LimitationsAppendix A. Clinical variables...Appendix B. Conference...References |
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6. Limitations |
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TopAbstract1. Introduction2. Materials and methods3. Results4. Discussion5. Summary6. LimitationsAppendix A. Clinical variables...Appendix B. Conference...References |
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Acknowledgments |
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Footnotes |
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Appendix A. Clinical variables evaluated |
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TopAbstract1. Introduction2. Materials and methods3. Results4. Discussion5. Summary6. LimitationsAppendix A. Clinical variables...Appendix B. Conference...References |
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Support and post-support variables: Atrial pressure, mean arterial blood pressure, ventilatory settings, pharmacological support, shunt open/closed, duration of support, reoperation, delayed sternal closure, creatinine during support, creatinine 24 h post-support, ultrafiltration, whole blood transfusion, packed red blood cells transfusion, weaning off support, mediastinal exploration, bleeding, respiratory failure, neurologic event, gastrointestinal complication, renal dysfunction, sepsis, circuit complication, ICU days, duration of mechanical ventilation, length of hospital stay.
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Appendix B. Conference discussion |
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TopAbstract1. Introduction2. Materials and methods3. Results4. Discussion5. Summary6. LimitationsAppendix A. Clinical variables...Appendix B. Conference...References |
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I would like to just ask you, what are your criteria for this? Is it based on lactic acid, mean arterial blood pressure, do you measure mixed venous oxygen? How do you determine that systemic perfusion is inadequate and that you need to partially or completely occlude the shunt?
Dr Pizarro: Certainly, the issue of shunt management has been raised by different groups, and it looks like the patients who had the shunt closed since the inception of the support tended to do poorly and some people attributed that to the fact that if you leave the shunt closed, then you have some problems with pulmonary complications, reperfusion injury and so forth.
I think that part of the problem is the fact that patients select out themselves. If you need to close the shunt because the run-off is excessive, the diastolic blood pressure and coronary perfusion are compromised and the overall systemic perfusion is also inadequate, those patients are certainly the sickest patients who need the largest amount of support for the most prolonged time. It is fairly difficult to manage those patients, and whatever you do, probably your outcome is going to be worse than if you are able to leave the shunt open.
Our approach has been to watch for mean arterial blood pressure, a minimum diastolic blood pressure, in the 25–30 range, normalization of the ECG, and, avoid cardiac distension, and for that we will just have a quick look at the echocardiogram or direct cardiac inspection if we are exploring the patient and make sure the heart is decompressed. If we can't decompress the heart because there is large run-off through the lungs, then that heart is going to have a fairly large end diastolic volume and the chances of recovery are going to be very poor. So that is basically what we used.
Dr A. Corno (Lausanne, Switzerland): I have two questions. As a result of this retrospective study, how did you change your policy on indication for ECMO after a Norwood? For instance, I noticed in prematurity you have all failures of the ECMO application. Are you now intending to refuse ECMO for a premature child after a Norwood?
And the second question, of course you are dealing with a patient who is cyanotic after a Norwood procedure; saturation is generally 73%. How do you begin and how do you run the ECMO, with a normoxic style or hypoxic or hyperoxic style?
Dr Pizarro: First, premature babies or babies with low birth weights, CBR, IUGR, are certainly the most difficult subset of patients, and we actually had no survivors among those. However, I would say that before we could declare somebody dead if somebody crashes and has a significant collapse, our first initial response now is going to be to place them on support and see what happens in the first 48 h, and that is how actually this whole experience began. It turned out that some patients did well, and certainly premature babies, so far we haven't been able to rescue any of them.
In reference to your second question, we normally put the patient on full flow or whatever flow is necessary for adequate systemic perfusion, and let's say if we have a flow of over 75 ml/kg per min, we tend to set the ventilator at resting mode, ten breaths/min and between room air and 30%. We will just run that patient normoxic with hematocrits between 30 and 35. The difficulty begins when you try to start weaning and that transition between the patient, assuming cardiopulmonary function and then you are decreasing the amount of support, that is where trying to balance the two circulations, it gets very tricky, and some patients fail in that stage.
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References |
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TopAbstract1. Introduction2. Materials and methods3. Results4. Discussion5. Summary6. LimitationsAppendix A. Clinical variables...Appendix B. Conference...References |
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