Cardiac extracorporeal life support: state of the art in 2007.

Mechanical circulatory support is an invaluable tool in the care of children with severe refractory cardiac and or pulmonary failure. Two forms of mechanical circulatory support are currently available to neonates, infants, and smaller children, namely extracorporeal membrane oxygenation and use of a ventricular assist device, with each technique having unique advantages and disadvantages. The intra-aortic balloon pump is a third form of mechanical support that has been successfully used in larger children, adolescents, and adults, but has limited applicability in smaller children. In this review, we discuss the current experiences with extracorporeal membrane oxygenation and ventricular assist devices in children with cardiac disease.A variety of forms of mechanical circulatory support are available for children with cardiopulmonary dysfunction refractory to conventional management. These devices require extensive resources, both human and economic. Extracorporeal membrane oxygenation can be effectively used in a variety of settings to provide support to critically-ill patients with cardiac disease. Careful selection of patients and timing of intervention remains challenging. Special consideration should be given to children with cardiac disease with regard to anatomy, physiology, cannulation, and circuit management. Even though exciting progress is being made in the development of ventricular assist devices for long-term mechanical support in children, extracorporeal membrane oxygenation remains the mainstay of mechanical circulatory support in children with complex anatomy, particularly those needing rapid resuscitation and those with a functionally univentricular circulation.As the familiarity and experience with extracorporeal membrane oxygenation has grown, new indications have evolved, including emergent resuscitation. This utilization has been termed extracorporeal cardiopulmonary resuscitation. The literature supporting emergent cardiopulmonary support is mounting. Reasonable survival rates have been achieved after initiation of support during active compressions of the chest following in-hospital cardiac arrest. Due to the limitations of conventional circuits for extracorporeal membrane oxygenation, some centres have developed novel systems for rapid cardiopulmonary support. Many centres previously considered a functionally univentricular circulation to be a contraindication to extracorporeal membrane oxygenation, but improved results have been achieved recently with this complex subset of patients. The registry of the Extracorporeal Life Support Organization recently reported the outcome of extracorporeal life support used in neonates for cardiac indications from 1996 to 2000. Of the 740 neonates who were placed on extracorporeal life support for cardiac indications, 118 had hypoplastic left heart syndrome. There was no significant difference in survival between these patients and those with other defects. It is now common to use extracorporeal membrane oxygenation to support patients with a functionally univentricular circulation, and reasonable survival rates are to be expected. Although extracorporeal membrane oxygenation has become a standard of care for many paediatric centres, its use is limited to those patients who require only short-term cardiopulmonary support. Mechanical ventricular assist devices have become standard therapy for adults with cardiac failure refractory to maximal medical management. Several devices are readily available in the United States of America for adults, but there are fewer options available to children. Over the last few years, substantial progress has been made in paediatric mechanical support. Ventricular assist devices are being used with increasing frequency in children with cardiac failure refractory to medical therapy for primary treatment as a long-term bridge to recovery or transplantation. The paracorporeal, pneumatic, pulsatile "Berlin Heart" ventricular assist device is being used with increasing frequency in Europe and North America to provide univentricular and biventricular support. With this device, a patient can be maintained on mechanical circulatory support while extubated, being mobilized, and feeding by mouth. Mechanical circulatory support should be anticipated, and every attempt must be made to initiate support "urgently" rather than "emergently", before the presence of dysfunction of end organs or circulatory collapse. In an emergency, these patients can be resuscitated with extracorporeal membrane oxygenation and subsequently transitioned to a long-term ventricular assist device after a period of stability.

Extracorporeal membrane oxygenation to cardiopulmonary bypass with a single circuit exposure.

Due to the short supply of donor organs available, many patients decompensate or die while waiting for transplantation. Options for mechanical support for infants and pediatrics with congenital heart disease are limited because of the patient's size and device availability. Extracorporeal membrane oxygenation (ECMO) is the most common means of cardiac and respiratory support for these patients. One of the many indications for ECMO use in cardiac patients is as a bridge to transplantation, with patients being transported to the operating room (OR) on ECMO support. Converting the ECMO circuit to an open cardiopulmonary bypass system in the OR minimizes the patient's exposure to new circuitry, decreases further donor exposures and provides continuous support for patients in cardiac and/or respiratory failure. In addition, the ability to use modified ultrafiltration post-bypass aids in reducing extracellular fluid, increasing the hematocrit and improving hemodynamic stability following an extended duration of ECMO and bypass support. The integrity of the ECMO circuit is maintained and can be converted back to ECMO for support postoperatively if needed.

Alleviating heat loss associated with modified ultrafiltration.

Modified ultrafiltration (MUF) has been described and utilized for the removal of extracellular water in the immediate postcardiopulmonary bypass (CPB) period. This technique has been associated with improved hematological status and hemodynamic stability post cardiopulmonary bypass. Hypothermia during the MUF period has been described as a complication associated with this technique. Decreased patient temperature may be associated with increased bleeding causing an increase in time to sternal re-approximation, OR time, decreases in cardiac function, peripheral vascular perfusion, and an increase in blood product utilization. These complications may reduce some of the benefits described with the use of MUF. The purpose of this study was to evaluate the use of a heated MUF infusion line to reduce the heat loss associated with this technique in a pediatric population. After obtaining Committee for Protection of Human Subjects exemption, a retrospective review to evaluate the efficiency of the hot MUF infusion line was undertaken. Twenty patients under 10 kg who underwent MUF before the change to a heated infusion line were retrospectively identified and matched to patients undergoing MUF with a heated infusion line with regard to weight, lesion, procedure, surgical staff and technique, and disposable equipment. Groups were evaluated for temperature and hematocrit change during the MUF period, blood loss and transfusion postprotamine in the OR and 24 h, and time to sternal re-approximation postprotamine. Statistical significance was seen between the two groups in temperature (-0.24 +/- 0.72 vs. - 1.58 +/- 0.89 degrees C; p < .0001) with the HotLine group having little change post MUF. Significance was also seen in the last OR temperature recorded (37.0 +/- 1.2 vs. 36.0 +/- 1.0 degrees C; p = .01) with the HotLine group having the higher temperature. There were no significant differences in hematocrit levels at 24 hours, last in the OR, or the change after the MUF period. No significant difference was found in blood transfused postprotamine in the OR, 24-h blood transfused, 24-h chest tube loss, or sternal closure. The study suggests that the use of a heated MUF infusion line safely reduces the heat loss associated with MUF in the immediate post-operative period.