Carbon Dioxide Prevents Pulmonary Overcirculation in Hypoplastic Left Heart Syndrome David R. Jobes, MD, Susan C. Nicolson, MD, James M. Steven, MD, Margaret Miller, MD, Marshall L. Jacobs, MD, and William I. Norwood, Jr, MD, PhD The Children's Hospital of Philadelphia and The University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
Circulatory and metabolic homeostasis in patients with hypoplastic left heart syndrome is dependent on a delicate balance between systemic and pulmonary blood flow. Hypocarbia can result in a marked decrease in pulmonary vascular resistance accompanied by pulmonary overcirculation, systemic hypotension, metabolic
acidosis, and death. This report illustrates that early and precise control of the arterial carbon dioxide tension using inspired carbon dioxide can be effective in preventing or treating instability arising during management of a patient with hypoplastic left heart syndrome. (Ann Thorac Surg 1992;54:150-1)
H
adjunct to limit pulmonary blood flow in a neonate both before and after stage I palliation for HLHS.
emodynamic and metabolic stability after birth and before operation in the neonate with hypoplastic left heart syndrome (HLHS) requires the presence of an interatrial communication, patency of the ductus arteriosus, and a ratio of pulmonary blood flow (Qp) to systemic blood flow (Qs) near unity. The preoperative goal, in addition to maintaining ductal patency, is to avoid alterations in the Qp/Qs ratio. A Qp/Qs in excess of 1results in systemic hypoperfusion and metabolic acidosis. A Qp/Qs far less than 1 results in metabolic instability from hypoxemia. Except in the rare child in whom the interatrial communication is absent or restrictive, the Qp/Qs in neonates with HLHS is greater than or equal to 1. Control of the ratio of blood flowing to the pulmonary and systemic circuits is effected by adjusting the arterial carbon dioxide tension (PaCO,) through its impact on the pulmonary vascular resistance. An increase in PaCO, will result in an increase in pulmonary vascular resistance [l]. Thus in infants with a QpIQs greater than 1, the ratio can be reduced toward unity by increasing the PaCO,. The postoperative management of the child with HLHS after first-stage palliation shares the same goal and potential problems because of the continued parallel relationship of the pulmonary and systemic circulations [ 2 ] . Pulmonary overcirculation in either the preoperative or postoperative period will result in death if not rapidly corrected. Occasionally, when ventilatory adjustments prove inadequate to increase PVR and redistribute blood flow more evenly, the only effective maneuver has been immediate sternotomy with occlusion of the right pulmonary artery and, if necessary, institution of cardiopulmonary bypass. After stage I, reduction of the diameter of the shunt may be considered in the treatment of destabilizing pulmonary overcirculation. We report the use of inspired CO, as an Accepted for publication Oct 15, 1991 Address reprint requests to Dr Jobes, Department of Anesthesia, The Hospital of The University of Pennsylvania, 4 North Dulles Bldg, 3400 Spruce St, Philadelphia, PA 19104.
0 1992 by The Society of Thoracic Surgeons
The patient was a 6-day-old 4.2-kg male infant with the diagnosis of aortic atresia, mitral atresia scheduled for stage I palliation. The child arrived in the operating room in hemodynamically stable condition breathing room air through a natural airway while receiving prostaglandin El. The systemic blood pressure was 75/40 mm Hg and arterial blood gas analysis showed a pH of 7.39, PaCO, of 41 mm Hg, and arterial oxygen tension (PaO,) of 53 mm Hg. After induction of anesthesia, ventilation was controlled using air and sufficient inspired CO, to keep the PaCO, at 40 mm Hg or greater. Inspired CO, was increased from 2% to 4% as surface cooling produced a rectal temperature of 32°C. Systemic blood pressure and arterial oxygenation remained stable until initiation of cardiopulmonary bypass. An atrial septectomy, creation of neoaorta and placement of the 4-mm modified right Blalock-Taussig shunt were accomplished. The patient was weaned from cardiopulmonary bypass without difficulty. On arrival in the intensive care unit monitoring was reestablished and the child was placed on controlled mechanical ventilation with an inspired oxygen fraction of 0.3. Approximately 5 minutes later systemic arterial blood pressure was 82/48 mm Hg, atrial pressure was 4 mm Hg, and results of arterial blood gas analysis were as follows: pH, 7.58; PaCO,, 25 mm Hg; and PaO,, of 37 mm Hg. During the next 2 hours there was a progressive increase in PaO,, a decrease in systemic arterial pressure, and increasing metabolic acidosis. Treatment consisted of decreasing the inspired oxygen fraction and minute ventilation, and administration of sodium bicarbonate, dopamine, and sodium nitroprusside. These efforts were unsuccessful in improving systemic perfusion and reducing pulmonary blood flow, and the child was brought to the operating room emergently to reduce the size of the shunt. In the operating room, the 0003-4975/92/$5.00
CASE REPORT JOBES ET AL CO, IN HLHS MANAGEMENT
Ann Thorac Surg 1992;54:150-1
child’s systemic blood pressure was 58/25 mm Hg, the atrial pressure was 9 mm Hg, and results of arterial blood analysis were as follows: pH, 7.33; PaCO,, 35 mm Hg; PaO,, 42 mm Hg; and base excess, -4.3. Four percent CO, was added to the fresh gas flow, the base deficit was corrected with sodium bicarbonate, and dopamine and nitroprusside administration was discontinued. Within minutes there was evidence of a reduction in pulmonary blood flow and an increase in systemic blood flow (increase in systemic blood pressure, decrease in peripheral oxygen saturation, improvement of peripheral pulses) sufficient to delay surgical intervention. The patient remained in stable condition in the operating room for the next 2 hours on an inspired CO, ranging from 0.04 to 0.01. During the third hour the inspired CO, was weaned while a PaCO, of 40 mm Hg or more was established using adjustments in minute ventilation. The child was transported to the intensive care unit and remained with balanced circulations as evidenced by adequate systemic blood pressure, arterial oxygenation, and no metabolic acidosis. The remainder of the child’s hospital course was unremarkable, and he was discharged to home on the 12th postoperative day.
Comment Survival of the neonate with HLHS is dependent on patency of the ductus arteriosus, mixing of blood at the atrial level, and maintenance of a delicate balance between pulmonary vascular resistance and systemic vascular resistance. We have found that the most important physiologic variable in preserving the preoperative pulmonaryisystemic vascular resistance ratio is the maintenance of PaCO, at or above 40 mm Hg. The most common undesirable situation is pulmonary overcirculation and systemic hypotension when acute decreases in PaCO, occur during induction of general anesthesia and the transition from spontaneous to controlled ventilation. Surface cooling before bypass results in a significant decrease in metabolic rate and CO, production, adding to the probability of reduced PaCO, and increased PaO,. Our attempts to maintain the arterial blood gases at preanesthetic values by reducing tidal volume or respiratory rate or both often resulted in arterial desaturation. It is hypothesized that this occurs because of declining functional residual capacity, closure of small airways, atelectasis, and alveolar hypoxemia. Maintaining the functional residual capacity with an appropriate tidal volume and respiratory rate will minimize these effects, whereas adding sufficient CO, to the fresh gas flow will maintain the PaCO, at 40 mm Hg. We employed this technique initially in September 1988, and have used it routinely for approximately 200 neonates not only with HLHS but whenever the same circulatory physiology exists (eg, truncus arteriosus). It is frequently begun at the initiation of controlled ventilation during anesthetic induction and maintained until cardiopulmonary bypass. We have not observed myocardial ischemia or the frequent severe diastolic hypotension described by Wong and associates [3]. Except for 1 patient (with HLHS), no
151
other measures to maintain the Qp/Qs ratio at or near unity have been necessary after induction of anesthesia. In that patient, systemic perfusion pressure could only be maintained by occlusion of the right pulmonary artery until institution of cardiopulmonary bypass. It is believed that progressive systemic vasoconstriction during surface cooling to 28°C resulted in pulmonary overcirculation despite a PaCO, of more than 40 mm Hg. After completion of stage I, both circulations continue to be supplied from the ventricle in a parallel arrangement. In the majority of patients termination of bypass is uneventful and requires no unique interventions. Fewer than 5% of neonates will have inadequate pulmonary blood flow through the shunt as evidenced by a PaO, less than 20 to 22 mm Hg. Differential diagnosis of inadequate pulmonary blood flow includes inadequate shunt (too small, anastomotic stricture), elevated pulmonary vascular resistance (pulmonary dysfunctiodarterial hypoxemia, acidosis), and inadequate systemic pressure secondary to myocardial dysfunction. Assuming that the technical aspects of the operation are adequate, efforts to improve pulmonary blood flow include augmentation of intravascular volume and inotropic support to assure adequate systemic pressure and reducing pulmonary vascular resistance by lowering the PaCO, and increasing the inspired oxygen fraction. A greater percentage of infants, however, will behave as did this child and show signs of pulmonary overcirculation postoperatively. Once established this situation is difficult to reverse. The interventions that were applied to increase pulmonary vascular resistance (hypoventilation, reducing the inspired oxygen fraction, hyperinflation, and positive end-expiratory pressure) and reduce systemic vascular resistance (sodium nitroprusside) were intended to relocate blood from the pulmonary to the systemic circulation. None were successful in this patient, resulting in the decision to return to the operating room to mechanically limit pulmonary blood flow. The application of the technique used preoperatively was successful, and reoperation was not necessary. Following this case maintenance of alveolar ventilation with the minimum required inspired oxygen fraction and the addition of CO, sufficient to keep the PaCO, at 40 mm Hg or more has been regularly applied to the immediate postoperative care of patients with parallel circulations. The incidence of pulmonary overcirculation has been remarkably reduced in these patients. The earlier and more precise control of this important variable in determining pulmonary vascular resistance facilitates their care in both the preoperative and postoperative periods.
References Morray JP, Lynn AM, Mansfield PB. Effect of pH and Pco, on pulmonary and systemic hemodynamics after surgery in children with congenital heart disease and pulmonary hypertension. J Pediatr 1988;1132:474-9. Pigott JD, Murphy JD, Barber G, Norwood WI. Palliative reconstructive surgery for hypoplastic left heart syndrome. Ann Thorac Surg 1988;45:122-8. Wong RS, Baum VC, Sangwan S. Truncus arteriosus. Recognition and therapy of intraoperative cardiac ischemia. Anesthesiology 1991;74:378-80.
Circulatory and metabolic homeostasis in patients with hypoplastic left heart syndrome is dependent on a delicate balance between systemic and pulmonary blood flow. Hypocarbia can result in a marked decrease in pulmonary vascular resistance accompanied by pulmonary overcirculation, systemic hypotension, metabolic
acidosis, and death. This report illustrates that early and precise control of the arterial carbon dioxide tension using inspired carbon dioxide can be effective in preventing or treating instability arising during management of a patient with hypoplastic left heart syndrome. (Ann Thorac Surg 1992;54:150-1)
H
adjunct to limit pulmonary blood flow in a neonate both before and after stage I palliation for HLHS.
emodynamic and metabolic stability after birth and before operation in the neonate with hypoplastic left heart syndrome (HLHS) requires the presence of an interatrial communication, patency of the ductus arteriosus, and a ratio of pulmonary blood flow (Qp) to systemic blood flow (Qs) near unity. The preoperative goal, in addition to maintaining ductal patency, is to avoid alterations in the Qp/Qs ratio. A Qp/Qs in excess of 1results in systemic hypoperfusion and metabolic acidosis. A Qp/Qs far less than 1 results in metabolic instability from hypoxemia. Except in the rare child in whom the interatrial communication is absent or restrictive, the Qp/Qs in neonates with HLHS is greater than or equal to 1. Control of the ratio of blood flowing to the pulmonary and systemic circuits is effected by adjusting the arterial carbon dioxide tension (PaCO,) through its impact on the pulmonary vascular resistance. An increase in PaCO, will result in an increase in pulmonary vascular resistance [l]. Thus in infants with a QpIQs greater than 1, the ratio can be reduced toward unity by increasing the PaCO,. The postoperative management of the child with HLHS after first-stage palliation shares the same goal and potential problems because of the continued parallel relationship of the pulmonary and systemic circulations [ 2 ] . Pulmonary overcirculation in either the preoperative or postoperative period will result in death if not rapidly corrected. Occasionally, when ventilatory adjustments prove inadequate to increase PVR and redistribute blood flow more evenly, the only effective maneuver has been immediate sternotomy with occlusion of the right pulmonary artery and, if necessary, institution of cardiopulmonary bypass. After stage I, reduction of the diameter of the shunt may be considered in the treatment of destabilizing pulmonary overcirculation. We report the use of inspired CO, as an Accepted for publication Oct 15, 1991 Address reprint requests to Dr Jobes, Department of Anesthesia, The Hospital of The University of Pennsylvania, 4 North Dulles Bldg, 3400 Spruce St, Philadelphia, PA 19104.
0 1992 by The Society of Thoracic Surgeons
The patient was a 6-day-old 4.2-kg male infant with the diagnosis of aortic atresia, mitral atresia scheduled for stage I palliation. The child arrived in the operating room in hemodynamically stable condition breathing room air through a natural airway while receiving prostaglandin El. The systemic blood pressure was 75/40 mm Hg and arterial blood gas analysis showed a pH of 7.39, PaCO, of 41 mm Hg, and arterial oxygen tension (PaO,) of 53 mm Hg. After induction of anesthesia, ventilation was controlled using air and sufficient inspired CO, to keep the PaCO, at 40 mm Hg or greater. Inspired CO, was increased from 2% to 4% as surface cooling produced a rectal temperature of 32°C. Systemic blood pressure and arterial oxygenation remained stable until initiation of cardiopulmonary bypass. An atrial septectomy, creation of neoaorta and placement of the 4-mm modified right Blalock-Taussig shunt were accomplished. The patient was weaned from cardiopulmonary bypass without difficulty. On arrival in the intensive care unit monitoring was reestablished and the child was placed on controlled mechanical ventilation with an inspired oxygen fraction of 0.3. Approximately 5 minutes later systemic arterial blood pressure was 82/48 mm Hg, atrial pressure was 4 mm Hg, and results of arterial blood gas analysis were as follows: pH, 7.58; PaCO,, 25 mm Hg; and PaO,, of 37 mm Hg. During the next 2 hours there was a progressive increase in PaO,, a decrease in systemic arterial pressure, and increasing metabolic acidosis. Treatment consisted of decreasing the inspired oxygen fraction and minute ventilation, and administration of sodium bicarbonate, dopamine, and sodium nitroprusside. These efforts were unsuccessful in improving systemic perfusion and reducing pulmonary blood flow, and the child was brought to the operating room emergently to reduce the size of the shunt. In the operating room, the 0003-4975/92/$5.00
CASE REPORT JOBES ET AL CO, IN HLHS MANAGEMENT
Ann Thorac Surg 1992;54:150-1
child’s systemic blood pressure was 58/25 mm Hg, the atrial pressure was 9 mm Hg, and results of arterial blood analysis were as follows: pH, 7.33; PaCO,, 35 mm Hg; PaO,, 42 mm Hg; and base excess, -4.3. Four percent CO, was added to the fresh gas flow, the base deficit was corrected with sodium bicarbonate, and dopamine and nitroprusside administration was discontinued. Within minutes there was evidence of a reduction in pulmonary blood flow and an increase in systemic blood flow (increase in systemic blood pressure, decrease in peripheral oxygen saturation, improvement of peripheral pulses) sufficient to delay surgical intervention. The patient remained in stable condition in the operating room for the next 2 hours on an inspired CO, ranging from 0.04 to 0.01. During the third hour the inspired CO, was weaned while a PaCO, of 40 mm Hg or more was established using adjustments in minute ventilation. The child was transported to the intensive care unit and remained with balanced circulations as evidenced by adequate systemic blood pressure, arterial oxygenation, and no metabolic acidosis. The remainder of the child’s hospital course was unremarkable, and he was discharged to home on the 12th postoperative day.
Comment Survival of the neonate with HLHS is dependent on patency of the ductus arteriosus, mixing of blood at the atrial level, and maintenance of a delicate balance between pulmonary vascular resistance and systemic vascular resistance. We have found that the most important physiologic variable in preserving the preoperative pulmonaryisystemic vascular resistance ratio is the maintenance of PaCO, at or above 40 mm Hg. The most common undesirable situation is pulmonary overcirculation and systemic hypotension when acute decreases in PaCO, occur during induction of general anesthesia and the transition from spontaneous to controlled ventilation. Surface cooling before bypass results in a significant decrease in metabolic rate and CO, production, adding to the probability of reduced PaCO, and increased PaO,. Our attempts to maintain the arterial blood gases at preanesthetic values by reducing tidal volume or respiratory rate or both often resulted in arterial desaturation. It is hypothesized that this occurs because of declining functional residual capacity, closure of small airways, atelectasis, and alveolar hypoxemia. Maintaining the functional residual capacity with an appropriate tidal volume and respiratory rate will minimize these effects, whereas adding sufficient CO, to the fresh gas flow will maintain the PaCO, at 40 mm Hg. We employed this technique initially in September 1988, and have used it routinely for approximately 200 neonates not only with HLHS but whenever the same circulatory physiology exists (eg, truncus arteriosus). It is frequently begun at the initiation of controlled ventilation during anesthetic induction and maintained until cardiopulmonary bypass. We have not observed myocardial ischemia or the frequent severe diastolic hypotension described by Wong and associates [3]. Except for 1 patient (with HLHS), no
151
other measures to maintain the Qp/Qs ratio at or near unity have been necessary after induction of anesthesia. In that patient, systemic perfusion pressure could only be maintained by occlusion of the right pulmonary artery until institution of cardiopulmonary bypass. It is believed that progressive systemic vasoconstriction during surface cooling to 28°C resulted in pulmonary overcirculation despite a PaCO, of more than 40 mm Hg. After completion of stage I, both circulations continue to be supplied from the ventricle in a parallel arrangement. In the majority of patients termination of bypass is uneventful and requires no unique interventions. Fewer than 5% of neonates will have inadequate pulmonary blood flow through the shunt as evidenced by a PaO, less than 20 to 22 mm Hg. Differential diagnosis of inadequate pulmonary blood flow includes inadequate shunt (too small, anastomotic stricture), elevated pulmonary vascular resistance (pulmonary dysfunctiodarterial hypoxemia, acidosis), and inadequate systemic pressure secondary to myocardial dysfunction. Assuming that the technical aspects of the operation are adequate, efforts to improve pulmonary blood flow include augmentation of intravascular volume and inotropic support to assure adequate systemic pressure and reducing pulmonary vascular resistance by lowering the PaCO, and increasing the inspired oxygen fraction. A greater percentage of infants, however, will behave as did this child and show signs of pulmonary overcirculation postoperatively. Once established this situation is difficult to reverse. The interventions that were applied to increase pulmonary vascular resistance (hypoventilation, reducing the inspired oxygen fraction, hyperinflation, and positive end-expiratory pressure) and reduce systemic vascular resistance (sodium nitroprusside) were intended to relocate blood from the pulmonary to the systemic circulation. None were successful in this patient, resulting in the decision to return to the operating room to mechanically limit pulmonary blood flow. The application of the technique used preoperatively was successful, and reoperation was not necessary. Following this case maintenance of alveolar ventilation with the minimum required inspired oxygen fraction and the addition of CO, sufficient to keep the PaCO, at 40 mm Hg or more has been regularly applied to the immediate postoperative care of patients with parallel circulations. The incidence of pulmonary overcirculation has been remarkably reduced in these patients. The earlier and more precise control of this important variable in determining pulmonary vascular resistance facilitates their care in both the preoperative and postoperative periods.
References Morray JP, Lynn AM, Mansfield PB. Effect of pH and Pco, on pulmonary and systemic hemodynamics after surgery in children with congenital heart disease and pulmonary hypertension. J Pediatr 1988;1132:474-9. Pigott JD, Murphy JD, Barber G, Norwood WI. Palliative reconstructive surgery for hypoplastic left heart syndrome. Ann Thorac Surg 1988;45:122-8. Wong RS, Baum VC, Sangwan S. Truncus arteriosus. Recognition and therapy of intraoperative cardiac ischemia. Anesthesiology 1991;74:378-80.
