Surgical Approaches, Cardiopulmonary Bypass, and Mechanical Circulatory Support in Children

Preoperative Resuscitation

ECMO can be beneficial for critically ill patients awaiting cardiac surgery, enabling preoperative stabilization and optimization or prevention of end-organ dysfunction before repair. These patients represent a small group (usually newborns), and indications include severely low cardiac output states (e.g., critical aortic stenosis), pulmonary hypertension (e.g., obstructed total anomalous pulmonary venous drainage), and severe hypoxemia (e.g., transposition of the great arteries and pulmonary hypertension).

Inability to Wean from Cardiopulmonary Bypass

The reported survival is poor for patients who are given ECMO because they were unable to wean directly from CPB in the operating room (i.e., without any period of stability off CPB). Issues such as primary myocardial dysfunction, pulmonary hypertension, severe hypoxemia, and refractory dysrhythmias are recognized as major factors in determining successful outcome, but unrecognized residual or irreparable defects are also important. Residual cardiac defects must be investigated in the operating room, using a combination of echocardiography and the careful measurement of oxygen saturations and intracardiac pressures. Ideally, only children with potentially reversible myocardial injury who cannot be weaned from CPB should be considered candidates for ECMO; however, this can be extremely difficult to determine in the operating room immediately after cardiac surgery. Additional considerations for use of ECMO in patients failing to wean from cardiopulmonary bypass after cardiac surgery include preoperative condition, intraoperative course, and the likelihood of being a transplant candidate. Severe hemorrhage is a major problem in the transition from the CPB circuit to the ECMO circuit. Although a lower activated clotting time (ACT; 160 to 180 seconds) can be used, small doses of protamine are often necessary to assist with the initial control of bleeding. We usually administer protamine in 1-mg/kg increments until a target ACT of 180 seconds is achieved. Infusions of antifibrinolytic drugs such as tranexamic acid (bolus of 100 mg/kg, followed by infusion at 10 mg/kg/hr), or ε-aminocaproic acid (bolus of 100 mg/kg, followed by infusion at 30 mg/kg/hr) should be considered. Exploration of the chest may be necessary, particularly if the bleeding persists at a rate greater than 10 mL/kg/hr and if problems with ECMO flow are encountered because of decreased venous cannula drainage from a tamponade-like effect. The large transfusion requirement can place a considerable burden on the supply of donor blood products. As an alternative, it is possible to connect a chest tube to cell-saver tubing to enable blood to be collected in the cell-saver reservoir and subsequently spun for retransfusion.

When a patient requires ECMO in the operating room, discussions with the patient's family must be clear and direct. Recovery of myocardial function should be expected within 2 to 3 days, and if this is not evident, either listing for cardiac transplantation, if appropriate, or withdrawal from support must be considered.

After Cardiotomy

ECMO is an effective therapeutic option for infants and children who have had a period of relative stability after successful termination of CPB and exclusion of significant residual cardiac defects. Myocardial or respiratory failure causing a low cardiac output state, hypoxemia, or pulmonary hypertension and cardiac arrest are the major indications in this group. This group of patients is large, with reported good survival rates (60% to 70%), provided ECMO is instituted rapidly and effectively.

Cardiomyopathy, Myocarditis, and Bridge to Transplantation

Patients with acute fulminant myocarditis can be managed successfully with ECMO. Patients with fulminant myocarditis may arrive at the hospital undergoing full cardiac arrest, but more commonly they are in cardiogenic shock from an extremely low cardiac output state or they have hemodynamically significant dysrhythmias, including ventricular tachycardia or heart block. The heart is usually distended and is contracting poorly. Prompt institution of ECMO may allow sufficient resuscitation and stabilization to prevent end-organ injury and to enable the myocardium to rest while awaiting potential recovery. After ECMO is instituted, the heart must be fully decompressed, and urgent atrial septostomy or left atrial vent placement may be necessary. The heart might not begin to eject for the first 24 to 36 hours after ECMO is started, although recovery of electrical activity within the first few hours should be expected. If recovery of ventricular ejection is not evident within 2 to 3 days, ECMO can be continued either as a bridge to heart transplantation or as a bridge to alternative longer-term support with a VAD, if feasible. ECMO should be viewed as a short-term bridge to transplantation because of the limited donor availability and the time-related risks for complications, such as infection, bleeding, end-organ impairment, problems resulting from immobilization, and difficulties in maintaining adequate nutrition. In our experience at Boston Children's Hospital, the median time spent on ECMO awaiting heart transplantation is currently 140 hours (range, 26 to 556 hours), and only 50% of our listed patients have been effectively bridged. In a small number of older and larger children, ECMO has been used to initially resuscitate the circulation and end-organs, and if a donor heart has not become available by day 6 or 7 of ECMO, we have successfully transitioned from ECMO to longer-term VAD. Survival for patients with acute myocarditis supported with ECMO was recently reported to be 61% using data reported to the ECMO registry of ELSO. Because ECMO can provide good survival in any patients with acute fulminant myocarditis these patients should be cared for in facilities that have an ECMO or other MCS options.

ECMO also has been used to support the failing heart after transplantation. This may be necessary immediately after transplantation because of graft failure, usually in the setting of pulmonary hypertension and acute right ventricle failure of the donor heart. ECMO also is effective in supporting the heart during periods of acute rejection. The inflammation and myocardial edema are similar to that seen with fulminant myocarditis, and they lead to a similar spectrum of clinical features. ECMO allows the transplanted heart to decompress with decreased wall tension while antirejection therapy is increased. In our experience, survival to discharge for this indication is currently 64%, and the median duration of ECMO support is 4 days.

After In-Hospital Cardiac Arrest and CPR

Survival and outcome after in-hospital resuscitation of pediatric patients after a cardiac arrest continues to be extremely poor. Even in a highly monitored and resource-intensive area such as a pediatric intensive care unit (ICU), the survival rate after cardiac arrest has been reported to be only 9% to 31%. The duration of cardiac arrest and resuscitation is also an important determinant of subsequent outcome, and a number of reports have noted a critical threshold of approximately 15 minutes. ECMO has been successfully used to support children after prolonged periods of cardiac arrest that have been unresponsive to closed or open cardiac massage and all other usual interventions. Again, it is important to emphasize that the underlying lesion, in conjunction with the effectiveness of CPR while instituting ECMO, is a major determinant of outcome when mechanical support is used in this setting. Although the exact place of ECMO in the CPR algorithm remains ill defined, patients with a witnessed arrest and rapid institution of effective CPR, and who have no apparent recovery of cardiac function within 5 to 10 minutes of initiating resuscitation and no contraindications, may be suitable candidates for ECMO.

Determining the relative contraindications to ECMO support during active resuscitation attempts can be difficult ( Table 109-5 ). Although not always possible, discussions regarding the use of ECMO in certain patients should be undertaken before an event occurs. We have been able to successfully use our rapid-response ECMO system during CPR in patients with acquired and structural heart disease, and in patients with double- or single-ventricle defects. In the latter group are neonates who have had a sudden, reversible event, such as acute thrombosis and obstruction to a systemic-to-pulmonary artery shunt after a Norwood procedure, and they have been readily resuscitated with ECMO. On the other hand, patients with cavopulmonary corrections (i.e., Fontan or bidirectional Glenn anastomosis) have been difficult to resuscitate using ECMO, in part because of limitations with cannulation, and an inability to maintain adequate systemic oxygen delivery and avoid cerebral venous hypertension during CPR with chest compressions. Although we have used ECMO in the resuscitation of patients with pulmonary hypertension and patients with systemic outflow obstruction, the severe limitation to cardiac output and oxygenations during CPR in these patients has meant that their overall outcomes on ECMO have been poor because of the development of severe end-organ injury.

Historically, successes using ECMO during active resuscitation and chest compressions (E-CPR) have been reported for a small number of series. A recent subanalysis of the ELSO Registry E-CPR data reports a 37% overall survival to discharge for patients placed on ECMO in this circumstance. To avoid significant delays, a rapid response ECMO system has been established at some institutions. The success of a rapid response system depends on a multidisciplinary approach, with equipment being immediately available, and the personnel with assigned roles being in-house, including cardiac surgery and intensive care fellows, respiratory and ECMO specialists, and trained nursing staff. At Boston Children's Hospital, a vacuum and CO ₂ -primed circuit using a roller pump and a 0.8- to 1.5-m ² membrane oxygenator is available at all times and is suitable for children weighing up to approximately 15 kg. Even in older children, this circuit initially provides sufficient flow for resuscitation, stabilization, and hopefully prevention of end-organ damage, until a larger oxygenator can be spliced into the circuit. Generally, however, for older children and adults, a new circuit with a hollow-fiber membrane is used, which takes little time to de-air and can be established within 15 minutes. Once the patient is in stable condition with ECMO, the hollow-fiber membrane can be exchanged for a conventional membrane for longer-term support as necessary. An alternative rapid response system has been described, which uses a heparin-coated circuit, centrifugal pump, and a hollow-fiber membrane with a priming volume of only 250 mL and a priming time of only 5 minutes.

In postoperative cardiac patients, atrial and aortic cannulation via a reopened sternotomy is usually the access mode of choice. In other patients, experienced practitioners can rapidly gain access via the neck vessels. During resuscitation, the circuit is primed with crystalloid supplemented with 5% albumin. We do not wait for donor blood to be crossmatched to complete a blood prime of the circuit because of the inevitable delay. We prefer to reestablish organ perfusion as soon as possible, and once ECMO is satisfactorily established, blood products can be added or the priming crystalloid can be removed via hemofiltration. To assist with neurologic protection, where possible we maintain mild hypothermia (34° to 35° C) for the first 12 hours after administering ECMO during active resuscitation. Using the rapid response system, we can be ready to place a patient on ECMO within 15 minutes, and the main limitation is then the problems associated with cannulation. We have deployed the rapid response system during active resuscitation in more than 170 children since 1996, and we have been able to achieve a survival-to-discharge rate of 51% in this group of patients.