Chapter 23 Congenital Heart Disease
Fundamental pathophysiology in congenital heart disease
1. When does shunting occur in congenital heart disease?
2. What is the usual limitation to the direction and amount of shunt flow?
3. When does a left-to-right shunt occur?
4. What is the physiologic effect of a left-to-right shunt on the pulmonary blood flow (Qp) relative to the systemic blood flow (Qs)?
5. What are the long-term effects of increased pulmonary blood flow that occurs in a left-to-right shunt?
6. Give an example of a congenital heart defect that results in a left-to-right shunt.
7. When does a right-to-left shunt occur? What is the physiologic effect of this?
8. Give an example of a congenital heart defect that results in a right-to-left shunt.
9. What are mixing lesions in congenital heart disease? How do mixing lesions affect the systemic arterial oxygen saturation?
10. What determines the Qp:Qs ratio in mixing lesions?
11. What is the ideal Qp:Qs ratio in mixing lesions? Why?
12. What are some factors that can increase systemic vascular resistance?
13. What are some factors that can decrease systemic vascular resistance?
14. What are five factors that increase pulmonary vascular resistance?
15. What are five factors that decrease pulmonary vascular resistance?
Perioperative management
17. What are some ways an anesthesiologist can prepare for a patient requiring surgery for congenital heart disease?
18. What preexisting conditions might be important to the care of patients with congenital heart disease?
19. What information might be gained from preoperative echocardiograms or magnetic resonance imaging (MRI)?
20. What is a risk factor from a previous sternotomy?
21. What are the fasting recommendations for infants and children scheduled for congenital heart surgery?
22. What is the most important feature of the intravenous administration set up for the patient scheduled for congenital heart surgery?
23. What are some common side effects of the induction of anesthesia using inhaled agents, such as sevoflurane or halothane?
24. What are some side effects of an intravenous induction of anesthesia using opioids such as fentanyl?
25. What are some side effects of an intravenous induction of anesthesia using ketamine, a drug that preserves sympathetic nervous system tone?
26. What are some general principles for the induction of anesthesia that might apply to all patients with congenital heart disease?
27. What are the goals for the anesthetic management in patients with a left-to-right shunt?
28. What are the goals for the anesthetic management in patients with a right-to-left shunt?
29. What are some considerations for the ventilatory management in patients with congenital heart disease?
30. For lesions with excessive pulmonary blood flow such as ventricular septal defects or atrioventricular septal defects, how should the pulmonary vascular resistance be managed prior to cardiopulmonary bypass?
31. For critically ill patients such as those with truncus arteriosus, what is an important feature of ventilator management prior to cardiopulmonary bypass?
32. For the Norwood procedure for hypoplastic left heart syndrome, what is an important aspect of anesthetic management prior to cardiopulmonary bypass?
33. During the Glenn procedure, what is an important aspect of anesthetic management?
34. What are poor prognostic factors of a successful Fontan procedure?
35. What are some common congenital lesions that result in inadequate pulmonary blood flow? What would be an important aspect of ventilatory management of patients with these lesions?
36. Where is the appropriate placement of an arterial line during surgery for coarctation of the aorta?
37. During induction of anesthesia for patients with obstructive lesions such as aortic stenosis, what is the most important to avoid?
38. What are some common abnormalities seen in patients with Williams syndrome?
39. How should the size of the endotracheal tube be selected?
40. What are some monitors that might be required for children undergoing surgery for congenital heart disease?
41. What are some general requirements for the selection of blood products for infants requiring cardiac surgery?
42. What are some antifibrinolytic drugs used in congenital heart surgery?
43. How is anesthesia maintained prior to cardiopulmonary bypass?
44. What patients may be able to have early extubation of the trachea?
45. What is a useful way to monitor the cardiac output and circulatory system?
46. How is anticoagulation for cardiopulmonary bypass achieved?
47. What is the target activated clotting time (ACT) value?
48. How are flow rates adjusted during cardiopulmonary bypass for infants and children?
49. How does the perfusionist control oxygenation and ventilation during cardiopulmonary bypass?
50. How is blood temperature adjusted during cardiopulmonary bypass?
51. How is mechanical quiescence and myocardial protection provided during cardiopulmonary bypass?
52. What is the lowest acceptable level of anemia during cardiopulmonary bypass?
53. What measures are used to provide cerebral and myocardial protection during cardiopulmonary bypass?
54. Which surgical repairs require the use of deep hypothermic circulatory arrest?
55. What are some potential negative effects of persistent hypothermia after cardiopulmonary bypass?
56. How can relative bradycardia and atrioventricular node conduction failure during separation from cardiopulmonary bypass be treated?
57. How are patients with long-standing excessive pulmonary blood flow treated on separation from bypass?
58. What is the best approach to the management of a patient who has had a palliative procedure and is left with a mixing lesion? What is an effective monitoring tool in these patients?
59. What are some common vasoactive drugs used during separation from cardiopulmonary bypass?
60. What are some causes of difficulty in separation from cardiopulmonary bypass in congenital heart surgery?
61. What rescue measure can be used if a patient cannot be weaned from cardiopulmonary bypass?
62. What are important complications of protamine administration?
63. What are contributors to postoperative coagulopathy in congenital heart surgery?
64. What is the best method to replace blood components in infants?
65. What is a common side effect of the administration of citrated blood products?
66. What agents can be used for refractory bleeding after cardiopulmonary bypass?
67. What are common parameters to be actively managed after pediatric cardiac surgery in the intensive care unit?
Answers*
Fundamental pathophysiology in congenital heart disease
1. Under normal physiologic conditions, pulmonary blood flow and systemic blood flow do not mix, and the entire cardiac output flows in one direction. Shunting occurs when a portion of the venous return is redirected back to the arterial outflow of the same circulation. The shunt occurs when there is an abnormal communication between the pulmonary blood flow and systemic blood flow. (418)
2. A shunt occurs when there is an abnormal communication, or defect, between the pulmonary and systemic circulations. The direction of the shunt flow is dictated by the relative pressures between the communicating structures. The amount of shunting is limited by the size of the defect. (418)
3. A left-to-right shunt occurs when part of the pulmonary venous return is redirected toward the pulmonary arterial system. This can occur through anomalies in the pulmonary veins, atrial septum, ventricular septum, or at the great vessels. (419)
4. The physiologic effect of a left-to-right shunt is that the total pulmonary blood flow (Qp) is greater than the systemic blood flow (Qs); that is Qp becomes greater than Qs. This can result in hypotension and pulmonary edema. (419)
5. Long-term effects of an increase in pulmonary blood flow, as occurs in a left-to-right shunt, are an increase in pulmonary vascular resistance and abnormal cardiac chamber dilation. In addition, prolonged hypotension can lead to circulatory shock and multiple organ failure. (419)
6. An example of a left-to-right shunt congenital heart lesion would be an atrial septal defect (ASD). (419)
7. A right-to-left shunt occurs when a portion of the systemic venous return is redirected to the systemic arterial outflow without first circulating through the lung. Physiologically this would result in desaturated blood returning to the systemic circulation, and potentially arterial hypoxemia. The degree of hypoxemia would be dictated by the magnitude of the shunt. (419)
8. An example of a right-to-left shunt congenital heart lesion would be tetralogy of Fallot. (419)
9. Mixing lesions in congenital heart disease describes a complete blending of the pulmonary and systemic circulations such that there is identical or nearly identical oxygen saturations in both circulatory systems. In mixing lesions the systemic arterial oxygen saturation decreases. (419)
10. In mixing lesions, the Qp:Qs ratio is determined by the relative resistance of blood flow in the pulmonary and systemic circulatory systems. That is, in mixing lesions, the ratio of blood flow is determined by pulmonary vascular resistance and systemic vascular resistance. (420)
11. The ideal Qp:Qs ratio in mixing lesions is 1. Any preferential flow toward the systemic circulation would be at the expense of greater desaturation and therefore less oxygen delivery. Conversely, any preferential flow toward the pulmonary circulation would be at the expense of cardiac output, and therefore less oxygen delivery to the tissues. (420)
12. Factors that can increase systemic vascular resistance are light anesthesia, systemic nervous system activation, administration of α agonists, and physical manipulations such as flexing the hips of infants and small children. (420, Table 26-2)
13. Factors that can decrease systemic vascular resistance are deep anesthesia and the administration of vasodilating drugs, such as nitrates and inhaled anesthetics. (420, Table 26-2)
14. Five factors that increase pulmonary vascular resistance are alveolar hypoxemia, hypercapnia, acidosis, light anesthesia, and hypothermia. Other factors include high lung volumes and pressures, or low lung volumes with atelectasis. (Table 26-2)
15. Five factors that decrease pulmonary vascular resistance are hyperventilation with resultant hypocarbia, alkalosis, oxygenation, pulmonary vasodilators such as inhaled nitric oxide, warmth, and bronchodilators such as albuterol. (Table 26-2)
16. Eisenmenger syndrome is a condition that can develop when pulmonary blood flow is increased over a long period of time, and the direction of the shunt flow becomes irreversibly left-to-right. This syndrome occurs due to a remodeling of pulmonary vasculature, an increase in pulmonary vascular resistance, and ultimately pulmonary hypertension yielding a pulmonary systolic blood pressure that is higher than systemic systolic blood pressure. (420)
Perioperative management
17. An anesthesiologist should prepare by understanding the physiology of the congenital heart lesion and the subsequent effects of the planned surgery. Aspects of the patient’s condition that can be improved prior to surgery should be identified. (421)
18. Preexisting conditions that might be important to the care of patients with congenital heart disease include a history of prematurity, trisomy 21, DiGeorge syndrome, and chronic illness such as renal dysfunction, pulmonary edema, and electrolyte abnormalities. In addition, the preoperative evaluation of morning admission patients scheduled for congenital heart surgery should include the usual preoperative evaluation of pediatric patients, such as evaluation for new upper respiratory tract infections. (421)
19. Important preoperative information that could be derived from the magnetic resonance imaging (MRI) and echocardiograms would be anatomic manifestations of disease, such as an existing ventricular septal defect and concomitant right ventricular hypertrophy. (421)
20. Risk factors from previous sternotomy include increased operative blood loss and cardiac trauma during dissection secondary to adhesions that may have formed adherent to the sternum and chest wall. (421)
21. Fasting recommendations for infants and children scheduled for congenital heart surgery should follow the standard American Society of Anesthesiologist guidelines. (421)
22. The most important feature of intravenous administration set up for patients scheduled for congenital heart surgery is to meticulously de-air the system. The inadvertent introduction of an air bubble into the patient’s vascular system via the intravenous tubing can result in an air embolus entering the systemic circulation in a patient with a left-to-right shunt. Although the risk is greater in patients with right-to-left shunts, patients with left-to-right shunts may have reversal of their shunt during certain phases of the cardiac cycle, during cardiopulmonary interventions as during manual manipulation of the heart during surgery, or with coughing in the awake patient. (421)
23. Some common side effects of induction of anesthesia with inhaled agents, such as sevoflurane or halothane, include myocardial depression, decreased heart rate and myocardial contractility, and decreased systemic vascular resistance. A halothane induction may also have associated myocardial dysrhythmia and ventricular irritability. (422-424, Table 26-4)
24. Some side effects of an intravenous induction of anesthesia using opioids such as fentanyl would include bradycardia and loss of sympathetic tone. (425, Table 26-4)
25. Some side effects of an intravenous induction of anesthesia using ketamine might include increases in heart rate and myocardial depression. (425, Table 26-4)
26. Some general principles for the induction of anesthesia that might apply to all patients with congenital heart disease would include the avoidance of dehydration, maintaining the patient in sinus rhythm, avoiding myocardial depression, and avoiding air entrapment in the intravenous and pressure tubings. (423, Table 26-5)
27. The goals for the anesthetic management in patients with a left-to-right shunt are aimed toward the avoidance of hemodynamic changes, such as an increase in systemic vascular resistance that will increase the magnitude of the shunt. Decreases in the magnitude of the shunt can be achieved through decreases in the arterial pressure and increases in the pulmonary vascular resistance, as with positive-pressure ventilation.
28. The goals for the anesthetic management in patients with a right-to-left shunt are aimed toward the avoidance of worsening arterial hypoxemia by increasing the magnitude of the shunt. Decreases in systemic vascular resistance and increases in pulmonary vascular resistance should be avoided.
29. Ventilatory management of the patient with congenital heart disease depends on how the circulatory system will be affected by changes in the pulmonary vascular resistance relative to the systemic vascular resistance. The goal is to minimize the impact on blood flow across shunts, and the cardiac lesion must be understood to best manage the patient. Adjustments in the fractional inspired oxygen concentration, minute ventilation, peak inspiratory pressure, and the possible use of the positive end-expiratory pressure are all considerations. (425)
30. For lesions with excessive pulmonary blood flow, such as ventricular septal defects or atrioventricular septal defects, one should avoid decreases in the pulmonary vascular resistance prior to cardiopulmonary bypass. (Table 26-5)
31. For critically ill patients such as those with truncus arteriosus, an important feature of ventilator management prior to cardiopulmonary bypass is to closely manage the ratio of systemic to pulmonary vascular resistance. (Table 26-5)
32. During the Norwood procedure (stage I for hypoplastic left heart syndrome), an important aspect of anesthetic management prior to cardiopulmonary bypass is to maintain the infusion of prostaglandins, maintain nearly equal systemic and pulmonary blood flow, and protect against myocardial depression and air embolism. (Table 26-5)
33. During the Glenn procedure (stage II procedure for hypoplastic left heart syndrome), an important aspect of anesthetic management is to maintain a high hematocrit and recognize that positive-pressure ventilation might decrease pulmonary blood flow and cardiac output. (Table 26-5)
34. Poor prognostic factors of a successful Fontan procedure (stage III procedure for hypoplastic left heart syndrome) include high pulmonary vascular resistance, tricuspid regurgitation, and decreased ventricular function. (Table 26-5)
35. Common congenital lesions that result in inadequate pulmonary blood flow include transposition of the great arteries, tetralogy of Fallot, tricuspid or pulmonary atresia, and total anomalous venous return. An important aspect of the ventilatory management of patients with these lesions would be to decrease pulmonary vascular resistance. (Table 26-5)
36. The appropriate placement of an arterial line during surgery for coarctation of the aorta is in the right arm. (Table 26-5)
37. During induction of anesthesia for patients with obstructive lesions such as aortic stenosis, it is most important to avoid tachycardia. (Table 26-5)
38. Some common abnormalities seen in patients with William syndrome are supravalvar aortic stenosis, pulmonary arterial stenosis, and coronary artery abnormalities. (Table 26-5)
39. The endotracheal tube size should be selected according to the age and size of the patient. (Table 26-5)
40. Some monitors that might be required for children undergoing surgery for congenital heart disease would include arterial pressure monitoring and transesophageal echocardiography. Monitors are selected on a case-by-case basis and what is standard for the institutional practice. (425)
41. Some general requirements for the selection of blood products for infants requiring cardiac surgery are that the blood should be the freshest when possible, that is less than 5 days of storage. Older blood can become significantly hypokalemic and result in leftward shifting of the oxygen-hemoglobin dissociation curve. (425)
42. Examples of commonly used antifibrinolytic drugs used in congenital heart surgery are aminocaproic acid and tranexamic acid. (426)
43. Prior to cardiopulmonary bypass, maintenance of anesthesia is usually achieved with a combination of intravenous agents and volatile anesthetics to avoid myocardial depression. (426)
44. Early extubation of the trachea may be performed in patients with simple defects, good cardiac reserve, and those undergoing the Glenn or Fontan procedure. (426)
45. A useful way to monitor the cardiac output and circulatory system is to conduct early and repeated arterial blood gas measurements to allow for appropriate ventilator and acid-base management. (426)
46. Anticoagulation for cardiopulmonary bypass is achieved using unfractionated heparin (3 to 4 mg/kg). (426)
47. The target activated clotting time (ACT) value is over 400 but the level required varies in individual practices. (426)
48. Flow rates are adjusted during cardiopulmonary bypass to maintain an age appropriate mean arterial blood pressure. Parameters used to calculate the flow rate needed to maintain metabolic function are the patient’s size and estimated blood volume. (426)
49. The perfusionist controls oxygenation and ventilation during cardiopulmonary bypass by adjusting the blend of air and oxygen (FIO2) and the flow rate (sweep) of the fresh gas. (426)
50. Blood temperature is adjusted during cardiopulmonary bypass by running cooled or warmed water through a coil in contact with the blood path. (426)
51. Mechanical quiescence and myocardial protection is provided during cardiopulmonary bypass through the administration of cold hyperkalemic crystalloid solution. (426)
52. The lowest acceptable level of anemia during cardiopulmonary bypass varies from institution to institution, but is commonly in the range of 20% to 30%. (427)
53. During cardiopulmonary bypass, cerebral and myocardial protection is achieved by mild to moderate systemic hypothermia. Active rewarming is usually initiated toward the end of cardiopulmonary bypass. (427)
54. Surgical repairs of the aorta and aortic arch require deep hypothermic circulatory arrest. (427)
55. Potential negative effects of persistent hypothermia after cardiopulmonary bypass include myocardial ischemia, cardiac dysrhythmias, elevated pulmonary vascular resistance, coagulopathies, and renal dysfunction. (427)
56. Relative bradycardia or atrioventricular node conduction failure that occurs during separation from cardiopulmonary bypass can be treated by temporary cardiac pacing. (427)
57. Patients with long standing excessive pulmonary blood flow may have underlying pulmonary hypertension, and may benefit from maneuvers that minimize pulmonary vascular resistance during separation from bypass. (427)
58. When a patient has had a palliative procedure and is left with a mixing lesion, the best approach to management is to balance the circulatory system so that the pulmonary vascular resistance and systemic vascular resistance yield a balanced circulation. An effective monitoring tool in these patients is the pulse oximeter. A balanced circulatory system in these patients will result in a systemic oxygen saturation of 80%. Excessive pulmonary blood flow exists when systemic oxygen saturation is greater than 85% to 90%, whereas when the systemic oxygen saturation is lower than 70% there may be inadequate pulmonary blood flow. (427)
59. Some common vasoactive drugs used during separation from cardiopulmonary bypass in congenital heart surgery are dopamine, epinephrine, norepinephrine, and milrinone. (427, Table 26-6)
60. Some causes of difficulty in separation from cardiopulmonary bypass in congenital heart surgery include inadequate pulmonary blood flow (arterial hypoxemia), inadequate systemic blood flow (hypotension and metabolic acidosis), valvular dysfunction, decreases in cardiac output, decreased systemic vascular resistance, cardiac rhythm disturbances, and hypovolemia. (428, Table 26-7)
61. A rescue measure that can be used if a patient cannot be weaned from cardiopulmonary bypass is extracorporeal life support. (428)
62. Important complications of protamine administration include anaphylactic, anaphylactoid, hypotensive, or severe pulmonary hypertensive reactions. (428)
63. Contributors to postoperative coagulopathy in congenital heart surgery include coagulation factor deficiencies, hypothermia, and hypocalcemia. (428)
64. The best method to replace blood components in infants is noting their small intravascular volume, and administering products carefully in aliquots. (428)
65. A common side effect of the administration of citrated blood products is hypocalcemia. (429)
66. Refractory bleeding after cardiopulmonary bypass can be treated with recombinant factor VIIa when conventional hemostatic therapy has failed to stop the bleeding. (429)
67. Common parameters that are actively managed after pediatric cardiac surgery in the intensive care unit involve the correction of various electrolyte, glucose, and ventilatory, circulatory, and hematologic parameters. (429)
