Topics within this page
- Classification of CHD (with pictures)
- Physiology of cardiac disease
- Fontan circulation
- Anaesthesia for CHD patients undergoing surgery
Classification of CHD:
Left to right shunts
Right to left shunts
Normal or series circulation
- Systemic and pulmonary circulation working together in series.
- Most repaired CHDs have this.
- Unrepaired CHDs with a ‘normal’ circulation have holes where mixing of blood can occur eg ASD/VSD. Blood flows through the holes down a pressure gradient and creates a shunt.
- Left to right shunts = increased pulmonary blood flow, decreased systemic blood flow
- Right to left shunts = increased deoxygenated blood in systemic circulation, cyanosis and decreased pulmonary blood flow
Parallel or ‘balanced’ circulation
- Pulmonary and systemic circulation communicate with each other and cause flow to vary based on relative resistance in each circuit. Blood flow to lungs and body = balance between SVR and PVR.
- Excessive pulmonary blood flow (due to High O2) causes pulmonary oedema/poor systemic perfusion and this may compromise coronary and splanchnic perfusion. Prolonged high PBF risks causing pulmonary hypertension.
- Insufficient pulmonary blood flow (due to low O2, hypercarbia, acidosis, stress and hypothermia) = profound cyanosis.
- Example of this is giving a large amount of induction agent to a patient with a large VSD, reducing SVR so much that their left to right shunt becomes a right to left shunt, thus leading to acute desaturation and cyanosis.
Single ventricle circulation
- Palliative procedure creating a circulation based on a single ventricle which pumps oxygenated blood around the body, while blood flows passively to the lungs down a pressure gradient from the pulmonary artery to the left atrium.
- Usually done for lesions such as hypo plastic left heart syndrome.
- Stage 1 is the Norwood operation (video below): First few weeks after birth. Moves aorta to come out of right ventricle instead of left, and a Blalock-Taussig shunt (tube to connect aorta to pulmonary artery) is inserted or a Sano shunt (tube to connect right ventricle to pulmonary artery).
- Second stage: Glenn operation (video below): Age 6m to 2y, removes Blalock-Taussig/Sano shunt. Superior vena cava connected directly to pulmonary artery for passive movement of blood from upper body veins to lungs. Venous blood from the lower part of the body returns to the right atrium and out through the aorta to the systemic circulation.
- Third stage: Fontan operation (video below). 1-5yr of age. IVC connects to the pulmonary artery with conduit placement. All venous blood returning from the body goes to the lungs first in a passive way, then returns to the heart to be pumped back out by the single (right) ventricle.
Complications of Fontan circulation
- All patients with a Fontan circulation have an abnormal cardiorespiratory response to exercise:
- Blunted heart rate response
- Limited ability to increase stroke volume with exercise
- Difficult to increase ventricular preload
- Myocardial failure and dysfunction occurs in about 70% of patients within 10 years, leading to systolic and diastolic deterioration. The limiting determinant of ventricular function is preload so that inotropes, vasodilators and beta-blockers have relatively little impact.
- Can get arrhythmias + risk of atrial thrombus, mainly from atrial enlargement
- Shunts from collaterals or residual right to left shunt through a fenestration lead to resting desaturation at rest. Drainage of coronary sinus blood into systemic circulation contributes. Shunts lead to volume overload on the ventricle and may induce an irreversible increase in PVR secondary to high regional pulmonary blood flow
- Protein-losing enteropathy (excessive loss of proteins from serum into intestinal lumen, possibly due to impedance of thoracic duct drainage by high superior caval venous pressure + mesenteric vascular inflammation). Prognosis is poor. Treatment includes low salt high calorie, high protein and high triglyceride diet. May need symptomatic treatment with diuretics, corticosteroids, heparin and octreotide.
- Developmental deficits
- Thromboembolism rate is 30%. Many are anti coagulated with warfarin or anti platelets.
Anaesthesia for Fontan circulation
- Main determinants: SVR, PVR, atrioventricular valve function, cardiac rhythm and ventricular function.
- Driving force for blood flow in pulmonary circulation = CVP – atrial pressure
- Intravascular volume = main determinant of CVP, so hypovolaemia is tolerated poorly.
- Sinus rhythm desired
- Maintain optimal ventricular filling + atrial emptying
- Negative inotropes eg beta blockers should be prescribed with caution
- Alpha agonists that increase PVR and other PVR increasing factors (eg. alveolar hypoxia, hypercarbia, acidosis) should be strenuously avoided.
- Highlights from prep assessment: History, biochemistry, haematology, end organ damage, 12 lead ECG and echo, perioperative antibiotic prophylaxis
- Intraop: Patients with a fenestration have high risk of air/fat emboli, monitor oxygenation, ABP, CVP, cardiac rhythm and blood gases. CVP reflects mean pulmonary artery pressure (mPAP), normally 12mmHg. TOE may be useful. Avoid induction agents that depress myocardial contractility (eg. thiopental). High concentrations (>1.5 MAC) of volatiles = arrhythmogenic if used for maintenance. Consider remi infusion + lower MAC inhalation agent. Increase in O2 requirement = increased right to left shunting. Spontaneous ventilation for shorter procedures preferable if severe hypercarbia is avoided (IPPV may lead to increased intrathoracic pressure, reduced venous return, decreased pulmonary blood flow and decreased cardiac output). If using IPPV, 5-6ml/kg, low PEEP, short inspiratory times. Avoid hyperventilation.
- Laparoscopy ok if <10mmHg intraabdominal pressure and short operation, adequate ventilation and intravascular volume: but risk of decreased venous return and cardiac output, CO2 absorption and thus increased PVR, CO2 embolism risk.
- Post op – monitoring in ICU/HDU, PCA/epidural for analgesia and minimise stress and sympathetic tone. Monitor O2 saturations. VTE prophylaxis. Coagulation bridging.
- Pregnant patients: Risk of harm-dynamic disturbance from increased blood volume and myocardial O2 consumption and heart rate, risk of tachyarrhythmias. Risk of VTE from abnormal circulation + pregnancy. Elective delivery preferable, epidural +/- intrathecal opioid is technique of choice. Assisted delivery for second stage better than excessive straining. Left uterine displacement. Vasopressors with alpha-agonist activity may increase PVR so avoid. CVP monitoring is essential.
Major physiological risk factors in congenital heart disease
- Cardiac failure
- Pulmonary hypertension
- Cardiac failure signs: tachypnoea, tachycardia, sweating, cool peripheries, poor feeding, failure to thrive, hepatomegaly
- Due to volume overloaded or pressure overloaded heart or both
- Children with cardiac failure + CHD = high risk of cardiac arrest (10%) and 96% required perioperative inotropes even with minor procedures. Need to attend specialist centres. If less degrees of cardiac failure, may be safe to perform procedure in local hospital with ketamine induction (avoid prolonged sevo/propofol). Venous access can be challenging.
- PA pressure >25mmHg at rest or >30mmHg during exercise. WHO has a classification system (Type 1-5 based on aetiology).
- Children with CHD + Pulmonary HTN = 8x more likely to get complications.
- Treat with 100% O2, inhaled nitric oxide, IV prostacyclin, inotropic support of right ventricle and other measures to maintain cardiac output and pulmonary blood flow may be required.
- Increased airway resistance and reduced pulmonary compliance is common. Resp infections poorly tolerated and greater impact on PVR compared to children without pulmonary HTN.
- Preop ECG essential. RBBB common, unlikely to become complete heart block. Ventricular ectopics are ominous as up to 30% of children with VEs die suddenly.
- Single ventricular circulation + arrhythmias = dangerous, needs paeds ICU and paeds cardiology on site.
- Common feature of partial palliation/unrepaired CHD
- Often have concurrent cardiac failure, pulmonary hypertension and arrhythmias
- All cyanotic children should have care in specialist centre
- Chronic cyanosis leads to polycythaemia and coagulopathy, hyper viscosity and complications such as cerebral venous sinus thrombosis. Dehydration, fever and iron deficiency anaemia increases risk. Perioperative fluid can minimise risk. Aspirin should be continued as risk of thrombosis may be greater than risk of bleeding.
Anaesthesia for CHD patients undergoing surgery
- Hx of underlying CHD anatomy, physiology, identify risk factors above
- Are changes in SVR/PVR likely to be significant for their lesion?
- Recent upper/lower resp infections – may lead to changes in PVR and airway reactivity
- Venous access
- Routine cardiac medications – consider coagulation and discuss with usual team
- Sedative premeds
- Endocarditis prophylaxis based on national guidelines
- If any high risk factors -> transfer to specialist centre
- Discuss with usual cardiology team for intermediate risk patients
- Build rapport with child and family and discuss perioperative risk
- Congenital syndromes associated with heart defects may have implications in Perioperative care eg. DiGeorge syndrome (irradiated blood products), CHARGE syndrome (choanal atresia precludes nasal intubation)
- Propofol dramatically reduces SVR and MAP
- Ketamine minimal effect so it is the agent of choice for patients who cannot tolerate SVR dropping or pulmonary hypertension
- Gas induction can be used but avoid prolonged 8% concentrations
- Consider cannulation plan
- Use iso/sevo for maintenance
- Opioids and epidural analgesia have been successfully used