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Ann Thorac Surg 2004;77:18-22
© 2004 The Society of Thoracic Surgeons
a Divisions of Pediatric Cardiac Surgery, Doernbecher Children's Hospital, Oregon Health & Science University, Portland, Oregon, USA
b Kosair Children's Hospital, University of Louisville, Louisville, Kentucky, USA
* Address reprint requests to Dr Ungerleider, Oregon Health & Science University, Doernbecher Childrens Hospital, 3181 SW Sam Jackson Park Rd, Mail Code L353, Portland, OR 97239, USA
e-mail: ungerlei{at}ohsu.edu
Presented at the Forty-ninth Annual Meeting of the Southern Thoracic Surgical Association, Miami, FL, Nov 79, 2002.
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METHODS: Eighteen consecutive infants undergoing Norwood operation for HLHS (Oregon Health & Science University [OHSU] 13; University of Louisville [UL] 5) were placed on a ventricular assist device (VAD) immediately following modified ultrafiltration in the operating room using the cardiopulmonary bypass (CPB) cannulas that were in the right atrium and the neoaorta. VAD flows were maintained at approximately 200 mL · kg-1 · min-1 and the patients were transported to the intensive care unit (ICU). Patients operated at OHSU also received neurodevelopmental testing before their Glenn procedure, approximately 4 to 6 months following their Norwood operation.
RESULTS: All patients were stable on VAD support and no attempt was made to balance the systemic and pulmonary circulation. The ventilator was manipulated to achieve systemic Pa02 between 30 and 45 mm Hg and PaC02 between 35 and 45 mm Hg. Evidence of hypoperfusion (increasing lactates) was managed by increasing the VAD flow. Lactates normalized [< 2 mmol/L]) by 1.8 ± 1.1 days following surgery. Average time of VAD support was 3.1 ± 1.0 (range, 2 to 5 days) and average time until chest closure was 3.4 ± 1.5 (range, 2 to 8 days). There were two cases of postoperative bleeding (11.1%) requiring reexploration and one case of mediastinitis (5.5%) in a patient who has now gone on to successful Glenn. Sixteen of the eighteen patients survived (hospital survival mean 89% with a 95% confidence interval of 63.9% to 98.1%; 12/13 OHSU [92.3%]; 4/5 UL [80%]). Neurodevelopmental testing using the Mullen Scales of Early Learning and the Vineland Adaptive Behavior Scale were normal for all infants tested.
CONCLUSIONS: Routine postoperative use of VAD can support the increased cardiac output demands of infants following Norwood operation and results in a stable postoperative convalescence that does not require aggressive ventilator or inotrope manipulation. Although not a panacea, this strategy can simplify postoperative management, lead to excellent hospital survival, and possibly augment cerebral oxygen delivery, resulting in improved neurologic outcomes for this challenging group of patients.
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| This article has been selected for the open discussion forum on the CTSNet Web site: http://www.ctsnet.org/discuss
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Since the initial success by Norwood with surgical palliation for hypoplastic left heart syndrome (HLHS) in 1980 [1, 2], numerous contributions have been made to improve the outcome for infants born with this defect. Although some centers have achieved excellent results, overall success with respect to hospital survival and neurologic outcome following the Norwood procedure at most centers remain inconsistent. Hospital mortality is relatively high, especially compared to the outcomes for surgery for other types of congenital heart defects [3, 4]. Survivors often showed a high incidence of neurologic impairment as manifested by mental retardation, cerebral palsy, and learning disability [57].
Experience with postoperative mechanical circulatory support following the Norwood procedure has been inconsistent [816]. Initial reports were discouraging and suggested that the use of extracorporeal membrane oxygenation (ECMO) was complicated, expensive, and only rarely successful. The major problem with ECMO related to bleeding, since patients on ECMO require anticoagulation. However, by leaving the systemic-to-pulmonary shunt open, it is not necessary to place an oxygenator into the circuit because the patient's lungs serve quite effectively as an oxygenator. Thus, a much lower level of anticoagulation is needed leading to less postoperative bleeding. This strategy has led to excellent results in patients who experience hemodynamic collapse following the Norwood procedure [17].
Unfortunately, it is not possible to reliably predict when a patient will suddenly deteriorate following the Norwood procedure and emergent institution of ECMO in these patients often results in poor outcome. Survival depends on an adequate cardiac output to perfuse the pulmonary and the systemic circulations. As long as cardiac output is adequate, systemic and pulmonary perfusion is maintained resulting in good hospital survival and neurologic outcome [18, 19].
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Reports of VAD support following Norwood stage I have focused on application to patients with severe hemodynamic compromise and, in most of these instances, VAD support has been emergently applied to the acutely deteriorating heart. Results have been poor with respect to patient outcome and the length of support time has been long [25].
The circuit we used for mechanical circulatory support was a modified ECMO circuit without an oxygenator. It would be relatively simple to add an oxygenator to the circuit and convert the patient to ECMO support if necessary. Because of the high flow rates (approximately 200 mL · kg-1 · min-1), it is not necessary to anticoagulate the patient (at least initially) and the ability to give protamine while the patient's cardiac output is being supported by VAD helps with hemostasis and maintenance of post repair stability. Because cardiac output is supported by mechanical means, it is possible to utilize larger shunts (all OHSU patients, including one who weighed only 1.6 kg, had 4-mm shunts and 3 of 5 UL patients had 4-mm shunts). This leads to improved pulmonary blood flow, higher oxygen saturations, and increased cerebral oxygen delivery. By maintaining cardiac output with VAD during the early postoperative period, patients achieve their own circulatory balance and they no longer require the same level of vigilant support from the ICU staff used for patients managed in more conventional ways.
The use of routine mechanical circulatory support after the Norwood procedure is not a panacea. Two patients died despite postoperative VAD support. One (OHSU) died from causes related to sepsis with positive blood cultures and hemodynamic collapse shortly after removal from the circuit. The other patient (UL) could not adequately oxygenate without mechanical support. Survivors were usually hemodynamically stable the day following surgery, but often were supported with VAD for an additional day or two so that they could be diuresed. When patients were weaned from VAD, it was commonly necessary to augment their hemodynamics with inotropic support for 1 to 2 days. All of this tends to increase the length of ICU stay compared to survivors of conventional management. However, the normal neurologic outcome of survivors, the excellent hospital survival, and the stability during the postoperative period make a compelling case for this strategy, especially for programs that are currently struggling with their results from Norwood.
The routine use of VAD may help some programs achieve excellent hospital survival with good neurologic outcomes for survivors, but will most likely increase cost as well as the need for additional support personnel. Recent enthusiasm for creation of an RV-PA shunt to produce more stable hemodynamics, with less stress on the ICU staff, may provide another feasible option to many programs. Postoperative convalescence may be shorter with the RV-PA shunt strategy and less costly. However, most of these patients have lower systemic oxygen saturation than patients who have a systemic-to-pulmonary shunt. Long-term neurologic outcomes and ventricular function utilizing this strategy will need to be evaluated.
Routine mechanical circulatory assist following Norwood procedure is a novel approach that addresses the increased cardiac output demands during the early postoperative period. Outstanding hospital survival is easily achieved by adopting a strategy that increases cardiac output rather than one that emphasizes ICU responsiveness to balancing a limited cardiac output. Neurologic outcomes for patients managed with this strategy appear to be normal, although more data relating to this issue are being collected in a randomized, comparative manner.
| Acknowledgments |
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| Discussion |
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I have just one question for you. Did you think that using this technique decreased the pulmonary vascular hypertensive crises you saw after you decannulated them, does it make any difference in that occurrence after you used this technique? I might also ask, what is the difference in expense, or is there any? It seems to be a large expense, but, it is a very interesting way to do things. You are to be congratulated, along with Earle, for this fine work. Thank you.
DR UNGERLEIDER: Thanks, John. I have not been impressed that we have had a problem with pulmonary hypertension in these patients at the time that they have been decannulated. I do think we see an increased pulmonary resistance in the operating room and that sometimes decreased the shunt flow initially. But the real advantage of the system is that we can maintain the excessive cardiac output that these patients require since they require at least double cardiac output to perfuse both the pulmonary and the systemic circulation. Irrespective of the capability of the heart immediately following surgery to maintain that output, we can provide it with a ventricular assist device, and then we can treat any pulmonary hypertension aggressively with oxygen, nitric oxide, whatever might be necessary. We do find that initially patients' oxygen saturations are lower, and it takes about 24 hours for them to come up to the levels that we want, but we ventilate these patients normally after surgery.
I can't comment on expense. I have no way of comparing that to the expense of more conventional therapy.
DR ERLE AUSTIN (Louisville, KY): Ross, as I anticipated, you presented the results well. I would like to make a few comments as a participant in this study at a different center, with different personnel, and a different set of patients.
In the early 1990s in an effort to better understand the Norwood circulation, myself and a couple of mathematically gifted colleagues developed a theoretical mathematical model of the post Norwood circulation. A key finding of this mathematical model was that balancing the pulmonary and systemic blood flow was especially critical when the total cardiac output was limited or marginal as is often the case in these patients after surgery. As such, we spent much of our time focusing most of our attention on a variety of pharmacological and respiratory manipulations to achieve and maintain that balance.
Conversely, the mathematical model also indicated that as the cardiac output increased, the need to delicately balance these two circulations was much less critical. Thus, possibly a more important part of getting good results is an expertly performed operation with excellent myocardial preservation, resulting in a right ventricle that generates a high cardiac output that therefore is more resilient to rapid changes in Qp/Qs that occur in the early postoperative period. I think the good results at many centers are much related to a well performed operation with the resultant good cardiac output as with the postoperative management techniques.
At centers, such as my own, that have had periods of good results with the Norwood but have had interming led periods with unanticipated deaths in the middle of the night despite vigilant postoperative management, I don't think it is unreasonable to be certain that these patients are assured a good cardiac output for the first 24 to 72 hours by routinely applying ventricular assistance, as you have presented in this study.
I think you should be congratulated, first, for recognizing that ECMO rescue can successfully salvage some Norwood patients that deteriorate suddenly and, more importantly, for recognizing the importance of leaving the shunt open and providing high ECMO flows to adequately perfuse both circulations. You have debunked the unsubstantiated warning that leaving the shunt open "floods" the lungs. With the shunt open, you and your colleagues soon realized that you didn't even need an oxygenator in the circuit.
You have taken this experience and thought process to another level with this routine use of ventricular assist in the early post-Norwood period. When I learned about this from you, I was impressed enough with the idea that I decided to apply it to a series of our own patients in Louisville, and you have presented that as a subset of your data.
Our experience in Louisville has reinforced my feeling that you have made a true contribution. In our experience Norwood patients on routine ventricular assist are remarkably stable: they have excellent perfusion and good urine output. They rapidly normalize their lactic acid, as you have indicated. The patients tolerate manipulations such as suctioning without problem, and if an acute potentially destabilizing event occurs, such as an endotracheal tube obstruction from a mucous plug, the perfusion is preserved while the problem is rectified. Without this support, such events are frequently fatal.
We used to have a "Norwood team" that would spend the first 24 to 48 hours never leaving the bedside, prepared to intervene with any adversity. Since beginning routine ventricular assist support, most of the team, including myself, goes home for a good night's rest.
In two of our patients we did discover problems with oxygenation and an oxygenator was introduced into the circuit. We took these patients to the cath lab; they were stable and supported. In one case a technical problem with the pulmonary arteries was identified and was repaired while the patient was on the ECMO circuit. Another patient was found to have a technically good operation, but we decided to increase the shunt size and also had a successful outcome.
Despite my very positive impression with routine mechanical assistance after a Norwood, it isn't without problems. First, we had one patient that we could not keep off of support for more than 24 hours despite a cardiac cath that showed a technically good repair with good systolic right ventricular function and a competent tricuspid valve. Diastolic dysfunction resulted in this infant's ultimate death.
Secondly, the management of anticoagulation while these patients are on the circuit, and particularly in the early portion of it, is not, in my mind, fully worked out. Despite the early administration of protamine in several of our patients and a delay in starting heparin, bleeding was sometimes a problem. Conversely, in one or two cases we had some small clots in the circuit that required circuit change.
Thirdly, a successful ventricular assist or ECMO program does require a dedicated and experienced team, which, of course, is not without significant expense, as John Calhoon commented.
Despite these reservations, I would like to congratulate you for recognizing the potential value of routine ventricular assist in the post Norwood patient and for having the courage to introduce a controversial, although effective, management technique for a challenging congenital heart defect.
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