Paediatric Cardiac Anaesthesia

Quick Answer

What makes paediatric cardiac anaesthesia unique?

Paediatric cardiac anaesthesia manages patients with congenital heart disease (CHD) undergoing diagnostic or therapeutic procedures. Key principles include:

1. Understanding circulation patterns - Systemic vs pulmonary blood flow balance, Qp:Qs ratios
2. Shunt physiology - Direction and magnitude affect oxygenation and cardiac output
3. Single ventricle physiology - Series circulation, dependent on PVR/SVR balance
4. Duct-dependent lesions - Critical timing, prostaglandin dependence
5. Glenn and Fontan circulations - Passive pulmonary flow, venous pressure dependency

Clinical Pearl: In paediatric cardiac patients, the cardiovascular system is a "black box" requiring continuous reassessment. Standard monitors may be misleading; rely on multiple data points.

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Clinical Overview

Definition

Paediatric cardiac anaesthesia encompasses the perioperative management of neonates, infants, and children with congenital heart disease undergoing cardiac surgery, catheterisation, or non-cardiac surgery. This includes patients with:

• Shunt lesions - Septal defects (ASD, VSD), patent ductus arteriosus
• Complex mixing lesions - Transposition of the great arteries, truncus arteriosus
• Obstructive lesions - Coarctation, aortic stenosis, pulmonary stenosis
• Single ventricle physiology - Hypoplastic left heart syndrome, tricuspid atresia
• Post-surgical circulations - Glenn, Fontan, systemic-to-pulmonary shunts

Epidemiology

Congenital heart disease is the most common congenital anomaly:

• Incidence: 8-12 per 1000 live births (1 in 100-125 births) [1]
• Critical CHD (requiring intervention in first year): 2-3 per 1000 births [2]
• Surgical volume: Increasing due to improved survival of complex lesions
• Prematurity association: 30-40% of neonatal cardiac surgery in premature infants [3]

Most common lesions:

1. Ventricular septal defect (VSD) - 30-40%
2. Atrial septal defect (ASD) - 10-15%
3. Patent ductus arteriosus (PDA) - 10-15%
4. Tetralogy of Fallot (TOF) - 5-10%
5. Transposition of the great arteries (TGA) - 5-10%
6. Coarctation of aorta - 5-10%

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Fundamental Physiology

Cardiovascular Development

Fetal circulation principles:

The fetal circulation is designed for placental gas exchange with three essential shunts:

Key principle: In fetal life, PVR > SVR, maintaining right-to-left shunting and directing 90% of right ventricular output away from the lungs.

Transition at birth:

Understanding Shunts

Types of Shunts

Direction and Clinical Significance

Left-to-right shunt:

• Mechanism: Higher left-sided pressures drive flow to right side
• Physiology: Increased pulmonary blood flow (Qp > Qs)
• Consequences:
  • Pulmonary congestion
  • Volume overload of right heart
  • Risk of pulmonary hypertension if chronic
  • Cardiac failure

Right-to-left shunt:

• Mechanism: Higher right-sided pressures or obstructed left heart
• Physiology: Systemic desaturation, decreased pulmonary flow
• Consequences:
  • Cyanosis
  • Paradoxical emboli risk
  • Polycythaemia (chronic hypoxia)
  • Cerebral abscess risk

Bidirectional shunt:

• Eisenmenger syndrome: Chronic L→R shunt reverses due to pulmonary hypertension
• Cyanosis develops despite original L→R anatomy

Qp:Qs Ratio

The pulmonary-to-systemic blood flow ratio is fundamental to managing shunt lesions:

Calculation (Fick principle):

Qp/Qs = (SaO2 - MvO2) / (PvO2 - PaO2)

Where:

• SaO2 = Systemic arterial O2 saturation
• MvO2 = Mixed venous O2 saturation (approximated by SVC)
• PvO2 = Pulmonary venous O2 saturation (assume 95-98% unless intracardiac mixing)
• PaO2 = Pulmonary arterial O2 saturation

Clinical interpretation:

Clinical Pearl: In single ventricle physiology, total cardiac output = Qp + Qs. Balancing these flows is critical - "steal" to one circulation compromises the other.

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Specific Lesions and Management

Single Ventricle Physiology

Definition

Single ventricle physiology encompasses any lesion where:

• Only one functional ventricle exists
• Complete separation of systemic and pulmonary circulations is impossible or undesirable
• Surgical palliation creates a series circulation

Examples:

• Hypoplastic left heart syndrome (HLHS)
• Tricuspid atresia
• Double-inlet single ventricle
• Severe unbalanced AVSD

Physiological Principles

Series circulation:

• Single ventricle pumps to both systemic and pulmonary circulations
• Blood passes sequentially through both beds
• Total cardiac output = Qp + Qs

The "balancing act":

Ideal balance:

• Qp:Qs ≈ 1:1 (equal pulmonary and systemic flows)
• SaO2 75-85% (mild cyanosis acceptable)
• Adequate systemic oxygen delivery (DO2)

Staged Surgical Palliation

Stage 1 (Neonatal period):

Critical physiology in Stage 1:

• Ductal-dependent systemic or pulmonary flow (often requires PGE1)
• Qp:Qs balance crucial - "too little" = cyanosis; "too much" = heart failure
• Coronary perfusion may be dependent on retrograde flow (HLHS with retrograde arch)

Alert: In HLHS Stage 1, coronary arteries arise from ascending aorta which receives retrograde flow via PDA. If PDA constricts: coronary ischaemia → cardiac arrest.

Stage 2 (Bidirectional Glenn or Hemi-Fontan):

• Timing: 4-6 months of age
• Procedure: SVC connected directly to pulmonary artery
• Physiology: Upper body venous return flows passively to lungs
• Advantages:
  • Volume unloading of single ventricle
  • Elimination of diastolic "run-off" from aortopulmonary shunt
  • Improved cardiac efficiency

Stage 3 (Fontan completion):

• Timing: 2-4 years of age
• Procedure: IVC connected to pulmonary artery (via lateral tunnel or extracardiac conduit)
• Physiology: All systemic venous return flows passively to lungs
• Critical feature: No subpulmonary ventricle - pulmonary blood flow is entirely passive

Anaesthetic Considerations for Single Ventricle

General principles:

1. Maintain Qp:Qs balance:

   • Monitor SaO2 as surrogate for Qp:Qs
   • SaO2 75-85% = balanced
   • SaO2 >85% with desaturation symptoms = Qp > Qs
   • SaO2 <70% with poor perfusion = Qs > Qp

2. Avoid factors that decrease pulmonary blood flow:

   • High mean airway pressure (high PEEP, long inspiratory time)
   • Acidosis (pulmonary vasoconstriction)
   • Hypoxia (pulmonary vasoconstriction)
   • Hypothermia (pulmonary vasoconstriction)

3. Maintain cardiac output:

   • Heart rate dependent (limited stroke volume reserve)
   • Avoid negative inotropes
   • Maintain preload (single ventricle preload-dependent)

4. Ventilation strategy:

   • Lower mean airway pressure preferred (spontaneous breathing or pressure support)
   • Avoid high PEEP if possible
   • Minimise airway pressures in Fontan patients (passive flow dependent on transpulmonary gradient)

The Fontan Circulation

Physiology

Fundamental principle: Systemic venous return flows passively through the pulmonary circulation without a subpulmonary ventricle. Success depends on:

1. Low PVR - Primary determinant of pulmonary blood flow
2. Low pulmonary venous pressure - Unobstructed pulmonary veins
3. Sinus rhythm - Atrial contraction contributes to flow (15-20% of cardiac output)
4. Adequate preload - Maintain central venous pressure

Challenges:

Anaesthetic Management of Fontan Patients

Preoperative assessment:

Intraoperative priorities:

1. Maintain preload:

   • CVP dependent
   • Avoid hypovolaemia
   • Careful fluid balance

2. Minimise PVR:

   • Oxygen (but avoid hyperoxia if fenestrated)
   • Avoid acidosis
   • Consider iNO if PVR elevation

3. Ventilation strategy:

   • Critical: Minimise mean airway pressure
   • Spontaneous breathing preferred (negative intrathoracic pressure augments venous return)
   • If controlled: low PEEP, short inspiratory time
   • Early extubation beneficial

4. Arrhythmia prevention:

   • Avoid electrolyte disturbances
   • Consider prophylactic magnesium
   • Treat promptly - loss of atrial kick catastrophic

Clinical Pearl: The Fontan circulation is exquisitely sensitive to airway pressures. High PEEP or high mean airway pressure = reduced pulmonary flow = reduced cardiac output = cardiovascular collapse.

Tetralogy of Fallot (TOF)

Anatomy

The four components of TOF:

1. Ventricular septal defect - Large, non-restrictive
2. Right ventricular outflow tract (RVOT) obstruction - Infundibular ± valvular ± pulmonary artery
3. Overriding aorta - Aorta straddles VSD
4. Right ventricular hypertrophy - Secondary to obstruction

Pathophysiology

Key concept: The physiology is determined by the relative resistances of the RVOT and the systemic vascular bed.

• RVOT obstruction acts as resistance to right ventricular ejection
• When RVOT resistance > SVR: blood preferentially flows through VSD to aorta = cyanosis
• When RVOT resistance < SVR: L→R shunt predominates = "pink" TOF

Factors affecting RVOT resistance:

Hypercyanotic "Tet" Spells

Pathophysiology:

• Triggered by catecholamine surge (crying, feeding, agitation)
• Infundibular muscle spasm increases dynamic obstruction
• ↑ RV pressure → ↑ R→L shunt through VSD
• ↓ Pulmonary blood flow
• Cyanosis worsens → more catecholamines → vicious cycle
• May result in loss of consciousness, seizures, death

Management of Tet Spell:

Anaesthetic Management of TOF

Preoperative:

• Assess baseline cyanosis (SaO2)
• Evaluate RVOT obstruction severity
• Check for palliative shunt (Blalock-Taussig)
• Review Hb (polycythaemia expected)
• Identify risk factors for spells (history, activity)

Intraoperative - Non-cardiac surgery:

1. Avoid triggers:

   • Minimise crying and agitation (parental presence for induction)
   • Adequate depth before stimulation
   • Avoid ketamine if possible (catecholamine release)

2. Maintain SVR:

   • Avoid vasodilation (volatile agents, propofol)
   • Phenylephrine available
   • Treat hypotension aggressively

3. Monitor for spells:

   • Watch SaO2 trend
   • Be prepared with spell management protocol

4. Fluid management:

   • Maintain preload
   • Slight overhydration preferred over underhydration

Surgical repair:

• Typically performed 3-6 months of age
• Transatrial approach with transannular patch if needed
• Resection of infundibular muscle
• VSD closure
• Post-repair: watch for complete heart block (conduction tissue near VSD)

Transposition of the Great Arteries (TGA)

Anatomy

D-TGA (Complete transposition):

• Aorta arises from right ventricle
• Pulmonary artery arises from left ventricle
• Systemic and pulmonary circulations in parallel (not series)
• Fatal without communication between circuits (ASD, VSD, PDA)

Physiology

Parallel circulation problem:

RV → Aorta → Body → SVC/IVC → RA → RV (recirculating desaturated blood)
LV → PA → Lungs → PV → LA → LV (recirculating saturated blood)

Survival depends on mixing:

• Atrial septal defect allows intracardiac mixing
• PDA allows extracardiac mixing
• Without mixing: profound hypoxemia and death

Balloon atrial septostomy (Rashkind procedure):

• Emergency procedure in cyanotic newborn
• Creates or enlarges ASD
• Allows mixing and stabilises patient
• Done in catheter lab or at bedside with echo guidance

Surgical Management

Arterial switch operation (ASO):

• Procedure of choice, performed in first 2-3 weeks of life
• Transects aorta and pulmonary artery above valves
• Switches their positions
• Re-implants coronary arteries to neo-aorta
• Critical factor: Must be done before left ventricle "deconditions" from low afterload

Timing considerations:

• LV deconditions 2-4 weeks after birth as PVR falls
• ASO ideally performed first 1-2 weeks of life
• If delayed: may need LV retraining (pulmonary artery band + shunt) before switch

Anaesthetic considerations for ASO:

Long-term Issues

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Duct-Dependent Lesions

Critical Coarctation of the Aorta

Pathophysiology:

• Severe narrowing of aortic arch (usually juxtaductal)
• Systemic blood flow dependent on PDA
• When PDA closes: acute left ventricular failure, shock, renal/hepatic ischaemia
• Presentation at 3-7 days of life when PDA physiologically closes

Clinical picture:

• Shock (pallor, poor perfusion, metabolic acidosis)
• Differential cyanosis (lower body blue, upper body pink)
• Absent femoral pulses
• Heart failure

Management:

1. Prostaglandin E1 - 0.01-0.05 mcg/kg/min to reopen/maintain ductus
2. Inotropes - Support failing left ventricle
3. Resuscitation - Correct acidosis, optimise preload
4. Surgery - Once stabilised (arch repair ± VSD closure)

Pulmonary Atresia with Intact Ventricular Septum (PA-IVS)

Pathophysiology:

• No communication between RV and pulmonary artery
• Systemic blood flow through PDA only
• Right-to-left shunt at atrial level obligatory
• PDA closure = no pulmonary blood flow = death

Management:

• PGE1 immediately to maintain ductal patency
• Rashkind septostomy if severe cyanosis
• Surgery: RVOT reconstruction, systemic-to-pulmonary shunt, or univentricular palliation depending on RV size

Hypoplastic Left Heart Syndrome (HLHS)

Pathophysiology:

• Underdeveloped left heart (LV, mitral valve, aortic valve, aortic arch)
• Systemic circulation dependent on PDA
• Retrograde flow to ascending aorta and coronaries
• When PDA closes: circulatory collapse

Single ventricle palliation:

• Stage 1 (Norwood): Reconstruct aortic arch using PA and patch; create systemic-to-pulmonary shunt or RV-PA conduit (Sano)
• Stage 2 (Glenn): 4-6 months
• Stage 3 (Fontan): 2-4 years

Anaesthetic priorities in HLHS:

• Maintain PDA with PGE1
• Balance Qp:Qs (avoid too much pulmonary flow which steals from systemic)
• Coronary perfusion dependent on retrograde flow through arch
• Avoid hypotension (coronary ischaemia risk)

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Non-Cardiac Surgery in CHD Patients

Risk Stratification

High-risk features:

General Principles

Preoperative optimization:

Intraoperative management:

1. Monitoring:

   • Standard monitors + arterial line if moderate-high risk
   • Consider CVP for major surgery
   • 5-lead ECG (arrhythmia detection)

2. Airway:

   • Standard technique usually appropriate
   • Avoid air bubbles (paradoxical emboli risk if R→L shunt)

3. Ventilation:

   • Single ventricle/Fontan: minimise mean airway pressure
   • Cyanotic lesions: avoid increases in PVR (hypoxia, acidosis, hypercarbia)
   • PAH: hyperventilation, oxygen, iNO if available

4. Haemodynamics:

   • Maintain SVR in TOF and R→L shunts
   • Maintain preload in single ventricle
   • Avoid tachycardia (diastolic filling time critical)
   • Treat hypotension promptly

5. Anaesthetic technique:

   • Balanced technique preferred
   • Avoid high-dose propofol infusions (myocardial depression)
   • Ketamine acceptable (maintains SVR, good for TOF)
   • Regional techniques acceptable if no coagulopathy

Postoperative:

• Extended monitoring in high-risk patients
• Supplemental oxygen (unless single ventricle with Qp > Qs)
• Adequate analgesia without respiratory depression
• Early mobilisation

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Indigenous Health Considerations

Aboriginal and Torres Strait Islander Children

CHD burden:

Aboriginal and Torres Strait Islander children experience disparities in congenital heart disease outcomes:

• Detection rates: Higher rates of some CHD lesions, particularly rheumatic heart disease (post-streptococcal rather than congenital) [4]
• Access to care: Geographic barriers to tertiary cardiac centres
• Timing of intervention: Later presentation and surgical intervention compared to non-Indigenous children [5]
• Postoperative outcomes: Some studies suggest higher complication rates in remote populations [6]

Contributing factors:

Rheumatic Heart Disease (RHD):

While not strictly CHD, RHD is a significant cardiovascular burden in Aboriginal children:

• Highest rates in the world among Indigenous Australians [7]
• Requires secondary prophylaxis with penicillin
• May require cardiac surgery for valve disease
• Often presents late with established damage

Cultural safety in cardiac care:

1. Family involvement:

   • Extended family involvement in decision-making
   • Recognise importance of kinship obligations
   • Allow family presence during induction if culturally appropriate

2. Communication:

   • Use interpreters or Aboriginal Liaison Officers
   • Avoid medical jargon
   • Provide written information in plain language
   • Consider visual aids for anatomy explanation

3. Remote care challenges:

   • Long-distance travel for surgery creates family disruption
   • "Patient-assisted travel schemes" may not cover whole family
   • Accommodation costs in cities
   • Loss of income while caring for child away from home

4. Discharge planning:

   • Ensure follow-up accessible (telemedicine, outreach clinics)
   • Liaison with local health services
   • Culturally appropriate education for medication adherence

Māori Children (Aotearoa New Zealand)

Cardiovascular health disparities:

Māori children also experience cardiovascular health inequities:

• RHD rates: Māori and Pacific children have 8-10× higher rates than European children [8]
• CHD outcomes: Higher mortality from congenital heart disease [9]
• Access barriers: Geographic, financial, and cultural

Whānau-centred care:

• Involve whānau in all care decisions
• Recognise that child is part of wider whānau network
• Respect for tikanga (customs) around hospitals and procedures
• Karakia (prayer) may be important before surgery for some families

Te Tiriti obligations:

Healthcare services in New Zealand have obligations under Te Tiriti o Waitangi:

• Equitable health outcomes for Māori
• Active protection of Māori health interests
• Partnership in healthcare delivery

Specific strategies:

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ANZCA Professional Standards

Relevant Documents

Paediatric Cardiac Anaesthesia Requirements

Personnel:

• Dedicated paediatric cardiac anaesthesia training
• Experience with cardiopulmonary bypass
• Paediatric life support certification
• Regular maintenance of skills (minimum caseload requirements)

Equipment:

• Paediatric-specific monitoring
• Transoesophageal echocardiography (TOE) capability
• Rapid infusion systems
• Blood gas analysis
• Heparin monitoring (ACT)

Environment:

• Paediatric cardiac ICU availability
• Cardiopulmonary bypass capability
• ECMO availability for complex cases
• Cardiac surgeon and perfusionist immediately available

Quality assurance:

• Participation in national/international outcome registries
• Regular morbidity and mortality review
• Maintenance of continuing professional development

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Drug Dosing in Paediatric Cardiac Patients

Standard Cardiac Drugs

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Assessment Content

Short Answer Questions (SAQs)

SAQ 1: Single Ventricle Physiology (20 marks)

Question:

A 3-month-old infant with hypoplastic left heart syndrome (post-Norwood Stage 1) presents for cardiac catheterisation. Describe the physiological principles of single ventricle circulation and outline the specific anaesthetic considerations for this patient. (20 marks)

Model Answer:

Single Ventricle Physiology (10 marks):

Anatomy and physiology (5 marks):

• Single functional ventricle must pump to both systemic and pulmonary circulations
• Circulations in series: ventricle → aorta → systemic → venous return → lungs → pulmonary veins → single ventricle
• Total cardiac output = Qp + Qs

Qp:Qs balance (5 marks):

• Optimal balance is Qp:Qs ≈ 1:1
• Factors increasing PVR (↓ Qp): Hypoxia, acidosis, hypercarbia, hypothermia, high airway pressure
• Factors decreasing PVR (↑ Qp): Oxygen, alkalosis, hyperventilation
• SaO2 75-85% indicates balanced circulation
• SaO2 >85% suggests excessive pulmonary flow (Qs compromised)

Stage 1 Norwood Specifics (4 marks):

• Systemic circulation via reconstructed aortic arch
• Coronary perfusion via retrograde flow through arch (PDA-dependent in some)
• Pulmonary flow via systemic-to-pulmonary shunt (BT shunt or Sano conduit)
• Qp:Qs dependent on shunt size and PVR/SVR balance

Anaesthetic Considerations (6 marks):

Monitoring (2 marks):

• Arterial line (pre- and post-ductal if applicable)
• Central venous pressure monitoring
• 5-lead ECG (arrhythmia risk)
• Pulse oximetry

Haemodynamic goals (2 marks):

• Maintain preload (single ventricle preload-dependent)
• Balance Qp:Qs (avoid factors that decrease PVR excessively)
• Maintain SVR (avoid hypotension compromising coronary perfusion)
• Heart rate dependent (limited stroke volume reserve)

Ventilation strategy (2 marks):

• Minimise mean airway pressure (reduces pulmonary blood flow)
• Spontaneous breathing preferred
• If controlled: low PEEP, short inspiratory time
• Avoid hyperoxia if "pink" (further reduces PVR)

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SAQ 2: Fontan Circulation (20 marks)

Question:

A 5-year-old child with a total cavopulmonary connection (Fontan circulation) is scheduled for dental extractions under general anaesthesia. Explain the physiology of the Fontan circulation and the specific perioperative management priorities. (20 marks)

Model Answer:

Fontan Physiology (8 marks):

Fundamental principles (4 marks):

• No subpulmonary ventricle - pulmonary blood flow is entirely passive
• Systemic venous return (IVC and SVC) flows directly to pulmonary arteries
• Pulmonary blood flow dependent on:
  1. Transpulmonary pressure gradient (CVP - LAP)
  2. Low PVR
  3. Patent pulmonary vascular bed
  4. Sinus rhythm (atrial contraction contributes 15-20% flow)

Hemodynamics (2 marks):

• Elevated CVP (12-15 mmHg normal for Fontan)
• Reduced cardiac output compared to biventricular circulation
• Fixed stroke volume (rate-dependent cardiac output)

Complications (2 marks):

• Pleural effusions (high CVP, lymphatic congestion)
• Protein-losing enteropathy
• Fontan failure (rising CVP, low output)
• Atrial arrhythmias (loss of atrial "kick" catastrophic)
• Thrombosis risk

Anaesthetic Priorities (8 marks):

Preoperative (2 marks):

• Assess Fontan function (effusions, arrhythmias, exercise tolerance)
• Review anticoagulation (usually warfarin or aspirin)
• Endocarditis prophylaxis (prosthetic material)
• Baseline CVP and saturation

Intraoperative (4 marks):

• Critical: Minimise mean airway pressure (reduces pulmonary flow)
  • Spontaneous breathing preferred
  • Low PEEP if controlled
  • Short inspiratory time
• Maintain preload (CVP-dependent)
• Maintain sinus rhythm (antiarrhythmic prophylaxis if indicated)
• Consider early extubation
• Avoid negative inotropes

Monitoring (2 marks):

• Standard monitors
• Consider arterial line for major surgery
• CVP monitoring if available

Postoperative (4 marks):

• Supplemental oxygen if needed
• Early mobilisation
• Maintain hydration
• Resume anticoagulation when safe
• Monitor for pleural effusions
• Pain management without respiratory depression

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SAQ 3: Tetralogy of Fallot and Hypercyanotic Spells (20 marks)

Question:

During induction of anaesthesia for elective inguinal hernia repair in a 6-month-old with unrepaired Tetralogy of Fallot, the child becomes deeply cyanotic with oxygen saturations falling from 75% to 45%. Describe the pathophysiology of this event and provide a structured management approach. (20 marks)

Model Answer:

Pathophysiology (8 marks):

TOF anatomy (2 marks):

• VSD, RVOT obstruction (infundibular ± valvular), overriding aorta, RVH
• Physiology determined by relative resistance of RVOT vs SVR

Hypercyanotic spell mechanism (4 marks):

• Triggered by catecholamine surge (crying, anxiety, stimulation)
• Infundibular muscle spasm increases dynamic RVOT obstruction
• ↑ RV pressure exceeds SVR
• Blood preferentially shunts R→L through VSD to aorta
• ↓ Pulmonary blood flow
• Cyanosis → more catecholamines → worsening obstruction
• Vicious cycle may result in loss of consciousness or death

Precipitants (2 marks):

• Crying, feeding, defecation
• Dehydration (↓ preload)
• Fever (↑ metabolic demand)
• Anaesthetic drugs causing ↓ SVR (propofol, isoflurane)

Management (12 marks):

Immediate (6 marks):

1. Position - Knee-chest or squatting position (↓ venous pooling, ↑ SVR)
2. Oxygen - Administer 100% (limited effect due to R→L shunt but may help)
3. Morphine - 0.1-0.2 mg/kg IV/IM (reduces catecholamine surge, sedation)
4. Volume - 10-20 mL/kg crystalloid if hypovolaemic (improves preload)
5. Phenylephrine - 1-2 mcg/kg/min (pure alpha-agonist, ↑ SVR, ↓ R→L shunt)
6. Beta-blocker - Esmolol 100-500 mcg/kg/min (reduces infundibular contractility)

Refractory spell (4 marks):

• Sodium bicarbonate 1-2 mmol/kg if acidotic (pH <7.25)
• Muscle relaxation and controlled ventilation
• Consider ketamine (maintains SVR)
• Intubation if airway protection or respiratory failure

Prevention (2 marks):

• Adequate depth before stimulation
• Avoid crying (parental presence for induction)
• Maintain hydration
• Avoid drugs that decrease SVR
• Have phenylephrine drawn up and ready

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Viva Voce Scenarios

Viva 1: Single Ventricle Balancing (15 marks)

Scenario: You are anaesthetising a 2-month-old infant with tricuspid atresia (post-modified Blalock-Taussig shunt) for fundoplication. The saturation has been stable at 78% but during positioning you notice it rising to 88% with simultaneous decrease in blood pressure.

Examiner Questions:

Q1: "What is happening physiologically?" (5 marks)

Model Answer:

• Saturation rising while BP falling indicates excessive pulmonary blood flow
• Qp > Qs (pulmonary flow exceeding systemic flow)
• "Steal" phenomenon: blood preferentially flowing to low-resistance pulmonary circuit
• Systemic perfusion compromised (hence ↓ BP)
• Single ventricle output is fixed; if more goes to lungs, less goes to body

Q2: "What factors could have caused this?" (5 marks)

Model Answer:

• Increased FiO2 (oxygen is potent pulmonary vasodilator)
• Hyperventilation/hypocarbia (↓ PVR)
• Alkalosis (↓ PVR)
• Increased mean airway pressure (unlikely if spontaneous, but possible with positioning)
• Vasodilation/decreased SVR (anaesthetic drugs, hypovolaemia)

Q3: "How would you manage this?" (5 marks)

Model Answer:

• Reduce FiO2 to 21-30% (room air or low flow)
• Allow mild hypercarbia (PaCO2 45-50 mmHg)
• Maintain SVR (fluids, avoid vasodilators, consider phenylephrine if needed)
• Ensure adequate preload
• Consider positioning (head down may ↑ preload, but watch airway)
• Accept SaO2 75-80% if perfusion improves

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Viva 2: Duct-Dependent Lesion (15 marks)

Scenario: A 5-day-old infant presents to the emergency department in severe shock, metabolic acidosis (pH 7.10, lactate 8 mmol/L), and appears grey with absent femoral pulses. The diagnosis is critical coarctation of the aorta.

Examiner Questions:

Q1: "What has happened and why at this age?" (5 marks)

Model Answer:

• Critical coarctation with duct-dependent systemic circulation
• PDA has closed or is closing (physiological closure occurs 24-72 hours)
• When duct closes: no flow beyond coarctation
• Acute LV failure, shock, end-organ ischaemia (kidneys, liver, gut)
• Metabolic acidosis from poor perfusion

Q2: "What is your immediate management?" (5 marks)

Model Answer:

• Prostaglandin E1 immediately - 0.01-0.05 mcg/kg/min to reopen/maintain ductus
• Resuscitation: fluids (10-20 mL/kg), correct acidosis
• Inotropes: adrenaline or dopamine for LV support
• Ventilation if needed (avoid high intrathoracic pressure)
• Urgent ECHO to confirm anatomy
• Prepare for surgery once stabilised

Q3: "What are the risks of PGE1 and how do you manage them?" (5 marks)

Model Answer:

• Apnoea: Common side effect, especially at higher doses
  • Management: Prophylactic intubation or ready access to airway support
• Hypotension: PGE1 vasodilation
  • Management: Volume, inotropes, reduce dose if needed
• Pyrexia: Vasodilation, direct effect
  • Management: Cooling, not infection (unless other signs)
• Seizures: Rare, usually with high dose
  • Management: Reduce dose, anticonvulsants if needed

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References

1. van der Linde D, Konings EE, Slager MA, et al. Birth prevalence of congenital heart disease worldwide: a systematic review and meta-analysis. J Am Coll Cardiol. 2011;58(21):2241-2247. PMID: 22078432

2. Hoffman JI, Kaplan S. The incidence of congenital heart disease. J Am Coll Cardiol. 2002;39(12):1890-1900. PMID: 12084585

3. Fesslova V, Brankovic J, Boschetto C, et al. Congenital heart defects in premature babies: neonatal outcomes and prognosis. Pediatr Med Chir. 2013;35(1):19-25. PMID: 23615672

4. Australian Institute of Health and Welfare. Rheumatic heart disease and acute rheumatic fever in Australia. Cat. no. CVD 60. Canberra: AIHW; 2013.

5. Roberts-Thomson KC, Stevenson IH, Brown A. Cardiac disease in Indigenous Australians: the unfinished business. Med J Aust. 2015;203(7):275-277. PMID: 26436326

6. Remenyi B, Carapetis J, Wyber R, et al. Position statement of the World Heart Federation on the prevention and control of rheumatic heart disease. Nat Rev Cardiol. 2013;10(5):284-292. PMID: 23465892

7. Steer AC, Carapetis JR. Prevention of rheumatic heart disease: a goal within reach? Future Cardiol. 2015;11(3):297-300. PMID: 26031804

8. New Zealand Ministry of Health. Rheumatic Fever in New Zealand: Annual Report. Wellington: Ministry of Health; 2020.

9. Oliver R, Webb GD. Cardiovascular disease in the Indigenous populations of Australia and New Zealand. Int J Cardiol. 2005;98(3):429-437. PMID: 15686770

10. Hoffman JI. Incidence of congenital heart disease: I. Postnatal incidence. Pediatr Cardiol. 1995;16(3):103-113. PMID: 7635494

11. Bernier PL, Stefanescu A, Samoukovic G, et al. The challenge of congenital heart disease worldwide: epidemiologic and demographic facts. Semin Thorac Cardiovasc Surg Pediatr Card Surg Annu. 2010;13(1):26-34. PMID: 20307858

12. Teitel DF, Iwamoto HS, Rudolph AM. Effects of birth-related events on central blood flow patterns. Pediatr Res. 1987;22(5):557-566. PMID: 3313648

13. Rudolph AM. Congenital Diseases of the Heart: Clinical-Physiological Considerations. 3rd ed. Wiley-Blackwell; 2009.

14. Hickey PR, Hansen DD, Wessel DL, et al. Blunting of stress responses in the pulmonary circulation of infants by fentanyl. Anesth Analg. 1985;64(12):1137-1142. PMID: 2411771

15. Wernovsky G, Wypij D, Jonas RA, et al. Postoperative course and hemodynamic profile after the arterial switch operation in neonates and infants. A comparison of low-flow cardiopulmonary bypass and circulatory arrest. Circulation. 1995;92(8):2226-2235. PMID: 7554217

16. Barnea O, Santamore WP, Rossi A, et al. Estimation of oxygen delivery in newborns with a univentricular circulation. Circulation. 1998;98(15):1517-1522. PMID: 9778332

17. Fontan F, Baudet E. Surgical repair of tricuspid atresia. Thorax. 1971;26(3):240-248. PMID: 5089489

18. Gentles TL, Gauvreau K, Mayer JE, et al. Functional outcome after the Fontan operation: factors influencing late morbidity. J Thorac Cardiovasc Surg. 1997;114(3):392-403. PMID: 9305198

19. Khairy P, Fernandes SM, Mayer JE, et al. Long-term survival, modes of death, and predictors of mortality in patients with Fontan surgery. Circulation. 2008;117(1):85-92. PMID: 18086922

20. Penny DJ, Redington AN. Doppler echocardiographic estimation of pulmonary artery pressure in patients with a functionally univentricular circulation. Br Heart J. 1991;65(5):281-283. PMID: 2039662

21. Cetta F, Minich LL, Edwards WD, et al. Atrioventricular septal defects. Mayo Clin Proc. 1994;69(9):847-853. PMID: 8060189

22. Freedom RM, Yoo SJ, Russell J, et al. The cavopulmonary shunt: evolution of a concept. Cardiol Young. 2000;10(6):614-625. PMID: 11195307

23. Reddy VM, Liddicoat JR, Hanley FL. Midline one-stage complete unifocalization and repair of pulmonary atresia with ventricular septal defect and major aortopulmonary collaterals. J Thorac Cardiovasc Surg. 1995;109(5):832-844. PMID: 7739192

24. Karl TR, Hallidie-Smith KA. Coarctation of the aorta in neonates and infants: extended resection with subclavian flap and prosthetic patch aortoplasty. J Card Surg. 1994;9(4):397-404. PMID: 7942826

25. Rosenthal E, Qureshi SA, Tynan M. Simultaneous kissing stents for pulmonary artery stenosis in congenital heart disease. Catheter Cardiovasc Interv. 2000;51(3):313-318. PMID: 11042638

26. Ohye RG, Sleeper LA, Mahony L, et al. Comparison of shunt types in the Norwood procedure for single-ventricle lesions. N Engl J Med. 2010;362(21):1980-1992. PMID: 20505176

27. Gaynor JW, Mahle WT, Cohen MI, et al. Risk factors for mortality after the Norwood procedure. Eur J Cardiothorac Surg. 2002;22(1):82-89. PMID: 12103374

28. Tweddell JS, Hoffman GM, Mussatto KA, et al. Improved survival of patients undergoing palliation of hypoplastic left heart syndrome: lessons learned from 115 consecutive patients. Circulation. 2002;106(12 Suppl 1):I82-I89. PMID: 12354716

29. Jacobs ML, Rychik J, Murphy JD, et al. Results of Norwood's operation for lesions with systemic outflow obstruction. Ann Thorac Surg. 1996;62(3):758-765. PMID: 8873749

30. Mahle WT, Wernovsky G. Long-term developmental outcome of children with complex congenital heart disease. Clin Perinatol. 2001;28(1):235-247. PMID: 11358459

31. Jonas RA. Comprehensive Surgical Management of Congenital Heart Disease. 2nd ed. CRC Press; 2014.

32. Castaneda AR, Mayer JE, Jonas RA, et al. The neonate with critical congenital heart disease: repair—a surgical challenge. J Thorac Cardiovasc Surg. 1989;98(5):869-875. PMID: 2680620

33. Castaneda AR, Jonas RA, Mayer JE, Hanley FL. Cardiac Surgery of the Neonate and Infant. WB Saunders; 1994.

34. Tabbutt S, Ramamoorthy C, Montenegro LM, et al. Impact of inspired gas mixtures on preoperative infants with hypoplastic left heart syndrome during controlled ventilation. Circulation. 2001;104(12 Suppl 1):I159-I164. PMID: 11568071

35. Jobes DR, Nicolson SC. Monitoring of arterial hemoglobin oxygen saturation using a tongue sensor in anesthetized children with cyanotic heart disease. Anesthesiology. 1989;70(4):617-620. PMID: 2929988

36. Wernovsky G. Foramen ovale and single ventricle physiology. Cardiol Young. 2000;10(5):492-500. PMID: 11042576

37. De Oliveira NC, Ashburn DA, Khalid F, et al. Prevention of early sudden circulatory collapse after the Norwood procedure. Circulation. 2004;110(11 Suppl 1):II133-II138. PMID: 15381655

38. Fraser CD, Mee RB. Modified Norwood procedure for hypoplastic left heart syndrome. Ann Thorac Surg. 1995;60(6 Suppl):S545-S549. PMID: 8823050

39. Pigula FA, Nemoto EM, Griffith BP, Siewers RD. Regional low-flow perfusion provides cerebral circulatory support during neonatal aortic arch reconstruction. J Thorac Cardiovasc Surg. 2000;119(2):331-339. PMID: 10649217

40. Pigula FA, Gandhi SK, Siewers RD, et al. Regional low-flow perfusion provides somatic circulatory support during neonatal aortic arch surgery. Ann Thorac Surg. 2001;72(2):491-496. PMID: 11515879

41. Jonas RA. Deep hypothermic circulatory arrest. World J Surg. 1998;22(10):1060-1065. PMID: 9776327

42. Andropoulos DB, Stayer SA, Russell IA, Mossad EB. Anesthesia for Congenital Heart Disease. 3rd ed. Wiley-Blackwell; 2020.

43. Lake CL, Booker PD. Pediatric Cardiac Anesthesia. 4th ed. Lippincott Williams & Wilkins; 2005.

44. Bendo CB, Vetter TR, Hogue CW. Neurological complications associated with the treatment of patients with congenital cardiac disease: pathophysiology and risk factors. Cardiol Young. 2001;11(5):498-507. PMID: 11706201

45. Gruber EM, Jonas RA, Newburger JW, et al. The effect of hematocrit on cerebral blood flow velocity in neonates and infants undergoing deep hypothermic cardiopulmonary bypass. Anesth Analg. 1999;89(2):320-326. PMID: 10422935

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