A 5-week-old infant was scheduled for bilateral inguinal herniorrhaphy. On preoperative evaluation, the infant was noted to be tachypneic and tachycardic. A IV/VI systolic murmur was heard at the left sternal border.
What is the incidence of congenital heart disease?
The incidence of congenital heart disease (CHD) is approximately 6 to 8 in 1000 live births. It is the most common congenital malformation. The incidence of CHD has increased as a result of improvements in diagnostic testing, increased awareness, and improved medical treatments of critically ill infants. Approximately 40,000 children are born each year with CHD in the United States. The most common CHD lesions manifest with a systolic murmur ( Table 63-1 ). The main consequences of significant CHD are congestive heart failure and cyanosis.
|Ventricular septal defect||25|
|Atrial septal defect||12|
|Patent ductus arteriosus||12|
|Tetralogy of Fallot||8|
|Coarctation of the aorta||7|
|Transposition of the great arteries||5|
What is the differential diagnosis for a systolic murmur?
Systolic murmurs can be either innocent or pathologic. Innocent murmurs are soft flow murmurs without physiologic consequences. Pathologic murmurs are loud, pansystolic or late systolic, and are associated with cardiac anomalies. The most common lesions associated with a systolic murmur in young infants are ventricular septal defect (VSD) and patent ductus arteriosus (PDA). These infants have signs of mild congestive heart failure (i.e., tachypnea and tachycardia) and should undergo a cardiology evaluation before surgery. Transthoracic echocardiography is presently the fastest, most accurate, and least invasive diagnostic tool to establish an exact anatomic diagnosis in most patients with CHD.
What are the general anesthetic considerations for common congenital cardiac lesions?
Associated extracardiac defects are present in 5–50% of children with CHD. In 17–18%, the defect is part of a syndrome or chromosomal anomaly. Genitourinary tract anomalies are among the most common lesions and are present in 4–15% of patients with CHD. Major chromosomal anomalies with associated cardiac lesions of anesthetic significance are Down (trisomy 21), Turner, Noonan, and DiGeorge syndromes.
Prevention of air embolism
All patients with shunt lesions (i.e., communication between the pulmonary and systemic circulation), regardless of the presence or absence of pulmonary outflow obstruction or usual shunting pattern, are at risk for air emboli to the systemic circulation. Shunts are often bidirectional, and owing to the earlier relaxation of the left ventricle compared with the right ventricle, a left-to-right shunt may transiently reverse during this portion of the cardiac cycle. On sudden obstruction to right ventricular output secondary to air embolism, a left-to-right shunt converts to a right-to-left shunt pattern. The following precautions should be followed whenever caring for a patient with a shunt lesion:
Intravenous (IV) tubing should be meticulously debubbled and then rechecked after warming the operating room. Warming could allow nitrogen to come out of solution in the IV fluid, forming additional hazardous bubbles.
All IV lines should be connected while free flowing.
All syringes should be cleared of air, and before injecting into an IV line, a small amount of fluid should be aspirated into the syringe to clear the needle and injection port of air. A recommended technique is to dilute medications in a 10-mL syringe such that each milliliter contains the calculated dose. In this way, aspiration of IV fluid into the syringe would not significantly change the medication concentration; this is in contrast to aspirating fluid into a small volume of undiluted medication.
According to the American College of Cardiology/American Heart Association (ACC/AHA) guidelines, endocarditis prophylaxis is required for the prevention of bacterial endocarditis before any surgical, diagnostic, or dental procedure that may result in bacteremia for the following patients:
Patients with unrepaired cyanotic CHD (including palliative shunts and conduits)
Patients with completely repaired congenital heart defect with prosthetic material or device, whether placed by surgery or by catheter intervention, during the first 6 months after the procedure
Patients with repaired CHD with residual defects at the site or adjacent to the site of a prosthetic patch or prosthetic device (which inhibit endothelialization)
Endocarditis prophylaxis is not needed for routine tracheal intubation or flexible bronchoscopy. It is not needed for diagnostic procedures involving the gastrointestinal tract (e.g., esophagogastroduodenoscopy, colonoscopy) and the genitourinary tract unless a urinary tract infection is present. The only dental procedures that require endocarditis prophylaxis are procedures that involve (1) manipulation of gingival tissue or the periapical region of teeth or (2) perforation of the oral mucosa.
It is recommended that patients with the above-noted CHD lesions receive endocarditis prophylaxis for procedures involving the respiratory tract, skin structures, or musculoskeletal tissues that are infected. Current medication regimens for endocarditis prophylaxis are listed in Table 63-2 .
|Oral||Amoxicillin||50 mg/kg |
Maximum 2 g
|Allergic to Penicillins:|
|Cephalexin||50 mg/kg |
Maximum 2 g
|Clindamycin||20 mg/kg |
Maximum 600 mg
|Azithromycin or Clarithromycin||15 mg/kg |
Maximum 500 mg
Cefazolin or Ceftriaxone
|50 mg/kg |
Maximum 2 g
Maximum 1 g
|Allergic to Penicillins:|
|Cefazolin or Ceftriaxone||50 mg/kg |
Maximum 1 g
|Clindamycin||20 mg/kg |
Maximum 600 mg
What are common intracardiac lesions with left-to-right shunting?
Common intracardiac lesions with left-to-right shunting include all forms of atrial septal defects (ASDs), VSDs, PDA, and other large aortopulmonary connections. The magnitude and direction of the shunt depend on the difference between the outflow resistances of the two connections and the size of the defect. Exceptions are communications between the left ventricle and right atrium where obligatory shunting of blood occurs owing to the large pressure difference that exists between these two cardiac chambers.
Atrial septal defects
In ASDs located in the area of the fossa ovalis (i.e., ASD secundum), shunting occurs between low-pressure circulations. Despite a large shunt volume resulting in marked increase in pulmonary blood flow, pulmonary artery pressure remains low over many years. These patients are generally asymptomatic throughout childhood and adolescence but may develop mild pulmonary hypertension in the third and fourth decades of life. In this lesion, the right ventricle is volume-overloaded. The main anesthetic concern in asymptomatic patients is prevention of systemic embolization from injection of air or debris from IV tubing. These ASDs are closed electively during childhood either surgically or with an intracardiac device. Device closure has become the preferred approach. Size of available devices and delivery systems precludes percutaneous closure in patients weighing <15 kg. There is a risk of late device erosion through the cardiac wall with large devices.
Ventricular septal defects
Small VSDs restrict the amount of left-to-right shunting and limit the hemodynamic consequences. With a large defect (i.e., approximating the size of the normal age-appropriate aortic orifice or larger), there is no restriction to flow, and shunting depends largely on the relative ratio of pulmonary vascular resistance (PVR) to systemic vascular resistance (SVR). In the early neonatal period, PVR is high and patients do not exhibit signs or symptoms related to the VSD. As PVR declines during the second and third weeks of life, left-to-right shunting increases, and larger volumes of blood traverse the pulmonary circulation. Substantially more blood returns to the left heart creating congestive heart failure (CHF) secondary to volume overload of the left ventricle. In this lesion, the pulmonary vascular bed is exposed to increased blood flow and systemic blood pressure.
An estimated 25–50% of all small to moderate-sized VSDs close spontaneously, generally during the first year of life. Many VSDs become smaller throughout life and are benign. Probably <5% of large VSDs undergo spontaneous closure. Surgery is indicated for primary closure of the defect during the first year of life in infants with CHF and failure to thrive despite medical therapy. Failure to close a large VSD leads to progressive pulmonary vascular obstructive disease, particularly after the second year of life.
Before the development of pulmonary vascular disease, the volume of the shunt may be manipulated by changing PVR or SVR or both. High oxygen concentrations, hyperventilation, and alkalosis lead to pulmonary vasodilation and may cause massive increases in left-to-right shunting. With the limited cardiac output of the small infant, this increase in left-to-right shunting can lead to severe systemic underperfusion and cardiovascular collapse. Similarly, an increase in afterload leads to an increase in left-to-right shunting, as long as PVR is less than SVR. Most patients with large shunts receive anticongestive medications (e.g., digoxin, furosemide) and an afterload-reducing agent (e.g., angiotensin-converting enzyme inhibitor) before cardiac surgery or if managed medically only.
Patent ductus arteriosus
Large PDAs have a similar clinical presentation to large VSDs and are managed surgically or with device closure to protect the pulmonary vascular bed. Small PDAs are closed percutaneously with coils or devices to prevent endarteritis of the PDA. Because of the size of the delivery system, percutaneous closure is not performed in infants <6 months old or weighing <6 kg. In premature infants, a PDA is not considered CHD. The ductus arteriosus often does not close in a premature infant because of insensitivity to the factors that would normally stimulate closure when the infant is born full-term. Pharmacologic closure of the PDA can be attempted with prostaglandin inhibitors (e.g., indomethacin) unless it is contraindicated. If closure is not achieved after three doses or if there is a contraindication to treatment, surgical closure is indicated.
What are the anesthetic considerations for left-to-right shunting lesions?
A left-to-right shunt influences the uptake of inhalation anesthetic agents only minimally, unless cardiac output is depressed, in which case induction is accelerated. However, induction with IV agents is delayed because much of the injected drug is recirculated to the lung. Agents that cause myocardial depression are poorly tolerated in infants with limited cardiac reserve. Infants with large left-to-right shunts have chronically congested lungs with decreased compliance, increased closing volume, and increased airway resistance. The airway should be secured and ventilation should be controlled during general anesthesia. It is important to maintain a relatively high PVR to avoid increasing pulmonary congestion from increased pulmonary blood flow. Inspired oxygen concentrations should be kept to a minimum that provides adequate oxygen saturation, and ventilation parameters should be aimed at maintaining normocarbia or mild hypercarbia. Prevention of paradoxical air embolism from IV sets is of paramount importance. Although mild afterload reduction leads to increased systemic output and a reduction in left-to-right shunting, excessive systemic vasodilation in the presence of a high PVR can lead to significant right-to-left shunting resulting in cyanosis. Ketamine, opioid and muscle relaxant techniques, and low-dose inhalation anesthesia with isoflurane or sevoflurane are usually well tolerated. Endocarditis prophylaxis is required only for the first 6 months after ASD, VSD, and PDA repair, unless there is a residual defect at or near the site of repair ( Box 63-1 ).
Prevent paradoxical air embolism
Debubble all IV sets
Check IV sets for rebubbling in warm operating room
Connect IV tubing while fluid flowing
After attaching syringe to IV line, before injection of medications, aspirate to remove air bubbles
Maintain relatively high PVR
Minimize inspired oxygen concentration to maintain normal oxygen saturations
Normocarbia to mild hypercarbia
Prevent significant decrease in SVR
Opioid and muscle relaxant
Low-dose isoflurane or sevoflurane
Inhalation induction minimally affected
IV induction delayed
First 6 months after ASD, VSD, or PDA repair
>6 months if residual defect at or near repair
What are common intracardiac lesions with right-to-left shunting and reduced pulmonary blood flow?
Tetralogy of fallot
The combination of VSD, pulmonary valvular or right ventricular infundibular stenosis, right ventricular hypertrophy, and a large overriding aorta is known as tetralogy of Fallot (TOF). It is the most common cyanotic defect seen after the first year of life, accounting for 10% of all congenital cardiac lesions.
The degree of right ventricular outflow or pulmonic obstruction determines the onset and severity of cyanosis. If obstruction is severe, cyanosis appears with closure of the ductus arteriosus in the neonatal period. Prostaglandin E 1 (by keeping the ductus arteriosus open) may be used to stabilize the patient before surgical intervention. Many infants do not develop symptoms until 3–6 months of age, and even then these infants may not appear cyanotic at rest. However, episodes of severe cyanosis with hyperventilation and acidosis, known as hypercyanotic spells (or “tet” spells), may occur. These episodes are caused by severe infundibular spasm, probably induced by changes in venous return and SVR. Reduction in peripheral vascular tone leads to decreased pulmonary blood flow because blood tends to be shunted to the systemic circulation. Decreased venous return further decreases pulmonary blood flow. In older children, squatting may improve symptoms through an increase in venous return from the lower extremities and by increasing SVR. Hypercyanotic spells may occur perioperatively because of the dynamic nature of the muscular infundibular obstruction. The treatment of hypercyanotic spells is based on the goals of decreasing infundibular spasm, by decreasing contractility and heart rate, and increasing preload. Another goal (especially in fixed right ventricular outflow obstruction) is to increase SVR to decrease right-to-left shunting across the VSD. Strategies to prevent and treat these complications are outlined in Table 63-3 .