Heart Disease

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© Springer Nature Switzerland AG 2020
Craig Sims, Dana Weber and Chris Johnson (eds.) A Guide to Pediatric Anesthesiadoi.org/10.1007/978-3-030-19246-4_20



20. Congenital Heart Disease



Serge Kaplanian1  


(1)
Department of Anaesthesia and Pain Management, Perth Children’s Hospital, Nedlands, WA, Australia

 



 

Serge Kaplanian



Keywords

Non-cardiac anesthesia in cardiac childPediatric anesthesia, heart murmurAnesthesia and the Fontan circulationEndocarditis prophylaxisCongenital heart disease, preoperative assessment


Congenital heart disease occurs in 6–10 per 1000 births and is one of the most common congenital defects.


Ninety percent of children born with congenital heart disease survive into adulthood and will present for non-cardiac surgery having had varying levels of surgical correction. This chapter focuses on the management of children for non-cardiac surgery, and the assessment of a child with a murmur.


20.1 Types of Congenital Heart Disease


There are numerous classifications of congenital heart disease, but the most useful for anesthetists is based on physiology. Lesions fall into one of four groups as shown in Table 20.1.


Table 20.1

Classification of congenital heart disease by main physiological defect

















Types of congenital heart disease


1. ‘Simple’ left-to-right shunt with increased pulmonary blood flow


 Atrial septal defect (ASD)


 Ventricular septal defect (VSD)


 Patent ductus arteriosus (PDA)


Atrioventricular septal defect (AVSD)


2. ‘Simple’ right-to-left shunt with decreased pulmonary blood flow


 Tetralogy of Fallot (TOF)


Pulmonary atresia (with shunting of blood through associated defect


Tricuspid atresia (with shunting of blood through associated defect)


Ebstein’s anomaly (Tricuspid obstruction with ASD or patent foramen ovale)


3. ‘Complex’ shunts: mixing of pulmonary and systemic blood flow causing cyanosis


 Transposition of the Great Arteries (TGA)


Truncus arteriosus


Total anomalous pulmonary venous drainage


Double-Outlet Right Ventricle (DORV)


Hypoplastic Left Heart Syndrome (HLHS)


4. Obstructive lesions


Aortic stenosis


Pulmonary stenosis


Coarctation of the aorta


Hypoplastic aortic arch



Commonly used abbreviations are in parentheses


20.1.1 Shunting of Blood Between the Systemic and Pulmonary Circulations


20.1.1.1 Left-to-Right Shunts


Blood flows through a defect from the high pressure systemic side of the circulation to the lower pressure pulmonary side. This increases pulmonary blood flow in proportion with the size of the defect and the difference in resistance between the systems. This occurs in lesions such as a ventricular septal defect (VSD) (Fig. 20.1). Oxygenated blood from the left side of the heart enters the right side of the heart and lungs, and arterial oxygen saturations are normal. Pulmonary blood pressure increases because of the higher pulmonary flow, but pulmonary vascular resistance is relatively normal in the short term and not problematic. Eventually however, muscle in the walls of the pulmonary vasculature hypertrophies and pulmonary vascular resistance rises, causing Eisenmenger’s syndrome. This is a major problem, and surgical treatment is timed to avoid this. Left-to-right shunts cause a volume overload of the right ventricle that is relatively well tolerated. Anesthesia is also well tolerated provided myocardial contractility is not significantly depressed.

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Fig. 20.1

VSD with left-to-right shunting of blood. Oxygenated blood from the left ventricle (LV) enters the right ventricle (RV) and increases pulmonary blood flow


20.1.1.2 Right-to-Left Shunts (Cyanotic Heart Disease)


De-oxygenated blood from the right side of the heart bypasses the lungs and mixes into the systemic circulation, causing cyanosis. This occurs in lesions such as a Tetralogy of Fallot (TOF). This is a more debilitating condition than left-to-right shunting as pulmonary blood flow is often reduced. Most cyanotic heart conditions have complex defects allowing variable mixing of blood between the right and left side of the heart, and the degree of mixing is affected by the balance between the pulmonary and systemic vascular resistances. If pulmonary vascular resistance increases, pulmonary blood flow decreases. However, the pulmonary blood flow is also affected by the systemic vascular resistance. If the systemic vascular resistance falls, more blood is shunted to the left side of the heart and pulmonary blood flow decreases. The balance between the pulmonary and systemic vascular resistances is the critical factor with anesthesia for children with cyanotic heart disease.


Anesthesia for this group of patients is much more problematic than for children with left-to-right shunts because pulmonary blood flow must not be reduced any further. Right-to-left shunts slow inhalational induction due to a reduction in pulmonary blood flow (Table 20.2). Intravenous induction is rapid and with a danger of overdose because a proportion of the induction agent bypasses the lungs and is immediately available to the cerebral circulation. Air bubbles from the IV line can cross to the arterial circulation and must be avoided. Filters are available for IV lines to prevent air bubbles entering the patient.


Table 20.2

Differences between the two types of pulmonary-systemic shunting of blood





















Shunt type


Example


Effects


Left-to-right


VSD


Normal arterial SaO2


Inhalational induction faster


IV induction slower


Risk from IV air bubbles slightly raised


Anesthesia generally well tolerated


Right-to-left


TOF


Cyanosed, minimal improvement with high FiO2


High risk from IV air bubbles


Inhalational induction slower


IV induction faster, reduced dose required



Keypoint


The balance between the pulmonary and systemic vascular resistances is the critical factor in anesthesia for children with cyanotic heart disease.


20.1.1.3 Duct-Dependent Heart Disease


Some children with cyanotic heart disease have very little blood flow from the right ventricle into the pulmonary artery and lungs. Although this is not a problem while the placenta is in the circulation, after birth it results in poor oxygenation and may not be compatible with survival. Some of these children rely on the ductus arteriosus that directs blood from the aorta into the pulmonary artery. This oxygenated blood from the aorta mixes with any de-oxygenated blood already in the pulmonary artery and then passes into the lungs. Although this is not efficient for oxygenation, it often permits survival, albeit with persisting cyanosis. These babies have duct-dependent cyanotic heart disease, and their ductus is kept open with prostaglandins until other methods of augmenting pulmonary blood flow can be achieved. These methods depend on the underlying cardiac problem but include atrial septostomy (in transposition of the great arteries) or a modified Blalock-Taussig shunt (modified BT shunt). A modified BT shunt connects the left or right subclavian artery to the left or right pulmonary artery with a synthetic graft.



Note


If an infant has a modified BT shunt, pulmonary blood flow depends on the systemic blood pressure. Increasing the SVR and blood pressure will improve the child’s saturation.


20.1.2 ASD and VSD


Children with an atrial septal defect (ASD) or ventricular septal defect (VSD) have a predominantly left-to-right shunt that increases pulmonary blood flow and causes volume overload of the right ventricle. The size of the defect and difference in chamber pressures determine the amount of shunting. Patients with small restrictive defects have minimal left to right shunting and minimal increase in pulmonary blood flow. On the other hand, patients with large non-restrictive defects have greatly increased pulmonary blood flow.


Both defects are associated with a systolic murmur maximal at the left sternal edge. Small defects may eventually close without treatment. Others require either surgical closure under cardio-pulmonary bypass or using a transvenous approach in the catheter lab.


As long as pulmonary hypertension has not developed, anesthetic management is relatively straightforward. Preload should be maintained, and the fall in systemic vascular resistance that tends to accompany anesthesia reduces left-to-right shunting. Although increasing pulmonary vascular resistance also reduces shunting, PVR is not deliberately manipulated. Inhalational induction is very rapid because of the increase in pulmonary blood flow, but intravenous induction is delayed because of recirculation of agent through the shunt and pulmonary circulation (Table 20.2). In practice however, the change from the normal speed of induction is not great. Paradoxical air embolism can occur during ventilation if high airway pressures are used—IPPV and PEEP increase right atrial pressure and can induce R-to-L shunting.


20.1.3 Tetralogy of Fallot


Tetralogy of Fallot (TOF) is the commonest ‘simple’ right-to-left defect resulting in cyanosis. It consists of four abnormalities:


  1. 1.

    VSD


     

  2. 2.

    Overriding aorta (the aorta is positioned over the VSD, communicating with the left and right ventricles)


     

  3. 3.

    Right ventricular hypertrophy


     

  4. 4.

    Right ventricular outflow tract obstruction (subvalvular, valvular and/or supravalvular)


     

Obstruction of the right ventricular outflow tract increases right ventricular pressure. Deoxygenated blood passes through the VSD and into the overriding aorta, causing cyanosis. Obstruction at the level of the pulmonary valve (valvular) or pulmonary artery (supravalvular) is constant, and the child is always cyanosed. The classical outflow tract obstruction in Tetralogy is due to hypertrophy of the infundibular myocardium at the subvalvular level (Fig. 20.2). The obstruction is dynamic and behaves in a similar fashion to hypertrophic obstructive cardiomyopathy—if myocardial contractility increases or the right ventricular volume decreases, the opposing ventricular walls at the level of the obstruction become closer and the outlet obstruction worsens. Outlet obstruction diverts blood from the right ventricle through the VSD, away from pulmonary artery and the lungs. Cyanosis worsens, and a hypercyanotic spell or ‘Tet spell’ occurs. The intensity of the systolic murmur also decreases during a Tet spell. Children with a dynamic obstruction may be acyanotic between spells.

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Fig. 20.2

Tetralogy of Fallot during ‘Tet spell’. RV pressure is increased by the dynamic RV obstruction causing right-to-left shunting, reduced pulmonary blood flow and cyanosis


Spells are triggered by reduced right ventricular volume (dehydration), and by increased myocardial contractility (sympathetic stimulation from hypothermia, hunger or pain). The first aim of anesthetic management is to stop spells occurring, as they can be frighteningly severe and difficult to reverse. Treatment includes fluid to increase the volume of the right ventricle, opioids and beta blockers to reduce contractility of the infundibular myocardium, and peripheral vasoconstriction with a pure alpha agonist agent (e.g. phenylephrine) to increase the left ventricular pressure above the right ventricular pressure to reduce shunting (Table 20.3).
Nov 27, 2021 | Posted by in ANESTHESIA | Comments Off on Heart Disease
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