Dr Christopher Holmes

Sydney Children’s Hospital, NSW, Australia

Congenital Heart Disease (CHD) is one of the most common inborn defects, occurring in ~ 0.8% of newborn infants.1
Relative frequency of common congenital heart defects1
Acyantoic lesions
Ventricular septal defect (VSD) 35%
Atrial septal defect (ASD) 9%
Patent ductus arteriosus (PDA) 8%
Pulmonary stenosis 8%
Coarctation of the aorta (CoA) 6%
Aortic Stenosis 6%
Atrioventricular septal defect (AVSD) 3%
Cyanotic lesions
Tetralogy of Fallot (TOF) 5%
Transposition of the great arteries (TGA) 4%

The major advances made over the last 30 years in congenital cardiac surgery have resulted in an increased number of children born with heart disease who enjoy long term survival - 85% of these babies are expected to reach adulthood.2 The anaesthetists role is pivotal in the management of these cases, particularly during non cardiac surgery when their understanding of the pathophysiology should lead the decisions of the operative team.2 Particularly as non-cardiac surgeons may be less familiar with the issues involved.

In the time available it is not possible to begin to discuss individual lesions in detail, but hopefully some general principles can be discussed.

Patients with CHD can be thought of in 3 categories:

1. Patients with previous complete correction of their defect. However even complete anatomic correction can leave haemodynamic sequelae.
2. Patients with partial or palliative surgery. The haemodynamic behaviour of these patients is frequently complex and far different from normal physiology.
3. Non operated patients. These include patients with benign lesions and the undiagnosed.

Surgery in children with CHD has long been recognised as posing an increased risk of morbidity and mortality particularly if their cardiac disease is poorly compensated. Patients with pulmonary hypertension, congestive heart failure or cyanosis and children with CHD who are younger than 2 years of age have an increased frequency of perioperative morbidity.3

Shunt
These include defects that permit abnormal communications between chambers or vessels with oxygenated and deoxygenated blood.4 The flow through a shunt is proportional to the diameter of the defect or the conduit and to the ratio of the impedances between the upstream and the downstream cavities - usually the Systemic Vascular Resistance (SVR) and the Pulmonary Vascular Resistance (PVR).2
A R-to-L shunt (e.g. TOF) increases when SVR decreases or PVR increases. The SpO2 varies with the ratio between the pulmonary flow and the systemic flow (Qp/Qs ratio), and monitors very precisely the degree of mixing of arterial and venous blood. Increasing the inspired oxygen concentration has minimal effect on cyanosis due to a R-to-L shunt, whereas arterial vasoconstriction increases arterial oxygen saturation.2
A L-to-R shunt (e.g. VSD) decreases with a drop in SVR or an increase in PVR. An artificial L-to-R shunt, such as a modified Blalock-Taussig shunt (BT Shunt), is created to supplement insufficient pulmonary blood flow. Its dimension is fixed so its output is proportional to the systemic arterial pressure. Pulmonary blood flow will fall in the presence of systemic hypotension. The SpO2 decreases with falls in SVR and will respond to treatment of the reduced systemic blood pressure.2
Patients with L-to-R or bidirectional shunts will have decreased delivery of oxygen to the systemic circulation to the extent that pulmonary blood flow exceeds systemic blood flow. The presence of high oxygen saturation does not ensure adequate oxygen delivery. The patient's increased arterial oxygen saturation is at the expense of systemic output, therefore a pink patient may paradoxically develop a metabolic acidosis. In the management of shunts, one should always keep in mind the balance of PVR and SVR.5
Pulmonary hypertension
Pulmonary hypertension (PHT) is a common complication of unrestricted L-to-R shunt. PHT is associated with a progressive muscular hypertrophy of the media layers of pulmonary arterioles. It leads to a hypertension that is at first reactive for many years but later becomes fixed. This last stage is the Eisenmenger syndrome. The shunt flow first becomes bidirectional and then reversed.
As long as the pulmonary arterial pressure is not fixed it will be increased by hypothermia, stress, pain, acidosis, hypercarbia, hypoxia and elevated intrathoracic pressure.6 Severe PHT is a major risk factor for perioperative morbidity and mortality. Children with suprasystemic PHT have a significant risk of major perioperative complications, including cardiac arrest and pulmonary hypertensive crisis.7

Cyanosis
Arterial hypoxaemia in CHD arises from two basic mechanisms: inadequate pulmonary blood flow and/or admixture of deoxygenated with oxygenated blood in the systemic circulation.4 Patients with cyanotic CHD and associated secondary polycythaemia are susceptible to develop coagulation abnormalities.

Ventricular dysfunction
Congenital heart anomalies place a pressure or volume burden on the heart causing the myocardium to become hypertrophied or dilated. If the haemodynamic load is relieved by intervention, myocardial remodelling occurs, permitting normal or near normal myocardial performance. Late correction or part correction commonly produces long standing ventricular dysfunction which is exacerbated if chronic cyanosis is present.8

Endocarditis prophylaxis
The American Heart Association guidelines on the prevention of infective endocarditis have recently received a major update.9 Infective endocarditis prophylaxis for procedures is reasonable only for patients with underlying cardiac conditions associated with the highest risk of adverse outcome from infective endocarditis. For patients with these underlying cardiac conditions, prophylaxis is reasonable for all procedures likely to produce a substantial bacteraemia.

Cardiac conditions for which prophylaxis with procedures is reasonable

1. Prosthetic cardiac valve or prosthetic material used for cardiac valve repair
2. Previous infective endocarditis
3. Congenital heart disease ONLY
4. 1. Unrepaired cyanotic CHD, including palliative shunts and conduits
   2. Completely repaired congenital heart defect with prosthetic material or device during the first 6 months after the procedure
   3. Repaired CHD with residual defects at the site or adjacent to the site of a prosthetic patch or device (which inhibits endothelialisation)
5. Cardiac transplantation recipients who develop cardiac valvulopathy.

An antibiotic for prophylaxis should be administered in a single dose before the procedure. The choice of antibiotic should reflect the likely microorganism involved in the bacteraemia. This will be the same antibiotic chosen for prophylaxis of surgical wound infection.

Preparing for theatre
In the perioperative management of patients with CHD, the anaesthetist need to understand the particular pathophysiology of their patient. Information can be obtained from Echo results, Cardiac Catheter data and old notes detailing previous procedures and interventions. Frequently the simplest resource is a copy of the last letter from the patients cardiologist to the patients GP. Important features to determine include ventricular function, presence of intracardiac mixing, patency of surgically created shunts, evidence of any right or left ventricular outflow tract obstruction, cyanosis and polycythaemia. Previous procedures may affect venous and arterial access and monitoring options e.g. after BT shunt or Fontan palliation. In patients with shunts great care must be taken to prevent the venous injection of air. The pulse oximeter is the single most useful monitoring device in CHD. An invasive monitor of arterial pressure is very helpful in sick patients or for major procedures in any patient with significant CHD. Nitrous oxide may increase PVR and exacerbate an air embolus and its use should be discouraged.5
Inhalational induction is generally well tolerated by children with minor cardiac defects. Sevoflurane is the agent of choice with good cardiovascular stability. Generally children with well compensated CHD tolerate intravenous induction with thiopentone or propofol in conjunction with an opioid, provided they are euvolaemic. In most children with well compensated or corrected CHD the same techniques can be used as in otherwise healthy children.10
1 Lovell A.T. Anaesthetic Implications of grown-up congenital heart disease. Br J Anaesth 2004; 93:129-39
2 Chassot P. Anesthesia and adult congenital heart disease. J Cardiothorac Vasc Anesth 2006; 20(3):414-437
3 Warner MA, Lunn RJ, O'Leary PW et al. Outcomes of noncardiac surgical procedures in children and adults with congenital heart disease. Mayo Clin Proc 1998; 73:728-34
4 Galli KK, Myers LB, Nicolson SC. Anesthesia for adult patients with congenital heart disease undergoing noncardiac surgery. Int Anes Clinics 2001; 39(4):43-71
5 Heggie J, Karski J. The anesthesiologist's role in adults with congenital heart disease. Cardiol Clin 2006; 24:571-85
6 Fischer LG, Aken HV, Burkle H. Management of pulmonary hypertension: physiological and pharmacological considerations for anesthesiologists. Anesth Analg 2003; 96:1603-16
7 Carmosino MJ, Friesen RH, Doran A, Ivy DD. Perioperative complications in children with pulmonary hypertension undergoing noncardiac surgery or cardiac catheterization. Anesth Analg 2007;104(3):521-7
8 Stayer SA, Andropoulos DB, Russell IA. Anesthetic management of the adult patient with congenital heart disease. Anesthesiology Clin N Am 2003; 21:653-73
9 Wilson W, Taubert KA, Gewitz M et al. Prevention of infective endocarditis. Guidelines from the American Heart Association. Circulation 2007; 116:1736-54
10 Sumpelmann R, Osthaus WA. The pediatric cardiac patient presenting for noncardiac surgery. Curr Opin Anaesthesiol 2007; 20:216-20