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Ann Thorac Surg 2000;69:1476-1483
© 2000 The Society of Thoracic Surgeons
a Pediatric Cardiovascular Program, Duke University Medical Center, Durham, North Carolina, USA
Address reprint requests to Dr Jaggers, Division of Thoracic Surgery, Duke University Medical Center, Box 3474, Durham, NC 27710
e-mail: jagge003{at}mc.duke.edu
Presented at the Forty-sixth Annual Meeting of the Southern Thoracic Surgical Association, San Juan, Puerto Rico, Nov 4–6, 1999.
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Abstract |
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Methods. Thirty-five consecutive children (age 1 to 820 days, median 19 days) out of 1,020 patients (3.4%) required mechanical support (ECMO) after repair of congenital cardiac lesions from February 1994 to April 1999. Twenty-five patients underwent two ventricle repairs and 10 patients had single-ventricle palliation. Various parameters analyzed included strategies of shunt management, presence of presupport cardiac arrest, and timing of support initiation.
Results. Overall hospital survival for these 35 patients was 61%. There were four additional late deaths. Hospital survival was the same for those patients in whom support was initiated for failure to wean from cardiopulmonary bypass in the operating room versus those patients in whom support was initiated after successful separation from cardiopulmonary bypass (6 of 10 vs 15 of 25 or 60% survival). In those patients with shunt-dependent pulmonary circulation, survival was significantly improved in those patients in which the aorto-pulmonary shunt was left open (4 of 5 with open shunt vs 0 of 4 with occluded shunt (p = 0.048).
Conclusions. The ability to readily implement postcardiotomy support is vital to the management of children with complex congenital cardiac disease. Overall survival can be quite satisfactory if support is employed in a rational and expedient manner. In patients with single-ventricle physiology and aorto-pulmonary shunts, leaving the shunt open during the period of support can result in markedly improved outcomes.
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Material and methods |
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Anticoagulation is initiated with 100 U/kg body weight of heparin and maintained to an activated clotting time of 180 to 200 seconds. In those patients who were cannulated in the operating room, every attempt was made to separate from cardiopulmonary in order to reverse heparin effects and achieve hemostasis before reheparinizing and transferring to the ECMO circuit. In those patients who were successfully weaned from CPB and who later required support, cannulation was carried out via repeat sternotomy in all but 2 patients. In these 2 patients cannulation was carried out via the right common carotid artery and right internal jugular vein, as is our practice for noncardiac neonatal ECMO. Hematocrit was maintained at greater than 40% and platelet counts of greater than 100,000. Flow rates of 100 to 200 mL/kg/min were maintained depending upon the physiology and the mixed venous oxygen saturation. Venting of the left atrium in order to prevent left-sided distention was performed in only 1 patient with two-ventricle anatomy and, of course, is not usually necessary in those with single-ventricle anatomy. Inotropic support was decreased slowly to maintain mean blood pressure at 40 to 50 mm Hg. High levels of positive end-expiratory pressure (PEEP) were not routinely employed, as this may artificially elevate central venous pressures and inhibit venous return to the pump. In those patients who had a shunt that was left open to perfuse the lungs, the ventilation was continued at a set rate of 10 to 14 breaths per minute and tidal volume of 10 to 15 mL/kg. Serial serum lactate levels, blood gases, and mixed venous oxygen saturation are typically followed to assess the efficacy of the ECMO. For the most part, patients who were on ECMO were heavily sedated with benzodiazepine and narcotic analgesia. Paralytic agents were not routinely employed. Weaning from ECMO was typically accomplished by slowly reducing the flow from the device while optimizing filling pressure in a fashion similar to weaning from cardiopulmonary bypass in the operating room. This generally can be accomplished in only a few minutes. Prolonged periods of reduced flow are avoided. If separation from the ECMO circuit is accomplished, cannulas are clamped and the pump is left to recirculate at a low flow across the bridge. The cannulas are removed after a period of 1 to 2 hours of hemodynamic stability.
Patients’ charts were reviewed for significant events and complications including: hospital mortality, late mortality, late functional status, maximal serum lactate levels, pre-ECMO base deficit, time on ECMO, time to initiation of ECMO, indication for ECMO, the presence or absence of a systemic to pulmonary shunt, and the management of that shunt. Mean follow-up time was 18 months.
Statistical analysis
Patients’ data were presented as a range of the mean or as a percentage of patients in a group. The statistical package (Statistica; Statsoft, Tulsa, OK) was used for all examinations. Differences between mean values were analyzed using Student’s t test or Fisher’s exact test where appropriate. All other dichotomous variables were analyzed using a 
2 test. Differences were considered significant at p less than 0.05.
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Results |
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Nine of the 35 patients had aorto-pulmonary shunt-dependent pulmonary circulation (Table 3). Of those 9 patients, 4 survived to hospital discharge. Of these 9 patients, the first 4 in the series were placed on ECMO with the shunt occluded in order to prevent "pulmonary over-circulation" and ensure systemic perfusion. Of these 4 patients, none survived. Two had documented pulmonary infarcts at autopsy. In the next 5 patients with shunt-dependent pulmonary circulation, the shunt was left open to perfuse the lungs during support. ECMO flow rates were "doubled" to achieve perfusion of approximately 200 mL/kg/min. Patients were ventilated "normally" with respect to standard protocols for the management of infants after Norwood stage I procedure. In this group, 4 of 5 survived to discharge from the hospital. The only mortality in this group was an infant who underwent Norwood operation for HLHS and had preoperative renal insufficiency and renal hypoplasia with a creatinine of 2.0 mg/dL. His death was related to renal insufficiency, despite attempts at dialysis. There was also one late death in this group in a child who sustained neurologic impairment during the initial operation and subsequently died at the time of his bidirectional Glenn shunt with severe mesenteric and renal ischemia.
There were 6 patients in this series who were cannulated for ECMO while undergoing cardiopulmonary resuscitation for postoperative cardiac arrest (Table 3). All of these patients were cannulated in the intensive care unit via a repeat sternotomy. Three out of 6 of these patients survived to discharge from the hospital, and 1 of the 3 survivors died at 16 months postoperatively. Both of the surviving patients were neurologically normal. The infant who died late was also neurologically normal but had severe cardiac dysfunction after repair of truncus arteriosus and died while awaiting cardiac transplantation.
Table 4 displays the incidences of major complications in survivors versus nonsurvivors. There were no significant differences between the two groups except in renal dysfunction. Nonsurvivors were more likely to have suffered significant renal injury either during operation or in the postoperative period.
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Comment |
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In this study, the only variables that we were able to identify as predictive of survival were lack of significant renal impairment and leaving the shunt open during ECMO in those patients with shunt-dependent pulmonary circulation.
The use of ECMO for postcardiotomy support in neonates and infants with aorto-pulmonary shunts is controversial, especially in patients with hypoplastic left heart syndrome (HLHS). While there is no consensus regarding the management of the shunt during the ECMO period, the "popular" convention has been to either occlude the shunt completely or partially in order to limit the pulmonary blood flow while on ECMO. There has been widespread "concern" that if the shunt is left open, there will be excessive pulmonary blood flow that may "steal" flow away from the systemic circulation and produce pulmonary injury. Some groups have even stated that the presence of an aorto-pulmonary shunt may be a contraindication to ECMO. Our experience in the early 1990s with occlusion of the shunt in infants placed on ECMO after Norwood stage I procedure was indeed dismal and supported this contention. We observed 2 patients with HLHS and a shunt-dependent pulmonary circulation after the Norwood operation who were unable to be weaned from ECMO because of severe pulmonary dysfunction, despite vigorous cardiac function. It became clear that the lungs had sustained a severe injury while on ECMO with the shunt occluded. These children ultimately died shortly after being taken off ECMO on postoperative days 5 and 7, respectively. An autopsy revealed severe ischemia to the lungs without emboli or infection. This experience prompted a study from our laboratory regarding the effects of no antegrade pulmonary blood flow during CPB (total CPB), on parameters of respiratory function, and pulmonary vaso-reactivity [11]. In this study, pulmonary vascular resistance, A-a gradient, and pulmonary compliance were all adversely affected by no antegrade flow to the lungs during CPB. It may be that reopening an occluded shunt just before coming off ECMO sets the stage for an ischemia-reperfusion injury. In our laboratory study, we were able to measure significant injury to pulmonary endothelial function in the group maintained on CPB without antegrade pulmonary blood flow, suggesting that pulmonary blood flow (beyond what is available from the bronchial circulation) is necessary to preserve normal pulmonary vascular endothelial cell function. In June 1997, after a Norwood stage I procedure for HLHS, a neonate suffered shunt thrombosis and required emergency postcardiotomy support with ECMO. Because of the information generated by our previous clinical experience and from our laboratory investigation, we elected to alter our existing ECMO protocol for this patient. We left the shunt open and increased our flow rate while on ECMO to 200 mL/kg/min, presuming that in that manner we could support both the pulmonary and systemic circulation. We ventilated the infant in the standard manner we would use after a Norwood procedure in order to balance systemic and pulmonary blood flow. This infant made an uneventful recovery, has since undergone a Fontan procedure, and is functionally normal.
In this article, we report on an additional 4 patients who were managed in a similar fashion. In all cases, the infants had no problem "balancing" their circulation while on ECMO as long as the circuit provided adequate flow. This experience supports the concept that a patient with single-ventricle, shunt-dependent circulation after a Norwood stage I procedure has an increased cardiac output requirement compared with an infant with a "normal" circulation. The need for a double-cardiac output (one for the lungs and one for the body) is occasionally more than the infant can produce after surgery, and they enter the spiral of hemodynamic collapse that is often described after this procedure. If provided with a normal cardiac output for their needs, these infants can "balance" their circulation without difficulty. In fact, we have found that intentional hypoxemia and hypercarbia are absolutely unnecessary and potentially harmful. We ventilate normally and have experienced no problems from "pulmonary overcirculation."
ECMO is not the only option for infants and children who require postcardiotomy support. A recent report suggests that mechanical support that does not utilize an oxygenator is also an option if the patient’s own lungs can be used [12]. In this series, the most common lesion supported in this manner was HLHS (12 patients). Because this approach does not involve an oxygenator, the shunts of these patients with shunt-dependent pulmonary circulation must be left open to perfuse the lungs during the period of support. In this series, 7 of 12 patients could be weaned from support, but only 3 of 12 were discharged from the hospital. The elimination of the oxygenator may result in less inflammatory effects related to the device and requires less anticoagulation, which makes management of perioperative bleeding much easier. The lower hospital survival rate reported by Thuys and associates [12] might related to the timing of intervention because, in our experience, the mortality rate for infants placed on ECMO who have had a Norwood stage I procedure is near 100% if ECMO is instituted during a cardiac arrest. The simplicity of this system has led us to consider early intervention with ventricular assist device in those patients with low cardiac output after the Norwood procedure.
Despite improvements in survival for patients requiring postcardiotomy support, the rate of complications remains high. In this series, there did not seem to be any difference in major complications between survivors and nonsurvivors except for significant renal dysfunction (p = 0.02) present in nonsurvivors. This finding is consistent with other reports [5]. The actual rate of neurologic complications is difficult to measure because it may be that some neurologic complications may not have been manifest in those patients who died while still on support. It is, however, gratifying that in the patients who survived long term, only two suffered obvious neurologic deficit. Bleeding is also a very common complication in all series, especially in those patients who require ECMO for failure to wean from CPB, because the heparin is unable to be reversed. In our practice, we make every attempt to wean from CPB long enough for heparin to be reversed and hemostasis obtained. We find that this lessens the severity of bleeding in the postoperative period. When this is not possible, we have found it reasonable to withhold heparin until bleeding is under control, with a "back-up" ECMO circuit (or oxygenator) available in case it is urgently required. Our more recent experience with ventricular assist device for infants with aorto-pulmonary shunts has enabled us to control bleeding in this group while still providing circulatory support.
Although our hospital survival of 61% is comparable with other reported series, it is our impression from reviewing this experience that future results might be improved by altering postcardiotomy support strategies in the following ways. (1) Failure to wean from CPB is not a contraindication to the use of support and in appropriately selected cases. Support that is initiated in a timely manner before hemodynamic collapse has a better chance of immediate success and improved long-term outcome. (2) The biggest "impediment" to early initiation of ECMO is circuit "set-up" time. We think that it is prudent to keep a circuit available and "primed" with crystalloid solution for rapid deployment. (3) Infants with shunt-dependent circulation can have excellent outcome with ECMO if the shunt is left open and the infant is ventilated normally. In these instances, ECMO flow rates should be increased to satisfy both the systemic and pulmonary flow requirements. With normal ventilation, the infant will balance his own systemic-pulmonary circulations. Treatment with hypoxia and/or hypercarbia is not necessary and may have a negative effect on long-term outcome. (4) The use of ventricular assist device (we have coined the term "NOMO-VAD" for no membrane oxygenator-ventricular assist device) for infants after Norwood stage I procedure has significant advantages because the ventricular assist device supplies full cardiopulmonary support by utilizing the patient’s own lungs for respiration and oxygenation. In these cases, postoperative bleeding will be more easily controlled because systemic heparinization is not necessary.
Summary
The timely application of ECMO for postcardiotomy support can result in improved survival. If used appropriately and expeditiously before end-organ injury or cardiac arrest has occurred, results can be excellent. Patients with shunt-dependent pulmonary circulation have been problematic using conventional protocols that include some form of shunt occlusion. Despite the limitations of this small review, the results of our experience, corroborated by data from our animal laboratory, support the strategy of leaving the shunt open to perfuse the lungs during the ECMO period and increasing flows to satisfy the needs of both the systemic and pulmonary circulation. This experience helps to redefine the requirements for treating patients after a Norwood stage I procedure with respect to ventilation and underscores the need these infants have for an adequate cardiac output.
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